KX3 VSWR problem

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KX3 VSWR problem

WD4SDC
My last post might have been too long, so I'll try again - just the facts:

Equipment:
KX3 S/N 7210, FW 02.25

Problem:
6M band -> VSWR 1.8:1 (KX3 meter) on 50ohm load connected directly to ant connector (no cable).
ATU - bypass
Load verified good.
All other bands good.
ATU will match to 1:1 if enabled and tune requested.
After ATU match, 25ohm load yields 2:1 (KX3 meter test - OK).

MSG to Elecraft support unanswered (which seems uncharacteristic, based on rep)

Looking for input on how to identify/fix problem.

Thanks,

Steve, WD4SDC.
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Re: KX3 VSWR problem

WD4SDC
WD4SDC wrote
MSG to Elecraft support unanswered (which seems uncharacteristic, based on rep)
I was contacted by elecraft support shortly after this post.  Will be running some tests per their advice.

Steve WD4SDC
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Re: KX3 VSWR problem

Rick Robinson
Could it be your load is not rated to 50 MHZ ? Some are only good to 30 MHZ.

On Wednesday, October 7, 2015, WD4SDC <[hidden email]> wrote:

> WD4SDC wrote
> > MSG to Elecraft support unanswered (which seems uncharacteristic, based
> on
> > rep)
>
> I was contacted by elecraft support shortly after this post.  Will be
> running some tests per their advice.
>
> Steve WD4SDC
>
>
>
> --
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Re: KX3 VSWR problem

WD4SDC
Rick Robinson wrote
Could it be your load is not rated to 50 MHZ ? Some are only good to 30 MHZ.
Hi Rick.  Good point.  I should have included my load spec w/ the "facts":
I'm using a Narda 40W DC->12GHz w/ N->BNC adapter I borrowed at work. And verified it @ 50MHz - just because sometimes test equipment gets abused ;)

Steve.
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Re: KX3 VSWR problem

WD4SDC
In reply to this post by WD4SDC
WD4SDC wrote
Equipment:
KX3 S/N 7210, FW 02.25

Problem:
6M band -> VSWR 1.8:1 (KX3 meter) on 50ohm load connected directly to ant connector (no cable).

MSG to Elecraft support unanswered (which seems uncharacteristic, based on rep)
UPDATE:
Just to complete this for anyone searching this problem....
Elecraft support did respond.  I had sent the msg to support@elecraft.com and not the correct address which is k3support@elecraft.com.  The test was to disconnect the remove the ATU board and connect the RF board directly to the antenna port - which worked OK - 1.2:1.  With ATU installed and auto-tuned, I get 10 watts delivered to the load, so in my case the bypass VSWR is little high, but not really a concern.  Since the ATU *is* installed, just tune it and everything works fine.

Steve.
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Re: KX3 VSWR problem

Jim Rodenkirch
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Re: KX3 VSWR problem

WD4SDC
Jim Rodenkirch wrote

I'm not sure I understand......are you saying with the ATU removed the VSWR is 1.2:1 and with it

installed but not tuned it's 1.8:1 until the ATU "kicks in and does its job???


Hi Jim,

Sorry for the confusion. I'll pull everything into this post to put it in the correct context:

Problem:
6M band -> VSWR 1.8:1 (KX3 meter) on 50ohm load connected directly to ant
connector (no cable).
ATU - bypass mode
Load verified good.
All other bands good.
ATU will match to 1:1 if enabled and tune requested.
After ATU match, 25ohm load yields 2:1 (KX3 VSWR meter test - OK).

So the issue was that the ATU in bypass mode on 6M into good load gives a 1.8:1 VSWR.

Working with Elecraft support, I removed the ATU board to check VSWR w/o the ATU in the line.  That checked good 1.2:1. The ATU in bypass mode on 6M does not quite function as a 50 ohm transmission line.  For my particular unit, it was higher than expected.  1.4:1 is considered OK.  If the ATU is enabled and tune is engaged, it has no problem matching the output stage to the load and delivering rated power. So, operationally not really an issue. Just leave the ATU enabled and tuned.

The reason for going into bypass mode was to perform a TX gain cal procedure, which specifies the ATU must be set to bypass. I used the KX3 utility to do this and it sets the ATU to bypass and steps thru each band.  When it got to 6M, it failed - probably because the foldback circuit was kicking in @ 1.8:1 and/or the output stage can't deliver the 6 watts need to complete the cal into that mismatch.  Doing the cal manually with the ATU on and matched for 6M band works fine.

Hopefully, this provides a more useful note for anyone else that may have a similar issue.

Trying to contribute back to the list - as I have learned a lot using this resource.

Steve
WD4SDC