[Elecraft] K3 SWR Anomaly

Mon Jan 21 08:34:22 EST 2019

Hi Barry,
     I think what I am seeing is related to your experience. I ran through some additional testing. I see perhaps some slight differences between ANT1 and ANT2 positions as far as SWR readings, but nothing significant, at least on 40 meters.
     I do now see something I’m even more puzzled over. While collecting SWR readings into a dummy load on 10 meters, I initially did see a high (2.0:1) reading on the K3 meter. I switched in the K3 tuner, and brought the SWR down to 1:1.  But when I then bypassed the tuner, the low 1:1 SWR remained.  This was true for either ANT1 or ANT2.  I really don’t understand that.
     So back to 40 meters, where I first noticed the high SWR anomaly. I thought I would try the tuner again, and then bypass it, to see if SWR would stay low on the K3 meter as it did on 10 meters.  It did not.  So I still have the anomaly on 40 meters, and it is the same on either ANT1 or ANT2 positions.  
     To summarize:
1.  SWR using a dummy load on 40 meters remains constant using an external LP-100A meter, but varies greatly using the K3 meter. As you tune up in frequency on the 40 meter band, the SWR on the K3 meter rises to almost 3:1, and the K3 output power drops back significantly. 
2. Antenna tuner settings appear to “stick” on 10 meters, even when the tuner is bypassed.

I believe some users, assuming there are others that have K3s which would exhibit this behavior, may not have noticed this anomaly. I do believe it may be responsible for what some users have noticed when using their K3 with an amp such as the KPA1500. That is, power overshoot. I suspect the K3, at least for me on 40 meters, is folding back power in response to a false SWR reading, and this can be seen in how the KPA1500 amp correspondingly drops back in power as the user transmits.  That is perhaps why (again, for my situation) I see the power overshoot only on 40 meters when using my KPA1500.
--Ed—

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From: Barry Simpson
Sent: Monday, January 21, 2019 1:51 AM
To: Ed G; Elecraft Mailing List
Subject: Re: [Elecraft] K3 SWR Question3

Hi Ed

I recall having had a similar experience with my K3 some years ago, although it wasn't on 40m. I think it was either 10 or 12m and related to an antenna connected to the ANT 1 socket.

Eventually I tracked it down to having previously had an antenna connected to the ANT 2 socket and having used the ATU in the K3 to tune it at that time although I think that there was no antenna on ANT 2 when the problem cropped up.

I believe that the feed through between ANT 1 and 2 sockets was sufficient to give a false SWR reading on the K3.

It might be worth investigating this and possibly swapping over your antenna/dummy load to the ANT 2 socket to see what happens.

I think I eventually just retuned the ATU on ANT 2 with a dummy load in place and the problem went away.

Good luck.

Barry  VK2BJ

On Mon, 21 Jan 2019 at 04:17, Ed G <ed.n3cw at gmail.com> wrote:
Hello,
     My K3 is exhibiting some SWR meter behavior I don’t quite understand. To eliminate any possible effects of antennas or cabling, I hooked a Palstar DL2K dummy load directly to the K3 antenna connector. All bands except 40 meters seem fine, with SWR reading as you would expect with a dummy load. The anomaly I am seeing is that SWR as shown on the K3 meter looks fine at 7.01 MHz (approx. 1.2:1), but as I go up in frequency, the SWR as shown on the K3 meter rises. When I transmit into the dummy load on 7.298 MHz, the K3 meter reads almost 3:1.   I can switch in the K3 internal tuner and bring the SWR down to 1:1.  
     I also tried an older Cantenna dummy load with the same puzzling results.  Any ideas as to what may be causing this 40 meter only problem?  I first noticed this problem during NAQP SSB when using my Steppir, which of course retunes itself as I change frequency. When going from the low part of the phone band to the high part on 40 meters, I noticed SWR increasing on the K3 meter, even though it was not increasing and stayed at 1.2:1 on my inline LP-100A.  The K3 also started to fold back power.  That prompted me to do the further testing with the dummy load as I discussed above.
--Ed—

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