Neat ham radio fact of the day:
VHF/UHF are line-of-sight. That means that for the most part, they won't transmit beyond the horizon, or around a mountain.

So, what if you were ON TOP of a mountain?

Your line-of-sight would be very, very good! It would extend to a much farther-away horizon than it would if you were in the flatlands.

That is why "REPEATERS" are sited on top of mountains. They receive your transmitted signal, and re-transmit it, so that everyone with a UHF or VHF transciever can communicat with you! Neatest thing since the advent of FM communications!

Originally Posted By XM21Nick: I'd like to see a thread about it also cause I don't know diddly about it. Please keep it in simple terms for us dummies.

Post or IM your questions. I try to get on this board every day.

Originally Posted By FrankSymptoms: Neat ham radio fact of the day: VHF/UHF are line-of-sight. That means that for the most part, they won't transmit beyond the horizon, or around a mountain. So, what if you were ON TOP of a mountain? Your line-of-sight would be very, very good! It would extend to a much farther-away horizon than it would if you were in the flatlands. That is why "REPEATERS" are sited on top of mountains. They receive your transmitted signal, and re-transmit it, so that everyone with a UHF or VHF transciever can communicat with you! Neatest thing since the advent of FM communications!

Can't get over that mountain? Want to talk over the horizon using 2m? Download echolink! This program allows you to connect to the many repeaters that have an internet link and transmit from that repeater. Very cool.

-Foxxz

ok so bear with this newbee question....let's say I have a cheapo China-mart FRS radio claimed to reach "6 miles" (they're selling here for $19). I'm assuming that this REALLY means they're good only for 1-2 miles but haven't tested them yet.

However even so, would they work line of sight if one is on a mountain top 50 miles away and the other is in the back yard - line of sight facing the mountain? Is it that simple?

I.e. would it work if I go out and stand on the roof of a 20 story building and call someone 12 miles away?

Thanks

Tips on making antennas for HAM, GMRS, and FRS would be nice.... I.E. how do you figure out antenna length for the freq you are working

Would a wire hanging from the negative battery terminal of my handheld make it a Dipole? Would the length of the dipole have to be the same as that of what the rubber ducky is tuned to?

Why is it illegal to converse with another HAM in a country who doesn't allow their people to use HAM frequencies? This seems counter to the idea of America's Free Speech. Somehow I don't think it should be a crime for me to speak to a person in China or North Korea...

Frank
KG5S took the question right off my computer screen. And I am not doing a very good job at giving an understanding and logical answers that non Hams can understand.

With out upsetting them. I hope you can do it better. I know that we say that Vhf is line of sight. as KG5S says he talks 100 miles all the time.

I do the same With a 100 foot tower stacked 16s and 200 watts out to 200 miles or so. On a daily basis.
I know why it is: but have been having a hard time getting it across to the non hams.

When you get time would you give it a whack. I see that a lot of the guys here on the S/F are looking at communications from 30 to 150 miles, And It seems like given the right equipment and the (terrain factor) is the part that throwing them all off. Given the Mountain question above would be a good example, as an answer all.
SM

Originally Posted By TxLewis: How about info on simple but effectice antennas. What people can do to improve their reception on a first base station/portable that does not cost alot. Might start with a bi-pole unless there is something easier. TXL

Good one.

A dipole is perhaps the simplest antenna you can make. It is a coax fed wire antenna with two legs. It is fed at the center and the legs are kept so as to make the whole thing as straight as possible.

Now, in simple terms, you would feed a dipole with coaxial cable (like your CATV wire). But the dipole is "Balanced" while coax is "unbalanced."This could result in your radio waves traveling on the outside of the coax, so you need what is called a "balun" at the feedpoint to "choke" the RF at that point so that it does not come back down the line. You can buy these or make them for pretty low cost.

Dipoles can be constructed to work at specific frequencies using the formula 468/ {frequency in Mhz} . For example, a dipole built to work on the Arfcom net frequency of 7.261MHz, you would calculate 468/7.261=64.453 feet. Divide that number by two and you have the length of your legs. Each leg of the dipole would be 32.23 feet long.

Theoretically, you should be able to cut two legs this length, attach the two centers to your balun, attach the ends to supports and the center to a support, then attach your coax to the balun and the other end to the radio. You would then be able to tune in to the Arfcom Net and send and recieve without much hullabaloo. It is always best, however to obtain an SWR meter to check to make sure your antenna is performing. Variables will affect it's performance so that you may have to trim the length. These include soil condition, height above ground, nearby objects, etc. So always cut a little longer than the formula, set it up, test, trim as needed, test again, trim again, etc. You want as close to a 1 to 1 SWR match as possible. High SWR means your waves are not efficiently leaving the antenna. This is to be avoided.

Dipoles are cheap and effective. They are directional antennas in that your signal will be much stronger in areas broadside to the run of the wire. For example, if your dipole is running in a north-south orientation, your signal will be best to the east and west.

