KAT100 problem

[K4TM]

John-
        I worked SS contest last night (SSB) and had a similar problem
running at 100+ watts with my K2-100 and the KAT tuner.  I had a
difficult time getting a match when in high power (anything above 11+
watts).  When I transmitted, the KAT-100 would switch to "Ant #1" for a
second before switching to "Ant #2" which is what I had selected (#2).
#1 is my tri-band beam and #2 is my 135' dipole fed with open-wire
feedline with a 4-1 balun near the KAT-100.
        I tried tuning at low power (10 watts or less) and everything
worked as designed, even if I then cranked the power to 100 watts.  So,
when I would change frequency, I'd power down and tune for a good match,
then power up and the problem disappeared.  Seems the KAT-100 wants to
tune at low power first...if I do high power first, I got the antenna
switching and high SWR that you did.
        I can't explain it, I'm just glad I stumbled onto a solution
because it was mighty frustrating - I even, perish the thought,
considered putting my ICOM 706 MkIIG on line!
        73,
        "H" Cary, K4TM
        K2-100 #5266
        "I love my K2!"


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[Don Wilhelm-3]

That certainly sounds like a problem induced by RF Feedback from the
multiband antenna.
Just as  thought, perhaps a bit longer length of coax to your 4:1 balun
might be in order.
L B Cebik suggests a scheme for using open-wire feed - run coax through the
wall to the outside and install a 1:1 ferrite bead type balun (note NOT a
4:1 balun) on the outside.

A point of information that many folks seem to have trouble with is that the
output of the balun must match the feedpoint impedance of the transmission
line, and that has little to do with the characteristic impedance.  Just
because you are using a 600 (or 450) ohm feedline does not imply that a 4:1
balun should be used - in most cases, a 1:1 balun will do a better job
across all bands.

73,
Don W3FPR

> -----Original Message-----
> John-
> I worked SS contest last night (SSB) and had a similar problem
> running at 100+ watts with my K2-100 and the KAT tuner.  I had a
> difficult time getting a match when in high power (anything above 11+
> watts).  When I transmitted, the KAT-100 would switch to "Ant #1" for a
> second before switching to "Ant #2" which is what I had selected (#2).
> #1 is my tri-band beam and #2 is my 135' dipole fed with open-wire
> feedline with a 4-1 balun near the KAT-100.
>

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