Posted: 8/10/2007 8:42:02 PM
[Last Edit: 9/9/2011 6:25:38 PM by ar-jedi]
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ham radio 101
Originally buried on page 4 of this thread, here it is in it's entirety + more info for new folks to read through.
Please note that this thread is for the most part a compendium of my prior ham-related posts AND informational posts from a number of fellow ARFCOM SF members. I have attempted as best as i could to preserve the original attributions, but if I missed some authors I assure you it was not intentional. Drop me an IM and I will correct the oversight immediately.
Here is a start at a soup to nuts ham primer...
I'll take a shot at this, and provide some links as well since my fingers would fall off before I could type everything you might want to know.
The usable-for-communications electromagnetic spectrum spans a frequency range from about 100KHz to 100GHz. (Aside, only a portion of that is usable by inexpensive equipment). In the USA, the Federal Communications Commission (FCC) is responsible for administering the spectrum for US users; however, the FCC works closely on this with international bodies, for reasons which will soon become clear. The "administering" that the FCC performs includes dictating what frequency bands are to be used for what purposes, and also specifying operational requirements for those bands (e.g. TX power output, ERP, modulation type, etc).
Since examples are worth thousands of words, I'll provide a few...
1) the FCC has decided that broadcast FM music stations are to exist in the 88MHz to 108MHz range, with maximum power limits.
2) the FCC has decided that CB exists at around 27MHz, and that the maximum TX power output is 4W.
3) the FCC has decided that FRS exists around 462/467MHz, with a maximum ERP specified.
And for the last example,
4) ham (amateur radio) has a number of bands allocated, each with associated limitations on power/modulation type etc.
I could go on and on with cell phones, marine radios, garage door openers, keyfobs, microwave towers, etc etc etc. Basically, if the device is what is referred to by the FCC as an "intentional radiator", they have an assigned slot (band) for it and constraints on it's operation.
Why the constraints? Well, one reason is for your physiological protection. High RF power can cause burns, blindness, and other problems. (The "invention" of the microwave oven was an accident 末 technicians working on early radar antennas were developing burns when the units were powered). Another reason for the constraints is public safety. The last thing a 747 pilot on emergency approach into Kennedy airport needs is crosstalk with taxi dispatchers in NYC. Hence the wide berth the FCC gives around police, fire, and EMS frequencies.
Now then, we see that the FCC regulates intentional radiator use by dividing the frequency spectrum into bands, and then sets characteristics for each of those bands that users must obey by.
A common question is, "is one frequency band 'better' than another"? The answer is "sometimes". For certain applications (more on this in a moment), a given frequency band may provide better range, fidelity, immunity to interference, and so forth. These factors, and others, that make a frequency usable for a given application were taken into consideration when the spectrum was allocated.
It is important to note here that transmitter power output is one of many, many factors that influence the range at which you can communicate over a given transmission path. While important, transmitter power output plays only one role in a multi-faceted problem. Antenna gain, antenna polarization, modulation type, receiver sensitivity, background noise level, path loss, and a dozen other issues factor into the equation. Show me a well designed 2W transmitter and I will show you a way to communicate ~6.5 billion miles. NASA does this every day with their Voyager 1 & 2 probes 末 they are now twice as far away as Pluto.
Now that you understand a little of the background of radio communications, we can move on to discussing amateur (ham) radio specifically.
To simplify things, amateur radio communication can be thought of in two segments: HF and VHF/UHF.
First, i hate to break this to you, but THE EARTH IS ROUND. No, I'm not kidding 末 it really is spherical despite what they told you in school or at church. Ok, now that you are past that, you should visualize in your head that radio waves travel in a straight line. Since the earth curves, it is not possible to talk over distances of over about 20 miles without "help". This "help" can come in a multitude of ways, and is somewhat dependent on the height of the transmitter and receiver, the gain of their respective antennae, the frequency of transmission, the weather and other atmospheric conditions, the sun cycle, hams around you erecting things called repeaters, and a few dozen other things. Nevertheless, the key point here is that the further you are away from each other, the more likely it is that the curvature of the earth is going to be the limiting factor. Always remember that without "help", radio communications of any type are "line of sight".
HF, or high frequency (roughly defined as everything below about 30MHz [10 meters wavelength]) signals can bounce off of a charged belt (called the ionosphere) which completely envelopes the earth. HF thus can communicate over long distances by using one or more "bounces" 末 you may have heard the CB term "skip". With just a few dozen watts, and a proper antenna, it's possible for you to talk (or more likely communicate using morse code) with a station 2000 miles away. Interestingly, it is sometimes difficult to talk to nearby stations that are "under the skip", that is they are too close to you to hear the reflected wave. One primary disadvantage of HF communications is that the antenna has to be physically long. Nevertheless, HF can be a valuable asset in emergency commications 末 like it was during hurricane Katrina when everything else was tits up. In general, when you think of HF you should think of long distance communications. With some exceptions, most HF rigs are designed for desktop use and the supporting equipment (power supplies, antenna tuner, etc) is heavy and not so portable. But there is a class of mobile and low power HF rigs which allow you to talk over great distances with just a few pounds of equipment.
Aside: there is an entire "sub-culture" within ham radio of people dedicated to QRP, or long distance very low power communications. Hundreds or thousands of miles on 5W, 1W, or even 0.5W is their goal. Antenna selection and a very good idea of what the ionosphere is doing are prerequisites.
VHF/UHF, or very/ultra high frequency (roughly defined as everything above about 50MHz [6 meters wavelength]) signals do not bounce off of the ionosphere. Hence, VHF/UHF is pretty much "line of sight" except for some atmospheric effects which occasionally allow communications to take place out to a few hundred miles. These effects can not be "scheduled" though, mother nature has her own clock. In other words you can not depend on these phenomena for reliable communications. When you think of VHF/UHF you should think of short distance comms. Amateur radios in the 6M (50MHz), 2M, (146MHz), 1.25M (220MHz), and 70cm (440MHz) bands are examples of VHF/UHF equipment. Hand held radios in these bands are knowns as "HT's", or handy talkies. Of course there are mobile and base versions as well that sport more output power or additional capabilities.
Since a picture is worth 1000 words:
Continuing on, FRS (UHF, ~462/467MHZ) and GMRS (UHF, same) are examples of inexpensive general purpose you-don't-need-a-ham-license radios. Most commercial radios (tow trucks, florists, plumbers, Amtrak, mall ninjas, etc) operate in the 150MHz VHF band. And until somewhat recently, most public safety (police, fire, first aid) were in the 150MHz and 450MHz bands as well. However, within the last 5 years many have migrated to the 900MHz band using what are called trunked radio systems. long story there but trunking allows a lot of flexibility for the system. You'll note that VHF/UHF radios are cheap, small, have short antennas, and long battery life. Moreover, amateur VHF/UHF radios double as scanners for the public service and other frequencies as well. The most popular VHF/UHF "band" is 2M, or about 146MHz. There is a reason for this... read on...
an introduction to VHF/UHF repeaters
As noted above, the primary limitation of VHF/UHF is the short range imposed by the curvature of the earth combined with the fact that VHF/UHF signals do not bounce off of the ionosphere (in case you were wondering, they pass right through it). Of course it helps greatly with VHF/UHF to be up as high as possible, as this gives more "line of sight" distance 末 the same way you can see much farther when atop a tall building. But that's not always practical. e.g., I live right at sea level 末 no kidding. So how can I communicate with any distance using VHF or UHF? Am i stuck trying to use HF for communications more than a few miles?
Enter the "repeater". Simply put, a repeater is an unattended radio advantageously located on a hill or with the antenna high up on a tower. The purpose of the repeater is to retransmit your signal in real time. It does this by listening on one frequency, called the input, and simultaneously transmitting the input audio on a second frequency, called the output. Accordingly, my radio would be set to transmit on the repeater's input frequency, and listen on the repeater's output frequency. (The difference is known as the "offset".) All that is required from a radio implementation standpoint is a little bit of frequency agility 末 when you press the transmit button, your radio tunes it's transmitter to the required new frequency. When you unkey, it changes back. All this happens in milliseconds and without your involvement save for some initial settings. The beauty of this set up is that with a low power HT (typically, 0.5W to 5W) you can talk for perhaps hundreds of miles! The repeater provides the "help" for VHF and UHF, just like the ionosphere provided the "help" for HF.
Ham radio clubs set up, operate, and maintain repeaters. There are likely several repeaters reachable from where ever you are reading this from. From my home I can reach about 8 repeaters, of course I do live near a metro area with a high population density. Note that there are published books of public amateur repeaters, which denote their location and characteristics (e.g., output frequency and offset). The reason that 2M/146MHz radios are so popular and inexpensive is simply due to the fact that there are more repeaters on 2M than any other frequency. Note: don't think that repeater technology is something specific to hams 末 it's not. Police departments and the like use repeaters for the same reasons that hams do. In fact, this created a big problem on sept 11, 2001 as several of the NYPD and FDNY repeaters were located atop the WTC.
The disadvantage of repeaters is simple: in order for the repeater to work, you need power and the antenna has to be upright. These are not likely conditions in areas overcome by, for example, a category 4 or 5 hurricane. While tons of lead acid batteries may delay the inevitable, there is a finite amount of no-AC-power operation time for any repeater unless expensive measures have been taken (e.g. a diesel genset and good sized fuel tank, as you would find mounted behind a police station). Nevertheless, hams are resourceful people and generally fixing the local repeaters is an immediate priority in disaster areas. Moreover, all of the equipment necessary for a repeater can be carried in the back of a pickup truck, with room to spare. So if a makeshift antenna can be erected on the mountainside, a substitute repeater can be up and running in a few hours to replace the one crushed by the flying oak tree.
One way to look at a ham repeater is as an analog of a cell site. Having many cell sites make it possible for your low power cellphone to communicate anywhere the global phone network reaches. Similarly, hams link repeaters using point-to-point RF, the phone network, or these days using the Internet. All of these methods allow greater "reach" from your low power HT. Of course with the exception of point-to-point RF, the other methods require public infrastructure that may or may not be available when the SHTF.
Speaking of the Internet, I've discussed above mainly voice communications. However, hams also have packet radio technology at their disposal. So email and traffic nets can be set up without relying on the Internet 末 instead of wire and fiber, RF is substituted. Think of it as a wireless LAN, capable being accessed by anyone in an area of a few dozen miles in diameter.
In short, ham radio is not a singular thing; it is a wide, expansive hobby with many aspects to it 末 you simply choose the parts that you enjoy. It's no different than with trucks, some like lifting and then offroading their trucks, and others make lowrider bling-bling trucks out of them. Similarly, hams do HF, VHF, UHF, microwave, CW, packet, APRS, DXCC, contesting, SSTV, fox hunting, RACES/ARES, and so on and so forth.
Posted: 8/10/2007 8:42:34 PM
[Last Edit: 8/20/2011 10:15:02 PM by ar-jedi]
how to get a ham radio license,
Can you get the License online?
No. There are three levels, called "classes", of amateur radio (ham) licenses, which give increasing privileges on the bands assigned by the FCC for exclusive use by amateur radio. None of the license classes require learning Morse code, but they all require taking a written exam given by volunteer amateur radio operators in your area. The steps to get the base license, called a Technician (abbr. "Tech") class license, are like so...
(1) Go here: http://www.hello-radio.org/whatis.html
there you will find out more about amateur radio and the multitude of facets to the hobby.
(2) Get a Technician class study guide (example). you may be able to get one for free (or near so) from one of the folks here who have recently earned their Tech license (it's a pay-it-forward kind of thing). you will need to read through the Tech study guide over the course of a few evenings. you can also find a lot of info on the web to help study for the Tech exam 末> link
(3) Take the practice exams located at www.qrz.com/p/testing.pl. repeatedly take the Tech exam until (a) you have seen all of the questions in the question pool (the question pools are public, and located here), and (b) you get a passing score every time. it is certainly possible to memorize all of the answers to all of the questions, but i dissuade you from doing so as you'll need some of that knowledge down the road.
(4) Go here www.arrl.org/arrlvec/examsearch.phtml and put your zipcode in. This locates a nearby VE (volunteer examiner) session. The exam session itself will likely be located in a school classroom, a library, or similar civic building. In some areas they may be as often as every other week. In some areas they may be once a month. You'll bring a pencil, some government issued ID like your driver's license, and $15. You can take the Tech exam in about 15-20 minutes, and you are a ham. Note that there is no additional charge to take higher class exams on the same day; hence, if you want you can study for both the Tech and General exams, and take them both. The General class license gives a ton more operating privileges than the Tech class license, and is especially needed for long distance (>50 miles) communications. I highly recommend studying for both your Tech and General licenses and taking them both in one sitting.
(5) About a week after you pass your exam, a letter will arrive from the FCC with your assigned amateur radio callsign. Congratulations!
how much are they?
As demonstrated above, you can't "buy one", per se. It's ~$15 for the exam session 末 see link above 末 but you can take tests sequentially at the session if you want, all for the same cost.
My question: is morse code required for any of the licenses any more?
No, not since February 2007 末 it is not required for any class license.
reason i ask i know you have to walk before you can crawl, but if i wanted to get the general or the extra license would morse code be required ? also at what level do they require morse code to be learned?
Per above, you can learn morse code on your own volition, or not. It is not a requirement for licensing. This, by the way, is not a uni-lateral move by the FCC (the USA's spectrum authority). The ITU, a committee which helps regulate and harmonize international spectrum use, recommended in 2006 to it's member countries (basically everyone) that morse code be dropped as a requirement for amateur radio licensing. Several countries did so immediately; naturally it took us longer to wind the rule change through our bureaucracy. But here we are 末 no more Morse code requirement for licensing.
By the way, that does not mean Morse code has "gone away" from a usage perspective. For example, go listen at the bottom of the 40meter band (day or night) and you will hear dozens of Morse code conversations (called QSO's) in progress, from all over the world. CW (Morse code) is a remarkably efficient mode, and can be used for communications when there is no way to get the spoken word through.
