[Elecraft] K2 Antenna Tuner Question

Fri Jan 17 11:51:00 2003

I know this is obvious and pardon me for bring up what everyone
already knows, but it is really asking for trouble to allow two
automatic tuners in cascade to be operated at the same time. They will
chase one another's tails either until the operator gets tired of
hearing relays or the relays get tired and quit.  At QRP,  damage is
unlikely, but at higher power very high voltages and currents can be
developed between the tuners.

If you have in mind using the SGC first to tune the load and then turn
it off and connect its input to the KAT2, I suppose that would cause
no problem, although if the SGC has done its job, the KAT2 will see
only 50+j0 and be quite content to do nothing. Assuming that the SGC
is unable to attain that load for the K2, then letting the KAT2
"finish the job" should work. However, I would really be concerned
about power loss in the SGC under those conditions.

Seems like a more favorable solution would be to determine an optimum
feedline length from the EZNEC model driving-point impedance data  - I
prefer the TLDetails program - to present a load to the KAT2 that it
can handle.

 I have developed a procedure for modeling an antenna in EZNEC,
finding its DPI, finding input Z of a given line type and length, and
then seeing if the KAT2 can handle that load Z by first computing the
ideal L-network values for a match and then seeing how close the KAT2
values come. I then wrote a program that analyses an L or PI network
with various L and C values and with a given load to determine its
input Z.

Using the suite of programs and procedure, I can take any arbitrary
antenna setup - within reason- such as one would use in the field and
ultimately determine whether or not a KAT1 or KAT2 can tune the load
presented by the feedline. I have not looked into modeling and using
the procedure on endfed wires, etc. But it has proved very useful with
conventional dipoles, etc. with coax and ladderline feeders.

73/72, George
Amateur Radio W5YR -  the Yellow Rose of Texas
In the 57th year and it just keeps getting better!
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
K2 #489  IC-765 #2349 IC-756 PRO  #2121 IC-756 PRO2 #3235

----- Original Message -----
From: "Julian (G4ILO)" <[email protected]>
To: "Elecraft List" <[email protected]>
Sent: Friday, January 17, 2003 4:46 AM
Subject: Re: [Elecraft] K2 Antenna Tuner Question

> 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