Thanks.. So I am slowly filling the gaps here but it seems as though one really only needs an antenna tuner for HF. I see very few available that can be used for UHF/VHF, which I'll assume at this point has to do with these types of antennae ease of adjustment due to shorter physical length and fewer bands to actually tune for. Is this correct? I am getting too far off ar-jedi's actual topic so I'll start posting up new threads for my questions. But one other thing boggles me now and that is with the fixed length mobile dual band 2m/440mz type antennae.. Diamond offers some that are "pre-tuned -no adjustment necessary" yet they recommend verifying the installation with a SWR meter. Since there is nothing to adjust are we looking for excessive SWR as an indication of a faulty connector or something? |
awww shucks... 
IMHO, this is the very best way to approach your communications needs -- by defining what your system (collection of radios, antennas, and power sources) has to provide. and of course you want to allow for a little "growth" room, just in case.
these are good questions...
this is highly dependent on the antenna setup. for some situations (such as an end fed antenna deployed at a field location) you will probably get much better performance by grounding the rig or antenna feed point. the issue of grounding is also instrumental in the operation of a vertical antenna -- the more the better. an added complexity is the bulk soil resistivity; in some locations your will find the ground is quite conductive, in others not so much. nevertheless, one good indicator is your SWR and the resultant difficulty you have getting a good match by either adjusting your antenna length and/or fiddling with a tuner. should you be unable to get the SWR to sit down with the rig or antenna ungrounded, try getting a ground of some type in place. remember that the better the match the antenna is, the less power you lose in the coax and tuner. so, strive for a good antenna setup, ESPECIALLY with QRP rigs.
the common power bus is just that, a power bus. normally it doesn't go anywhere from an RF perspective, especially not out in the field. so an adjunct ground wire must be equipped if you are going to ground at the rig, or as mentioned above you can usually do it at the feedpoint of the antenna. one way or the other may affect your SWR, so a little experimentation is usually in order.
i really need to fix that schematic. my charging circuit is somewhat more complicated than that schematic depicts. i wrote it up in another thread, hopefully the ARFCOM search facility can save my fingers from typing.
for the charging circuit i use a diode (1N4004 type, available at radio shack and every other electronics outfit like IEI, Digi-Key, and Newark) to isolate my charging source. the latter is a DC/DC converter, you can see the picture here: losdos.dyndns.org:8080/public/ham/races-box/construction/DSCN1067_sm.jpg
there will be no problem. as an added precaution against RF noise from external AC power, you may want to put a line filter in series with the AC power connection, near the Samlex supply. for an example of such, see the line filter in the foreground of losdos.dyndns.org:8080/public/ham/races-box/construction/IMG_1836_sm.jpg losdos.dyndns.org:8080/public/ham/races-box/construction/IMG_1813_sm.jpg and the far right of losdos.dyndns.org:8080/public/ham/races-box/construction/IMG_1808_sm_annotated_sm.jpg
one note about internal tuners. there is a cost/space/capability tradeoff with any tuner. most built-in tuners (such as you find on an Icom 703+) have somewhat limited matching capabilities. Icom advertises 3:1 but i and many others have found that the spec is quite conservative. most folks find that the 703+ will match 5:1 or so. this means that the radio will match most "reasonably resonant" antennas -- but it will not match an end-fed random wire with it's ~3000ohm impedance. for that type of application you need an external 4:1 balun or some other arrangement to better mate the antenna with the radio. i'm not picking on the 703+ in particular here, either. even Icom's venerable $1400 internal tuner-equipped IC746Pro is only advertised to match 3:1. it does usually do better than that, but again there is a cost/space/capability tradeoff. an external tuner, in most cases, will do a better job -- but at additional cost and space.
this is the case with almost all small form factor 100W radios (Icom 706MkIIG, Icom 7000, Yeasu 857/897, etc), so you are certainly not alone.
you can adjust the antenna length but there are 8 million variables which will fight you if you expect to operate in the field and on multiple bands. antenna height above the ground, nearby vegetation, soil resistivity, and so on. summary: get a tuner. it will resolve a lot of these issues and make operating more enjoyable. many external tuners have a control cable which connects to the radio -- you push the "TUNE" button on the radio, and the tuner goes to work to match the attached antenna. seconds later, you are ready to operate on your chosen frequency. it is very straightforward.