With the new knowledge that Morse is no longer needed. I plan to go out and buy some study aids immediately and start studying... Seems like as you have said the best bang for the buck is the General. That will be my goal in the not too distant future.
Yes, with the General class license you get 99% of the privileges you'll ever need. The Extra class license gives you additional slices of the HF bands. Again, I'd suggest studying for the Tech and General concurrently 末 you can pass them both in the same day in under an hour, and one $15 test fee covers them both.
now i have to get study materials.
Suggestions 末 (a) Post that you need a Tech/General study guide in the ham radio forum. Someone will send you slightly used one for a couple of bucks. It's a "pay-it-forward" thing with hams. (b) Find a local club and drop in on their monthly meeting. There are no scary animal acts or anything like that, LoL. You'll find a good bunch of guys/gals. The folks in the club probably are the same folks giving the exams and they will go out of their way to help you out.
On-line study guides:
LINK UPDATED FOR NEW 2010 TECH QUESTION POOL:
LINK UPDATED FOR NEW 2011 GENERAL QUESTION POOL:
For more information on the above guides, and/or to order printed or Kindle/Nook versions, see
Meanwhile, I'm going to keep up on the Tech questions and try to bring the General scores up to a more comfortable margin... well, really, I don't want to just scrape by. I want to actually learn the material.
WARNING THIS IS THE OLD 2006 TECH QUESTION POOL 末 NO LONGER VALID!
WARNING THIS IS THE OLD 2007 GENERAL QUESTION POOL 末 NO LONGER VALID!
I have just started today gathering up info for the Extra exam.
use this 末>
Originally Posted By JaxShooter:
In addition to just reading the question pool, here are some sites you can try for practice exams:
And probably my favorite, RadioExam
I like RadioExam because you can narrow it down to a particular section. That way you can focus on your problem areas rather than taking complete tests. This is especially valuable for the Extra exam since it's 50 questions.
Originally Posted By JaxShooter:
Originally Posted By ar-jedi:
what kind of facility do you administer the test at?
Our club uses a meeting room at one of the local malls. I have also conducted sessions at a branch library for another club.
how much does the test session cost?
The ARRL VEC Exam Fee for 2011 is $15.00. W5YI's current fee is $14.00. Volunteer examiners are permitted to charge a fee to recover their out-of-pocket costs in administering an examination so it's possible for this amount to vary slightly.
how long does a typical technician test take to complete?
This depends on you. I've seen people ace it in about 15 min while others take 30-45 depending on their confidence level and the time they spend re-checking their answers. If there are a lot of people testing your longest wait may be in getting your exam graded. Each exam is graded by all three examiners. Multiply that by the number of people testing and figure 10 min or so for us to fill out all of the paperwork.
can i take more than one test at a single sitting?
If you fail the exam you can retake it after paying the fee again. This may be time dependent, though. For example, our location closes at 9pm and we have to be out before that so we may not have time to administer another exam.
assuming i pass the technician test, does taking the general test cost extra?
Following on with the previous question, when you pass your exam you can take the next exam at no cost. As long as you keep passing you can keep testing for the cost of the single exam fee. It's possible to go from zero to hero and get your Extra for one fee if you pass Tech and General together.
If you feel confident about your Technician and think you may like to try General, please let the VE team know ahead of time (especially if you pre-register). This allows the team to have your paperwork and multiple exams in order.
can i skip taking the technician exam and just go right to general?
what happens after i pass 末 you send the results somewhere and then what?
When you pass your Technician exam you will be given a CSCE that says you passed. The VE team will then take all of your paperwork and send it (either via USPS, FedEx/UPS, or electronically) to the VEC. Once they have your paperwork it will be transmitted to the FCC so your call sign can be assigned. Since you do not have a license yet cannot transmit. Typically within a week your call should show up in the FCC ULS database. Once your call appears you can get on the air. You don't have to wait for the paper license to appear in the mail.
If you are upgrading your license you can start using your new privileges once you walk out the door with your CSCE as long as you use the appropriate designator for General (/AG) or Extra (/AE).
useful/interesting amateur radio sites
www.qrz.com/p/testing.pl <<< ***
Originally Posted By GlockTiger:
Cool link I found
For all the guys new to HF, this is a great primer!
As a side note:
But now I think a ham is the way to go
Like firearms, ham radios come in lots of different sizes and shapes, and are suited for different purposes. You can't go elephant hunting with a .22LR, and similarly you won't have much to eat if you go squirrel hunting with a .50 BMG.
What i'm getting at here is that you first need to define what you want to do, and then figure out what kind of ham radio you are looking for. Some are multi-purpose, and cover 90% of what you'll ever need to do. However, a good setup requires as much attention to the antenna system as the actual radio. It is quite easy to get poor results with an expensive radio and a crappy antenna. It's no different than trying to corner quickly in a Ferrari equipped with junk tires.
but how much are they?
See above. It could be $100 to $2000 for the radio, and $0 to $1000 for the antenna system. Few folks will need a $2000 radio and a $1000 antenna, unless they are really into the hobby. But I've noticed that a few folks who are really into guns buy Accuracy International rifles at ~$5K each as well, and then mount a $2K optic on top.
Posted: 8/10/2007 8:43:08 PM
[Last Edit: 8/17/2008 12:26:38 AM by ar-jedi]
simplex communications and approximate ranges
For mobile to mobile communications, such as would occur when off-roading, you can use "simplex" (direct) communcations in the VHF 2 meter band. No repeater needed, you are talking directly to each other. A common frequency for initiating this is 146.52MHz, the national simplex calling frequency. Once you have contact made you can move up a few hundred kilohertz and use any of the designated simplex frequencies to carry on.
Using an HT (handie-talkie) running 1 to 5W, you can expect up to about 5 miles of range. It depends highly on the terrain (flatter better) and what sort of antenna you have connected.
Using a mobile rig running about 50W into a roof or bracket mounted antenna will net you anywhere from 10-50 miles of range. Generally the curvature of the earth will cause problems, so it is better to be up on a hill of you are trying to reach out past 20 miles or so.
A 2M-only HT is about $130-150.
A 2M-only mobile is about $140-180.
Many HT's and mobiles are "dual-band" in that they operate on both 2M (~146MHz) and 70cm (~440MHz). This gives more flexibility for operating. note however there are far far far more repeaters on 2M, so there is no significant downside to getting a 2M-only rig. However, some public service agencies use frequencies in the 460MHz range, which a 2M-only radio will not be able to receive.
Popular HTs and mobiles come from the Big Three: Icom, Yaesu, and Kenwood all make fine radios with marginal differences. Mostly it's individual preference, unless one feature is striking you just right.
The Icom V8000 is a very nice 2M-only 75W mobile rig. I happen to own two of them. As for HT's, there are also many types; I own a Yaesu VX6R -- tri-band (incls 220MHz) super small and completely waterproof. I also own an Icom 24AT, a rugged dual-bander which I have had since 1991. It has never let me down and i've worked through a few Nor'Easters and hurricanes with it.
One thing i just realized, i never really explained what modulation is. Simply put modulation describes the technique used to put the audio input to the radio (i.e. your voice) onto the RF carrier. There are many ways to do this, each with advantages and disadvantages. Moreover, not only can it be done in the analog domain, but it can be done digitally as well. I'll only discuss the former as there are very few consumer digital radios to be had.
The most common analog modes are CW (continuous wave), AM (amplitude modulation), FM (frequency modulation), and SSB (single sideband [suppressed carrier]) modulation.
CW is used for morse code and is very efficient for long range comms. CW is not really a modulation method per se, but nevertheless we treat it as such.
AM, as you may be aware, is used for broadcast radio stations (hence the "AM band" name) and for shortwave stations (like Voice of America and Radio Free Europe). Because of the low fidelity of AM, and it's susceptibility to interference, AM radio has been relegated mainly to talk and newscasts. Note that CB uses AM as well.
FM, as you are also aware, is used for broadcast radio stations and also is the mainstay for VHF/UHF communications. Above 50MHz (6M), 99% of ham, all of FRS/GMRS, marine, and all public service/safety use frequency modulation. FM provides far greater fidelity (accuracy of the receiving radio's output to the transmitting radio's input) than any other modulation type. Therefore, FM is very useful for music transmission. And similarly, FM makes 2 way radio communications crystal clear. Most folks who have only used a CB are incredulous at what a 2M ham rig sounds like. the difference is due to the use of FM -- and not power or anything else. In addition, FM is all but immune to atmospheric disturbances such as lightning.
SSB is the most complicated of all of the noted modulation techniques. Simply put, SSB is an adaptation of AM with a little math (a Hilbert transform) thrown in. The result is a VERY efficient way to transmit speech over long distances. SSB is the primary modulation method used by hams when operating below 50MHz (6M). There are actually two variants of SSB (USB and LSB) and in order to communicate both parties need to use the same type. Nevertheless, SSB is one reason you can talk a few thousand miles on a couple of watts.
SSB is one type of "modulation" -- which is an expensive word to describe the process that radio uses to get your voice encoded onto a radio signal. You have heard of AM, FM, and so on, these are modulation methods as well. SSB is uniquely suited for long distance work as it is extremely power efficient, has a narrow spectral bandwidth, and a very weak SSB signal can easily be recovered by the receiver at the other end. SSB does suffer in terms of fidelity, that is trueness of sound to the original source; SSB is also more prone to noise from atmospheric disturbances such as lightning.
The clear winner for fidelity is FM, which is why FM is used to broadcast music. But FM requires a wide swath of a given band. AM is not so great in *any* department -- it is prone to interference, has poor fidelity, and the spectral efficiency is mediocre. Nevertheless, the design complexity of both an AM transmitter and the corresponding AM receiver is very low, and therefore overall "system" cost is very low. A basic AM receiver can in fact be constructed from a single diode and in some case requires no external power. This is not the situation with FM or SSB.
Amateur (ham) radios designed for high frequency (HF =~ 1Mhz [300m] to 30MHz [10m])) operation have a selector switch which allows the operator to select the modulation type, choosing from AM, FM, SSB (USB or LSB), and finally CW (for sending morse code). By convention, international agreement, or other reasons, certain radio frequencies (aka bands) use certain types of modulation. For example, the BBC World Service shortwave stations transmit in AM. But the US Coast Guard rescue HF frequencies use SSB.
Now then, I've talked about the various modulation methods such as AM, FM, and SSB. Frequency comes into play because the "skip" effect you referred to is wholly dependent on the whims of the ionosphere (a region high up in our atmosphere). The "reflectivity", if you will, of the ionosphere is a function of many things, including high energy particle emissions from our sun. To sum up, depending on conditions, at a given frequency, you can can get excellent skip, marginal skip, or no skip. And, for a given time and place, there is a maximum frequency for which there will be no skip whatsoever -- this is known as the MUF -- maximum usable frequency.
The basic problem with skip communications is it doesn't help for the area "under" the skip. In other words, with skip you can sometimes talk to Europe from New York, but you can't talk to NJ. Because of this issue, generally a different approach for "medium range" comms. Hence, i think you are going to have some trouble with your proposed usage of 10m SSB, for a couple of reasons. Keep reading...
For the distances you are looking at, 60 to 100 miles, IMHO you really have two choices:
(1) Use 6m or 2m SSB, decent amplification (typ 200-400w), and high mounted, highly directional antennas (e.g. 4 to 12 element horizontally polarized yagis). This is basic "line of sight" communications -- no fancy skip here. A few folks near me clear 100 miles using this approach all of the time. Note that maximizing antenna height at both ends is critical! If the antennas can "see" each other, without a hill or mountain in the way, you'll have good comms.
(2) Use 80m or 40m SSB, normal power (typ 100w), and a NVIS antenna setup. With NVIS, which is an acronym for "near vertical incidence skywave", your transmitted signal is more or less directed straight up -- the resultant reflected wave will cover the surrounding few hundred miles. The military uses this approach for HF communications in tactical (battlefield) applications (although less so these days with so many milsats overhead). My fingers will fall off before i can type all that is possible to describe NVIS in details, hence I suggest reading the following...
To quote from the first link above, which sums things up nicely:
Note that SSB can be done two ways: upper side band (USB) and lower side band (LSB). While SSB (single side band) describes the general modulation concept, the receiver operator must actually select either USB or LSB in order to correctly hear the signal.
Posted: 8/10/2007 8:43:43 PM
[Last Edit: 8/17/2008 12:28:10 AM by ar-jedi]
Since someone is bound to ask... what does 2M mean? Why is it seemingly used interchangably with 146MHz?
Hams simultaneously use one of two terms to describe the band they are discussing: frequency or wavelength. The two are related by a constant known as C, the speed of light. It turns out that after you crunch the numbers, you can easily convert between the two terms using the following rule of thumb...
300/freq in MHz = wavelength in meters
or the same rule but turned around,
300/wavelength in meters = freq in MHz
300/146MHz ~= 2 meters
and now you see why 146MHz and 2M are used interchangably.
Simlarly, some wavelength to frequency conversions for other popular HF and VHF/UHF ham bands...
40M --> 300/40 ~=7.5MHz
20M --> 300/20 ~= 15MHz
10M --> 300/10 ~= 30MHz
6M --> 300/6 ~= 50MHz
1.25M --> 300/1.25 ~= 220MHz
70cm --> 300/0.70 ~=440MHz
Other cool/random radio-related links...
wiki stuff of interest:
ham radio bandplan:
Posted: 8/10/2007 8:44:19 PM
[Last Edit: 8/17/2008 12:35:35 AM by ar-jedi]
general ham topics Q & A
Yes, CB exists within the "HF" frequency range (~1MHz to 30MHz), as does amateur radio. CB is allocated, as you already know, a band right near 27MHz (~26.965 to ~27.405), and the amateur 10meter band is just slightly higher at around 28.0 - 29.7 MHz. All things being equal, a CB and and a 10m ham radio would have approximately the same range since they are both affected the same way by the ionosphere. But clearly there is something else different, something that gives one an advantage over the other... keep reading...
