Topband: Feeding 160M Vertical on 80M

[Charlie Cunningham]

Well, sometimes, life is the art of the possible. At the time I was living
in q small duplex on a corner lot and running a bunch of on-ground radials
wasn't an option. Still I was working YBs and DUs etc. on the evening LP on
40m that others weren't even hearing! They'd come up on frequency and send
??? -during and after my qsos. In my experience a vertical 1/2 wave is a
very potent antenna because its high current portion is up 1/4 wavelength
and it's take-off angle is so low for DX work even without that last 1 dB!!
Just like some guy s like to dig in the dirt  and bury thousands of feet of
radials under their inverted Ls when they could do just as well, or better,
with 4 elevated resonant radials. But in the end - "if you believe, no proof
is necessary - if you don't believe, no proof is possible". Some people are
more taken in by popular opinions than by measurements or modeling!

73,
Charlie, K4OTV

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Jim Brown
Sent: Tuesday, January 07, 2014 1:27 AM
To: topband at contesting.com
Subject: Re: Topband: Feeding 160M Vertical on 80M

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


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