A model will give you an accurate SWR curve for any height and would provide
the best answer to your question. I think 15' is too low for adjusting, I
would pull it up to 35 - 40' high which should get you close to your final
settings. What are you adjusting? Some people have had success adjusting a
hairpin match by pointing the antenna straight up and leaving the reflector on
the ground. OWA antennas require little if any adjusting.
John KK9A
To: <towertalk@contesting.com>
Subject: [TowerTalk] ANTENNA RESONANCE VS HEIGHT ABOVE GROUND - DATA POINTS?
From: "Larry
Date: Sun, 23 Aug 2009 21:54:06 -0400
Hi all,
We're in the midst of building a fairly long boom yagi for 20M. When
completed it's going to be at 190ft. We expect to initially tune it (T
Match) at 15 ft and then tram it to 80 ft or so for further tuning before
bringing it up to full height.
Initial thought is to tune it 200khz low at 15 ft, but that's just a guess.
Are any of you aware of data available that might make this a little easier
than simple trial and error. This will no doubt display a curve that sharply
rises as one moves an antenna from ground level to some height above ground
and from there on up to our working height the percentage of change becomes
fairly small. I'd guess from 30 feet on up the rate of change would be
greatly reduced from what one would see between ground level and that
height.
As I think about the question, I find I'm asking myself if there is anything
in modeling that might provide some answers, but if that were possible I'd
expect that Steve NR4M who developed the design based on YO would not be
looking for your help!
73 de Lar K7SV
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|