On 8/30/2020 9:34 AM, Dennis W0JX via TowerTalk wrote:
Jeff's (AC0C) comments are an excellent summary of the choices available for
radials on 160. My main point in posting was that you can install an effective
radial system for the low bands with radials that are shorter than 1/4
wavelength with little efficiency penalty and a possible improvement in
radiating pattern.
The link I have posted earlier in this thread is largely a summary of
good work by others on radials and counterpoise systems, including a
very innovative solution that NC0B published in the '70s in Ham Radio.
It includes all of the ideas discussed here, and many others.
http://k9yc.com/160MPacificon.pdf
Lastly, depending upon angle of radials and other factors, the feedpoint
resistance will usually be less than 50 ohms and SWR greater than 1 to 1 at
resonance. This can be remedied by an adjustable shunt coil across the
feedpoint.
Unless the feedline is VERY long, loss is negligible on 160M in RG8-size
coax or larger, so the only thing that matters is that the power amp is
happy enough to supply power to it. Belden 8267 is 0.6 dB/200 ft
matched, and 0.7 dB/200 ft driving 30 ohms, so the added loss due to
mismatch is 0.1 dB.
I use Commscope 3227 (#10 solid copper center, robust copper plus foil
braid), which has a matched loss of 0.33 dB/200 ft; LMR400 has the same
loss, is copper over Al center. Buryflex is 0.4dB/200 ft. My runs are
about 200 ft. I was lucky to score a lot of 3227 and 2427K (plenum
version) from a friend years ago at a great price ($200 for 1,000 ft
spools) -- it was leftover from a 2000-era telecom bankruptcy, and my
friend bought a truckload of it! He paid $100/1,000 ft!
Below UHF, feedline loss is essentially all resistance unless it's coax
that has gotten wet inside, or 2-wire with a lousy dielectric. Ten years
ago, I helped N6RZ's widow dispose of his very large stash of "stuff"
that included a lot of coax and hard line. I bought all the hard line,
and took most of the coax to an NCCC meeting to offer it for free to
members. They turned up their noses, so I took it home and made stubs
from it. Stub performance is all limited by resistance, and these stubs
made from 20 year old coax measured as good as brand new coax. The only
exception was a piece that had obviously gotten wet. Note that this was
all good quality stuff -- Times, Belden, and Amphenol RG8/RG213.
There are graphs of loss vs frequency for a variety of coax types and a
table showing DC resistance for various popular coax types in this
tutorial. K1JT heard me present this material at Pacificon, and told me
he liked it.
http://k9yc.com/Coax-Stubs.pdf
Bottom line -- I use 7/8-in line for long runs to my tower for 40M and
up, but I would spend for hard line on 160 only for much longer runs.
73, Jim K9YC
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