Don Wilhelm wrote:
Such fail-safe mechanisisms can certainly be devised if deemed necessary.
The 8R signal mentioned is actually the inverse of the Amp-Key line, so that
signal can be produced with an inverter and no additional connections to the
internals of the K2.
Amp-key is derived from 8r and is in some sense the inverse of it, but
neither 8r not amp-key are high/low outputs. They both have one state
which is indistinguishable from 'disconnected'. If you use amp-key by
itself you can't distinguish between these situations:
1) Amp-key output is open and the K2 is receiving; and
2) Amp-key output is accidentally disconnected and the K2 is transmitting.
8r by itself can't distinguish between
1) 8r is open and the K2 is transmitting; and
2) 8r appears open (accidentally disconnected) and the K2 is receiving.
So I suggest adding logic *inside* each rig to assert a signal (called
'safe') only when 8r is on or amp-key is not grounded. Then you would
connect safe and amp-key to the interface. The interface would connect
rig 1 to the antenna only when rig 2 is asserting safe and not grounding
amp-key, and vice-versa.
Now let's see what happens when things get disconnected. If you
disconnect rig 2's safe line, rig 1 will always be disconnected from the
antenna. If you disconnect rig 2's amp-key then safe will still go low
when rig 2 transmits (because of the logic inside rig 2), disconnecting
rig 1 from the antenna. And vice versa.
Of course, then you would have to turn on both K2s to listen to either
one of them. I am still trying to figure out a way to avoid this without
losing the fail-safe nature of the system!
One of the ways to accomplish such 'fail-safe' operation is to inhibit
keying (or PTT) until all other conditions are properly satisfied
I think the complications/limitations that this introduces are worse
than turning on both radios!
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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