[Elecraft] K3- How Robust iis the Tuner?

[Ron D'Eau Claire]

I would think any danger would be to the external tuner or the coaxial link
between the K3 and external tuner.

The built in tuner (or any tuner) simply tries to find a match - compensate
for any reactance and transform the remaining resistive impedance to 50
ohms. It doesn't matter why there's a mismatch. If it can find a match it's
fine. Obviously, the KAT3 is rated to handle any impedance it can match at
up to 100 watts, with a decent safety margin beyond that. 

If the impedance presented to the rear panel is too far off, it should not
be able to find a match and you'll see that on the display, but that wasn't
the case in your situation. 

What possibly happened, assuming you have coaxial line connected to the K3,
is you melted the coax center insulator. That takes a lot of current or
voltage, but a really high SWR can exceed the coax's ratings at significant
power. Remember, the "match" you see on the K3 display only says that
there's a 50 ohm non-reactive load on the final amplifier in the K3. It says
nothing at all about the impedance (and so SWR) present at the antenna
connector on the back of the K3. 

Usually what happens if you overheat the coax is that it shorts as the
center conductor insulation melts and the center conductor touches the
shield. If it didn't get hot enough long enough for that to happen, you'll
not know about it and everything will be fine unless you check your SWR on
the line. An easy way to do that is to check the SWR at your external tuner,
adjust it to 1:1 and then see if the K3 agrees it's 1:1 with the KAT3 in
bypass. If the coax was damaged enough to move the center conductor
significantly, it will no longer be a 50-ohm cable. But it would  take
pretty extreme damage to show up that way unless you have a very long piece
of coax running between  the K3 and your external tuner.

Ron AC7AC

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Lee Buller
Sent: Monday, October 13, 2008 7:08 AM
To: Elecraft Reflector
Subject: [Elecraft] K3- How Robust iis the Tuner?



Well, I finally got a minute to turn on the K3 this weekend.  Flipped over
to 40 meters and set everything up for some RTTY contacts.  Tuned the tuner
and let out a call on RTTY at 100 watts during the sprint.

Forgot that I had the Big Tuner in the line set for 20 meters.  Of course
the SWR was off the scale but the K3 had tuned it to 1:1. After the first
transmission, I realized this were not right looking at the external meters
and quickly change things.  The K3 was working OK....but....I did smell a
stink.  Smelled like a component got hot.

Now then, the K3 seems works OK....tunes up well with the tuner (with the
right switches in the proper place on the tuner) and it seems OK.  

So, how tough is this tuner in the K3?

Lee - K0WA
"Mistakes are bound to happen"


In our day and age it seems that Common Sense is in short supply. If you
don't have any Common Sense - get some Common Sense and use it. If you can't
find any Common Sense, ask for help from somebody who has some Common Sense.
Is Common Sense divine?	

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