Keith has it right, below...
Try this to isolate the problem.
Get a full power dummy load...heathkit cantenna or assorted high power dummy
loads
Disconnet the coax at the antenna and feed on 15 meters:
Feed for good long time, taking care to not abuse the transmitter, if it is
not continuous duty rated.
1. first direct to the dummy load
2. 2nd via the balun to the dummy load.
Measure SWR during the tests, and you should be able to isolate the problem.
My bet is on the Balun.
'best...
Pat Barthelow aae6g@hotmail.com
>From: "Keith Dutson" <kjdutson@earthlink.net>
>Reply-To: keith@dutson.net
>To: <towertalk@contesting.com>
>Subject: Re: [TowerTalk] SWR Problem with Tri-Bander - help!
>Date: Tue, 22 Feb 2005 16:29:30 -0600
>
>This symptom is likely heat-related which would explain the variance over
>time on 500 watts. Simple fact, heat is generated by power that is
>consumed
>but not radiated. It could be that this heat is affecting the physical
>connections to the balun, which of course has the strong likelihood of
>changing impedance.
>
>Keith NM5G
>
>-----Original Message-----
>From: towertalk-bounces@contesting.com
>[mailto:towertalk-bounces@contesting.com] On Behalf Of RLVZ@aol.com
>Sent: Tuesday, February 22, 2005 3:11 PM
>To: towertalk@contesting.com
>Subject: [TowerTalk] SWR Problem with Tri-Bander - help!
>
>Hi Guys,
>
>I've got a Hy-Gain TH3-Mark4 that has a rather unusual SWR problem and
>wonder if you have any thoughts on fixing the problem. Here's the scoop:
>
>1) The SWR is always fine on 10 and 20 meters.
>2) On 15-meters the SWR starts out fine but the longer I transmit the
>higher
>it goes. Such as, when running 500 watts the beginning SWR is 1.3 to 1 but
>after 45 minutes it's 2 to 1.
>
>Here's various things I've tried but they didn't fix the problem:
>1) Replaced the coax.
>2) Replaced the balun.
>3) Replaced the 15-meter traps on the driven element.
>4) Took all traps apart and checked for solid connections.
>5) Locked the elements together with aluminum screws.
>
>This is not my main antenna so it's not a life or death matter. But I
>really like the antenna and want to correct the problem so I have a working
>backup and multiplier antenna.
>
>Any idears?
>
>Thanks! Dick- K9OM
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