There is some good stuff in ON4UN Low Band Book - Chapter 9-10 on Elevated
Radials.
He suggests that an elevated system would be even better above ground versus on
the ground in poor conditions. References 0.1 wave height or less. For 160m
that could be 50 feet down. In Section 2.2.7 K3LC says that there is no point
in raising radials any higher than 6 meters on 160 or 3 meters on 80 meters.
Such a height would be between 0.2db of what can be achieved with 64 buried
radials... N7CL says they need to be higher....
The perfect on ground system might be 50-100 1/4 wave ground radials...
In 2.1.2 he warns of trusting modeling because of outside factors.
9-12 Figure 9-18 (modeling) regarding 160m gain using 1/4 wave is interesting
over average ground. If you wanted max. it suggests using 120 - 80meter
radials. But the difference between 120 (1.5 dbi gain) and going with 32 (1.0
dbi gain) would make one wonder if it was really worth it for another 1-2 miles
of wire.. work? 0.5 dbi gain?
The Conclusion in 9-14 is interesting.. basically saying..
"Take the example of an 80-meter vertical over average ground: going from a
lousy eight 20-meter long radials to 120 radials would only buy you 1.4db of
gain, which is less than what I think it is in reality. In very good ground
that difference wold be only 0.7 db!"
2.1.3.2 - "From these almost 70-year old studies, we can conclude that 60
quarter-wave long radials is a cost effective optimal solution for amateur
purposes.
K3NA's work in 2.3.1.3 talks about using 1/16 wave radials.. not going beyond
48.. but that doesn't match up with N6BV's work several years prior.
In 2.2 Elevated Radial and beyond it's gets really interesting and less
conclusive?
The Conclusion States - "If you want to play it extra safe, and if you have the
tower height, get the radials up as high as possible and add a few more. Use
a ground screen if you have it.
"It all is very logical. Get away from the lossy ground or hide the lossy
ground with a dense screen using many radials. No free lunch!".....
This was one book and it goes on.....
All of this sounds like a great episode for Ham Radio Myth Busters.......
73,
Bryan
WH7DX
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