Hi Sal,

On Saturday, 25 June 2011 04:16:42 UTC+10, Sal M. Onella wrote:
....
being the most promising, I think. With the help of EZNEC (evaluation
version), I modeled a promising 20m dipole at 30'. It's almost exactly
75 ohms resistive at the freqs I want to use and I'm going to feed it
with RG-6, 0.7 dB/100 feet. My radio has an internal tuner to match
the 75-ohm cable, if I need it.

That sounds fine as far as it goes.

You might consider a 1:1 current balun, a W2DU style one should suit this application fine.

I applaud your efforts to understand the thing using a modelling tool. To some of us, the inquiring mind and the interest in the technology of radio communications is what ham radio is really about. For those not so interested there are contests!

Your model though contains a guess for ground parameters, and possibly other site effects not included. You must expect some variation from model, but those variations would not cause very high VSWR on the line, line losses should be quite acceptable, and an ATU should transform the load it sees to that required for rated output from the transmitter with quite acceptable losses.

In my experience, antennas less dependent on ground are more likely to give consistent performance for field operations where you usually cannot afford to be installing significant ground systems.

Well done OM.

Owen