[Elecraft] KAT3 - Antenna tuned or not?

[Tom Hammond]

Hi Ted:

>I am attempting to tune a Zero-Five Vertical with the KAT3.  How do 
>I determine if the KAT3 has found a match?  I see the SWR on the K3 
>close to 1:1and full power out but my external SWR meter is still 5:1.

Yes... and the SWR (AT THE POINT AT WHICH YOU'RE MEASURING IT) is going to
REMAIN 5:1 for a long time... hopefully... if it changes, then there's a
problem with your antenna.

The KAT3, while commonly referred to as an ATU (antenna tuning unit), which
is a misnomer, it does NOT "tune" then antenna... it attempts to provide a
match BETWEEN the antenna/feedline combination and the transmitter. Years
ago these units often were referred to as TRANSMATCHES, rather than ATUs
because transmatch was a better description of what they did.

The ATU/transmatch (take your pick) provides a 'match' (hopefully 1:1) between
the antenna/feedline combination (connected to its INPUT) and the transmitter
OUTPUT (connected to its OUTPUT. It does not however CHANGE the SWR ON THE
FEEDLINE, and this is where your other SWR meter (reading 5:1) is located in
the RF circuit... it IS between the antenna and the KAT3, right?

The ONLY 'change' in SWR created by the KAT3 occurs (and is measured) at the
INPUT to the transmitter PA, NOT on the feedline.. so the SWR presented by
the antenna/feedline combo (and present at the end of that coax, is still
whatever it was before the ATU was connected... complete with coax losses
and other characteristics which come with a somewhat mismatched antenna/
feedline on whatever frequency you are attempting to use the system.

The Radio (K3 in this case) 'sees' a low SWR because the 5:1 SWR is being
compensated for within the KAT3, so the radio thinks it's working into a
nice flat load.

I hope this helps 'splain thing s a bit better.  Normally, I'd have included
a diagram or two, but this reflector doesn't allow in-line graphics in
replies. I can, if you wish, send something directly to you however. Just ask.

73,

Tom Hammond   N0SS