There are various ways for a computer to key a rig.
(1) From the computer's parallel port, using a transistor/resistor
combination to translate parallel-port levels to typical +5 volt
straight-keying line level. The cable runs from the parallel port
to the rig's straight-key jack.
(2) From the computer's serial port, using a similar transistor/resistor
combination, again to the straight-key input jack. This is NR4C's
situation.
(3) In the case of the K3 only, from the computer's serial port
to the K3's RS232 input, using a straight-through cable just like
the one used for firmware updates.
In case (1) or (2), if the rig uses one jack for both straight-key
and paddle input, that jack must be set for straight keying when
the computer is plugged into it. This is the situation when I computer-key
my K1. If the rig has separate jacks for straight key and paddle, or
if your computer program provides for it, the paddle can be used
simultaneously with the computer program to key the rig. This is
convenient when the computer gets snarled during a contest.
In case (3), the K3 CONFIG menu must be set to key via the serial cable,
as Don Wilhelm noted. I computer-key my K3 this way.
Methods (1) and (2) work with any rig, although you might need an adapter
if the rig uses grid-block or cathode keying, where the voltages/currents
are out of the range of the little transistor/resistor combination. For
example, I computer-key my Heathkit SB-401 (about 20 volts negative)
using (1) and an optoisolator IC.
As far as I know, method (3) is unique to the K3. But I'm not familiar
with the no-front-panel software-defined rigs, so maybe they have similar
inputs.
73, Paul W8TM
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