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Old April 5th 04, 11:03 PM
Mark Keith
 
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"Dave VanHorn" wrote in message

Though it's entirely done in the HF spectrum, a pretty detailed analysis is
presented he
http://www.cebik.com/58-3.html
A good ground, and cleaner near-field space, is easier to come by at VHF and
UHF, so I would expect results to be somewhat better than what was seen here
even at the high end of the HF spectrum.


It's more decoupling than anything. Although the usual 5/8 GP with 1/4
wave radials is a flawed animal from the git-go. I think the best
article to describe the effect is from a Dr. Reynolds , "I think thats
the name anyway", that wrote an article for AEA about this problem.
They put out a small brochure with the article and some pictures. They
described the problems with most of the common verticals used. IE: 1/2
waves, 5/8's, and collinears. The result of all that led to the
development of the AEA isopole. Probably the best decoupled dual 5/8
collinear ever designed. And thus , the highest performing compared to
less well decoupled competitors. Thats why cushcraft modified their
ringo ranger, and added a decoupling section, and renamed it the ringo
ranger 2. The effects of a lack of decoupling was glaring when
compared to an antenna of the same appx size, using good decoupling.
The RR was also an appx dual 5/8, although slightly perverted in
dimensions...The RR2 is a good antenna. But the isopole will still
usually beat it. The 5/8 GP or other poorly decoupled antenna does
have the rare chance of the feedline currents adding in phase and
creating some gain, but this is like a one in twenty chance...Like
going to Vegas...Doesn't usually work out that way for most people.
Never did for me...I've never had an elevated 5/8 GP on 2m that was
worth a hoot. Not a one...
Only on a car were they ok. But you look at a car...It's large enough
to usually provide a lower 5/8's of sorts, and also there is no
feedline radiation to skew the pattern upwards. The feedline radiation
if any, is shielded by the car body.
HF is a whole different story. On 10m, a 5/8 GP is best over both a
1/4 wave and a 1/2 wave. I've tested this many times in the real
world...
HF is less critical as far as using a real low wave angle, and also
the average angle used , even locally, is probably slightly higher.
But it doesn't apply to VHF or UHF. It's a whole different world
there, and feedline decoupling is by far the most critical part of a
good antenna. Not brute gain numbers. It won't do any good if the gain
is not where you need it. And thats under 5 degrees for local VHF. MK