Power is one aspect of range, an important one -- but not the only one. As I discussed in the third or fourth post in my "Ham 101" thread, the way the audio is modulated onto the RF carrier is extremely influential on how easy or difficult it is to recover the audio at the other end. AM is one of the worst possible ways to transmit voice, and that's the type of modulation CB uses. AM, combined with only 4 watts output, is just not going to make it as far as a superior modulation method combined with more power. In contrast with AM, SSB is much much much (i can't emphasize this enough!) more efficient in terms of using the available power to greatest effect. Ergo, SSB, combined with the higher power available on ham rigs, allows for far greater communication distance at very nearly the same frequency as CB. So as you can see, it's not just about power.
(I would also like to point out here that the receiver section on a typical ham radio is miles ahead of the receiver section on a typical CB radio. You need to cut some pretty big corners in order to make a CB that sells for $50. A ham rig, on the other hand, is at a price point that allows for better components (oscillators, filters etc) and additional circuitry (especially DSP [digital signal processing]).
If you look at the entire communications path from strictly a power perspective, there are two factors: how powerful the transmitter is and how sensitive the receiver is. Hence, you can improve range by increasing transmitter power and/or increasing receiver sensitivity. If you do both, you get a lot more range. This is the case with the higher power output and excellent receivers on ham radios. And we haven't even plugged in the benefit of using SSB modulation yet! remember, IT'S NOT JUST ABOUT POWER. Lots of hams use less than 10W to talk around the world. The art here is understanding propogation conditions, using the right modulation mode, driving a proper antenna, and having a good quiet (low noise floor) receiver.
The ionosphere does not reflect frequencies above about 30MHz. Above that, they just keep on going, off towards Mars. So, unless under very infrequent conditions, 2M (~146MHz) can not be used for long distance comms as it will not bounce back down to earth. (Aside: there is a aspect of ham radio which consists of bouncing 2M signals off of the moon. This is called "EME", or "earth-moon-earth" communications. In this manner you can use 2M/144MHz to talk to the other side of the earth. Warning: you need a lot of power and a big ass beam antenna array to pull this off. Moreover, the antenna must be able to track the moon as it crosses the sky, guided either by optical means or by using ephemeris data)
You can use the "national simplex frequency", 146.52 sort of like CB channel 19. My 2M radio is set up to scan it in one of the memory banks. Often i will hear someone call on it, and answer back. Sometimes they are just trying a new radio out, other times they are from out of town and looking for popular local repeater frequencies, and other times it's just to say "hi" and so forth. Generally you can "meet up" on .52 and then move off slightly to allow others to use the calling frequency. Or you can simply chat on .52, allowing a little extra time between alternating transmissions -- then if someone wants in, they will interject with just their callsign. At that point you will "recognize them" by repeating their call back and saying "go ahead" (in effect, handing them the baton for the moment), and thus allowing them the opportunity to either join your conversation or to call for another station that they may have had a prearranged hook-up time for. This is actually all very simple and the first time you hear it happen live it will be very clear to you how to do it yourself in the future. The operating procedures in place on ham radio make it a much more enjoyable environment for everyone.
That is correct. Pass the Technician class written test (no morse code test required) and will you have full operating privileges over 50MHz (6 meters). Your FCC callsign will arrive in the mail in about a week, and you are a ham. Borrow/buy a 2M radio, and you can chat with the nearby hams on 146.52 and of course use the local repeaters as well. For any new ham I would suggest listening to conversations (called "QSO's") on the repeaters for a bit to get the operating procedure down. Again, it's VERY simple but you should listen first to see how it's done before jumping in with both feet.
You absolutely need a license to operate HF! You only need to pass the General or Extra written test in order to operate HF (again, no morse code test). The morse code requirement went away in February 2007 away, as the ITU (International Telecommunications Union, sort of like a "global FCC") and many countries have already done away with it.
Oh, maybe you have a basic misunderstanding about something -- hams don't own ALL the spectrum above 50MHz!!! Hams have been allocated tiny little chunks, that's all. Other chunks are used for hundreds of other purposes, including police, EMS, fire, military, coast guard/marine, national park service, business band radios, taxis, aircraft, cellphones, NASA, and so on. Even your garage door opener has it's own band, as does the 802.11 wireless router you probably have at home. Things you don't even think about, like the little RFID tags used to prevent shoplifting, have their own bands.
Along those lines, the FRS (family radio services) and GMRS (general mobile radio services) have bands allocated in the 462/467MHz range. These are "the new CB's" -- walkie talkies sold in pairs EVERYWHERE (walmart, sears, you name it) and seen at amusement parks, ballgames, and soccer fields, etc so kids can stay in touch with their parents, hunters in a group can talk to each other, and so on. Power limited and with fixed antenna sizes, they are channelized like a CB to keep operation simple. "mom, i'll be on channel 2, mmm-kay?" is all it takes. FRS, no license required. GMRS, you just need to send the FCC a filled out form and $50(?) to get a 5 year "family license" or something like that.
Due to power limitations, there is no such thing as an FRS mobile radio, so you are limited to the little walkie talkies and about 2 miles range (approx). No FRS repeaters either to help things. So an FRS radio is not a substitute for a ham radio in all cases. You can't get the same range simplex nor can you utilize repeaters for even more range. On the other hand, FRS radios are dirt cheap, and if you are in a caravan of cars they sure are handy to use to talk between them.
Posted: 8/10/2007 8:54:28 PM
[Last Edit: 9/15/2008 10:48:26 PM by ar-jedi]
setting up a station at home using a mobile radio
I'm going to assume that you are trying to take a VHF (2m) or VHF/UHF (2m/70cm) mobile radio and use it at home as a base.
The radio itself will come with a microphone, an unterminated DC power cable, a mounting bracket, and a variety of screws. On the back of the radio is an antenna connector, which for these rigs is typically the UHF/SO239 type.
AC->DC POWER SUPPLY
A 50W VHF/UHF mobile will need approximately 10-12A at 12Vdc for full output. There are two types of AC->DC power supplies: the tried-and-true linear regulated power supply and the newer type called a switch-mode power supply (sometimes abbreviated SMPS).
The linear regulated power supply uses a large transformer and large capacitors, hence it is bulky and heavy for a given current output. They also can run hot. one advantage however is that it is "quiet" electrically -- that is, this design produces very little to no RF "hash" which can sometimes interfere with weak signal work.
The switch-mode power supply uses a much more compact design, and is lighter, but can be more "noisy" from an electrical perspective. Newer switch-mode power supplies have largely tackled the RF noise issues, and in any case these noise issues affect HF operations to a greater extent than VHF/UHF operations. For this reason I suggest getting a good SMPS like the SAMLEX 1223. This 23A output model is very well regarded and costs about $99 at the various ham outlets. Shipping is inexpensive since it weighs about 3 lbs. Contrast this light weight with a comparable output linear regulated power supply.
In addition to using the AC mains for input power, you will want to investigate using a battery for backup, and also integrate some method of recharging the battery. There are a lot of options here. One is to get a sealed gel/cell (aka AGM) battery and use a small charger called a "Battery Tender Jr" to keep it topped off. When the AC fails, simply connect your radio to the battery and you are back in business. A second method is to use a device called a Powergate to simultaneously hook up your radio to a battery and a power supply. The Powergate will keep the battery charged and instantly switch over from the AC->DC power supply input to the battery if the AC mains fail.
Depending on the length of the run, you can use one of two types of coax: RG58 (approx 0.250" in dia) or RG8 (approx 0.400" in dia). All things being equal, the larger diameter coax will have less loss; this means more of your transmitter power gets to the antenna, and your receiver hears better as well. For runs under 50', i think you'll do OK with the less expensive RG58 type. Over 100', I'd consider RG8 a necessity. Notice that these two generic types come "branded" by different manufacturer's somewhat differently. Nevertheless, find and study a coax cable loss table with an eye towards 150 and 440MHz; see for example www.hamuniverse.com/coaxdata.html. There are a number of high quality low loss coax types from manufacturers such as Belden, Andrew, and Times-Microwave. Times LMR400 (RG8 type) is especially popular, as is Belden 9913F7.
You will need good quality PL259 connectors for both ends of the coax. Avoid the Radio Shack plated crap. AMP and Amphenol make quality connectors.
My recommendation is to get a quality dual band fiberglass antenna, such as a model from Diamond or Comet. I have a very "low profile" 6 foot high Diamond X50 on my house and it works fantastic. You can get more gain with longer antennas but you may get more questions from your homeowner's association as well. YMMV here. You want the antenna as high up as possible, with no structure within about 10 feet of the vertical element.
Posted: 8/10/2007 9:02:35 PM
[Last Edit: 9/15/2008 10:58:49 PM by ar-jedi]
using a repeater, part I
I think that you have already figured it out ... listen for a bit to how it works.
Ok, i'm going to make some assumptions here; namely, you know the repeater input and output frequencies differ by (typ.) 600Khz (0.6MHz), and you know that the repeater may employ a PL tone on the input, and finally you know how to set your radio to use the correct offset and PL tone. You can test this by making a short TX while no one is using the repeater. Some call this "kerchunking" the repeater. Set up your radio, press the PTT button for about 3 seconds, and release. Immediately you should hear the repeater output (strong signal but no audio), then the courtesy beep, and then the repeater signal will go away. Make sure you can get this far. If you have to do additional testing, simply repeat but add "this is <your callsign>, testing only" to your transmission. Note that if you don't press the PTT long enough (say for only one second), the repeater may not come up. This is a desired feature, so that any short-lived RF noise does not inadvertently activate the repeater.
As opposed to, say CB, using a repeater requires following some specific operating procedures. This is done to ensure that everyone has access to the repeater, and higher priority (for example, emergency) communications can have precedence over daily chit-chat.
Let me give you an overview of the common, daily repeater operations.
In general, if the repeater is not "in use", you can thow a stone into the pond as follows:
Situation 1a: the repeater is silent, no one is around...
Note a couple of things about the plot above: The "passive" opening gambit. The pauses. The retreat.
Situation 1b: the repeater is silent, someone is around...
Note a couple of things about the above: it's strictly back and forth. DO NOT DROP THE REPEATER AND THEN START TO TRANSMIT AGAIN. Once you let go, no matter what you thought of next, do not TX again out of turn. At this point, the other guy has the baton. He may, if he realizes you had more to say, give control of the conversation right back to you. This is even more important when there are three or more in a round table on the repeater. Do not interject out of turn -- it is poor operating practice. We'll get to emergencies in a moment.
Situation 2a: the repeater is silent, someone is around, and someone joins briefly...
Situation 2b: the repeater is silent, someone is around, and two people briefly meet up then move on...
There are a couple of important concepts illustrated above. First, the moment you let go of the PTT, the other guy you are speaking with has the ball. When the new arrival interjects his call prior to the beep terminating your transmission, it is NOT your responsibility to deal with him. It is the other guy you were speaking with. Likewise, as soon as the new arrival is finished, he gives it back to the other guy. In other words, the arriving guy slipped into the space between you and the other guy. When the arriving folks finish, the other guy has the baton and will deal with it however he wants. He may even turn it right back over to you with "hey keith, what was it we were talking about?"
You can help the flow of any repeater QSO by finishing with "back to you, Ed" or similar. This is usually not necessary to keep two people in sync, but with three or more in a roundtable it's very useful (expected, really) to know who is before you and who is after you.
The other little tidbit is that the arriving guy interjects his call prior to the courtesy beep. This is why you must ALWAYS wait for the beep prior to transmitting during the course of a normal conversation.
Finally, there is an immense significance to the word "break" to amateurs. Do not use this word at any time on any repeater unless you are 100% sure you want everyone's immediate and complete attention -- this word signifies an emergency condition and you should never use it (or derivatives like "breaker") unless it's a bona-fide emergency.
The important thing to remember is that it's like tennis. You do not get two swats at the ball. This keeps order in the game.
I have a few tips for you. (1) Solicit feedback on your audio. this will help you learn how to speak into your radio. And (2) always wait for the repeater beep; this allows other stations the opportunity to get their call in as I showed above. Finally, (3), after you key the mike on your radio, allow a small amount of time before speaking -- a half a breath or so. There are a variety of relays, decoders, and so on that are actuated when the repeater goes from RX to TX. If you start speaking right away you may lose the first syllable.
Good luck with your first QSO. It will go fine and you'll meet some nice folks.
Posted: 8/10/2007 9:03:35 PM
[Last Edit: 9/21/2008 8:30:17 AM by ar-jedi]
using a repeater, part II
There are two "goals" of repeater operation:
(1) avoid doubling, and
(2) avoid dead air.
Doubling occurs when two folks transmit at the same time. The output of the repeater will be garbled, or one guy will overpower the other but when he drops the repeater you'll immediately hear that there was another guy talking.
Dead air occurs when it is not clear who actually has the baton. Like in the Olympics, often this is a result of a poor handoff. For example, "I don't know who gets it next, but i'm done talking..." is an example of a poor handoff in a roundtable. Learn the NAME or CALLSIGN of the guy downstream of you. This is the most critical piece of info. You'll instantly recognize your call or name when someone is about to hand you the baton; if you do likewise, there will be no problem for the guy downstream from you.
You'll note that dead air often leads to doubling, and doubling often leads to dead air.
Both of these issues usually happen during busy sessions or when one guy loses track of who is the next in the roundtable. This happens most often with mobile operators, since it's (a) difficult to write things down while driving, and (b) your attention is where it should be, namely concentrating on properly driving and navigating a 4000 LB moving object.
For this reason, I suggest that when learning the ropes you use a small notepad to write down callsigns and names on the repeater you are working. scribe the names and then you can draw arrows to show who is next etc. This will help you immensely at the beginning -- it's hard enough to figure out how things should be working when you are also trying to keep track of callsigns/names in your head. So write the latter down.
Down the road, with practice, you will automatically keep track of the next guy in the list, and when he leaves the roundtable you can update the pointer in your head to the "next next" guy on the list.
As a last resort: if you don't know or forgot who is next, give it to SOMEONE -- ANYONE in particular -- by using their name and/or callsign. It's far better to have a temporary "out of roundtable order" situation (which will quickly be rectified) versus having dead air and the inevitable doubling which will occur next.
