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 Homebrew External Keying Circuit...

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MM0IMC
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Call Sign : 108-CT-226 / MM0IMC
Posts : 88
Times Thanked : 2
Join date : 2023-03-10
QTH or Location : Ayrshire
Equipment Used : Amstrad 901 Sidebander

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PostSubject: Homebrew External Keying Circuit...    Homebrew External Keying Circuit...  Icon_minitimeThu Aug 03, 2023 8:38 am

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. Homebrew External Keying Circuit...  20230812
Homebrew External Keying Circuit...  20230810
Homebrew External Keying Circuit...  20230811


Last edited by MM0IMC on Thu Aug 03, 2023 10:47 am; edited 1 time in total

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Victor
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Victor


Call Sign : 26-CT-3228 / M7VIC
Posts : 5829
Times Thanked : 355
Join date : 2019-11-10
QTH or Location : Bedford
Equipment Used : Various

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PostSubject: Re: Homebrew External Keying Circuit...    Homebrew External Keying Circuit...  Icon_minitimeThu Aug 03, 2023 9:42 am

Well done there Ian. Homebrew External Keying Circuit...  1f44d 

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! Smile

Thanks for posting.

All the best,
Victor

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https://www.qrz.com/db/M7VIC
MM0IMC
Contributor
Contributor



Call Sign : 108-CT-226 / MM0IMC
Posts : 88
Times Thanked : 2
Join date : 2023-03-10
QTH or Location : Ayrshire
Equipment Used : Amstrad 901 Sidebander

Homebrew External Keying Circuit...  Empty
PostSubject: Re: Homebrew External Keying Circuit...    Homebrew External Keying Circuit...  Icon_minitimeThu Aug 03, 2023 10:43 am

Victor wrote:
Well done there Ian. Homebrew External Keying Circuit...  1f44d 

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! Smile

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.
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PostSubject: Re: Homebrew External Keying Circuit...    Homebrew External Keying Circuit...  Icon_minitime

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