Optimal height for a dipole is 1/2 wavelength above the ground. WTF is wavelength? It's the size of one complete AC cycle of the radio wave. The Arfcom net is held in the "40 Meter" band, so-called because generally the waves or cycles in that range are 40 meters long. Thus our antenna in this example would perform best at 20 meters above the ground, or about 64 feet up.

If the antenna is lower to the ground, the waves will come off it at a higher angle. This is how you get an NVIS or "Near Vertical Incidence Skywave" antenna system. With the antenna low to the ground (say 15 feet or less) your signal will go almost straight up, bounce off the atmosphere, and come back down, covering your surrounding region with your signal, but not reaching out too far. This is good for statewide or regional comms.

Height is good, the higher the better for really reaching out, but antennas work pretty well even when you can't get them to tower heights.

Another kind of dipole can be built to work on several bands without the need for additional equipment, like an antenna tuner, is called a "Fan Dipole." It looks like it sounds. You have one center feed point, then you do the above calculations for seperate dipoles of the bands you want to work. Cut the legs, attach all the centers to the same feed point on your balun, and fan out the legs, like the supporting structure of an umbrella, keeping the legs that go together in straight lines, or you can put them all in the same plane, sort of stacked up on each other, but don't let the legs touch.

When you tune up or switch bands, the RF will automatically choose the correct antenna because it will be the path of least resistance.

Lastly, you can go with a "random long wire" dipole and an antenna tuner. In this scheme, you just get as much wire up in the air as possible. Feed it through an antenna tuner, and you can tune it to whatever frequency you wish to operate on. The drawback that comes with this convenience is efficiency. You will lose some signal in the components of the tuner.

Hopefully this is helpful.
Scott

Originally Posted By JusAdBellum: ok so bear with this newbee question....let's say I have a cheapo China-mart FRS radio claimed to reach "6 miles" (they're selling here for $19). I'm assuming that this REALLY means they're good only for 1-2 miles but haven't tested them yet.

I really doubt that. Even the 1-2 miles. FRS are limited by law to one quarter watt. That's next to nothing, esp in tose VHF freqs.

However even so, would they work line of sight if one is on a mountain top 50 miles away and the other is in the back yard - line of sight facing the mountain? Is it that simple?

You are going to have signal attenuation in the atmosphere. Your 1/4 watt is not going to make it 50 miles, except in the vacuum of space.

Scott

Originally Posted By TheOtherDave: Tips on making antennas for HAM, GMRS, and FRS would be nice.... I.E. how do you figure out antenna length for the freq you are working

FRS radios are limited by law. The antenna MUST be an integral part of the radio. You can't even change to another "rubber duck" antenna.

See my other post for the dipole formula.

Would a wire hanging from the negative battery terminal of my handheld make it a Dipole? Would the length of the dipole have to be the same as that of what the rubber ducky is tuned to?

No and No.
Ducks are usually helical, and have coils in them too.
Don't attach wires to the battery. It's not like a car's electrical system. Neg is not Gnd.

Scott

Originally Posted By speedracer422: Is it possible and practical and purchase a ham radio for ~$300-$400 w/o any expensive upgrades (i'm thinking a portable model) and actually talk to people reliably 100 to 200 miles away w/o the use of repeaters?

Yes, but it requires the use of HF frequencies only open to General class licensees and above.

How much better are hams than gmrs in woods and urban settings?

They are probably comparable, if you are talking 2M or 70CM frequencies. HF is a different story, and it is not available to GMRS.

i.e.; can I really use ham radio as practical form of comms in an all out emergency?

Yes.

FWIW, I've tried GMRS radios around town in my AO and found them (8 mile cobras and cheapo cina mart unidens) to be lacking. My 8 mile cobras won't even go more than 12 blocks (no building over 3 stories in between us either).

VHF and UHF HT's in the ham bands running 5 watts would definitely outperform those radios.

Scott

Speed

Originally Posted By speedracer422: Is it possible and practical and purchase a ham radio for ~$300-$400 w/o any expensive upgrades (i'm thinking a portable model) and actually talk to people reliably 100 to 200 miles away w/o the use of repeaters? How much better are hams than gmrs in woods and urban settings? i.e.; can I really use ham radio as practical form of comms in an all out emergency? Speed

It is possible to communicate with people 100-200 miles away with ham radio. You would want to use HF frequencies (which means you need a General Class or better license) and what is called a near vertical incident skywave antenna. This antenna will send your signal nearly straight up and it will bounce back down off the Ionosphere. Picture it like using the ionospere as a repeater, sending the signal to a high point then sending it back down to other stations.

For more NVIS information look at this website www.tactical-link.com/field_deployed_nvis.htm

For your question about GMRS vs HAM in the woods I'll assume you mean a handheld radio. Any handheld radios are going to be limited in power to make them small enough to be hand held. You cant expect huge range out of something that small (without a repeater). Your "8 mile" radios are probably putting out around 2 watts. Most handheld ham radios will put out 5 watts. Also with ham radio you can put more efficient antennas on to maximize results from that 5 watts.

This thread is a great idea! I hope this was helpful.

Good thread , I havnt learned enuff to ask questions yet ,but as soon as I do I will.

Thanks