[Elecraft] KX3 High SWR Only on 6M

[Raymer, Timothy]

Folks:

My KX3 is just over a year old.  It has developed an odd problem.  It shows a high SWR on 6M, and only 6M.  It may not be there on initial power up, but it shows up shortly after a bit of Morse code is sent, and does not seem to reliably go away until being shut down. 

Here are the specifics:
KX3 113xx.  Configured with:  KX3, KXFL3, KXAT3, KXFL3, KX3-2M, KXBC3.

I have been operating exclusively 6M, connected to a KXPA100 Amplifier.  the SWR issue presents itself hooked up to the KXPA100 as well as disconnected and running barefoot.  (I have to bypass the ATU to fully diagnose and simulate the connection to the KXPA100.)  I have verified the issue on a known good 50Ω dummy load.  Radio sees ~3.4:1 SWR when ATU is bypassed.  The SWR rises to 3.8:1 at the high end of 6M band when testing.

SWR		Band (Freq.)
3.8:1		  6M (53.995)
3.2:1		  6M (50.090)
1.4:1		 10M (28.025)
1.3:1		 12M (24.900)
1.2:1		 15M (21.025)
1.1:1		 17M (18.100)
1.0:1		 20M (14.025)
1.0:1		 30M (10.125)
1.0:1		 40M  (7.025)
1.0:1		 80M  (3.550)
1.0:1		160M  (1.810)

When the ATU is not bypassed and running barefoot, all the other bands quickly seek and find a 1.0:1 SWR and bypass the ATU.  But 6M band has a 1.3:1 SWR and had to ratchet a bit on the relays to get to it.

The problem started out as an occasional issue, and I could fiddle with changing bands, push a configuration file into it, or just let it be for a bit,  and it would behave for a while.  But it has gotten worse.  

I fired the radio up this afternoon, and all seemed okay for a couple of minutes.  But after just a few dits and dahs, and a callsign or two, suddenly... 3.4:1 SWR.  The radio reduces power out, and thus the KXPA100 is running less than the set/requested power out.  

I have gone through several troubleshooting steps to this point.  Checked radio without KXPA100.  Bypassed ATU in radio, and checked direct to a known good load.  

I am looking first at the 'KX3 Antenna Connector Assembly with LPF' (E850552) as a suspect.  Is that a good first substution?  Is there something on him that may visually reveal an issue?  Can I do an check with a multimeter to verify if it is a likely issue?

Where else should I start looking?

And, has anyone else encountered this issue with a KX3 running a lot of 6M into a KXPA100?

Thanks for any insight on getting my issue identified and resolved.


Tim Raymer
73 de KA0OUV