[Elecraft] Re: kat100 question

[Wayne Burdick]

Ken,

If there's RF on the auxBus or VRFDET line between the K2 and KAT100, it can
sometimes cause the KAT100 to miss its message from the K2 signalling start of
auto-tune mode. Such high RF could be due to the antenna presenting a very high
impedance on a particular band. For example, an 80 m dipole may appear to be
well over 1000 ohms on 40 meters, depending on the actual length and the type of
feed. Even at 20 watts, such a mismatch could result in very high voltages at
the antenna jack, and excessive RF on the control cable.

If this happens, there are four simple things to try:

1. Do your auto-Tune in QRP mode (with the POWER control set to 10W or less,
auto-tune will happen at 2 watts). This may only be necessary on one or two
bands for a given antenna. Of course you can go back up to QRO levels after tune-up.

2. Use a balun between the antenna and ATU. 4:1 is often a good choice.

3. Use a "choke balun" between the ATU and the K2.

4. Install a miniature RF choke (47-200 uH) inside the control cable backshell,
at the K2 end. The choke should go in series with the VRFDET line. If the KPA100
module is installed in the K2, you can actually just disconnect the VRFDET line
completely at the K2 end, since it is not used by the KAT100 in this case. If
that works, so should the RF choke. If you ever take the KPA100 out of the K2,
the VRFDET line *will* be needed, and the RF choke should keep RF off the line
in all cases.

Please let me know what your results are.


73,
Wayne
N6KR