if we assume a horizontal dipole antenna, you basically need a length per band (160m, 80m, 40m, 20m, 10m, etc). in some cases there are means to use the same length antenna for multiple bands, due to the correlated odd harmonics. a 30 meter antenna can often be driven at 10m as well, and so on. performance may range from excellent to non-existent.
not easily. there are HF antenna designs which are somewhat broadband/mutiband. the G5RV is an example, but you need at least 102' to stretch it out in, and the centerpoint has to be at least 35' off the ground. depending on your AO and SHTF status, this may be easy or impossible -- i don't know.
at a given length, you will be able to work one band, or in some cases "most" of one band. if you want to change to another hand, you will have to adjust the length. for this reason, many folks use a small auto-tuner, hang the yo-yo tenna out at it's maximum length, and let the tuner sort it out as you dial around the bands. this will at least give you something to work with, although a perfect match can again be found by adjusting the length of the antenna (plus or minus a foot) to suit the frequency of interest.
any 2m/70cm antenna will receive NOAA and local law enforcement perfectly. dont' worry about this, there is plenty of signal there for a modern VHF/UHF ham radio despite the antenna not quite matching the frequency. heck, you can get perfect reception of local NOAA broadcasts with a 5" rubber duck antenna -- anything longer than that is simply going to help more.
this is my thinking as well. i don't operate HF mobile. many do however.
i have read the ATAS 120 is the best thing since sliced bread. i have also read the ATAS 120 is the most expensive 50ohm resistor ever made. i don't have one but my engineering judgment tells me that the performance of the antenna is EXTREMELY dependent on the vehicle and the installation approach. as for reliability, a motor-driven screwdriver antenna tuned by RF feedback sense is by definition a fairly complex electro-mechanical system -- and one which is protected from the elements by rubber seals and what not. seals fail, anyone with a hydraulic tractor will tell you this... 
my $0.02: your favorite radio + external autotuner (LDG or equivalent) + broadband antenna will suit you better than chasing perfect antenna lengths in blustery 15 degree weather. ar-jedi |
correct. or you mounted a 1/4wave groundplane antenna on top of a fiberglass jeep.  ar-jedi |
correct. VHF/UHF -- no tuner needed. 2m and 70cm are conveniently related at the third harmonic -- 150MHz x 3 = 450MHz. so one antenna design can suit both bands with proper engineering. a Comet SBB5 is an excellent example. and, as long as the antenna + installation resonance is centered at the right place, will present a good match across the narrow (4MHz) 2m band and a reasonable match across the 70cm band. HF, unless you are running one monoband dipole for every band you want to operate on, you probably need a tuner. even with a matched dipole, at the extremes of the band you may notice higher than wanted SWR. summary: buying an HF rig? budget for a tuner (preferably one that communicates with your radio when tuning). LDG in particular offers excellent, low cost tuners. ar-jedi |
Wow.. thanks for taking the time to answer everything. I've got allot to chew on now. I'll be sure to check in with the AR15.com net once I get everything sorted and the proper licensing. Looking forward to it. Your efforts are a great service to this community! Thank again... |
| I once listened (in Texas) to a mobile HF conversation by a couple motorcyclists in California. Not entirely sure how they were hearing each other, or if I'm remembering it wrong and there was only one, but it was still impressive. They came through clear as a bell. |
Watch out. This bug has bit me already cause of ar-jedi. He has a gift to make it look easy but at least he is helpful once your hooked. |
