Цитата:
Some electrical tests
One of the objects of testing the SteppIR was to develop a radial system for field day which would work well on all bands from 40 through 10m. SteppIR recommends using "20 to 30 radials 16' or more long". I thought this was little odd since on 40m a 1/4-wave is about 33' and on 10m about 8'. I though that a broadband radial system should have a few radials for each band, each about 1/4-wave on that band. As a first pass we decided to try four radials on each band cut to 1/4-wave. Boy was that a mistake!
There are two serious problems with that approach. First, as illustrated by the work reported in experiments 3, 4 and 5, four physically 1/4-wave (free space 1/4-wave) radials lying close to ground can be very lossy. As shown in the earlier reports, when using only a few radials (8 or less) it is necessary to shorten the radials so that they are close to resonance over the particular soil at the site.
The second problem observed was the coupling between multiple different length radials lead to unexpected resonances and the resonant length for the vertical was often very different from the preset lengths from SteppIR. We also noticed that some of the resonances led to very large drops in signal strength.
Seeing this, the next step was to determine the optimum radial length on each band, 40, 30, 20, etc, etc, by observing the signal as the radials were trimmed down from the physical 1/4-wave. For this experiment we used 8 radials on each band. In all cases we were able to optimize the radials and the resulting vertical heights for resonance were close to those provided by SteppIR.
But when we put all these radials on the base plate simultaneously we had a real rats nest, totally impractical for portable use. More importantly the strange resonances were back. In short, this idea didn't work either!
What works is to do what SteppIR suggests: use a bunch of radials! When all else fails, read the instructions!
We found that 30 or more radials eliminated all the resonance and coupling effects and was provided an efficient ground system. Radial lengths of 20' to 25' seemed to work noticeably better than 16' radials and that was over good soil. Poor soils would probably benefit from even longer radials if you want to operate down to 40m which is of course the bread-and-butter band for DXpeditions while the sunspot cycle remains low.
These remarks are just observations. No doubt a more extensive and careful set of experiments would have been better but we really didn't have the time for that. But even still I think these observations deserve consideration until we have more to work with.