[Elecraft] [KX3] Unstable SWR Reading (maxwelltl at aol.com)

[Gary Hawkins]

Hi Tom,

Regrading your comments below:

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

 From responses to my original post, several people have mentioned SWR 
instability they believe associated with the KX3 rather than 
connections, feeder, antenna, etc.  Of course, that being said it is 
completely possible the problem might indeed be an antenna (in my case 
often used in windy conditions when mountain-topping), feeder, etc., 
heating issue in antenna or component or poor connection, most likely in 
feeder.  So far this week I've not had the opportunity to investigate 
further but I plan to.  Please keep me posted on anything you discover 
in further conversations with Elecraft. Thanks to everyone else for your 
input on the topic and I'll let you know what I find as soon as I have 
the chance to try a few equipment combinations.  Interestingly enough in 
my case this problem has only started to occur recently.  So something 
has changed, whether associated with antenna, feeder or radio.  I did 
not see this issue on my first 14 or so SOTA activations.

Best regards,

Gary K6YOA