----- Original Message -----
From: "Chuck Counselman" <ccc@space.mit.edu>
But a G5RV, including one rigged as an inverted-V, is _not_ an
inefficient antenna, and no one should avoid using it because of
comments like "I wouldn't mount a G5RV as an inverted vee; actually a
G5RV's not much of an antenna on 80m at all, so I wouldn't bother
with it."
73 de Chuck, W1HIS
I think the important thing to remember is that any dipole style antenna,
even the OCF's when they become appreciably longer than a half-wave, do not
respond favorably to being installed as inverted vee's. Put up as flat-tops
they do an exceptional (if a bit lobe'y) job, but that very same antenna
when the legs are substantially inverted in a vee, start concentrating an
awful lot of the energy at high angles, despite the antennas height above
ground.
I had a heck of a time figuring out why my 130' cf (open wire feed) dipole
inverted vee at 72' didn't work worth a darn on 20m and above (compared to
what it should have). It wasn't like it didn't work at all....it just never
really performed like I expected it to. Then I modeled it with EZnec...
I started with just a flat top 130' and boy it looked like it should be a
real fine performer on 20m, at least in several directions. My experience
with the Vee told me otherwise, so I went to the trouble to model it exactly
as it hung, as an inverted vee. I had thought the effects of going inverted
vee vs. flat-top would be pretty much like a simple half-wave dipole in
either configuration. That turned out to be terribly wrong! The inverted vee
(130 feet, center fed), had most of it's heavy performance at angles above
45 degrees! I looked at it in 3D mode and I was shocked. I looked at the
flat-top configuration and it looked exactly like I had expected, the
take-off angle was right on the dot for the formula:
TOA=arcsin(1/(4*h)), where h=height of antenna in wavelengths. This formula
didn't work at all for the inverted vee.
As a verifying experiment, I put up a 20m extended double zepp @ 52' in a
flat-top configuration. Wow! Great performer. Then I inverted the legs, each
at about 10 or 12'...peformance STUNK.
So, before we get completely lost in the pro/anti G5RV shuffle, my modeling
and experiments suggest that for any dipole that is appreciably longer than
a half-wave, one NOT use the inverted vee configuration except out of utter
necessity. Doing so will cause the signal to be concentrated at high angles,
and create much more of a "cloud warmer" antenna for the higher bands.
The antenna still works, but a severe penalty is being paid at the angles of
best dx.
...hasan, N0AN
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