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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 |
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