[Towertalk] TH11 SWR Problem

[Barry]

Tod,
I had a problem with a TH7 and SWR variation after rains. After taking 
down the driven elements (while antenna still on tower), I disassembled 
them, including the traps. The traps were full of debris - grass clippings, 
spider eggs, etc. Amazing how those little buggers got all that stuff up in 
there! (unless it happened while on the ground in storage - I bought this 
antenna from a guy in NC, so I don't know its history. My other TH7s, 
purchased new, have not had this problem) In any case, even though 
the water drained, this wet slop took weeks to dry, after a rain. Once I 
cleaned out the traps, the problem went away.
Barry W2UP


On 16 Apr 2002 Tod-Idaho wrote:

> 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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--
Barry Kutner, W2UP              Internet: w2up@mindspring.com
Newtown, PA                     Frankford Radio Club