With a typical ground plane antenna, the feedline can radiate
significantly, distorting the pattern. This effect could easily be
different for the different antennas. Modeling indicates that two baluns
are often needed to suppress the current on the outside of the feedline.
A model which includes the feedline might give some insights as to why
the antennas behave so differently.

Roy Lewallen, W7EL

Mark Keith wrote:

Dan Richardson wrote in message . ..

On Mon, 17 May 2004 10:42:49 -0500, (Richard
Harrison) wrote:
[snip]

Power varies as the square of the voltage. One can see the difference in
the field strength is hardly worth the effort for an amateur to try to
increase the length of his antenna. It`s about a 3 dB gain from 1/4-wave
to 5/8 wave.

[snip]

The 3 dB gain figure is valid when mounted on theoretical perfect
ground. For a ground-plane elevated above real ground you'll find the
gain to be rarely greater than 1 dB.



Dunno. My real world tests don't quite agree. In using 30 mile ground
wave tests across town, I tested 1/4 GP's, 1/2 waves including
decoupling sections, and a 5/8 GP with 3/4 wave radials. All at 36 ft.
The 5/8 ate the 1/4 GP for lunch. Probably 2 plus S units better than
the 1/4 GP. The 5/8 beat the 1/2 wave by 1.5 S units. And this was
tested and repeated over a period of months. Never varied. Ground wave
testing is quite stable, and accurate for those low angles involved.
Much more accurate than trying to compare using constantly varying
skywaves. In real world gains, thats more than 1 db. 5/8 antennas are
weird animals. On 2m, they suck. On HF, they can do fairly well, cuz
the angles involved are not as critical. I used a 5/8 GP on 17m for
2-3 years. "also at 36 ft at the base".
It mangled every other antenna I had on that band. On 10m, the 5/8
beat any other length radiator quite handily. Again, on the critical
2m band, peeeyooooo.....they stink. BTW, on skywave, using a quick A/B
test, all preferred the 5/8, over the other antennas. So it wasn't a
low angle ground wave fluke. MK

Roy Lewallen wrote in message ...
With a typical ground plane antenna, the feedline can radiate
significantly, distorting the pattern. This effect could easily be
different for the different antennas. Modeling indicates that two baluns
are often needed to suppress the current on the outside of the feedline.
A model which includes the feedline might give some insights as to why
the antennas behave so differently.

Roy Lewallen, W7EL

It's quite possible. The 1/2 was the only one I actually added a
decoupling section to. It was a 1/4 wave length of coax below the
feed, and a grounded set of 1/4 wave radials at the base of that
section. About the same scheme as cushcraft uses on their ringo ranger
2 verticals. It did improve the antenna. I never added extra
decoupling to the 1/4 or 5/8 antennas. But I did try both 1/4 and 3/4
wave radials on the 5/8 antenna. Ended up prefering the 3/4
radials..The 1/2 wave was a very good antenna, but in my case, not
once did it ever beat the 5/8. Actually, thinking about it, and even
included many CB antenna setups going back years and years, I've never
seen a 5/8 GP that didn't handily beat a 1/4 GP by 2 S units to a
local ground wave station. Even using the 1/4 wave radials, which I'm
not crazy about for a 5/8 antenna. These were all using various
length feedlines I'm sure. MK