[TowerTalk] Raised Radial Spacing

[Brian Beezley]

W6FB:

"In this design the “ground wire” is actually a 1/4 wave ring that wraps 
around the base of the antenna."

One issue with a compact counterpoise is that feedline decoupling 
becomes more difficult. Imagine a 1" counterpoise with a series 
inductance to resonate it. If you were the inner shield current coming 
up out of coax, would you rather go there or down the outside of the 
shield? You can model this issue to get some idea of its severity.

Another issue is that a compact counterpoise gives up the directivity 
provided by a single straight radial. A single radial is not something 
I'd ever imagine might work well. However, some of the SOTA people use 
one as part of a portable hilltop antenna. The Elecraft KH1 includes 
one. When I first modeled a vertical with a single radial, I was 
surprised how directive it could be. In one modeling session, I had to 
increase the number of radials from two to four to regain the gain at 
low angles provided by just one. Symmetric deployment of two or more 
radials cancels the electric field directly below, minimizing current 
induced in lossy ground. So I had always assumed two radials was the 
minimum you'd ever want to consider. A little modeling dispelled this 
notion.

For these antenna systems, frequency and height above ground can make a 
big difference as can the details of the counterpoise or radial. It's 
easy to wrongly generalize by examining too few models. Results also 
depend on the ground constant values you use. The generic values your 
antenna analysis software offers are inappropriate. You'll find more 
realistic generic values here:

https://k6sti.neocities.org/hfgc

Dale, I don't know whether using a single radial for each band instead 
of two would be worthwhile for your situation, but it's something to 
consider.

Brian