[Elecraft] REF: KX3 Unstable SWR Reading

[Jim Farmer]

Hi Tom,

Reading this, I wondered if you might have something in your antenna 
system that is going non-linear with higher power - the symptoms seem 
consistent with that possibility.  For instance, if you had something 
that was arcing (e.g., a surge protector), or if you had a balun with a 
ferrite core that was saturating.  This would be particularly suspect 
if, like me, you were starting with a high VSWR and the KXPA was getting 
it down low - I have this situation right now on 80 meters.  Dummy load 
testing as you suggest would be a good idea.

jim

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Jim Farmer, K4BSE
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On 4/1/2014 12:00 PM, elecraft-request at mailman.qth.net wrote:
> Message: 3
> Date: Mon, 31 Mar 2014 20:43:00 -0400 (EDT)
> From:maxwelltl at aol.com
> To:elecraft at mailman.qth.net
> Subject: [Elecraft] REF: KX3 Unstable SWR Reading
> Message-ID:<8D11B5A778BBE18-2FA8-C6DB at webmail-d162.sysops.aol.com>
> Content-Type: text/plain; charset="us-ascii"
>
>
> I am seeing a similar concern with my KX3/KXPA100 home station.  The KXPA100 ATU tunes it right down to 1.1-1.2.  Then when I start transmitting it jumps up between 2 and 3.  This doesn't happen all of the time nor on all bands.  I have worked with Dick and he has put a lot of effort into my concern, much of it off hours by the way.  Great service and great concern demonstrated by Dick.  Try to get a response from the big three at all-let alone on weekends. We ran traces on the tuning process and it shows a good tune right down to where it needs to be.  However, the SWR then jumps up when I go to full power.  I am not sure it is a real problem as the power meter shows I am getting out OK.  But it is concerning to be transmitting 100 watts and seeing the SWR jump up to 3 after it has tuned down to 1.2.  I don't believe it is in my antenna because I put an LDG tuner in the line and it tunes solid and stays there.  I know gut feel isn't very scientific but I think there could be
>    an issue with the SWR circuitry.  At lower tuning powers it senses SWR OK, but with higher power levels it doesn't. It may well be that my SWR is varying and maybe the sensing circuits in the KXPA100 are just more sensitive than the LDG circuits, I don't know.  All we really know at this point is that the traces look really good, the ATU takes the reported SWR down to more than acceptable values even when the antenna SWR is above 10.  I may try putting a variable dummy load on it to see if I can duplicate the problem into a known stable load.  Keep in mind that this is more of a nuisance item to me and I love the KX3/KXPA100 combination. 10m was wide open this weekend and I worked Japan, New Zealand, Hawaii, and China with a very minimal horizontal loop at 15 feet.  I know this is anecdotal but I believe the low noise receiver and filtering made it possible. Good stuff!
>
>
> Tom/AE5QB
>