[Elecraft] K3 SWR Anomaly

[Ed G]

Hi Mike,
     Have not heard from Support yet.  But this is an interesting discussion and I am learning some things from the group.  I had not kept up with the differences between the KAT3 and the KAT3A, but it would seem that’s at the center of the issue I have.
     My K3 is S/N 02977, and I have the KAT3 tuner.  Apparently the KAT3 is not really bypassed in the BYPASS position. From reading earlier posts, the KAT3 supposedly sets itself for what it thinks is a 50 ohm match when in the BYPASS position. It was suggested by Joe, W4TV, that the user could enable the tuner, tune into a dummy load and then bypass the tuner, and that process would reset the bypass settings.    That seems to have worked for me on 10 meters, but not on 40 meters.  So part of my original post has been answered, but here’s what remains:

1. With my particular KAT3, I am not sure why the recal of bypass settings per W4TV does not work on 40 meters.
2. If the KAT3 is not truly being bypassed, can there be some unexpected results when using the K3 with the KPA1500, such as power overshoot?
3. Am I ok to enable the KAT3 in my K3 and also use the tuner in the KPA1500?  Otherwise I am having to readjust the K3 power out setting as I change frequency on 40 meters, to keep from overdriving the KPA1500.

It would appear that I might have some unknown tuner circuit issue when bypassing the tuner on 40 meters due to whatever is still in the RF path, or perhaps even the faulty trap component Mike mentioned.  Elecraft – do I need to replace the KAT3 with the KAT3A to get rid of this problem, and eliminate the need to readjust power up when using my KPA1500? I appreciate all the responses so far!

--Ed—

Sent from Mail for Windows 10

From: Mike Wetzel
Sent: Monday, January 21, 2019 1:33 PM
To: ed.n3cw at gmail.com
Subject: K3 SWR

Ed,

I’m sure you have heard from Elecraft Support on this but just in case.  I had a very similar problem on 40 meter a couple of years ago.  It turned out to be a faulty trap component on a nearly vacant board near the ant terminals.   The trap is not needed I removed a cap and all has been fine ever since.

Mike W9RE


     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?





---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus