Topband: Fw: Shortened Radial Experiments

[Tom Rauch]

> 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