Homebrew External Keying Circuit...

Most CB radios don't have a facility to key (trigger) an external linear amplifier. They have to rely on the amplifier sensing the RF from the radio, to key it up. 

I've built an external circuit to do exactly the same, but to use with my own linears amplifiers. For example, if you wanted to connect a President Lincoln to say an Acom ham amplifier, then you'd need to use a footswich to key the amplifier into transmit, whilst pressing the PTT on the radio's mic. 

This external circuit does away with that, as it automatically detects the RF from the rig and puts the amplifier into transmit. I've also included a SSB delay, so that the relay doesn't chatter. 

I based this circuit on a design from the keying circuit in a Zetagi B47. 

Well done there Ian.  

Love a bit of homebrew especially when there's perfboard, hand wiring, diecast boxes and dymo embossed labels involved....you scored right on every count!

Thanks for posting.

All the best,
Victor

Victor wrote:

Well done there Ian.  

Love a bit of homebrew especially when there's perfboard, hand wiring, diecast boxes and dymo embossed labels involved....you scored right on every count!

Thanks for posting.

All the best,
Victor

This is the second one that I've built, the other one was in a nicer box.  It's now being used by someone else, to do the same job.

I've used hot glue to anchor the perfboard, but to also insulate it from the metal chassis.  The relay used could probably key up an old Yaesu FL-2100 or Heathkit type amplifier, without any problems.  That's important, as these older amps have high voltage on them to switch them into transmit and can damage modern ham rigs.  Modern amps in comparison, use 12V DC at very low current to put the amp into transmit.