Home Brew T/R Switch for my Boat Anchors

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Home Brew T/R Switch for my Boat Anchors

Post by WB2VVV » Fri Jun 26, 2015 5:31 am

I refurbished my old Johnson Viking Adventurer crystal controlled CW transmitter (807 final), and also a Hammarlund HQ-110A receiver, but I needed a T/R switch to use them conveniently with a common antenna line. The Hammarlund receiver doesn't have mute contacts so I also needed to incorporate some receiver protection.

I decided to build some 12 VDC coil "ice cube" relays into a die cast Bud box with three SO-239 connectors (Receiver, Transmitter, Antenna) on the back of the Bud box, and a manual toggle switch on the front of the Bud box - flick the toggle switch down to transmit, up for receive (Red TX and Green RX LED indicators). The antenna relay is normally closed for transmit and fired to the normally open side for receive. When in transmit the receiver connection is also shorted to ground to provide some muting protection. I included a pair of RCA connectors that short to "Ground On Transmit" with their own relays for possible future flexibility if I ever want to use a receiver that has mute contacts, or for keying an amplifier. I used a 1N4148 diode backwards across each relay coil to suppress any transient when the coil de-energizes.

You can see the T/R switch box mounted to the side of of Johnson Viking Adventurer Transmitter:

ImageWB2VVV Shack 4 by Ski Freak, on Flickr

It works well, so see you on the air.

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