Don:
Thanks for the quick reply !
I'd reply off list with the nitty gritty details but I did have a request from
another interested ham to make the results public.
I have now put together a much more controlled test setup for the K2 that
doesn't involve high levels of RF all over the shack ! I now have a low power
crystal oscillator/multiplier source at about 146 MHz (which puts about 0.5 mW
into a 50 ohm load) connected to the XVTR OUT jack connected in parallel with a
50 ohm load using a BNC Tee just behind the rear panel. This reliably
reproduced the observed effects (KEY OUT going to ground, receiver quiet and
S-meter to maximum), and simulates the loading effect of having a transverter
connected.
> Check the gate of Q4 to see if the voltage there drops -
> that causes 8R to drop.
Yes it does drop when I key the 146 MHz test source, and the collector of Q2
(8R) does too.
> Also check the state of the TX signal from the
> microprocessor (gate of Q3)
That voltage remains unchanged at approximately zero volts, as does the
collector of Q1 (8T).
So clearly the K2 is switching into an odd state.
> My guess that the PTT
> input may be the culprit is only a guess, but it is possible
> for severe noise (high RF levels) on the PTT line to cause
> the microprocessor to become 'mixed up'.
If the K2 is in CW mode it does not start sending dots, so the PTT line is not
going low. Which doesn't mean it doesn't have RF on it, but we are now talking
about a pretty low level (500 microwatts) of generally shielded RF so I would
be surprised if stray coupling to the PTT line would be the culprit.
Back to head scratching.....
73,
Steve VE3SMA
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