Saturday, May 5, 2012

The Antennas on the Antenna Farm

Hey,
So my food garden is stinking right now. Not really stinking, I just got to figure out the magic in my yard. I get a lot of shade from the neighborhood trees. That makes for great fun for the kids playing in the back yard, but it doesn't help me growing anything at all.
That's another blog for another day.
Having a big tree in the back yard is useful for antennas though, especially if you are as much of an antenna junky as I am.  Antennas to me, represent the greatest opportunity for doing something new. I can't go out and buy all the kits, and cool radios, but I can get some speakerwire, old buttons, used pulley, tarred nylon string, paracord, or whatever, and have some fun. A tree is an environmentally friendly antenna tower! Just add wire.
There are some things to remember about trees that will affect your antenna performance.

1.  Touch the tree as little as possible with the wire. A tree is a living thing full of electrolytes in solution, and electrolytes in solution conduct RF! That means your tree can detune your antenna if it touches it. During the spring, some people even go as far as to intentionally try to load the tree itself and use it as an antenna. I've never done it, and I don't plan on it. I have enough fun with speaker wire as it is.

2. Trees that are drought stressed get weak after a heavy rain. Basically, they suck up a lot of water, and get top heavy quick. Couple that with waterlogged dirt, and if it's an ongoing wind event (like a hurricane) and it becomes easy for trees to become uprooted. Practice safety at all times! Try to make sure there is a weakpoint in your achoring system so that if the tree does go over, it will break, and won't cause damage from an anchor point pulling out.

3. As an extension of rule 1, reduce transmit power. I don't have the capability to go over 100w right now anyway, so that's fine by me. Amateur rules and regs (Part 97.313) tell us to use only the minimum power necessary to carry out reliable communication anyway. Remember the tree is alive, and too much RF is generally bad for any living creature.

4. Expect the tree to detune the antenna some. This is another application of the principles I explained in rule #1.


With those rules in mind, here are some pictures:


 This is my 2m/70cm dualband copper J-pole. Yeah, I know they aren't supposed to work, but it's what I use to hit the local stuff! I had fun making it, and I have fun using it. No I don't get any RF in my shack from it.
Who knew, right? It is mounted on an old TV antenna pole that came with the house. I moved the pole from right smack in the way outside the back door to the shack. I've used it to talk to all the local 2m repeaters using 5w on my Kenwood mobile turned shack radio.









This is another j-pole, built for 10m. As soon as I got it deployed 10m activity dried up, lol. I don't have a real measure of how well it does yet. I've used a 'super-j-pole' on 10m before, and had great results. I couldn't quite get the line high enough to deploy that antenna, so I rolled it back up, and homebrewed up a quick regular style replacement. I got the design from this site: http://kk1cw.tripod.com/buildyourownwireant.html So far, that page has been a valuable resource for me. He has several downloadable spreadsheets that you can use to calculate how to build various antennas, not just j-poles.





In the middle of the branch that runs left to right is a white object. That object is the balun for my 40m dipole. From there, one leg runs North by Northwest, and the other runs East by Southeast. The vee in the horizontal plane is very wide.  This antenna was the first antenna for HF I ever purchased. I got in Atlanta at Ham Radio Outlet, and originally deployed it in the attic of the church where I worked at the time. I lived next door, and if I wanted to get active, I had to go upstairs, and use the antenna there.








Same antenna, but I faced north, looked up, and shot the pic, so you could get an idea of how it runs. The line that runs across the open area is the antenna. The pic of the other side of the dipole didn't quite turn out.
That leg kind of disappoints me. It somehow got trapped on these little scraggly branches on a limb and slopes down before leveling off and running east. Nomatter my efforts, I can't seem to free that leg. If I did, no bare wire would be touching any part of the tree.









Here's the previously mentioned deployed W3EDP. My back is to the shack, and I'm facing east.
















Not pictured is my 15m vertical loop. I'm considering taking it down, and reusing the mounting point for another antenna, either another loop (20m instead of 15) or using it as an experimental platform.
I need more trees!


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