In article . net, "KØHB"
writes:

"N2EY" wrote

Have to build an interface to key the Southgate Type 7, though. Nice old CP
Clare mercury wetted relay should do the job...

How much voltage on the keying line?

About 75-100 volts, 20 mA or so. Positive to ground.

Unless it's grid-block keying or
similar, you won't need a relay.

That works!

Serial port keying (assuming the radio is positive keyed) can be built into a

DB25 or DB9 connector shell using only a single resistor and a junk-box
transistor.

Hang a 1K resistor on DTR (pin 20 on a DB25, pin 4 on a DB9). Other end of
the
resistor to the base of a small-signal NPN (I use a 2N3904 cuz it was in my
junk
box, but 2N4401 or others similar will be just fine). Connect the emitter
and
the transmitter ground return to Signal Ground (pin 7 on a DB25, pin 5 on a
DB9). Connect the collector directly to the transceiver key input.

I'll check that out! Have some of junker DB9 and '25 connectors from various
sources. Might need something beefier than a 2N3904 but that's not a problem at
all. Beats dealing with the inductive kick of the relay coil.

Worse comes to worse, a small pentode could be used as a keyer tube to drive
the relay. With low plate voltage the key line could be just a few mils and
volts above ground. Probably won't need to go that far, though.

Thanks Hans!

73 de Jim, N2EY