Well I did without tracking collars for a while, then after I had saved up I bought some and a tracking receiver. Well now I needed an antenna. I found a smokin deal on a 4 element yagi from Ham Radio Outlet. It was great, with a nice front to back ratio and forward gain. The only problem is that the boom was long, the elements didn't fold, and it was generally a pain in the ars to set up. It was really a pain when it was cold and you had gloves on and you have to tighten these little nuts and bolts. But I've used that ol antenna for a long time, although I did convert it to a 3 element that I could fit in a long skinny sac that could be attached to my backpack. It solved one problem, but didn't cure the set-up/takedown problem.
So I started reading into these antennas and found they are very simple to make and so that's what I did. Now I had a few thing in mind when I started thinking about my antenna design.
1. It had to be cheap
2. It had to be light, I do most of my hunting on foot and the less weight the better.
3. It had to be durable, strong, and flexible. That last one was one of the most important things as some places where I hunt are so thick and hard to walk through, and I like to take a couple of readings 50 yards apart to make sure they are where the tracker says they are.
Now I didn't just throw a bunch of stuff together, and I never went to antenna school either, but I did find a bunch of good info on the web. At the end of this post is links to the various design programs and 3d field viewers that I used to make this antenna. In a day or so I will get the field pattern of this antenna up on here as well as a few other yagis for comparison.
I found an old camera tripod and removed one of the legs. Then I disassembled one of the legs so it only had two telescoping pieces instead of three. Great, now I had a boom to mount the elements to that collapsed.
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Now how to mount the elements to the boom, without screwing the elements into the boom. Well I had some old line piercing valves that you use to connect a swamp cooler feed line to a larger water pipe. They are technically called a saddle valve. I removed the valve portion and use the bolts on each side to mount the saddles to the boom and hold the elements to the saddle.
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Now how to make those darn elements bend so I don't get caught in the brush or bend them while walking. I used aluminum tube elements and I was able to find a spring that fit inside of it and the ring wire connectors. Then I simply, lightly, crimped down on the element over the spring, and the wire end of the ring connector. Bingo, now I had flexible, folding elements. Then I simply used some washers to attach them to the bolts on either side of the saddle valves.
I spoke with Ham Radio Outlet and they said I didn't need any matching system for a receive only yagi antenna(found out they were wrong), so I direct connect the RG58 cable to the middle(driven) elements. A matching system matches the impedance (resistance) of the antenna to what the receiver is expecting. Here's a picture of a typical yagi gamma match.
Here's what I was told to do.
Like I mentioned earlier they were wrong about the matching system, and when I tried it without it the performance was less than spectacular. I compared it with my 3 solid element yagi and where the collapsable would barely ping, the 3 solid element antenna would really PING. I added what is called a hairpin match. It is the simplest of matching systems as it can be as simp[le as a 3-8" piece of romex type wire or radio coax that you connect each end of to the points where you connect the feedline that goes to the receiver. It is basically a short circuit with a length of insulated wire, but it does the trick. I used a piece of the antenna cable for my hairpin,but here is an illustration that might better explain how it is done.
- hairpin.gif (11.04 KiB) Viewed 8653 times
The performance is almost as good as the solid element, but I have a much smaller antenna that I can very easily pop out and use and either put away or if need be hike with it out and not have to worry about the elements snagging in a bush or tree. It's not quite as strong as I would like, but it can take some abuse. When all folded up is is less than 4" wide and less than 17" long and very light weight. The picture below is without a strap that I use to pull all the elements in a bit.
Here's how she looks extended. When fully extended it is approximately 27 inches wide and 22 inches long.
Now of course I could have just saved up and bought a Marshall antenna or some other folding yagi, but why not make one that is modeled after the Marshall antenna, optimized and tuned to my collars a little more precisely and a WHOLE LOT CHEAPER. All of the parts were scavenged or bought from Ace, all in all it cost me about $40.00.
Feel free to contact me with any questions as I am sure I have forgotten to list something.
Links:
http://www.hamuniverse.com/yagibasics.html
http://www.raibeam.com/wa7p1.html - Quick Yagi Design Program with Field Viewer.
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=6997 - Absolutely the finest free antenna design, optimizer, and 3-D field viewer. I used this one a lot.
