[Elecraft] SGC-239 vs KAT2

[Julian, G4ILO]

Thanks to all who responded to my question on this topic. After a bit of
research and experimentation, I've decided to stick with using the SG-239
at the feedpoint of the loop. Here's why.

Unfortunately I don't have an antenna analyzer or know anyone I can borrow
one from to measure the actual impedance. However, simulation of the loop
in EZNEC shows that the SWR only dips below 10:1 at the frequency where the
loop is close to a full wave. On 18, 21 and 24MHz bands, the calculated SWR
is 25:1, 66:1 and 67:1 respectively. On 10MHz and below it is > 100:1. Only
on 14 and 28MHz is it below 10:1.

I downloaded a very useful Excel spreadsheet from this URL:
http://www.ifwtech.com/g3sek/in-prac/ . This spreadsheet lets you plug in
the matched loss per metre at 10MHz of your preferred feedline (or the one
you're stuck with) and get graphs allowing you to see the mismatch loss at
any frequency/SWR combination. On 15 metres, I would be losing 6dB to
mismatch loss feeding my antenna with 5m of RG58!!! Even if I used RG213 or
RG8, and got the length down to 3m by taking the most direct route, I'd
still be losing 3dB.

I'm convinced that feeder losses are the reason why the KAT2 could match my
loop on all bands. An open ended 15m length of RG58 produced an SWR of only
6.6:1 on 28MHz, according to my KAT2.

By the way, if you plug in the figures for open wire feeder you can see why
so many people on this reflector are fans of that stuff...

It's a shame I can't use the KAT2, but using a matching device at the
antenna feedpoint seems to be the right solution for my situation. What I
really want is a standalone KAT2 that can be controlled remotely by the K2.
The SG-239 seems to be the closest approximation to that at the moment.

73, and thanks again for all the ideas and advice.
--
Julian, G4ILO. (RSGB, ARRL, K2 #392)
Homepage: http://www.qsl.net/g4ilo