Topband: Feeding 160M Vertical on 80M

[Jim Brown]

On 1/6/2014 10:14 PM, Charlie Cunningham wrote:
> No, you don't need any radial field under a vertical 1/2 wave. You'll be
> driving a few thousand ohms, so a a few ohms or even 50-100 ohms of ground
> resistance won't add any significant loss. A simple ground rod will do fine.

Yes, but radials DO help -- a bit. See the ON4UN book. Modeling shows 
that adding a lot of half-wave radials under a half wave antenna 
increases signal strength by 0.5 - 1.5 dB at low angles, roughly twice 
as much at higher angles, the greater improvement for lousy ground.  To 
understand this, we must remember that radials serve TWO functions -- to 
return the antenna current, and to SHIELD the fields produced by the 
antenna from lossy earth.  That is, of course, a lot of copper for 1 dB.

Another common way of feeding a half wave vertical is an autotransformer 
resonated by parallel capacitance.  I've done that, and it worked.

73, Jim K9YC