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K2 low power and SWR problems

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Christer Karlsson

K2 low power and SWR problems

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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Don Wilhelm-3

RE: K2 low power and SWR problems

Chris,

That is very strange, but if the K2 operates properly into a dummy load, but
not into the tuner, then the problem is not in the K2, but either in the
tuner or in the coax between the K2 and the tuner.

If your tuner is adjusted for a perfect match, that alone tells us that it
should be exactly a 50 ohm non-reactive load - just the same as your dummy
load. How are you determining that your tuner is set to a 'perfect match'?

The only other reason that I can think of is that you may have a significant
amount of RF in the shack if the RF return path is different when you have
the K2 connected to the tuner input vs. the RF return path created when you
use the device (whatever instrument) that indicates your tuner is adjusted
for a perfect match. If you are not using a balanced antenna, this is quite
likely. You may wish to experiment with some quarterwavelength counterpoise
wires.

73,
Don W3FPR

> -----Original Message-----
>
> 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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ab4cz

Re: K2 low power and SWR problems

In reply to this post by Christer Karlsson

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
>
>
>
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com