As others have pointed out, Rudy N6LF has done some very complete and
EXCELLENT work in this area. I strongly urge anyone with an interest in
vertical antennas to take a look at it. Much of it was just published to
his website in the last couple of months. You will be both enlightened and
impressed with his measurement techniques and results.
If I could summarize just one result from the above that is relevant to this
particular discussion, it is this: In the case of on-ground radials with 16
or fewer radials, the maximum efficiency actually occurs with radial lengths
LESS than 1/4 WL. This is due to detuning by the ground. If I remember
correctly, in the case of 40 meters the optimal length was in the vicinity
of 25 ft rather than 32 ft. Of course it is dependent on the particular
soil condition, but still an important conclusion - and a rare case where
less wire equates to better performance. With 32 or more radials, the "more
wire is better" rule-of-thumb again applies. Just to whet your appetite,
his work also includes some very good results for elevated radials!
73
... Craig AC0DS
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|