[Elecraft] K3 Auto ATU Problem

[Michael Carter]

Tom,

Does the problem you describe occur
on each of the ANT1 and ANT2 ports
on the KAT3 output when the ports
are terminated in a good 50 ohm power
load?

Have you checked the K3 ANT selection
when the KAT3 is installed to be sure that
the port to which your 50 ohm load is
attached is the one selected on the front
panel?

The fact that the anomalous behavior
occurs with a substitute KAT3 board,
and that it doesn't occur with the KANT3
board installed, indicates that the K3's SWR bridge
circuit is operating properly.

The fact that putting the KAT3 in BYPASS
mode provides a correct SWR reading
indicates that the relays in parallel with
the series-connected inductors are
properly switched as are the relays
in series with the various shunt capacitors
of the L-network (the latter group of
relays all switched off their connections
to the associated capacitors).

You could try the KAT3 tests using
manual control mode (as described
on p. 56 of the K3 Owner's Manual,
rev. D10) to verify proper operation
of each of the relays in the L-network
individually. The manual control options allow one
to read out or clear the per-band memory of the
ATU L-C settings, which might also
be useful in diagnosis.

73,
Mike, K8CN