[Towertalk] TH11 SWR Problem

[Tod-Idaho]

Fred:

I have been seeing some SWR variation from previous SWR measurements made on
my TH7DX with a GenRad 1606A RF bridge. The before and after stems from the
event of installing a Cushcraft 40-2CD about 8-10 feet above the TH7DX.
Prior to the installation of the 40-2CD I had the TH7 down on the ground (
actually about three feet above the ground) and realigned the elements
relative to the boom. At the same time taped the end caps of the traps to
protect them from the actinic stress of the sun here at 5000 feet above mean
sea level. Although I don't think I taped over the drain holes, after six
months I can't be absolutely , positively sure I did not do that. Normally,
here in the high desert of Idaho, one does not worry about water in traps.
(About 7 inches of precipitation per year, mostly snow). <<Currently we have
12 inches of snow delivered just yesterday >>.

When I read your note I got to thinking. My wife insisted on using the
irrigation sprinklers while my antenna was down. A couple of the sprinklers
are in the vicinity of where it the TH7 was located when it was down. The
fool things sprinkle UP not DOWN like good old rain! It may be that "her"
sprinklers injected water into "my" traps and I, unthinkingly, taped the
water into the trap. The biggest SWR change is on 10 meters with a smaller
change on 15 meters. I had rationalized that the 15 meter change was
attributable to the proximity of the 40-2CD, but have never been able to
explain the change in the 10 meter SWR after the 40-2CD was installed. Your
explanation may be the one that applies.

If you have any additional information about the SWR changes due to water in
a trap I would appreciate it. If you have information on how to 'remove' the
water that would be  nice too. I guess that I will need to lower the TH7
(after the snow finally goes away) and really dry out the traps. I have a
copy of a note from Roger Cox to a ham in Spain giving him the expected
resonant frequencies for the TH7 traps so I can check them out when I get it
down and after I assure that they are dry.

Thanks for the suggestion.

73, Tod, KOTO




-----Original Message-----
From: towertalk-admin@contesting.com
[mailto:towertalk-admin@contesting.com]On Behalf Of Fred Hopengarten
Sent: Tuesday, April 16, 2002 8:04 AM
To: DK2GZ@aol.com; towertalk@contesting.com
Subject: Re: [Towertalk] TH11 SWR Problem


SWR variation is a common occurrence in the TH3/TH5/TH6/TH7/TH11series
opf antennas when water is trapped in a trap. A hole in the end caps
should be pointed down, to allow water to escape. If there is no hole,
drill one.

Fred Hopengarten K1VR                       hopengarten@post.harvard.edu
Six Willarch Road * Lincoln, MA 01773-5105
781/259-0088 *eFax 419/858-2421

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