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Wimpie[_2_] · April 4th 14, 02:39 PM posted to rec.radio.amateur.antenna

El 03-04-14 23:29, escribió:
On Thursday, April 3, 2014 2:28:40 PM UTC-5, Wimpie wrote:

Again, in free space the maximum is ALWAYS at zero elevation.

Except for the 5/8 lambda, as I mentioned.

That's only because you used 1/4 WL radials, which is a very
perverted design. Try it with 3/4 WL radials. That will give you
close to your textbook gain.

For zero elevation (relevant for line of sight comms in VHF and up),
the gain will virtually not improve when using horizontal 3/4 WL
radials. The horizontal radials don't contribute to the vertically
polarized wave.

And for an even better pattern use sloping 5/8 WL radials, which
will start approaching the gain of a dual 5/8 WL collinear.

Agree, that really helps! You have to take care of mast/feeder
radiation that may distort the pattern (hence gain) significantly.

I've compared 1/4 wave GP's, 1/2 wave's with decoupling, and
5/8 GP's with 3/4 and 5/8 radials on 10m to distant local
stations, which is a good test of low angle performance.

The 5/8 was always the best antenna in the real world using
low angle space wave paths 30-40 miles across town.

Probably this was because of the added heigth for the 5/8 lambda
radiator over a half or quarter wave, or you had (somewhat) sloping
5/8 WL radials.

And the 1/2 wave was better than the 1/4 GP.
The only reason the poor 5/8's get a bad rap is because people
insist on using 1/4 WL radials under them. That's a disaster,
particularly if used on VHF/UHF where the pattern is really
critical.

Agree, this was the reason I mentioned "over-rated" for the
commercially sold 5/8 lambda antennas, they all have 1/4 lambda
radials. If you make them 3/4 WL, the antenna will be significantly
more expensive and the visual appearance becomes massive (and many
people don't like that).

I had long discussions about this, as many people still believe that
there is a big difference between the 5/8 lambda with 1/4 radials and
the "GPA 27" (the half wave end-fed with no or short radials).

--
Wim
PA3DJS
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