Beach 40 Build: Part 6 – T/R Switching

This post is part of a series: Building the VK3YE Beach 40 DSB Transceiver.

The T/R switching for the Beach 40 is pretty straightforward.A single DPDT relay is controlled directly through the PTT  switch on the mic. Half of the relay switches the low pass filter connection between the transmit and receive sections. The other half routes power to the audio amplifier on receive and to the mic amp and RF amps on transmit.

Or it would be, it would have been straightforward if I hadn’t soldered the connections incorrectly twice. The first time, I turned the relay 180-degrees before soldering it down, so that the control voltage across the Normally Open pins, which obviously didn’t do anything. The second time, I reversed the coil and normally closed (receive) sections, so while I was able to test the receiver, the transmitter section would never get power.

But at long last, this section is complete. It’s a pretty adorable little relay, an NTE R40-11D2-12. It’s rated at 2A, which is way overkill for this project, but it’s what was available at Microcenter. The 12V coil voltage is driven directly from the battery input voltage.

Beach 40 TR Relay-08

It’s very satisfying to hold a mic in my hand for the first time on this rig, and hear the audio click in and out in the headphones when pressing the push-to-talk button. After a couple weeks away from this project, it feels like I’m closing in on completion.


Hear you on the air!


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