Some other thoughts... Commuting times are simultaneously the best time to make 2M repeater contacts but also could be the hardest if the repeater gets busy. Weekends are easier for beginners, as folks aren't so rushed and the roundtable won't be so dynamic with lots of folks coming and going as they start out for work or arrive at work.
You will notice that on a given repeater there are different types of people with different types of personalities -- just like in actual life, say at where you work. You will observe that some folks are more than willing to help out beginners, some are always in a rush to get somewhere, some are retired and want to talk endlessly about their gall bladder surgery, some are tech heads and want to discuss electromagnetic theory, and others are there to chit-chat about Bush or the Sopranos because the repeater is in essence an extension of the water cooler at work. Different repeaters will have different "feels" due to the people who frequent them, again this is no different than your local bars. If you find a repeater crowd that fits with you, great. If not, spin the dial and try another. Or simply try another timeslot -- maybe the commuter crowd is not your clique.
One last thing. Repeaters are run by repeater clubs. The club members, and other organizations, will likely have scheduled activities on the repeater. These are called "nets". For example, there may be an every other week "member net" on Tuesday at 8pm, wherein all the members get together to discuss repeater issues, improvements, or whatever. A second example is an emergency communications net -- you may hear the acronyms ARES or RACES during such nets.
If you tune into the repeater during a net, of any type, you are not to transmit without understanding first what the net is about, and whether it is a "public" net. If it is not, it is time to shut up and listen only. Otherwise, you are simply interfering in an organized proceeding -- which is sort of like driving onto the oval during a NASCAR race and asking "what's going on guys?".
When the net is done, the control operator (for example, a repeater club member acting in that capacity) will announce that the net is over, and that "the repeater is now returned for general use". At that point you are free to use the repeater once again. This just reinforces the amateur radio concept that you always listen first.
Posted: 8/10/2007 9:05:33 PM
[Last Edit: 9/21/2008 8:35:27 AM by ar-jedi]
PL/CTCSS, aka tone squelch
In normal FM ham radio communications, such as with a typical 2M radio, the speaker only emits the received signal when the received signal strength exceeds the squelch setting. In other words, you hear nothing until and unless there is someone talking on the frequency and their signal is strong enough to overcome the squelch threshold.
You can of course increase the squelch setting to prevent weak, far away signals from being heard. However this approach may cause you to miss communications when your buddy is inside a building or behind a hill, making his signal weak. Similarly, increasing the squelch level on a repeater causes more problems than it solves -- the biggest problem being that weak signals from portable HT's are now unable to bring up the repeater. This completely defeats the intent of a repeater in the first place -- that is, giving low power stations good communications coverage.
As you can see, using the squelch setting alone to discriminate stations doesn't work for repeaters. If the squelch is set too low, distant stations will bring up the repeater, even though they have no hope of being intelligible over the noise floor. Even intermod from other nearby transmitters would bring up the repeater. If the squelch is set too high, well we have just excluded folks with HT's from the repeater user base unless they are quite close to the repeater.
Suppose, instead of just using the squelch level, we also employed some other (additional) way to discriminate legitimate signals worthy of repeating versus those signals which should not be repeated. If valid users could send a signal to the repeater that indicates they REALLY want to be repeated, it would be most helpful and completely end the "where to set the squelch" guessing game by the repeater operator.
In the early 1980's Motorola brought out this feature for commerical/public service radio users and misnamed it "PL" for "Private Line". (note: there is nothing "private" about it in terms of encryption or even obfuscation). Commercial/public service radio users with repeaters face the same problems that amateur repeaters face, as described above. So Motorola designed a system whereby the remote radios would transmit a very low frequency (subaudible) tone along with the voice audio when the mic was keyed. The repeater says to itself "ok, i'm receiving a valid signal that clears the squelch setting -- check; AND that signal includes the PL tone that i'm looking for -- check. So, I'll repeat this signal."
As you can see, there is now a two part check at the repeater: (1) signal strength and (2) correct PL tone. This eliminates a lot of "falsing" at the repeater -- weak transmissions and/or intermod no longer erroneously bring up the repeater.
Hence, don't think of PL as some sort of barrier to using a repeater. PL is employed to make the repeater MORE useful, MORE available, and MORE enjoyable. In addition, with PL in place the squelch can be set lower and this will increase the repeater's coverage area. Some repeaters, by the way, employ "dual mode squelch": if the received signal is strong enough, no PL is needed to bring up the repeater. However, weaker signals require an accompanying PL tone. This is sort of a "best of both worlds" approach but really only works when there are no nearby strong intermod sources.
Later on in recent history, the trademarked Motorola term "PL" was given a more representative, accurate acronym: CTCSS. Continuous Tone Coded Squelch System.
Continuous / because the tone is present whenever you are transmitting.
Tone Coded / describes that a tone is sent with the voice
Squelch System / which is exactly what it does (versus that "private line" nonsense)
DCS (digitally coded squelch) is a newer selective squelch system which sends low speed digital data along with the audio. repeaters can use theis data to enable the output transmitter, just like PL does. DCS is rarely used in the amateur community at this point in time, for a lot of reasons. The biggest is that only recently have ham HT's and repeaters become available with DCS features. If you set up a repeater with DCS access, you will end up with a only a very small group of users who have the latest (~2005 on) radios.
The real value of digital selective squelch systems is in modern commercial/public service trunking systems, where additional digital codes either at the beginning of the transmission or on a separate control frequency are used to arbitrate and select talk groups. This allows maximal frequency reuse in busy radio environments (like NYC), and rapid centralized assignment/re-assignment of talk groups (like connecting a subset of NYPD radios to a subset of FDNY radios during a rescue operation).
Hope all that helps explain the technical rationale for selective squelch systems.
Almost all modern VHF/UHF HT's and mobile rigs will scan for and then display the received PL. On my Icom V8000 mobile for example, you hold down the TONE button for 1 second and it begins stepping through the PL tones (about 5 per second). When it finds the correct one it stops there and displays it. Similarly my Yaesu VX6R will auto-determine both PL and DCS (although DCS is rarely used on amateur repeaters). If you are considering a certain model radio, go to the manufacturer's website and download the PDF manual. There you will learn whether the feature is available and how to make use of it.
Some repeaters do strip the PL, but most do not. Hence, on the output of the repeater you should in most cases be able to detect the PL. If not, you have to listen on the input (typ +/- 600KHz on 2M, +/- 5MHz on 70cm)
Understood. The PL search feature is very handy when traveling as you may not be able to read a repeater book (ARRL or Artsci) while you are driving. I don't think ANY amateur radio operator/club is going to get wound up to any degree if you respectfully use their repeater. On occasion you may inadvertently intersect with some repeater activity (say a RACES drill, or an about-to-happen repeater club check-in) but that's the case on ANY repeater. You'll be politely asked to simply listen or QSY to another repeater.
Posted: 8/10/2007 9:09:34 PM
[Last Edit: 8/13/2007 10:40:17 PM by ar-jedi]
ham radios vs CB radios vs FRS/GMRS/MURS radios:
why don't they interoperate with one another?
(1) CB and FRS/GMRS are two total separate things. CB operates at around 27MHz and uses AM modulation. FRS/GMRS operates at around 460MHz and uses FM modulation. there is no way to communicate with CB radio at one end and a FRS/GMRS radio at the other end.
note: you may have been led astray by none other than the FCC... on their web pages, they refer to all unlicensed "civilian" radio allocations as "Citizen's Bands". but the old school CB units we all know and love from Smokey and the Bandit DO NOT interoperate with the new FRS/GMRS radios.
(2) no ham radio (aka amateur radio) transmits on CB frequencies. for that matter, there is no such thing as a multi-mode ham radio in that it transmits on ham AND another band (marine, CB, GMRS/FRS, etc). ham radios transmit on ham frequencies, period. so the answer to your question is "no" -- a V8000, FT8800, IC208H, etc can not communicate with a CB radio. besides the fact that CB is AM at around 27MHz, and a 2M radio is FM at around 146MHz, it is not lawful to use an amateur radio on CB frequencies.
in summary, you'll need both types of rigs. if this poses a mounting problem, look into the 2M and 70cm radios that have remoted faceplates. the main unit can be mounted under the seat (etc), and only a very thin faceplate is mounted on the dash or other area. the very first post in this thread contains a link to pictures of installed radios, and many of those pictures show both a ham radio and a CB radio.
that covers the non-ability of using a common VHF/UHF mobile (or HT) ham radio on frequencies assigned to CB's.
now then, most HF-capable amateur radios can receive AM in the CB band, so you can listen to CB. but no HF-capable amateur radio transmits on CB band.
in summary: ham (amateur) radios are SINGLE PURPOSE: they transmit on ham bands only. while many ham (amateur) radios have wide band receive (and scanning features) so you can listen to all kinds of things like NOAA weather (~162MHz FM), police/fire/EMS (~150MHz/450MHz FM), aircraft (~120MHz AM), and so on, these radios do not transmit outside of the amateur bands.
ham radios generally fall into two categories, HF and VHF/UHF -- although, within the last few years several ham radios that TX in all ham bands HF to UHF (and all modes) in one unit have become available. (modes = AM, FM, SSB, CW).
the typical 2M-only VHF mobile ham radio will TX 144-148MHz FM, but RX from 137-168MHZ -- which covers all of the NOAA weather and public safety "high band". some 2M mobiles also RX "air-band" around 120MHz, in AM mode.
the typicial 2M/70cm VHF/UHF "dual band" mobile ham radio will TX 144-148MHz and 420-450MHz, and RX 137-168MHZ and at least 400-470MHz. public safety agencies not on the 150MHz band and not yet converted to 800/900MHz digital trunked systems can be found in the 450-470MHz range. some 2M/70cm mobiles RX "air-band" around 120MHz, in AM mode, and also RX "mil-air" around 300MHz in AM mode.
the typical desktop HF ham radio will RX *at least* from 1.8MHz to 54Mhz continuous, again across all modes. This covers the 160M to 6M ham bands, and shortwave radio stations, and a million other things. as for TX, there are defined areas within 1.8-54MHz where the transmitter output will be enabled. operation outside those areas is unlawful. as you can see, it is possible with a HF ham radio to RX CB frequencies (~27MHz AM) -- but TX is inhibited.
Posted: 8/10/2007 9:13:32 PM
[Last Edit: 9/7/2008 12:47:07 AM by ar-jedi]
buying a radio (VHF/UHF-centric)
as noted above, ham radios come in basically two flavors: HF and VHF/UHF. for mobile applications, you want a VHF/UHF type. this will give you point to point communications with another ham at a range of about 20 miles, depending on terrain. using a repeater, that range can be extended up to 50 or more miles.
with the same external antenna, a proper mobile radio will provide a better solution than using an HT (handy-talkie). the HT will have at max about 6W output, in contrast the mobile will have 8-12 times that (50 to 75W). moreover, the antenna connector on a modern HT is somewhat fragile, and will not appreciate constant connection and disconnection. to continue, a mobile radio is much more tolerant, thermally, of long transmissions versus an HT. at 6W output, an HT is going to get hot, there is no way around that. finally, the larger speaker on the mobile will make it easier to hear incoming transmissions in the noisy cab of your truck.
for these reasons, and several others, i recommend that your first radio be a true mobile rig, and not an HT. that said, good 2M HT's are quite inexpensive; you can pick up a Yaesu VX170 for about $130. so getting a mobile and then getting an HT a bit down the road is the usual approach.
btw, i speak from some experience here. i initially used an HT for a mobile. over the course of a year (~1991) i wore the nubs off of the BNC connector. i replaced it. i didn't learn from this. somewhat later, the internal wire connecting the BNC to the RF power amplifier broke. disassembly time again.
summary: get a mobile for your truck. the reliability and the audio output level will make it much more enjoyable.
basic "starter" systems...
2M (VHF) only:
Radio: Icom V8000
Antenna: Comet SBB5-NMO (NMO mount).
Mount and coax: NMO type, attachment dependent on installation (trunk lip, gutter, through-hole, magnet, etc)
2M/70cm (VHF/UHF aka "dual band"):
Radio: Yaesu FT7800 (or FT8800 if you can spring for another $100)
Antenna: Comet SBB5-NMO (NMO mount).
Mount and coax: NMO type, attachment dependent on installation (trunk lip, gutter, through-hole, magnet, etc)
with both (a) and (b) above, if your local PD/EMS is operating in the 150MHz range, you'll be able to tune into them. you'll be able to RX NOAA weather on 162MHz as well. setup (b) will allow you to listen into your local PD/EMS if they are in the 450MHz band. neither (a) or (b) will help if your local PD/EMS is in the 800/900MHz band or if they are using a digital trunked system.
note that i selected the same antenna for both applications above. the cost differential between a 2M and a 2M/70cm (dual band) antenna is minimal. so, by buying a dual band antenna right away you will avoid having to get a new antenna if you decide to change out your mobile or you get a dual band HT that you want to use in the truck.
no. in fact, that rubber duck gives the worst performance across the bands. a longer antenna will give better wideband receive than the stock antenna.
don't get hung up on this -- to reiterate what i wrote above, ANY modern VHF/UHF amateur radio has sufficient out of band sensitivity that the choice of antenna is somewhat irrelevant. this in fact can be a problem in urban areas when using HT's in a car with a external high gain antenna (e.g. a 5/8 lambda whip). the high sensitivity of the HT, combined with the high gain of the antenna, make for a nice recipe for intermod from nearby high power transmitters (pagers, taxis, commercial radios, etc).
intermod, for those just starting out in amateur radio, is interference on your radio from sources other than those on the frequency you are tuned to. even though the transmitter may be on a wholly different frequency, the strong nearby signals overload the front end of the receiver, which unsquelches the audio -- and you hear a distorted, unintelligible sound from the speaker.
in commerical radios, resistance to intermod is greatly improved by the use of narrowband RF filters as part of the front end. this prevents unwanted out-of-band frequencies from reaching the discriminator circuit. commerical radios sit on one unchanging frequency though, so the rejection filter(s) can be quite narrow.
why can't these types of filters be employed on amateur HT's? because we want super wide-band RX, that's why. you can't have your cake and eat it too here. either you have narrow front end filters and very little tuning range, OR you have wide/no front end filters and a very large tuning range. in the latter case some unwanted signals are going to slip in.
in an amateur HT, the combination of no/wide front end filters and very high sensitivity make for an intermod-prone solution when used with an antenna other than the stock duck antenna (aka 50ohm rubber resistor). this is generally not a problem out in the fields of kansas but in urban areas you may find that you are much better served with a proper 2m-only mobile rig.
get the VX6R, great 2m/1.25/70cm radio with wideband AM/FM receive. get a short, very flexible duck antenna so you can put the radio in your vest without putting undue stress on the SMA connector. get an SMA->BNC adapter, and a short piece of RG58 coax with a male BNC on one end and an PL259 on the other end -- all this so you have some external antenna flexibility, for example connecting your HT to a mag-mount 5/8 lambda car antenna in a pinch. get the external power cable (E-DC-6) and add on a pair of alligator clips with an inline 1N4001 diode for reverse polarity protection.
