[Elecraft] Strange SWR change on 20 at

[Brian D]

Diddn't proof read enoough, meant voltage transformer.

Brian D <groups at planet3.freeuk.co.uk> wrote:

> I have had similar problems with swr trips on my KPA500, only after
> several transmissions on some bands. By a process of elimination it was
> traced to a toroidal voltage
transformer
> heating up in an external coupler. It came on
> suddenly after about 5 minutes of transmissions, and came good after a few
> minutes to cool. Replacing the toroid with a larger one cured the problem.
> 
> 
> 
> "Ron D'Eau Claire" <ron at cobi.biz> wrote:
> 
> > Hi Dave: I thought you said it happened after you sent CQ+Call a few
> > times. When a core heats to its Curie temp, the inductance change
> > happens "instantly". You are right - if it happens instantly when you
> > hit the key it is not heating. Something is breaking down.
> > 
> > 73, Ron AC7AC
> > 
> > -----Original Message----- From: Elecraft
> > [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Dave Cole Sent:
> > Saturday, May 13, 2017 10:39 AM To: elecraft at mailman.qth.net Subject:
> > Re: [Elecraft] Strange SWR change on 20 at
> > 
> > I added the SWR meter...  My actual SWR jumps instantly up about1 SWR
> > unit...  I believe it is a bad connection on the Challenger where the
> > main antenna connects to the 20 meter tuning stub...
> > 
> > Just sort of surprised me to see a second person with the exact same
> > issue is all...  SWR change is instant, so it is not heating...  Happens
> > at 30 watts, or 1 KW...  Time for a rebuild.
> > 
> > 73s and thanks, Dave NK7Z http://www.nk7z.net
> > 
> > On 05/13/2017 10:07 AM, Dave Cole wrote:
> > > Hmmm...  I am having the exact same issue...  My SWR changes after a
> > > few transmissions, then returns...  Up until now, I have been
> > > suspecting my antenna...  Time to add an external SWR bridge between
> > > the tuner and antenna as a permanent thing...
> > >
> > > 73s and thanks, Dave NK7Z http://www.nk7z.net
> > >
> > > On 05/13/2017 09:07 AM, Terry Brown wrote:
> > > > I recently started using my horizontal loop that is about a full
> > > > wavelength on 80, for 20 meters.  I took down my yagi as we are
> > > > moving; drat!  My Horizontal Loop is at 40 ft.  height and fed with
> > > > 450 window line into a 4:1 voltage balun with about 15 ft. of coax
> > > > to rig.
> > >>
> > >>
> > >>
> > > > I am running 100 watts through my KXPA100.  I tune a frequency in
> > > > the CW portion of 20 to about 1.2 :1 and start sending CQ.  After
> > > > about 3 to 4  3x3 CQ's,, the SWR goes off the charts and power drops
> > > > to zero. I can retune the antenna and the process repeats itself.
> > > > 20 meters is the only band affected.
> > >>
> > >>
> > >>
> > > > I am wondering if I am having RF problems in that part of the 20
> > > > meter bands This only occurs on 20 meters.  The Amp is grounded, but
> > > > the KX3 is not bonded to the Amp.
> > >>
> > >>
> > >>
> > > > I would appreciate any advice.
> > >>
> > >>
> > >>
> > > > Thanks and 73's,
> > >>
> > >>
> > >>
> > > > Terry de N7TB
> > >>
> > > > ______________________________________________________________
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> > >>
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> > > > dave at nk7z.net
> > >>
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> > 
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> > 
> 
> 


-- 
Brian Duffell   Yarm    England