Jim,
You said : "Also, it really helps to raise the antenna and use
elevated radials. While it's BEST for those radials to be resonant, I'd
put in as many shorter ones as I could before giving up."
To me anyway this begs the question would it be an advantage to use four
elevated radials (too short) and
put a loading coil in each one so they are resonant ?
Bob
K6UJ
On 10/25/16 1:26 PM, Jim Brown wrote:
On Tue,10/25/2016 12:35 PM, Tom_N2SR via TowerTalk wrote:
Go back and read K9YC's articles about many short radials close to
the feedpoint. Isn't the idea to reduce/eliminate losses?
Exactly right. With on-ground radials, more copper is better, longer
is better. I covered this in great detail in the piece about 160M.
When I added added the HF2V, I had about 4 radials and the BW on
80 was about 150 kc. I kept adding radials, and the bandwidth kept
dropping - which is good, since that means that that ground losses
are being reduced.
The bandwidth finally dropped to about 50 kHz. For an 1/8 wave
antenna, that is pretty good.
Yes. AND loss in coax is quite small on 160 and 80M, so it's very
practical to use a tuner in the shack once you've got it close to
resonance in the middle of the range where you want to work. This is a
great application for big coax (RG8 or RG213 size), not for power
handling, but to reduce loss with mismatch.
"Also, it really helps to raise the antenna and use elevated radials.
While it's BEST for those radials to be resonant, I'd put in as many
shorter ones as I could before giving up." NEVER let the perfect be
the enemy of the "good enough." And best, by far, is one of those
vertical dipoles that doesn't need radials.
Yes, top-loading is ALWAYS a good thing if it doesn't reduce the
overall height of the vertical section. If, for example, you're using
conductive guy wires as top loading, the vertical part of the guy wire
will shorten the effective height of the radiator, reducing its
efficiency. Let's say that you've got a 40 ft tall radiator, are
guying it with wires that form a 45 degree angle with the ground, and
the conductive section of the guy is 14 ft long. Doing the trig, the
wire drops 10 ft, so the effective height of the radiator is 40 ft -
10 ft = 30 ft. This means that SOME top loading is a good thing, but
don't overdo it, or try to tie off the guys as far from the antenna as
possible.
73, Jim K9YC
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