FOR YOUR CHARGES:
get qty 2 of yaesu VX170 2M radios. get qty 2 of the 4 x AA battery packs (FBA-25A) for SHTF use. i can't think of a better, more reliable, simple-to-operate HT than the VX170. it's a great value for the (current) price. get another one or two E-DC-6 power cables and attach a cigarette lighter adapter plug. even if a car battery it too weak to start a car it will run a VX170 for 10 days.
i'd like to make one final comment here: a technician class amateur radio license is required to transmit using any of the radios above. licensing exists for a reason: to make the hobby enjoyable for everyone by getting folks educated about the art of amateur radio communications. the technician class test is very straightforward, and can be studied for in a few nights. you will be in and out of the exam session in 20 minutes flat. there is simply no excuse for not getting a license before transmitting.
Posted: 8/10/2007 9:19:32 PM
[Last Edit: 8/13/2007 10:50:50 PM by ar-jedi]
how to find your local repeaters
paper version --> www.artscipub.com/mapbook/
online version --> www.artscipub.com/repeaters/
don't ignore eventually getting the paper version; when you are traveling, it is very handy to have a repeater book in your glove box/map pocket. there is also a palm-sized repeater guide published by the ARRL; click the following link:
note that getting a repeater book is *not* a yearly expense. from my experience (ham licensed since 1991), a repeater directory is good for about 5 years. this is because there is very little "turnover" in ham repeaters, so it's not like the data is changing all of the time. in fact, if you can pick up an older 2005 or 2006 edition book for a buck or two at a used book bookstore, grab it. i'd say that 99% of the repeater information inside will still be useful for the next couple of years.
the data in the repeater books/websites will be as such:
this means that the repeater is located in Middletown, NJ, with the repeater output on 145.485MHz, with a (-) (=minus) offset. the usual offset for the 2M band is 600KHz, or 0.600MHz. so, 145.485-0.600=144.885MHz. this is thus the input frequency -- but note that in some repeater books (like the ARRL's), due to space reasons they show the offset direction but don't show the actual input frequency. others do, like the example above that i pulled off of the artsci web page.
aside: with most modern rigs, the radio is preprogrammed with a 0.600MHz offset, and the offset direction is calculated automatically from the tuned frequency. one radio manufacturer calls this "ARS", for "automatic repeater shift". the radio "knows" which way the offset direction is because of the standardized 2M bandplan. that is, repeaters between M and N MHz offset UP, and repeaters between X and Y MHz offset DOWN. i don't remember offhand the exact frequencies for the repeater allocations in the 2M bandplan but you get the point.
the next number over in the example listing above, 151.4, is the PL/CTCSS tone frequency (in Hz). without setting up your radio to emit this PL tone while you are transmitting, the repeater will not activate. with most modern radios you first must set the PL tone frequency, and then enable transmission of it. both steps are required. finally, the last item in the repeater listing is the FCC callsign of the repeater trustee or repeater group, in this case N2DR.
Posted: 8/10/2007 9:24:13 PM
[Last Edit: 8/14/2008 6:31:50 PM by ar-jedi]
mobile antennas and mobile mounts
the NMO mount antenna will not become a hazardous flying object if/when you get into an accident like a mag mount will.
the NMO mount antenna will not damage your car finish like the dirt trapped under a mag mount will.
the NMO mount antenna will not fly off when you hit a frost heave on the highway at 80 MPH like a mag mount will -- leaving scars where it bounced along the side panel of your car while you slowed down.
the NMO mount antenna will be imtimately grounded to the chassis of the car, and will exhibit better performance (=range and noise immunity) than the capacitively-coupled mag mount.
summary: there is a reason that law enforcement, government, commercial, industrial utility, and other applications rely on the NMO mount --> it works.
for those unfamiliar with this type of mount, see the pics of my 2m/70cm truck antenna intsallation, near the top of page 11 in this thread...
the 3/8" hole version (developed by Antenna Specialists) is fairly new (a few years) and of course needs a smaller hole than the original Motorola-designed 3/4" version.
above the sheet metal they are exactly the same, that is they both accept all NMO mount antennas. the two sizes differ only in the mounting hole diameter. that said, i have heard from more than one person that the 3/8" version, because of the ferrule it uses, is less-than-watertight compared to the normal 3/4" version. moreover, evidently on some models the coax exits straight down with the 3/8" version, compared to the right angle of the 3/4" design. hence, the 3/4" version needs less underside clearance.
so i side with the 3/4" version because it is tried and true; the mount in my pics above is a 3/4" type. it is a MAXRAD part number SMML195-NC, a commerical quality stainless steel 3/4" NMO mount w/ 17' of LMR195 low loss coax -- a very nice setup.
or more generally
MAXRAD mounts are available from
Harrisburg PA Office
(aside: why did i go stainless vs brass? i live 100yds from the atlantic ocean -- crap corrodes around here like you would not believe. the PN above is the exact type that the radio guys who outfit our local police and county sherrif's cars use.)
the connector on the back of a 2M rig is called by several names, including "UHF connector", "SO239", and "PL259". the first two are "more correct", with SO239 being exact. SO239 describes the female end (on the radio) and PL259 describes the male end (on the coax). this, btw, is the same two connectors that CB radios use. note that the SO239/PL259 pair is NOT weatherproof so it should never be used for outside applications. moreover, it is not a great connector for frequencies above 150MHz; even for 70cm use (440MHz) it is a compromise. there is a reason that BNC and N connectors exist: they are markedly better RF-wise and they are weatherproof in contrast to the inexpensive SO239/PL259 pairing.
MAXRAD is commerical quality but most NMO mounts i've seen are pretty decent.
also see models from Diamond and Comet.
note that the NMO mount part number i referenced above does not include a connector at the radio end of the coax. so you need to procure and solder a PL259 onto the coax after you are finished reeving the coax cable over the hills and through the valleys from the roof down to wherever you mount the radio. get an AMP brand or Amphenol brand PL259, and not some junk from radio shack (which are plated crap connectors). wherever you get a quality mount from will be able to supply you with a quality PL259. make sure to get the solder-on type, and not the crimp-on type. the crimp-on type requires specialized (expensive) tools to attach to the coax.
one more thing:
you install an NMO though a hole in the sheetmetal of your vehicle. i know this sounds scary. will it leak? the answer is no -- millions of taxis, police vehicles, gov't vehicles, and so on use the NMO mount without problem. it is the best mount avaliable from a weather, RF, and reliability perspective..
the best ways to make the mounting hole are (1) use a 3/4" dia chassis punch, or (2) use a step drill made for specifically this purpose. the former is available wherever Greenlee punches are sold, and the latter can be hard to come by but consult with Google. i use a chassis punch.
Posted: 8/10/2007 9:31:32 PM
[Last Edit: 8/13/2007 10:34:52 PM by ar-jedi]
suggestions on radios and accessories
i assume you are talking about getting a VHF/UHF radio first...
as for a base. there are two ways to go here, and they are as follows: get a mobile (aka compact) rig and an external power supply, OR get a proper base station radio.
now then, in light of recent regulatory developments, i'd suggest that you start saving your pennies and pick from one of the following radios which will give you VHF/UHF and HF capabilities:
if you go with separate VHF/UHF and HF rigs, i would not hesitate to recommend the Icom IC718 -- it really is the HF amateur radio bargain of the century.
all of the above assumes you want to go with a new rig. if you want or can only afford a used rig, scan the reviews at Eham for high ratings and then watch the Eham and QRZ.com classifieds. or, if you come across a good rig (like a IC735 or TS50) at an estate sale, snap it up.
-- get a battery pack that accepts AA's. then get a 6 pack or two of Lithium AA's (very long shelf life).
-- construct/buy a roll-up J-pole antenna made from $0.89 worth of TV twin lead. will extend your range 10-fold.
-- buy a suitable power cable to connect the external power in jack to a cigarette lighter, so you can always power/recharge the HT in the car.
-- construct/buy/McGuyver a soft case so when you drop it (inevitable, btw) it doesn't break your heart.
-- get a 4AH, 6AH, or 12AH gel-cell/AGM battery and a suitable power cable so you can use your HT for a couple of days while without commerical AC power.
-- scroll back a few pages in this thread to where i posted a list of recent ham radio-related links, and find the one that has SF'er Rjsteed's setup in it. this will give you lots of ideas on how to make a convenient, pack-portable setup for on-the-go comms.
-- look up the origin of the ham radio signoff "73" and report back to us.
ok, you are on the right track with both of the links you picked out...
the design above is a center-fed vertical dipole. one advantage is simplicity of construction; however there are several practical disadvantages; namely that the feedpoint is halfway up the antenna, and that the feedline must "exit" the antenna proper at a 90degree angle for some distance (at least 1 meter would be a good idea). the combination of these two issues make for a more cumbersome hanging arrangement in a field expedient design. the result of the feedline hanging down too close to the lower element of the antenna will be poor field uniformity. moreover, by driving a balanced antenna (dipole) with an unbalanced source (HT) and transmission line (coax), you are all but guaranteed to have feedline current on the shield. this will make the antenna even less uniform from a gain perspective -- you may find a big lobe in one direction and poor performance in another.
that said, the dipole is of course a proven design and if you can solve the "how to hang it" issues it will work well.
the design linked above is a 1/2 wave J-pole. the Jpole is a method of end-feeding a half wave radiator. properly constructed, performance will be on par with the dipole, and the easier "hanging" of the Jpole make it more useful as a field-expedient antenna. you are right about the 37.25" piece -- it is just along for the ride. the real work is done by the radiating element (54") and the matching section (15.25"). while the thought of driving a dead short such as is found at the bottom of the Jpole may scare you at first, in RF-land things work a little different.
IMHO, for SHTF applications, the Jpole is the antenna of choice due to low cost, ease of construction, ease of hanging, and good overall performance.
in both of the cases above, the coax type should be RG58 (50ohm characteristic impedance) and you will terminate the coax with a BNC connector. the SMA is not suited for RG58 coax, so the best way to get to attach the coax to the HT is to use a BNC<-> SMA adapter. these are very commonly available at ham places for a couple of bucks.
see "#0531 -- SMA M-BNC F -- SMA male to BNC female adapter" here:
you can also get a short patch cable, such as the HB05 as is shown here:
note that using this type of adapter cable will impose less stress on your HT's SMA connector than using a BNC<->SMA adapter. this is because the coax shown above is more flexible than the typical RG58.
if you have the coin, you can get an Icom 706 MkIIG. one of the best radios ever. decent receiver, 100W out on HF, 50W on VHF, and 20W on UHF, all in a very small form factor. it is a tad thirsty on RX (~1.5A) so keep that in mind when operating from batteries.
icom 706 MkIIG. then sneak a $140 2M mobile into the truck a few months later.
Posted: 8/10/2007 9:37:22 PM
[Last Edit: 9/20/2007 8:45:28 PM by ar-jedi]
lightning protection / station grounding
great radio, a great start for you.
perfect, excellent, outstanding in fact.
yes. the right way to do is this is to make a bulkhead entrance panel. for example, get a small sheet of 1/8" aluminum and drill a hole to accept a UHF bulkhead connector (female to female). mount this as part of the exterior wall on your basement. the coax from the antenna screws onto the outside, the coax from the radio screws onto the inside. the aluminum panel should be grounded by using a hefty piece of #6 AWG wire running to one or more copper grounding rods driven into the earth. a lightning protector (Polyphaser brand is OK, but I.C.E. (*) is the best) should be installed on the outer side of the bulkhead, and the ground tied to the aluminum panel.
also check out
and follow the link to "Lightning Protection Tech Articles" within.
you need good coax, nothing less than RG8, perhaps 9913F7 or LMR400. don't skimp, every dB lost on the way down to your radio means fewer stations that you will be able to hear.
yes, that's what is common on HF and VHF gear.
perfect. see lightning protection strategy outlined above and read the following:
www.iceradioproducts.com/31a.htm <------ !!!!
i would not interconnect your antenna system with the house grounding system. i say this for two reasons...
one, your antenna system is an attractive lightning target (even a nearby strike is going to couple thousands of volts into the antenna). this is not voltage/current you want in the house, on the house ground system. you want to keep this out of the house when possible, in order to prevent any collateral damage.
two, you may have an ineffective or otherwise compromised house grounding system, and it may not provide an adequate path for the high currents induced by a direct or nearby lightning strike.
for the reasons above, i suggest that you keep your house and antenna grounds completely separate. this means that the metallic tower should be grounded, and then the antenna downlead(s) should be grounded/protected using the bulkhead panel method i outlined above.
regarding the grounding rods, more is better than deeper. two or three 6' long rods, driven in approximately 6' apart and interconnected with heavy guage wire, make for an optimum ground.
keep in mind that the above methods, while not guaranteeing 100% that you will never have lightning damage, is far greater protection than most folks employ. in areas such as Florida (the lightning capital of the US), i would say that the above approach is mandatory.
the SMPS will not have any problem cleaning up the power.
you may want to browse through the following:
Get grounded: protecting electrical devices from lightning transients (Part 1 of 2)
Get grounded: protecting electrical devices from lightning transients (Part 2 of 2)
Posted: 8/10/2007 9:43:14 PM
[Last Edit: 12/5/2008 1:21:03 AM by ar-jedi]
more info on mobile antennas
1) I have about settled on the Icom V8000 2M mobile. Since I want a "pro" installation and I don't know any hams yet IRL, should I have it installed? I know where I want it installed. You think a stereo shop could do the physical install or should I seek out a 'radio shop'?
the V8000 is an excellent radio 末 i have two. the front facing speaker is great, and the unit is very tough. mounting and powering the radio is not at all complicated 末 you can do it yourself in a few hours. if you want to get "pro" help, i would look for a place that installs two way radios. look in the yellow pages for a "Motorola" or "Vertex" installation shop. they will have the necessary know-how and tools to not only put the radio where you want it but also route your antenna coax.
