> If you stick the high voltage end of an antenna near earth, it generates
a lot of loss.
If I have my voltages and currents right, a standard 1/4 wave vertical has
its high current end near earth, while the GAP -- a vertical dipole -- has
its high voltage end near the earth. Does that explain the inferior
performance of the GAP?
> I can't think of a single "no ground" antenna, including the Gap, that
isn't a notoriously
> poor performer. In a QST review of a Gap, a small trap vertical with a
modest ground blew it
> away. I had the same experience here.
Ditto. It's so bad that my full-size 40M vertical with 60 radials on the
ground is 10-15 dB louder on receive than the GAP Titan. Yes, 10-15 dB! My
TH7 is on the order of 20+ dB louder.
Other issues with the GAP Titan:
1) It's a dummy load on 80M.
2) It cannot handle full power on 80M. The lit is downright misleading about
this.
3) Poor design of plastic standoff insulators causes arcing at high power on
other bands.
4) Critters seem to love chewing on the internal coax.
5) Counterpoise must be kept free of ice and snow.
On the other hand, it was the only antenna I was able to put up before
clearing forest for my tower and 4-square (before that, not enough room for
radials.) It got me on the air and allowed me to work some decent DX and
have fun in a contest or two (hunt-and-pounce only -- could never hold a
frequency with it.) I even worked Heard Island with it on 40M. In fact, I'd
say the 40M performance is probably the best, followed by 20M. Performance
on the rest of the bands is quite poor. I still use it for the WARC bands
(not much interest in those) and working stations off the back of the beam
in contests.
I think the larger GAP antennas aren't really suitable for roof mounting. My
Titan is 25 feet high and would have to be at least three feet off the roof
for the 40M counterpoise to stay above snow on the roof. Also, the antenna
has to be well-guyed (nylon rope will do), which can be tough to do on a
roof. If you're going to go through that much trouble, consider a
roof-mounted beam. Otherwise, if you have room for radials, I'd go for one
of the trapped 1/4 wave multiband verticals.
By the way, I've never had a ground-mounted multiband vertical, with or
without radials, that could do anything on 10M. First time I put up a beam I
couldn't believe how many 10M signals I hadn't been hearing!
73, Dick, WC1M
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