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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