2) What are a few 2M antennae which are generally considered solid?
you need two pieces: the mount and the antenna. the mount comes with coax attached (usually about 15-17 feet).
the choice of the mount is dependent on two things: the surface type you are mounting to, and the connector which will interface with the antenna proper.
for the first part, antenna mounts are offered in gutter rail mount, trunk lip mount, through-hole mount, mirror arm mount, and others. you just need to decide where you are going to mount the antenna and pick a mount type. you will note that trunk lip mounts have a short piece of very thin diameter flexible coax which allows the coax to pass through the seal without causing a leak or causing damage to the coax itself. good mounts come from Diamond, Comet, Larsen, and Maxrad.
for the antenna connector, there are really three choices: NMO, UHF, and N. let's start at the end, the N connector. the N has unparalleled frequency capability and is completely weathertight, and therefore is only the choice for 900 and 1.2Ghz mobile operation. however, you will generally not want to use an N for 2M/70cm work as the number of 2M/70cm antennas with N connectors is limited. the UHF connector is the tried-and-true PL259/SO239 combo. it sucks at almost everything: it is neither constant impedance nor is it very good at 440MHz/70cm nor is it designed to be weathertight. antenna manufacturers have done their best but it does have its limitations. there are many many 2M/70cm antennas with the UHF connector. which brings us to the NMO. this Motorola-designed connector was built from the ground up for mobile applications. it is weathertight, has excellent frequency span, and there are a bajillion commercial/industrial/public safety users out in the Real World using it every day. this is the very same connector you see at the base of the antenna(s) on any police, EMS, or firefighting vehicle. the NMO is the connector type you should use.
now then, once you have decided on a mount and connector type, you can pick an antenna. it obviously must have the mating connector on the bottom. the height is the primary influence on performance, though there is one other important factor which i'll discuss in a moment. however, taller antennas drag on garage doors, attract more attention, and put more stress on the mount. so it is a tradeoff. nevertheless, i would not choose a 2M/70cm antenna of less than ~19 inches. there are too many limitations below that length and moreover you don't really want to shove 75W into an antenna that small.
reputable antenna vendors include Diamond, Comet, and Larsen.
3) I plan on mounting the antenna on the back of my Jeep very near the spare tire. Can I take any special precautions not to let it touch the tire, or should I reconsider the mounting location?
i mentioned above one other factor... some antenna designs, such as the 1/4wave ground plane, rely on 末 you guessed it 末 an underlying ground plane for good performance. should the ground plane not exist (say on a fiberglass roof) or should the ground plane be asymmetric (for example, if you mount the antenna in one corner of the roof), the antenna will not operate to your expectations. you may have problems getting the SWR to sit down as well. keep this in mind as you pick an antenna type. it may not be easy for a beginner to determine what mobile antenna designs are "more compatible" with a given mounting location. in that case, post a pic of where you'd like to mount the antenna, and what height you are looking to use, and we can make some recommendations.
Posted: 8/10/2007 9:45:39 PM
[Last Edit: 1/26/2008 11:59:44 AM by ar-jedi]
Building your own repeater
it's not simple.
there is no way to build a modest size radio that does "same band repeat". it certainly can not be done in an HT or mobile radio. the problem is that the TX output saturates the RX input, causing desense. the net result is that your "pseudo-repeater" is nearly completely deaf and for the most part is listening to itself.
in a "real" 2M repeater, there are cavity duplexers which provide DEEP notch filtering on the input to the RX, with the notch centered directly on the TX frequency just 600KHz away. the absolute best way to get the depth of the notch you need is via a mechanical cavity filter, and not some collection of discrete components. typically, you will need between 60 and 100dB of TX to RX isolation in order to have an effective repeater. note that you can sometimes "cheat" by using seperate TX and RX dipole antennas, and putting one about 20-40 feet directly above the other. this gives some isolation but does not completely solve the problem. so you are back to needing a cavity duplexer. in general, the selection, procurement, and tuning of the duplexer(s) are the most difficult parts of a repeater construction project.
hence, the reason that your radio will never do same band repeat is because the cavity duplexers for 2M are roughly the size of large gas welding tanks.
so you'll need:
a repeater controller,
and most importantly, a duplexer.
the duplexer is the key to the whole operation. the TX and RX frequencies for a 2M repeater are separated by a mere 600KHz. isolation between the two is critical, assuming you want to use one antenna. a proper duplexer is neither cheap (~$500 -> $2000) nor small (think medium size water heater).
link --> http://www.repeater-builder.com/rbtip/repeater101.html
1) "cross band repeat" on HT's and mobile rigs works because the TX and RX frequencies are widely separated (by hundreds of MHz), and this in turn makes filtering the TX RF on the RX input much less critical. you'll also note that duplexers for the 440MHz/70cm band are easier to design and build, due to the fact that the offset in the 440/70cm band is 5MHz, in contrast to the narrow 600KHz split used on 146/2M.
2) nothing, besides the repeater band plans and de facto operating practices, prohibits you from having a larger than 600KHz split on the 2M band. for example, you could RX at 144.05 and TX at 147.95. that is an almost 4MHz oddball split. this would make design of the duplexer easier and potentially allow it to be constructed much smaller than the typical 2M 600KHz split setup. nevertheless we are still not talking about something that you can hang on your belt.
see also these pics for examples of duplexers:
Posted: 8/10/2007 9:46:14 PM
[Last Edit: 5/14/2011 10:19:16 PM by ar-jedi]
crossband repeat with a dual-band mobile radio
what are some decent mobile radios which can be used as repeaters for my HT?
the Yaesu FT8800 comes immediately to mind. it has a good rep (check eham's reveiws) and moreover it is very straightforward to set up LEGALLY as a crossband repeater. some mobile rigs are tough to convince to do simplex crossband repeat, which is the correct, legal way to do it.
the in-car mobile radio should ONLY crossband the 440MHz input from your HT onto the 2M input to the repeater. it is neither necessary nor strictly legal for the in-car mobile radio to crossband the 2M output from the repeater onto 440MHz towards your HT. the latter is superflous as your HT has more than enough sensitivity to hear the output of the repeater.
this scheme meets the letter of the law in terms of ID'ing ALL of your station transmissions. the general method of full crossband repeat does not. any time the repeater output is active, your crossband mobile radio will be TX'ing on 440MHz. if you went to sleep, the mobile would continue to crossband and thus you are violating the ID-every-10min rule right off the bat.
two other advantages of this simplex crossband repeat configuration are that the in-car radio will stay much cooler and vehicle battery consumption will be markedly reduced as well.
to configure simplex crossband repeat on the FT8800, set the 440MHz side TX offset to an absurdly high value, such that the transmit frequency falls outside the 70cm band. when the 2M repeater is active, the FT8800 would normally be trying to crossband it onto 440MHz, but now the FT8800's display will show ERROR as it is refusing to TX outside the 70cm band. in this configuration there will be NO 440MHz emissions from the FT8800. when your HT is transmitting, the FT8800 will RX on 440MHz and crossband that to 2M, which will be set to the 2M repeater input frequency. your HT should be set for "split" or "crossband" operation. TX on 440MHz to the vehicle, and RX on 2M from the repeater.
So I'm just bragging today. I'm pretty excited about my crossband repeater. Now that its set up, it will only take seconds to get the radios ready when I go hunting.
a few words of caution.
(a) the way that you have it configured, if the club repeater is a busy one your truck radio and battery will both have very short lives. a typical mobile radio is not designed for high duty cycle (meaning lots of TX time) applications. it will get hot, very hot, fairly quickly with an active club repeater. and when set up for full duplex crossband, your radio will be be pulling 5, 8, 10, 15A or so (depending on your 70cm crossbanded power output) whenever the club repeater is active. in general, the club repeater output is going to be active more than you will be active with your HT, so the primary contributor to current draw and heat generation is crossbanding the club repeater output.
(b) the setup you describe is, to the letter of the law, illegal. the issue is that transmissions from the crossband repeater are not guaranteed to be ID'd by the station operator every 10 minutes. while the club repeater is active, but you are not personally using the crossband repeater, there is no ID and this becomes the legality problem noted prior. if, for example, you left the crossband repeater active while you are hunting but decided to take a short nap or perhaps a swim, you have this exact situation. your mobile rig continues to crossband the club repeater but there is no ID on the output.
both problems (a) and (b) above are easily avoided by configuring the mobile for "simplex crossband repeat" instead of full duplex crossband repeat. how does simplex repeat differ?
in full duplex crossband repeat:
from the club repeater:
the approach with simplex crossband repeat relies on the fact that your HT can very often hear the club repeater output just fine. hence it is NOT necessary for the mobile radio to crossband repeat the club repeater output. not doing so saves vehicle battery power and makes the entire setup completely legal since all transmissions from the vehicle are properly ID'd.
in simplex crossband repeat:
from the club repeater:
so what is different? for one, the HT is set up for "split" or crossband operation. the HT TX's on 70cm and RX's on 2M. most all dual band radios can do this 末 for example it's simple to set up on a Yaesu VX6R. and second, the mobile radio is set up not to TX on the 70cm side with an active 2M input. this mode of operation is not straightforward to set up as it is not generally a feature documented in the instruction manual. nevertheless, most all dual band, crossband-capable radios can be set up this way using a small cheat. the popular FT8800 is such an example, on the case of this radio, set the 70cm side TX offset to a frequency outside the amateur band. then enable crossband repeat. when the club repeater is active (that is, the radio is RX'ing on 2M and attempting to TX on 70cm), the display will indicate "ERROR" as it will not TX outside the 70cm bandplan. however, the reverse direction (RX on 70cm, crossband onto 2M) will continue to work just fine. in this manner, the FT8800 can be set up for the desireable "simplex crossband repeat" mode.
again: using this simplex crossband repeat concurrently saves you a ton of battery power AND prolongs the life of your mobile radio AND keeps you legal.
I really like the idea of being able to use a radio in my car or house to repeat for my handheld.
get an FT8800, keep the power down, and keep your conversation lengths to a minimum. no 2M/70cm mobile can be utilized as a true repeater 末 it will simply get way too hot and you'll end up cooking the power amp.
one trick that most folks employ on the FT8800 does two things: it helps you stay legal and it helps keep the heat to a minimum. it goes as follows...
recall that with an HT you can generally hear the repeater, you just can't hit the repeater (too little power into a 50ohm rubber resistor antenna). so, you really only need the crossband repeat radio to repeat what you are TX'ing, not what the repeater is TX'ing. (some folks refer to this as simplex repeat).
in other words, when you TX on 70cm, the crossband repeater RX's your signal and simultaneously TX's it on 2M. this is what gets you into the repeater. when the repeater TX's on 2M, the crossband repeater does nothing. you receive the 2M signal directly by using split operation on your HT (TX on 70cm, RX on 2M). by the way, this scheme improves the legality of the whole situation since the crossband repeater's 2M output is always ID'd by you. (in a normal crossband repeater setup, there is no way to "truly" ID the 70cm output per the 10minute FCC rule. if you turn off your HT but forget to turn off the crossband repeater, it will merrily contine repeating without any ID 末 which should be your call).
so how do we get the crossband repeater to do nothing when it receives a 2M signal (from the repeater), but crossband repeat when it receives a 70cm signal (from your HT)?
on the FT8800, you can't directly do this. there is no "simplex repeat" mode to accomplish this. but, you can fool the radio another way... set the TX frequency on the 70cm side to a invalid frequency, outside the radio's TX range. say, 480.000 MHZ for example. now when the 2M input is active, the radio display will show "TX Error" as it is refusing to TX outside the amateur band. but when the 70cm input is active, the radio will happlily crossband repeat the signal. sneaky, but it works nice 末 it's legal, and it saves on TX power dissipation since the crossband repeater is only making RF power for half the conversation.
Originally Posted By cliffy109:
I found a great link on cross band repeating. It describes both the simplex and regular cross-band. It also reminded me to set up tones to prevent accidental use of the truck radio.
Posted: 8/10/2007 9:48:08 PM
[Last Edit: 10/12/2008 7:57:38 PM by ar-jedi]
notes on operating from batteries during SHTF
i thought i'd post a few notes on power conservation and field-expedient power techniques for radio operations during SHTF...
1) PREP! if AC power fails, you'll have (a) what power is on hand (stored batteries, UPS's, and so forth) and (b) what power can be made (solar, genset, etc). line up your resources ahead of time so that you'll have primary and fallback sources during SHTF. also look at it from an immediate and long term perspective: "first i'll run from gel-cell, then i'll get the genset started to power the house heat, and i'll recharge the gel-cell while the genset is running."
2) to that end i suggest that every ham have at least one 12V 12AH battery on hand. these can be had for about $20 and vastly increases operating time compared to an HT's internal battery. and of course you can power a mobile at low power as well. (example)
3) buy or build any cables necessary to get power from a source into your HT, mobile, or base station. modern rigs have specialized power connectors so it's not alwasy easy to rig up a field expedient solution for the radio end -- especially on HT's. the power source end could be a pair of aligator clips, or an Anderson Powerpole, or a pair of 1/4" quick-connect (faston) tabs to mate with a gel-cell battery. don't forget to keep these cables where you can find them!
