Topband: Inverted L with elevated radials for topband

[Jim Brown]

On 3/5/2020 11:26 AM, Mike Waters wrote:
> Many hams --including myself-- have had very good results using only a few
> elevated radials.

Yes. One of the key factors is the height of the radials. N6BT, who has 
done a LOT of work with elevated radials on topband, told me that 18 ft 
is a minimum height. After my first tower (120 ft) was up, I had sloping 
wires rigged to points about 60 ft from the tower base, insulated from 
the tower and fed from the base against elevated radials. The tower has 
about ten on-ground radials to improves its performance as a reflector.

I had started out based on Rudy's early work with much lower elevation 
and wasn't satisfied with the result -- I had directivity, but the gain 
was poor. When I raised them to 18=20 ft (gull wing from about 3 ft at 
the feedpoint), I started seeing the few dB of gain that NEC predicted.

A few other important points. The ends of the radials are a high voltage 
point, so must be carefully insulated. Second, Rudy emphasizes that four 
elevated radials is a minimum, and twice that number is better. He also 
observes that they work better if current distribution between them is 
equal, that current distribution can be varied by variations in the soil 
underneath them, and that cutting them slightly shorter than a quarter 
wave minimizes those variations.

These are slides for a talk I've given about 160M antennas and 
counterpoise/radial systems, all based on good work by others.

http://k9yc.com/160MPacificon.pdf

73, Jim K9YC