a 2 meter ground plane with an HT
I built the 2m ground plane
like the instructions showed in the project link above.... although I
just used 3 legs instead of 4. Please refer to it for lengths using
the handy calculator provided as a starting point.
The previous week I had attended a radio club meeting where the topic was HT antennas and how well they performed, which was to say not all that well for the most part. They usually depended on using your body as a poorly coupled ground plane or counterpoise. I was bored one evening and thinking about that while flipping through the hamuniverse web site. I saw the 2 meter ground plane project, and the "nerdtenna" idea started to come together.
The parts list:
Whats going to happen here is that we're going to build a 2 meter 1/4 wave antenna and mount that on a short section of very stiff coax, and put this (via an adapter or 2) on a HT.
I soldered first and cut second. In this case I took what would have been the ground wire (bare copper), straightened, and inserted it into the center conductor of the SO-239. Solder that in. I took the other three wires (red/white/black), stripped the ends and bent hooks into them and put them into 3 corners of the SO-239. You're going to bend these so that they are 120 degrees from each other and down about 30-45 degrees. Get them in the general direction you'll want them when you solder them in. You can fix it later, so don't sweat the details. Let this cool a bit since the connector body will be wicked hot for a little while. Once it cools, check to make sure you have got good solder flow.
I'm going to wave my hands here and assume you'll figure out how to terminate both ends of the coax. Crimp or solder, I'm not religious. Tip to tip, mine ended up being about 20 inches. I wouldn't go much longer, since it'll bend under it's own weight and I'd be worried about over-stressing the HT connector. I actually cheated and cut a good end off a damaged cable I had sitting around so I only needed to solder on one connector. Use a meter to make sure you don't have any shorts.
OK, now lets trim the antenna "elements". I mounted mine on a MFJ-259 and kept trimming till I was happy. YMMV, (your milage may vary), offer not valid in Delaware or where prohibited by law.
These should get you close, but if you have a good VSWR meter or antenna analyzer, you could sneak up on these and probably get a better trim. Mine tested under 1.5:1 144-148 MHZ, so I think thats good enough.
It turns out that by looking straight down you can eyeball these to about 120 degree angle. A little off doesn't seem to effect things much. The "dip" from horizontal for the ground plane wires should be about 30-45 degrees. Again, pretty easy to eyeball and close seems to work pretty well. You can also balance it on your finger tip (minus the coax) and it turns out it will lean away from the wire that needs to come up. If for any reason you think this will be exposed to rain/snow, weather seal the connections, and put a little non RTV bath and kitchen caulk around the vertical base.
You have to remember that these wires will get bent for whatever reason, and you'll be putting them right, so don't get too obsessed with the angles. Just try and get them straight, equally spaced, and equally deflected down.
Now we get to the nerdy part. Going outside, I keyed up a local repeater using the "rubber duck" antenna. I got through, but had reports of a fair bit of noise. I swapped in the "nerdtenna". The reports back were full quieting and some questioning that I was still on my HT. While I was outside, the wife let it be known that I looked like the silliest thing she'd seen for awhile. She thought it looked like an umbrella frame. Ah, no one understands genius in its own time.
The nerdtenna ranks pretty low on the practical scale. You probably wouldn't walk down the street using it (Hey, you could put someone's eye out!). I did it more as a proof of concept, yet the more I thought about it the more I liked it. It's not something you'd leave on, but you could fold and store it pretty easily. I made mine out of scrap I had lying around (I only used one new PL239). It would be cheap even with new parts. It performed unexpectedly well over the stock antenna (which I guess isn't saying much). I'm thinking it would make a good backup antenna for when you needed more reach. For a new ham with just a HT, it could mean a cheap way to hit local repeaters with a solid signal. In a pinch, you could gin up a taller unit by supporting the coax against a building or with a pole. Another ham here at work suggested soldering a fishing swivel to the top so you could haul it into the air suspended with small cord or string and feed it with rg58 to the HT.
If any piece breaks off, it's trivial to fix. The gain.... would be equal to about half of a theoretical dipole or minus 3dBd.
And thats my "Stupid Ham Trick"
Jim - W6JMF
Email Jim for questions:
note: By using this simple method described in the project above,
you can extend the range much greater by the simple addition of more coax
and a ground plane to your ht..
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