On 9/16/2011 9:03 AM, Guy Olinger K2AV wrote: > This is an answer to an off reflector conversation, relating to a "too long" > electrical length over radials reducing performance. I am writing to the > list since the subject and it's objection occur in so many posted > conversations. Reduction of gain by too high current max has been touted by > some and called myth by others.
A 1/2 wave vertical over perfect ground has a theoretical gain of something like 2 or 3 dB over a 1/4 wave vertical. If we accept that the 1/2 wave vertical will have more losses, it is still that case that the 1/2 wave vertical only has to achieve 50% or 60% efficiency to equal a gold standard 1/4 wave vertical. I did some experiments on 20 meters and found that a 1/2 wave vertical with no radials was indistinguishable from a 1/4 wave vertical with 32 radials 1/4 wave long. A 1/2 wave vertical with a big radial field was about 2 or 3 dB better as predicted. WWVH with a 1/2 wave vertical plus a radial field is often cited as some sort of proof of concept. It obviously "gets out" but I haven't seen any citations of actual field strength measurements, and in any event, we don't know how it would compare to a 1/2 wave over no radials or a 1/4 wave over radials, and even if we did, it would be a function of local ground, etc. We don't know why the NBS engineers built it that way. Maybe it was a "belt and suspenders" design. If anyone knows anything published by NBS/NIST about this antenna, please post it. I'm still waiting to see an actual measurement showing that a 1/2 wave vertical with minimal radials is worse than a 1/4 wave vertical with radials. My measurements were over high conductivity ground. Maybe they would be different in the desert. Rick N6RK _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
