> The antenna measurements were: 56 ohms with two radials.
> 43 ohms with four radials. 30 ohms with eight radials. 26
> ohms with 16 radials. And, 24 ohms with 32 radials.
>
> One great feature of short radials that everyone seems to
> agree on is that FEWER of them are required. From the
> antenna measurements, you can see that doubling the amount
> of copper (& labor!) resulted in only 2 ohms improvement
> from 16 to 32 radials. My second antenna only has 16
> radials.
>
> My 48' or 49' radials are an efficient match for my 50
> foot verticals, but if I were to have a full-size (135
> foot) vertical, I would still go to resonant tuning. In
> this case, in my soil, the 3/4 wavelength radials would
> probably end up around 3X48' = 144'. (possibly slightly
> shorter due to the second order effect).
Brian,
All those impedance measurements are very nice, but the fact
remains the resistance presented at the base by the radials
has little to do with the loss of the system. Radials can
present a common mode impedance of ten ohms or 50 ohms and
losses can be the same. As a matter of fact a system with
higher "radial resistance" can have less loss than a system
with lower resistance.
Measurements of field strength also tend to disagree with
the implication radials need only be as long as the vertical
is high and that shorter verticals using efficient loading
systems obtain peak efficiency with fewer and shorter
radials.
As recently as few months ago W7EL and I measured a 40
meter vertical radial system here, and base impedance (when
only the ground system was changed) had no correlation with
measured field strength. Rudy posted a link here to his own
measurements which showed the same thing, and I think it was
N6RK found the same thing. There may be others I can't
recall who chimed in with the same results.
73 Tom
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