helix

I've been busy building my Arduino-based memory keyer (based on the work of K3NG) making antennas and doing some SDR work (with GnuRadio) in order to work some satellites.

You may recall that I'm trying to build a compact whole-band antenna for 80 meters, and the simulations I've done show some odd results that I'd like to resolve. To that end I've built a scale model that should work for both 10m and 12m. Unfortunately, the scale model doesn't work and it doesn't work in interesting ways. In particular, it looks like the antenna wire wasn't cut to the right length. I've been wondering what mistake I could have made that would give me the results, but I hadn't been able to come up with anything.

I re-measured and cut new wire and added a ground grid (a four-foot square of chicken wire) and it still doesn't work. The way that it appears to not work is interesting, so I'm recording it. The feedpoint impedance is very small. I was expecting about 100 ohms, and it's less than 20 ohms from 24.682 MHz to around 30.508 MHz and at most of the frequencies in the range, it's less than 10 ohms. I also discovered that I needed to disconnect the resonator from the ground plane to get those numbers. The simulations all connected the resonator to the ground plane.

I am attempting to create whole-band antennas for 80m and 160m that will actually fit on my yard. NEC2 says that a particular design will definitely work, but having built a 10/12m scale model of the larger antenna, well, it doesn't work. I'm going to be investigating why. I hope it is because I made a construction error.

A while back, I complained that I had misplaced my second copy of the Jerry Sevick's The Short Vertical Antenna and Ground Radial What I was trying to do was simulate one of the antennas that he had put in the book to see if I was getting a handle on NEC2. As an aside, I don't use EzNEC because I usually run Linux at home, not Windows, and EzNEC is pretty seriously a windows-only thing. I suppose I could get it to run under WINE, but I'm not really very interested in paying money for a product that could be rather difficult for me to use.