[Boatanchors] T/R switch question _ 221122_follow-up

[JAMES HANLON]

I operated break-in using two antennas (a long-wire for the HRO-50 receiver) back in the 50's.  I used a spdt relay which was energized from the keyed B+ line that was also feeding the vfo and exciter stages of my transmitter.  The swinger of the relay was attached to receiver ground.  The normally open (when not energized) contact was attached to the receiver antenna terminal.  It shorted the receiver antenna to ground when the key closed and cut back the input signal to the receiver.  I opened the ground return lead on my receiver's RF Gain control and put another 20K pot in series with that lead to ground.  The junction between the RF Gain control "ground" lead and the extra pot was connected to the relay's normally closed contact, and so my extra pot was shorted out when the key was open.  When the key was closed the extra pot cut back the receiver's RF Gain.  The extra pot was set to produce a comfortable level for monitoring my signal.  I didn't worry about the timing associated with that relay, but I was lucky that it operated before the transmitter turned on and that it stayed closed until the transmitter signal turned off.

Since that time I've used a multiple relay circuit that transfers my single relay from the receiver to the transmitter and cuts back the receiver gain, then turns on the transmitter low level stages, then turns on the transmitter final amplifier, in sequence, when I hit the key.  When I open the key the relays switch back in the opposite sequence.  It works well, and with a single antenna.

Jim, W8KGI