[Boatanchors] Re {Botanchors} T/R Switch question_221122

[JAMES HANLON]

For a very long time, since 1952, I've used a spdt relay to switch my receiver from receive to transmit for both CW and phone.  My receiver is an HRO-50 which has an RF Gain control ("Sensitivity" control) that electrically is connected between the cathodes of the RF amplifier and IF amplifier stages and ground.  It varies the cathode bias on those stages and thus their gain.  I open the lead from that pot and ground and connect it to the normally closed (with no power supplied to the coil) contact of my relay.  The relay swinger is attached to receiver ground, so that when the relay is not energized the RF gain control is connected to ground and acts normally.  I also connect an external pot between this normally closed contact and receiver ground so that when the relay is energized this external control is then connected in series with the receiver RF gain control and ground, and it becomes an additional RF gain control that I can adjust for desired monitor volume when I'm sending CW.  I also put a spst switch in series with the external control that I can set open when I'm on phone so that the receiver is completely muted.  The normally open contact of the relay is connected to the receiver antenna terminal so that when I energize the relay to go on "transmit," the antenna terminal is shorted to ground which further cuts back the signal input to the receiver.

I like to operate break-in CW, and I've concocted a time-delay keying circuit using several relays that 1) energizes the receiver cut-back relay and also a second relay that switches the antenna from my receiver to my transmitter, then after a short delay 2) closes a relay that keys on the oscillator stage of my transmitter, and then after that 3) closes an additional relay that keys on the buffer and final amplifier stages of my transmitter.  All of that happens in sequence when I close my key.  When I open my key, the relays open in the opposite sequence so that the receiver returns to listening mode between key closures.  I wrote up this break-in circuit for Electric Radio magazine several years ago.  If anyone is interested I can send along a scanned copy of the article.

Jim, W8KGI

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