4) at the onset of a blackout, immediately disconnect the loads from your household UPS's (e.g. PC, plasma/LCD TV, etc) and then turn off the UPS via the front panel. you have no idea how long the blackout will last, and the batteries in the UPS store an appreciable amount of power. you may need that power in the next few days -- but you probably don't need to watch TV on your 50" LCD right now. the power stored in the UPS's gel-cell batteries can be used directly (by removing the batteries from the UPS) or indirectly (by plugging AC loads into the UPS's outlets). either way, a UPS makes a somewhat portable, quiet, but time-limited "generator". the trick is not to piss away those electrons during the early stages of the blackout.
5) there is a lot of power stored in random places your house -- which in turn can be used for comms. for example, make an adapter/converter to allow you to connect a battery from your cordless drill to your HT. modern cordless drill batteries are really stout and will give great perfromance. typical 7.2, 9.6, 12, and 14.4V drill batteries will power your HT or mobile radio directly. higher voltage batteries (e.g. 18V) will need a step down regulator. if you have a DC-powered backup pump for your sump, that may be another source. of course the lead acid/gel-cell batteries in your lawn tractor, motorcycle, and home alarm system can be used in a pinch. similarly, laptop computer batteries store an impressive amount of power, although the connector arrangements and voltage levels may make them difficiult to work from. but any/all of these could be utilized if your primary backups become exhausted. there may be other options as well. for example, i have a little label maker made by a compary called P-Touch. it takes 6 AA batteries. coincidentally, so does my HT. so i keep the P-Touch whene I keep my AA batteries. i look at the label maker as storage for 6 AA's -- they may not be 100% but it's something.
6) be very careful with "auto-failover" power schemes. auto-failover seems like a good idea. but let me relate to you a little strory. i have a friend who powers his station at home with a big ass DC spply and a big ass Optima deep cycle battery. the two are interconnected via a Powergate (link). this device keeps the battery charged and automatically switches the load to the battery when the AC power fails. when the East coast blackout occured a couple of years ago, my friend was away camping out in PA. like most hams, he has certain equipment which is "always on". in this case, he had a 2M mobile on and a few accessories (powered speaker for his HF rig). well, at the end of his trip he returned home to find a dead battery. his auto-failover scheme had taken control of his available power out of his hands. this example shows that you should keep control over when your backup power is being used.
7) radio operating time on battery power is primarily constrained by TX time -- so keep your transmissions short and keep the RF power output set to the minimum needed for reliable comms. one other factor that can help is by setting the receive duty cycle on the radio. some radio manuals call this "battery saver". this feature reduces power consumption during standy -- effectively increasing the amount of operating time. it works by turning off parts of the receive circuit for a fraction of a second, and then turing these parts back on to check for a valid signal, and then repeating the cycle. during the time these circuits are off (aka sleep mode), the radio needs extremely little power. in Yaesu-HT-speak, this feature is found under "Receive Battery Saver Setup" in your manual. you select how long the receiver circuit is off -- 200ms, 300ms, 500ms, etc. during this time, the radio is fully asleep and the display blinks the "SAVE" icon. as long as your counterpart station transmits for longer than your "sleep" time, you'll hear them.
8) set the APO (automatic power off) function on your battery-operated radio. this way, if you fall asleep or forget that your radio is on, it won't consume all of the available power. on my SHTF HT's i set the APO to 30mins. on my vehicle radio, i set the APO to 1HR.
9) find out the RX power consumption of all of your radios. this is valuable info. put a label on the bottom of the radio or inside the battery compartment with this info. it will help guide how long a given power source will last. a typical HF base station needs about 1.5 to 3A on receive; a typical mobile, about 300 to 500mA on receive, and a typical HT about 150mA (30mA on battery saver standby). hence, if you are on gel-cell battery power it is much better to listen in on the local 2M repeater activities using an HT as compared to a mobile rig. the former will provide more operating time (more than 2x as much) from a given battery capacity. if everything local is down, and you want to listen in on national or world events via shortwave, pick the best HF/SW radio to make use of available power. your hyper-expensive HF rig may have a better front end but if the 10 year old $59 Sony "world band radio" gets the news to you at lower power consumption than that is the better tool for the job. if you have a designed-for-QRP rig (e.g. Icom 703+ or Yaesu FT817), use it in favor of a std HF rig as a SW receiver -- QRP rigs are very much optimized to conserve power (both spec ~300mA receive current).
as noted previously, the discharge curve is NOT linear. doubling the load does not half the time the battery supports the load -- the battery actually supports the doubled load less than half the time.
to wit, from
we see that the Trojan T-105 has the following characteristics:
Capacity Minutes, 447 @ 25A
Capacity Minutes, 115 @ 75A
so the "apparent capacity" with a 25A load is (447/60) x 25A = 186 AH
and the "apparent capacity" with a 75A load is (115/60) x 75A = 143 AH
continuing on, we see that the manufacturer also states:
5 Hr Rate, AH = 185
20 Hr Rate, AH = 225.
this tells us that the battery will deliver,
185AH/5h = 37A for 5h
225AH/20h = 11.25A for 20h
IF the discharge curve were linear, it would show that the battery could supply 4 times the current for 1/4th the time. but, 11.25Ax4=45A and 20h/4=5h. so ideally the battery would put out 45A for 5h. this is not the case; from the manufacturer's data (linked above), the battery can only supply 37A for 5h.
putting all of the above into a table, we have a total of 4 datapoints:
11A for 20h (~220AH)
25A for 7.5h (~187AH)
37A for 5h (~185AH)
75A for 1.9h (~142AH)
as you can see, the bigger the load, the lower the capacity of the battery. this is just physics, and every lead-acid (wet or gelled electrolyte) battery has a similar characteristic.
keep in mind that the T-105 is a 6V battery; you need two connected in series to drive a 12V inverter or to power 12V loads. using two in series does not double the AH capacity, it simply doubles the output voltage.
we'll ignore the tuner since it probably draws 500mA only while tuning.
.25 x 20.5A = 5.125A avg TX current / hr
.75 x 1.5A = 1.125A avg RX current / hr
5.125 + 1.125 = approximately 6.25A per hr of operation is required.
from the datasheet, a 9 LB 12V 12AH AGM battery, e.g.,
has the following capacities:
20 hour rate F.V.(1.75V/cell) (600mA to 10.50volts) 12.0 A.H.
from the average current we calculated above, we see that the 6.25A falls in between the 5 hour and 1 hour discharge rates. interpolating a little bit, we could assume that at 6.25A, the 12V 12AH rated battery has about 8AH of capacity.
8AH / 6.25A = 1.28 "theoretical" hours of operation. in practice, it will be less due to several factors, one of which should be you -- don't completely discharge a lead-acid battery (wet, gelled, or AGM type). i would use a safety factor or .5, meaning you should double your capacity to get an hour and a quarter of operating time.
hence, i would recommend at least a pair of 12V 12A batteries, wired in parallel. better yet would be a pair of 12V 18AH batteries wired in parellel, or a bigger single battery.
i would also recommend using as little TX power as possible (this will make a HUGE difference in operating time).
and now you you know why QRP rigs are popular for field operations.
8 x AA battery pack, from Digi-Key, link.
OEM Yaesu E-DC-6 power adapter cable, any online Yaesu store.
Andersen Powerpoles, Powerwerx.
the nice part about introducing the powerpoles is versatility. while not necessary, they allow you to easily connect the battery pack to anything that needs powering during SHTF.
AA battery pack shown close up powering a IC703+
and yes, i've just realized that was the worst possible background. thank you.
that 8xAA pack, by itself, is not going to work for the FT7800R.
from the 7800 manual:
minimum input voltage, from above spec: 13.8Vdc x 0.85 = 11.73Vdc.
maximum output voltage, 8xAA NiMH: 8 x 1.2Vdc = 9.6Vdc.
ergo, the 8xAA holder does not produce enough voltage to operate the FT7800R. you need *at least* qty 10 AA cells (=12Vdc when fully charged), and qty 12 would be better (=14.4Vdc when full charged).
moreover, AA's have a limited peak current out capability, and even though the radio requires around 0.5A on receive, transmitting even on low power is going to require appreciable current -- which will likely cause the voltage from 12 AA's to sag to a degree that the radio will not operate correctly.
for all of the reasons above, i think you will be better off using a small AGM/gel cell battery; for example, a 12V 7.2Ah unit. in contrast to the 12 x AA setup, this type of battery will provide the correct voltage and the peak current capability is far, far greater.
pre-made version of the AA battery pack pictured above:
Posted: 8/10/2007 9:55:23 PM
[Last Edit: 9/15/2008 11:00:49 PM by ar-jedi]
communications bug-out-boxes / emergency radios
very nice 2M radio.
in essence, yes. but you need to apply some thought to this as well, so that the results are both useful and in line with your expectations. for example, consider the 8 items that i listed at the top of my RACES box writeup:
since you are looking to do something similar but a bit simpler, ask yourself which of these requirements you might change, or even delete entirely. there may be other requirements that you may want to add. the list above is what i thought my box should do at the endpoint, but that list is not necessarily the same as your goals. so take a shot at how your box may differ. this will provide you a good starting point. it's imprtant to know about where you are going before you start out driving. you can certainly make some changes along the way, but there are some upfront considerations that will save you a lot of time and/or money down the road. as an analogy, if your goal was to build a lightweight CQB rifle, the last thing you'd want to start with is a 20" HBAR barrel. that barrel does not help you towards you goal one bit unless you have a lathe and gunsmithing expertise, or you pay someone who does have a lathe and expertise.
from the Yaesu website i found the brochure on the FT1802M. there i learned that the FT1802M has the following current draws:
so we can see that at maximim power out (50W), the FT1802M draws about 10A at 12V. this is a fair amount of power(10A x 12V = 120Watts). i would not recommend that you use the cigarette lighter for this application. the current required by the radio is quite large to be pulling it through the cigarette lighter. while it would appear that installation of the radio into your vehicle would be expedient using the cigarette lighter as the power source, i think you are going to run into a number of problems doing so. for that reason, and several others (electrical noise, primarily), i recommend running the radio power cables directly to the battery (properly fused, of course). if doing so is troubling you, let me know and i will walk you through the proper connections. it is extremely straightforward and can be backed out of if for example your vehicle is leased and needs to be returned without the radio in place.
i noted above that the FT1802M draws 10A at 12V, or about 120W. we know that 50W is going out the antenna connector, but where is the other 70W going? the answer is heat. at high output power, your FT1802M chassis is going to get quite warm. the radio housing incorporates fins which transfers heat from the chassis to the surrounding air. through a process called convection, buoyant hot air carries heat away from the radio, drawing in cooler air, and the cycle repeats -- and the radio hopefully stays in it's operating temperature range.
however, if the radio is placed inside an enclosure which limits the amount of cool air available, the hot air will just get hotter, and eventually the radio will overheat. mobile radios are quite durable, due to the environment they are designed for (imagine the inside of a car at noon in a hot arizona summer). but whatever enclosure you decide upon, you must make provision for an adaquate supply of cool air. and, that may mean using a fan or other means to move the air along. it all depends on the enclosure, and the amount of time you are planning on operating at high power. at lower power settings, cooling needs will be markedly reduced.
excellent article on choosing an EMCOMM radio:
here is a long article , chock full of little tidbits and interesting viewpoints:
"Which HF+ Transceiver is Best for Emergency Use?"
"Portable/Mobile Rig for an Emergency"
which starts off with
and see this as well for other angles:
"Emergency 'Go Kit' Ideas Needed"
here are some ham porn links of boxed radios:
mywebpages.comcast.net/cuti/N1HY/ARES/ <-- very good collection of info!
and lists of stuff if you are RACES or ARES inclined:
mywebpages.comcast.net/cuti/N1HY/Go-Kits/index.html <-- good stuff
NEW --> EXCELLENT GO-BOX WRITEUP:
Posted: 8/10/2007 9:57:58 PM
[Last Edit: 9/9/2007 10:05:45 AM by ar-jedi]
field expedient antennas for SHTF applications
www.tactical-link.com/field_deployed_nvis.htm <-- good practical info!
www.cebik.com/radio.html <-- excellent resource page!
www.ac6v.com/antprojects.htm <-- another great page
www.alpharubicon.com/elect/hamtennaswab.htm <-- ham n00bs, these are EASY!!!
www.tcoe.trinity.k12.ca.us/~tcarc/htant1.html <-- very nice J-pole plans
www.qsl.net/wx2nj/ <-- "ummmm..."
Posted: 8/10/2007 9:59:35 PM
[Last Edit: 6/6/2008 1:35:08 AM by ar-jedi]
DC power connectors / anderson powerpoles
The amateur radio community has pretty much standardized on a power connector called the Anderson PowerPole. These clever, asexual connectors are easy to assemble, handle up to 45A, and when paired they prevent reverse polarity mating accidents. Note that there is a PowerPole RED/BLACK orientation convention in widespread use within the amateur radio community, and adherence to proper crimping is essential.
Anderson PowerPole web page
Anderson PowerPoles are available from
Reccomended "Starter Kits"
for the powerpole, here are "set kits" -- everything you need to terminate 10 power connections:
15 Amp Red/Black Anderson Powerpole Sets
Recommended for use with 16-18 gauge wire
30 Amp Red/Black Anderson Powerpole Sets
Recommended for use with 14-12 gauge wire
the 15A and 30A connectors will mate no problem. the only difference is the diameter of the hole in the actual contact. the smaller one is designed for the lighter 16-18 guage wire, and the larger one is designed for the heavier 14-12 guage wire.
both contacts can either be crimped or soldered on. in an HT application, the 15A version will be fine. for a mobile application, get the 30A contacts.
you don't really have to "choose" per se.
the plastic housings for all three of your listed sizes are the same;
the only difference is the metal contact rating.
look closely at the pic below -- one contact is a 15A (left) and the other is 30A (right). they both fit into the same pair of plastic housings. i use the 15A contact size for smaller diameter wire (such as 16-18AWG) and the 30A contact size for larger diameter wire (such as 10-14AWG).
see for example,
note that where the individual pieces are sold,
you see you can get the 15/30/45A housings in different colors,
and you can get the three different sizes of contacts to fit the above housings,
however, it is generally more economical to buy the 10 or 25 piece "sets" which include the red/black plastic housings and the metal contacts.
the most popular size Powerpole is the 30A type, which covers about 99% of everything you'll ever need to do with ham radio. that said, i ordered some extra 15A contacts at the same time as buying a 25pc 30A set -- i use the smaller 15A contacts when connectorizing those 6xAA battery holders and similar low current, small diameter wire applications.
