[Elecraft] K2 Antenna Tuner Question

[Julian (G4ILO)]

That's a good idea, to try the SG-239 connected to the K2. It's no problem,
when I have some spare time, since the '239 is now sitting in a box doing
nothing, and it would help satisfy my curiosity. I don't believe the
feedpoint impedance could be unfavourable on all bands: for example the
calculated impedance (using EZNEC) on 20 is 135 - j9 for a SWR of 2.7, and
on 10m 300 - j80 for 6.4. Although I didn't get those exact SWRs when I
tried directly connecting the K2 to the antenna, they are in the ball park.

By the way, some time ago I did briefly try a coax connection straight to
the antenna and using the KAT2, with no balun at the feedpoint. The
impression then was that the SG-239 did make things better, especially on
those bands with the worst mismatch.

The other benefits of the KAT2, such as the stored tune-up settings, were
the main reason for trying again, this time using a balun. The fact that it
works so much better is a most unexpected bonus.

73,
--
Julian, G4ILO. (RSGB, ARRL, G-QRP, K2 #392)
G4ILO's Shack: http://www.qsl.net/g4ilo

Vic Rosenthal wrote:

I found this report fascinating, since I have played a bit with autotuners.
 One
possible explanation is that the SG-239 at the feedpoint was facing an
impedance
near the end of its range (perhaps very low), causing its efficiency to be
poor.  When you switched to the KAT2, it was seeing a different impedance,
as a
result of 2.5 meters of coax and the balun.  This impedance may have been
much
more reasonable, so the KAT2 was able to match it more efficiently.

One way to test this is to turn off the KAT2 and connect the SG-239
directly to
the K2, and then have it feed the coax/balun combination.  If it works as
poorly
as before, you can conclude that the SG-239 is inferior to the KAT2.  If it
works as well as the KAT2 or close to it, then you know the probalem was
that
the impedance at the feedpoint was unfavorable.

Of course, the KAT2 has other advantages, such as not needing to sense RF
to
select the appropriate parameters when you change bands and per-band
antenna
switching.