Posted by
ab4cz on
Jan 02, 2006; 3:47pm
URL: http://elecraft.85.s1.nabble.com/K2-low-power-and-SWR-problems-tp385100p385101.html
Christer,
If your antenna tuner is indeed properly matched on the band you want to operate and gives a high VSWR using the K2, that tells you the K2 is delivering power on another frequency. This happens if the transmitter is on the wrong band (probably not your problem) OR if the transmitter has high harmonic output. This is most likely your problem. The K2 might have high harmonic output if one or more of the output low-pass filter relays is not switching correctly. My guess based on your information is that one of the output filter relays (K8 through K12) is stuck in the closed position. This leaves one set of filter components in line all the time, allowing harmonic content to pass through the filter and into the tuner. The tuner, when tuned for example to 80M, indicates a high VSWR because it is also seeing power at 40M or 15M or whatever frequency. If only one relay is stuck closed, that band should NOT show this problem. Thus, if you tune your antenna tuner to each band
and try it, you may find one band that works OK. This band is the one with the stuck relay.
The reason you can tune OK into the dummy load is because the dummy load is not frequency selective and provides the proper match regardless of harmonic content. This is a key piece of information.
So .. you have harmonic output. A likely cause is a stuck relay, but in general you should be looking for problems around the transmit low pass filter. I think you will find your problem there.
Good luck and I hope you are successful in tracking down this problem.
Best Regards,
Jim, AB4CZ
K2 s/n 5230 (brand new Christmas present ! )
-------------- Original message ----------------------
From: "Christer Karlsson" <
[hidden email]>
> I built my K2 in late 1999 and it has behaved the same way ever since.
> Gary has been very helpful and once his advice was correct (bad soldered
> antenna connection) but it did not improve my K2. I did not want to
> bother Elecraft anymore so I have learned to live with my rig. However
> now I have decided to do something to cure my K2.
>
> When I change band I first have to tune into a 50 ohm dummy load before
> I switch to the antenna. If I first connect K2 to my antenna tuner
> (perfect match) the power is significantly reduced and my cross needle
> SWR meter shows high SWR.
>
> If I have tuned via dummy load, then connected to the ATU (with good
> match) and start reducing output from K2 the SWR meter will show a great
> mismatch when having decreased to about 2 watts. The "low power
> hostility" is most outspoken on 80 m.
>
> This I guess is also why I can not use K2 on SSB.
>
>
>
> Chris, SM7KJH
>
>
>
>
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