[K2] Odd "Hi Refl"/high current problem only in TUNE

[Elecraft mailing list]

This one cropped up just today, with no significant change in my home station setup, using a K2/100 on 40m using a low inverted Vee.

Sometimes (typically every other or every third time, but randomly), when pushing (and holding) the tune button with the power set to 11 watts or more, I get a high reflected power message on an antenna which is matched at low power.  The power supply voltage reads about the normal 14V and the ammeter in the power supply is pinned at 25 A (or more) when this happens.  An external SWR meter reads lots of reflected power.  Everything unplugged from the rig except the power cable and the coax to the external SWR meter/antenna tuner/antenna. It's fine on a dummy load.

I'd suspect a simple RF feedback problem, except that with 100 watts of CW everything is perfectly normal.  The problem occurs only when using the tune button around the nominal tune-mode 20 watts, so the external SWR meter reading implies that the PA is probably oscillating at some frequency where the antenna is not matched.  I haven't tried any other bands yet, but since there does seem to be RF feedback involved, I'm not sure they will tell me much of a diagnostic nature.

Any ideas as to what might be happening and how to stop it?

73,
Steve VE3SMA
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[Guy Olinger K2AV]

Sounds more to me like an arc out in feedline/antenna somewhere. While the
arc is flashed, the feed Z goes very low. And the SWR therefore goes very
high. And it takes less energy to continue the arc than to start it.

The key here is that the SWR changes when the trouble starts.

An antenna is constantly subject to mechanical stress. One thing you can
count on with any antenna you put up is that it will fail at some point and
require maintenance. It's not if, it's when and how.

73, Guy K2AV

On Sun, Apr 16, 2017 at 10:52 AM Steve Kavanagh via Elecraft <
[hidden email]> wrote:

> This one cropped up just today, with no significant change in my home
> station setup, using a K2/100 on 40m using a low inverted Vee.
>
> Sometimes (typically every other or every third time, but randomly), when
> pushing (and holding) the tune button with the power set to 11 watts or
> more, I get a high reflected power message on an antenna which is matched
> at low power.  The power supply voltage reads about the normal 14V and the
> ammeter in the power supply is pinned at 25 A (or more) when this happens.
> An external SWR meter reads lots of reflected power.  Everything unplugged
> from the rig except the power cable and the coax to the external SWR
> meter/antenna tuner/antenna. It's fine on a dummy load.
>
> I'd suspect a simple RF feedback problem, except that with 100 watts of CW
> everything is perfectly normal.  The problem occurs only when using the
> tune button around the nominal tune-mode 20 watts, so the external SWR
> meter reading implies that the PA is probably oscillating at some frequency
> where the antenna is not matched.  I haven't tried any other bands yet, but
> since there does seem to be RF feedback involved, I'm not sure they will
> tell me much of a diagnostic nature.
>
> Any ideas as to what might be happening and how to stop it?
>
> 73,
> Steve VE3SMA
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

--
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[Jack Brindle-2]

25 amps at 14 volts is 350 watts. That is an awful lot for a radio that is supposed to be putting out only 20. I would expect at most 2 to 3 watts drain at 20 watts TX output. Something is definitely going on here.
may load While I don’t suspect the antenna, have you tried testing into a good 50 ohm dummy load to see if you can duplicate the issue? You might also look for bad solder joints between the PA transistors and
the antenna. And, just in case, check to make sure there are no bad (arcing) connectors in the antenna path.

Perhaps W3FPR might be around on the Easter Sunday for some suggestions?

- Jack, W6FB

> On Apr 16, 2017, at 7:51 AM, Steve Kavanagh via Elecraft <[hidden email]> wrote:
>
> This one cropped up just today, with no significant change in my home station setup, using a K2/100 on 40m using a low inverted Vee.
>
> Sometimes (typically every other or every third time, but randomly), when pushing (and holding) the tune button with the power set to 11 watts or more, I get a high reflected power message on an antenna which is matched at low power.  The power supply voltage reads about the normal 14V and the ammeter in the power supply is pinned at 25 A (or more) when this happens.  An external SWR meter reads lots of reflected power.  Everything unplugged from the rig except the power cable and the coax to the external SWR meter/antenna tuner/antenna. It's fine on a dummy load.
>
> I'd suspect a simple RF feedback problem, except that with 100 watts of CW everything is perfectly normal.  The problem occurs only when using the tune button around the nominal tune-mode 20 watts, so the external SWR meter reading implies that the PA is probably oscillating at some frequency where the antenna is not matched.  I haven't tried any other bands yet, but since there does seem to be RF feedback involved, I'm not sure they will tell me much of a diagnostic nature.
>
> Any ideas as to what might be happening and how to stop it?
>
> 73,
> Steve VE3SMA
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

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