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ar-jedi.. I have a couple more questions related to a SHTF radio box.. so I'll post them here. Have you or anyone else seen an item like this battery booster that can bump up the voltage while running off of battery power? An article detailing why one might be needed can be found here on pg. 7 but the gist of it is that while running from battery power, normal battery voltage drop combined with any drop from wiring, connctors etc.. can decrease "effective" running time of some radios. Effective referring to where the author states that even though some radios might operate at voltages lower than 13.8, their transmissions can be impacted. Seems like this might be a nice item to add to the box. But I thought I'd gather opinions on this before dropping $100 on it. As it is, I think I might substitute a portable safe in place of a orange box at this point.  Also, I am no EE and would probably let the smoke out of the radio if I attempted to build a duplicate of what you have. The majority of the wiring, breakers, AC line conditioners, I can handle.. but a semi plug and play alternative for the charging, battery monitoring function would probably keep me out of allot of trouble. I did see in the 101 thread you mentioned the possible use of a powergate to switch power from the power supply to the radio and charge the batteries. And I found the PG40S made by West Mountain Radio, but its capacity seems like overkill for a small comms box.. plus it looks like it could add allot of heat. Do you know of any others that are worth considering? I didn't really find any others that are application specific for radios that you can just plug in. Chuck |
www.eham.net/reviews/detail/3404 see also www.eham.net/reviews/detail/6449
this is the case for many 100W output HF radios. the FT857 is an example, it does not like to operate below about 11.8Vdc. a friend of mine ran into this problem at a recent field day. however, as noted above, with typical batteries there is considerable power left at that terminal voltage. moreover, you may find that receive works fine but transmit doesn't -- when you key down the terminal voltage sags and either performance is poor or the radio drops out completely. you can see a comparison of two 100W HF radios and their respective performance over varying voltages here: www.bnk.com/W0QE/IC7000_vs_IC706_mobile_pwr.html
any power conversion device will cost you power. there is no way around that. if the cost in power lost is outweighed by the power "gained" back because you can operate the radio deeper into the battery's discharge curve, then you've won. my setup does not require any booster as the Icom 703+ is spec'd to operate down to 9.6Vdc, and it will actually receive-only lower than that. this low voltage operating ability is a feature of many QRP (5 or 10W output) HF radios -- they are expressly designed for portable/remote operation from batteries.
get a Battery Tender Jr from ebay or similar. mount it in your box, or keep it loose. plug it into the wall when you want to charge your battery. disconnect when you have to move out.
the PWRgate is probably overkill for this application. but it will work. the design of the PWRgate is quite efficient (read: not much heat produced). ar-jedi |
you guys make me sound like a crack dealer standing on the corner... ar-jedi |
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Not sure how I missed the eham.net reviews cause I have been looking everything up there but thanks for the links on the battery booster. Information overload has taken it's toll. It's probably best to familiarize myself with operating in general and how I'll operate off of battery then get some good baselines to determine if voltage drop is really going to be a problem. The booster can always be added later if needed. I already have a battery tender plus so that will work great while I get my feet wet. Key point is I have enough knowledge and gear on hand, thanks to all who have shared here, that should a hurricane roll through next week I should be able to get some kind of effective comms going. That's a good feeling to have right now as the tropics look like they are shaping up to be very active this year. Thanks all!! |
that right there sums up the purpose of this forum !!! ar-jedi |
And a Hurricane may do just that this comming week. Texas Army MARS is on alert and may possibly deploy as soon as Sunday evening, weather dependent. Tropical Storm Invest 94. 1. A STRONG TROPICAL WAVE LOCATED IN THE WESTERN CARIBBEAN SEA IS PRODUCING THUNDERSTORMS AND STRONG WINDS WITH GUSTS ABOVE TROPICAL STORM FORCE. AN AIR FORCE RECONNAISSANCE AIRCRAFT IS CURRENTLY INVESTIGATING THE SYSTEM TO DETERMINE IF IT HAS A CLOSED CIRCULATION. ENVIRONMENTAL CONDITIONS APPEAR FAVORABLE FOR THIS SYSTEM TO BECOME A TROPICAL DEPRESSION WITHIN THE NEXT DAY OR TWO AS IT MOVES WEST-NORTHWESTWARD AT 15 TO 20 MPH. REGARDLESS OF DEVELOPMENT...LOCALLY HEAVY RAINS WILL AFFECT JAMAICA...PORTIONS OF CUBA...AND THE CAYMAN ISLANDS TODAY AND TOMORROW. INTERESTS IN THE NORTHWESTERN CARIBBEAN SEA AND THE YUCATAN PENINSULA SHOULD CONTINUE TO MONITOR THE PROGRESS OF THIS SYSTEM. |