Posted: 8/10/2007 10:02:03 PM
[Last Edit: 8/14/2007 7:31:19 AM by ar-jedi]
amateur radio emergency communications
RACES/ARES web sites:
handout from my RACES org, originally done by the VA RACES folks, some good info even for novices and pros alike... (1.4MB PDF)
the original in microsoft powerpoint format is here:
also check out some of the info on this page, more VERY USEFUL stuff:
if you do nothing with the above PDF but give it to someone you know, i think we'll all be better off...
ARRL Emergency Communications Handbook
ARRL Emergency Power for Radio Communications
Dave Ingram's Guide to Emergency Survival Communications
i do have one comment here. i don't own any of the above books but i caution you as follows: many "amateur radio emergency operations" texts have chapter upon chapter of information related to message handling (e.g. NTS). this is the "formal" part of amateur radio communications which includes standardized processes, procedures, and forms related to accurate interchange of information between two operators. it is critical in an emergency situation (e.g. Katrina) that things be done in a somewhat organized manner so that the right people receive the right info in a timely fashion. in general, this whole art is called "traffic handling", and a well trained, experienced set of folks on an emergency net can move a lot of data accurately and quickly using these methods.
here is the standardized form:
moreover, a large part of emargency communications is regarding interaction with the "served agency" -- which may be the Red Cross, FEMA, your local police, or similar. as an example, RACES operators may be colocated in a trailer with FEMA and other disaster relief personnel. should ham radio be the only communications path in and out of the affected area, the RACES operator(s) will become focal points. if so, what you convey over amateur radio frequencies has to be carefully controlled, who you distribute that info to has to be carefully controlled, and so on. my point here is that "emergency communications" in amateur radio context is not just about using a battery and a piece of wire; it's a whole ball of wax. those of you ln law enforcement know what ICS is; the same system and hiearchy is used in amateur radio emergency comms.
only a few folks here may get involved with RACES, ARES, SATERN, SKYWARN, or similar -- and therefore the chapters on traffic handling and agency interaction may be interesting but for the large majority of you this info will not be as useful as actual techniques for remote operation, construction of field expedient antennas, and using/monitoring battery power.
for this reason i encourage you to review the table of contents prior to purchasing a book on "Emergency Communications", so that you get the technical info you are looking for rather than a lengthy discourse on traffic handling/messaging.
see also this forum
Posted: 8/10/2007 10:26:28 PM
[Last Edit: 9/9/2007 9:45:24 AM by ar-jedi]
EMP and ham radio (ack!)
there are so many factors which affect this question that it is nearly impossible to say, with any certainty, whether a given device will continue to function post-NEMP.
as i wrote some time ago here in the SF,
that said, in all likelihood, most all portable, battery operated, handheld devices (such as ham HT's, geiger counters, and the like) will not be affected by EMP. the distance-reduced field intensity and the minimal capture area will prevent any permanent damage, although there may be minor transient issues.
here is what an ARRL report on the EMP effects to ham radios says:
as you can see, as long as there are no long power cables or antennas connected to the device, it should survive an EMP.
ok, i am going to try to make this as simple as possible. however, i'm quite sure my simplification will result in AR15.com going down from the massive number of "corrections" offered by my peers. but let me attempt it anyway in nice, easy, practical terms.
let's start with something you know, an FM car radio. but first we have to start at the source, the FM radio station. the transmitter at your favorite station takes an audio signal (say from a CD player) and modulates it onto an RF (radio frequency) carrier at a frequency of say 100 MHz. modulate, in case you were wondering, in this context means that the input audio changes very slightly the output frequency that the radio station is transmitting on. you can read more on how FM (frequency modulation) works via google -- i can't explain it to you here without typing for 10 more minutes.
thousands of watts of RF are sent up a piece of coax into an antenna -- where that power is radiated as an electromagnetic wave. for our purposes, we can use a lightbulb for an analogy -- there electrical power gets turned into visible light, which is a type of electromagnetic energy. an electromagnetic wave carries with it energy, just as a wave of water on the ocean carries with it kinetic energy. this EM energy, as you will see in a moment, is what makes all this radio stuff happen. the EM wave that you are most familiar with is in your kitchen: EM waves in what is called the microwave region bombard whatever is placed in the appliance, rapidly spinning the boomerang shaped water molecules. this creates a lot of friction, which then produces heat -- as anyone who has used a belt sander knows. so you see, strong EM fields can boil water!
so back at our FM station, EM waves "spring" from the transmitter's antenna, radiating in all directions. btw, the strength of these waves decay as the square of the distance, and therefore are quite weak after a trip of many miles.
at your car, a long metal rod is used to capture these waves. the EM waves that impinge on the antenna create a very tiny varying current along the surface, and a very sensitive circuit built into the radio detects this current. that current is changed into a small voltage, and then amplified, and fed into another circuit which ultimately delivers the low frequency audio back to an audio amplifier and finally to a set of speakers.
the voltage seen by the radio at the antenna input is on the order of 10's of microvolts (millionths of a volt). the circuits are thus very sensitve and correspondinly quite delicate. moreover, even if the power to the radio is off these circuits still lie in the path of the applied voltage.
suppose, instead of a very weak EM wave being captured by the antenna, a strong EM wave is. what do think the effects might be? what if the EM wave is so strong that the sensitive circuit is not able to cope with the applied voltage? the answer is that the delicate transistors used in these circuits will fail, usually because of thermal reasons (tiny conductors fusing open) or a situation called dielectric breakdown (translated: insulator punch-through). what is going on inside a transistor's tiny body is conceptually no different that what is going on inside the hydraulics of a tractor. apply too much pressure (=voltage) or too high of a flow rate (=current) somewhere in the system and there will be a pop.
i have described how an FM radio with an exposed antenna might be susceptible to fail if the passing EM wave carries enough energy. the fact is that ANY exposed metal captures these same currents/voltages from EM waves. your house gutter, for example, at this very moment is receiving the Voice of America shortwave station. that energy goes nowhere, but suppose we take another example. your ADSL or cable modem sits on the end of a very long piece of wire (that's our antenna). a very strong passing EM wave can either temporarily interrupt (bit errors) or permanently damage (blown receiver) these devices. it will be useful for you to know that a lightning strike, besides the immediately visible bolt, produces a very strong EM wave that can damage equipment quite far from the actual strike point.
a toaster over, per your comment above, has no delicate circuits like a PC or radio both have. a toaster oven is basically a big resistor designed to get hot, sucking down 1000 to 1500W in the process. a radio is not designed for this!
any delicate circuit with long wires attached it can be affected by strong EM waves like the type produced by a nuclear EMP. how the equipment reacts is a function of dozens of factors, including how strong the EM field is, how long the attached wires are, how robust the circuit design is, and so and so forth.
thus there is no way to answer the question, "will X be affected by an EMP?".
additional reading material:
Posted: 8/10/2007 10:30:29 PM
[Last Edit: 8/13/2007 11:30:54 PM by ar-jedi]
constructing a J-pole antenna for VHF/UHF
the VX-170, like most current HT's, uses an SMA connector. the SMA has excellent RF characteristics, but less than stellar mechanical strength. the problem you are facing is that the antenna shroud completely encloses the male end of the SMA, and in turn when the antenna is attached to the radio the shroud mates intimately with the VX-170 housing, assuring a waterproof connection. you should not need a counterpoise with the OEM antenna, but trying it can't hurt. offhand, though, i can't think of a good way to attach the counterpoise without possibly reducing the water resistance at the same time.
any length of more than about 3' should be ok. i have about 7-8' attached to my J-poles, and that seems to work out just fine. you can of course go longer as needed. i routinely use a 15' "extension cord" with my J-poles, vis-a-vis a BNC barrel connector and a 15' piece of RG58 with male BNC's on both ends. now then, in theory the J-pole is a balanced antenna and you are feeding it with unbalanced line. in theory you would need a balun for this antenna. in practice, the unbal-balanced transition does not cause issues, especially at the power levels output from an HT. i would not dump 100W into a J-pole without a little more engineering work, though. if you find you have feedline current, make a 4" dia loop of 4 turns of the feedline coax, and you will be all set. see below for an example:
attaching the coax to the 300ohm twinlead is pretty straightforward. first -- only strip back the minimum amount of coax; you should have less than 1/4" of exposed center conductor and about the same amount of braid. twist the braid such that all of it comes to one side of the coax. lay the prep'd coax in line with where you made the connection cuts on the twinlead. now solder the center conductor to the long leg, and the coax to the shorter leg. now you can use heatshrink or electrical tape to wrap everything up. note: if, when you twist the coax, you can cause the center conductor to short to the braid, you have too much of each. pare back the two and try again.
the picture attached below is of a design using 450ohm ladder line, so the dimensions are a little distorted compared to your 300ohm TV lead -- but the method of attachment of the coax is exactly the same. keep the coax leads short, and run the coax parallel with the "base" of the J-pole.
ps to others considering the J-pole: see
home.comcast.net/~buck0/ll_coolj.html (the pictures above come from here)
for base use, i recommend the Diamond X50. the price is right and the performance can not be beat. it is physically unobtrusive as well. huge value for what you get.
some antenna designs will appear to be a short at DC or a complete open. it depends on the design of the antenna and also the arrangement of the elements. for example, the popular DIY J-pole is a DC short.
i know that it's sometimes tough to get your mind around, but RF and DC do different things. an inductor, for example, is a dead short to DC. but at a high enough frequency, RF will not pass through an inductor. the reverse situation is true for capacitors: DC open, but a high enough frequency signal will pass.
Posted: 8/10/2007 10:31:00 PM
[Last Edit: 4/11/2011 11:38:27 PM by ar-jedi]
coaxial cable selection
(impedance and loss)
I'm just a little confused on soldering the female BNC connector to the end of the coax.
where did you get the BNC from? is it an Amphenol/AMP type part with a bunch of separate components, or is it a "screw on" type which twists onto the cable?
Also, the only coax I could find locally was RGU6 (not sure of the letters as I'm at work and can't check). The package said it was 75 Ohm resistance. Will this work or do I need to order some other kind from gigaparts?
hard stop here. you need 50ohm coax or you will never get the SWR down below 1:1.5 or so. a 50ohm impedance coax like RG58 type (and all the derivatives like RG58AU, RG58U, etc are ok) is needed for your ham projects. you can probably pick up some RG58 at your radio shack.
note that you will need BNC's suited for RG58; i don't know what you have right now. RS carries "instant-on" twist type BNC's which don't need soldering. i would not recommend them for high power or outside use, but they work pretty well for J-pole type projects. basically you strip the coax per the directions on the back, and screw the connector onto the coax. see the upper right of the pic below.
75ohm coax for VIDEO applications (cable TV, sat TV) / 50ohm coax for RADIO applications (ham).
of the 1/4" dia coax types:
RG59 = 75ohm impedance
RG58 = 50ohm impedance
coax loss calculator:
Originally Posted By uscombatdiver:
His explanation lacks enough information on this.
luckily there is this new thing called the Internet.
then go here,
Originally Posted By uscombatdiver:
We used all sorts of different coax without particular impedance when I did towers and the antenna was still matched to the radio.
there are two common impedances for coaxial cable used in modern RF applications, 50 and 75 ohms. the reasons for this are historical and revolve around striking a balance between power handling, antenna matching, and attenuation 末 with 50 ohm impedance corresponding well to the drive impedance of a half wave dipole antenna in real environments, and 75 ohm impedance having less attenuation when used for long runs.
any modern radio communications device (including associated test gear, e.g. spectrum analyzers etc) will have 50 ohm impedance unbalanced inputs (e.g., receiver) and 50 ohm unbalanced outputs (e.g., transmitter) and therefore use 50 ohm impedance coax (e.g RG58, 9913/LMR400, etc) and 50 ohm impedance connectors (e.g 50 ohm BNC, N, SMA, etc).
similarly, since CATV systems have very low level signals and are benefactors of low attenuation for long coax runs, 75 ohm coax is used. examples of such are RG59 and RG6, plus several types of hardline used for headend to community distribution (pole-to-pole) applications in the CATV industry. the connectors used for termination in the CATV industry range from true 75 ohm impedance weatherproof types used on hardline to the ultra-cheap and ubiquitous "F" connector used for in-house distribution and on the back of set-top boxes.
in some applications, low loss 75ohm CATV coax or hardline can be employed in radio applications by using quarter wave matching stubs (or the discrete equivalent) at the transitions. for example, if a long "scrap" of 75 ohm impedance CATV hardline is surplussed by a local cable TV operator, an amateur radio club could employ it for use on a tall repeater tower 末 less attenuation of the received signal is the primary benefit. again, matching sections are required to connect the nominal 50 ohm impedance radio equipment (specifically the duplexer) and 50 ohm impedance antenna to the 75 ohm impedance hardline which joins the two.
that said, if as you stated you were employed erecting radio towers for cellular or two-way radio applications, the coax or hardline you were installing was 50 ohm impedance (such as Andrew/Commscope Heliax), and the connectors you were using were 50 ohm impedance (such as type N or type 7-16 DIN) . the coax may have come in many different sizes and construction types but the characteristic impedance was 50 ohms.
Originally Posted By uscombatdiver:
I guess I will need to hit the antenna theory book hard when it gets here (it's been over 10 years since my tower days but I'm not completely void of any memory of it).
the antenna is just another bump in the impedance graph of a very long transmission line.