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HF Antenna Advise

Aug 21st 2012, 06:35

dksac2

Joined: May 24th 2012, 23:18
Total Topics: 0
Total Posts: 0
It would be best to lay out the senerio first.
We are in a valley at 6200" sourounded by mountains on better than 3 sides that are from 8000' to in excess of 10,000' with the average being approx. 9000'. We have among others a HF radio in our Emergency Communications van, an Icom IC 7000 running 100 watts.

Right now it is equipped with a streight vertical long wire HFantenna attached to the top rear of the van. At present, it does not even have an antenna tuner, but that will change no matter what we end up with. (The antenna looks like something Army surplus)

The question is,what is going to be the best antenna to get the furtherest distance given the equipment we now have and the bowl we are in.

The problem will be getting a signal over the mountains. In many places the angle would not be too bad, but in others when close to the mountains, it's going to be a rather steep angle.

I was thinking about something like a Buddy Pole that could be set up and taken down in little time, but am looking for suggestions for something that could be deployed fairly rapidly without a lot of effort and a lot of complicated tuning to get a signal out of the valley further than just a signal going upward and coming down 400 to 500 miles away. I think the less technical, the better.
Something with a range of 6 meters to 40 meters would be ideal.
Horizontal polerization is most likely going to be the best. Something along the lines of the Buddy Pole or similar might be ideal if it would work.
We are in Idaho and not looking at getting outside of the USA, but would like more distance than the current set up is going to give us.

As an example, on UHF/VHF, repeaters are just about the only reliable way to get out of the valley, with simplex and some power being the exception sometimes if your in the right spot or have a good antenna on a tower and did I mention extra power?
The ECOM van is kind of cobbled togather (I'm being kind), I'm trying to get some other issues streightened out now also. They don't even have an SWR meter anywhere, not just in the van. I've got some work to do. They have got some nice radios, they just have antenna issues for the most part.
Also, with 2 different areas with radios, what is going to be the best way to ground. At this point I was going to ground each group of radios to a common buss bar, then run ground wire between the two areas and the temp ground rod, hooking both groups of radios up so they would all go to the common point of the ground rod. I'm trying to avoid grn. loops and want to insure static is bleed off. As to lightning, I'm going to seek some professional help on that one unless you have a solution.
It's never easy is it, but I volenteered.

73's, John

Aug 21st 2012, 11:09

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
The best way to get around mountains is to relay the signal--this is where the second 2 in ARRL came from--hams would relay signals to increase their distance. This is quite useful in Emcom---instead of trying to generate a good signal everywhere, you can concentrate on getting a good signal out somewhere, where it can be relayed to where you need it.

Now, if you really had to generate a signal that would hop over obstructions, one option is a crank up or adjustable tower. As you made the tower higher, you would get more low angle radiation. The height of the antenna would be adjusted to just clear the obstruction. Alternately, if you had a van, which presumably can move, you can just drive it over to different spots, assuming the roads aren't closed. One might drive it right up to a mountain peak, such as Mt Evans, to get the best distance. Actually, half way up works too, it you have good ground slope in the desired direction--the mountain can block unwanted signals.

As for for the question of multiple radios that have to be tied together with minimal interaction and good lightning protection, the solutions is to install a large radial field. The radial field will allow lightning to bleed off and decouple the radios from each other via a low impedance ground--precisely what you asked for. About a year or so ago we published a quick deploy radial system using inexpensive tape measures.

Zack Lau W1VT
ARRL Senior Lab Engineer
Aug 22nd 2012, 02:41

dksac2

Joined: May 24th 2012, 23:18
Total Topics: 0
Total Posts: 0
Thank You,good reply. As for the HF antenna, without a tower, is something like the Buddypole put on top of the van, horizontal going to be better than the vertical. Either case we would use a good automatic antenna tuner.I'll look for the radial system using the tape measures.
There are few roads the van can get up, the mountains are steep and many trees and rocks and in winter, it's not any kind of option at all.
I also intend to use straps to go from the body to frame, etc.
It's really kind of a unique situation.
I'm going to suggest a second HF radio on the 4 story court house with a larger antenna with a rotor if the county will let go of the money.
At least we are finally working on good ECOMS as far as radios go. The Emergency Coordinator really wants to do the best he can with what we have to work with.

Thanks, John
Aug 22nd 2012, 13:33

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

The mountain was just a good visual example for most people. Less obvious is the fact that you may get good propagation just by driving away from the mountain, so the obstruction is smaller. For instance, Newington CT is just 100 feet above sea level, surrounded by numerous hills. But, W1AW is far away enough from those hills that HF propagation is good to excellent. VHF propagation is lousy, as evidenced by consistently poor VHF contest scores.

Zack Lau W1VT
ARRL Senior Lab Engineer

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