An SWR anomaly….that suddenly popped up!!
Mike Weir, VE9KK, is a regular contributor to AmateurRadio.com and writes from New Brunswick, Canada. Contact him at [email protected].
|SWR on 15m...and hoping to see it again on 20m|
During the CQ WW CW contest last weekend the SWR on my K3 was jumping around from 1.4, 1.6, 1.3 and back to 1.6 and so on. This “flutter” has never happened in the past also it was only happening on 20m. All the other bands were just fine, I left this anomaly alone during the contest as most of my contesting was done on 15m. The next day once the contest was over it was time to look into it. I first wanted to check to make sure the issue still existed, as in the past I have had things just “disappear” to never happen again. The issue was still there so it was time to investigate.
My setup is as follows:
- Elecraft K3 operating at 5 watts.
- MFJ 1788 mag loop antenna.
- The coax is 30 feet of RG8X.
- There is an LDG switch allowing me to switch between the K3 and KX3.
Here is what I did and what I found:
1 - I switched the K3 to antenna B which is my dummy load. I found the SWR was stable as a flat match.
2 - I also have the Elecraft KX3 so I hooked that radio to the same antenna system. The SWR did not flutter as it did with the K3.
3 - I then hooked the antenna up to the antenna “B” connection on the K3 seeing the dummy load worked on antenna B. There was still a flutter in the SWR.
4- I then took the K3 out of service and opened it up tightening each and every screw I could find. This did not make a difference I still had the SWR flutter.
5- Even though the SWR was stable when using the KX3 I went ahead and made sure all the PL-259 connectors were tight. They all were good and snug.
I then posted on the Elecraft reflector site what was happening and the results I listed above. To my surprise all the advice that came back echoed the same……RF on the coax and making it back to the rig. I was informed that just because the KX3 did not have the issue did not rule out the feedline and or antenna. I did rule this out and was not going to look any further into anything other than the K3.
The following was some of the suggestions from the reflector.
1. If you can move the antenna further away from your shack. I am not able to do this as I am in a condo and the antenna is on the balcony.
2. Turn the antenna 90 degrees and see if the flutter becomes less.
3. Add a counterpoise to the ground lug on the K3.
Upon reviewing all this great feedback and wondering where to start, it was very odd that up until this weekend I had NEVER had an issue with the SWR on 20m. Then it occurred to me something I always do when it come to my trouble shooting which is to ask myself “Is there anything I have recently changed or added?” I went over in my head and there was nothing at all I added or took away from the radio setup. I proceeded to go out on the balcony to rotate the antenna 90 degrees as my other advice to myself when trouble shooting is preform the easiest things first and see what happens. The rotation of the antenna did nothing and back out onto the balcony I went to rotate that antenna back. While out there I checked out our balcony Christmas light to see if any had burnt out……….wait a minute the lights were just put up 2 days ago…….this equals a change!!! But could balcony lights funk up 20m??? I unplugged the lights and removed the extension cord I used to plug them in. I checked out the K3 and 20m was just fine now. I then placed the extension cord back out leaving it unplugged and the SWR I found fluttered just a tiny amount. I then plugged the lights in and check, I found the full-fledged SWR flutter returned. Therefor during the holiday season you will know I’m on the radio when the balcony Christmas lights are off!!
Nice sleuthing! Do your Christmas lights blink? If so, I wonder if the SWR would change in time to the lights.
Good evening Dave, sorry Dave no blinking with regards to the lights but I sure was happy to solve the issue.
Awesome story! Great sleuthing. Congrats, and thanks for sharing!
A fascinating conundrum and well done for persisting with the diagnostics until you found the answer. Pour yourself your favourite ‘tipple’ and raise a toast to yourself! Have a great Christmas. 73 Andy G4VIW
Thanks for sharing. A good reminder that any wire can create a resonant circuit.
Good evening Brian, no problem at all and I was very happy to have resolved the mystery.
Thanks for stopping by Brian.
Hello Andy, now that it’s Friday the glass has been raised and I am now waiting to see what Murphy brings my way….
73 have a great weekend.
Thanks for taking the time to comment Paul, one of the reasons I got involved with ham radio is nothing is how it may seem to be……it keeps me on my toes!