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I want to buy this 5 W transceiver kit from QRP Guys, link. My plan is to use it with JS8Call on an ARM64 Chromebook I have or even my smart phone with AndFlmsg (FSK modes).

It's clear that the radio has an input pin, that when forced to ground, will activate transmission. I've also seen that JS8Call has a configuration mode for audio, "Right Channel PTT".

I couldn't find documentation of what exactly that config setting does. It sounds like it might simply hold 5 V on the right channel and lower it to zero simulating ground on transmit.

Can anyone tell me how this feature works or suggest a good way to accomplish an automated PTT for a radio without CAT ?

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If you select that option, it makes sound on the right audio channel (a 1000Hz tone, if I recall) whenever it wants the PTT to be engaged. It's meant for the SignaLink devices (which only take TX audio from the left side, but have an "Auto-PTT" function that engages PTT if audio is present on either channel). You can work with that as well, but you can't hook it up directly to a radio — you would need need a circuit with something like an envelope detector and a comparator, driving a transistor that connects to the actual "ground to transmit" line on the radio. Ideally with a potentiometer to control the comparator's reference level so you can tweak the sensitivity.

For most constant-envelope digital modes like FT8, JS8, and any kind of MFSK you can usually get by without a dedicated "PTT on right channel" feature in the app; you can just have the app put your TX signal on both channels as usual, and the signal itself will open the PTT. But if your radio takes too long to engage TX (the beginning of your transmission gets cut off) or if you want to use modes that don't have a constant power level throughout the transmission, then the separate PTT signal will avoid problems.

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  • $\begingroup$ OK this is helpful. I think there's a delay option in JS8Call to allow time for Tx to open. Worst case I add extra character to make up the difference. There's some easy VOX circuits that should work well with a steady 1KHz tone. $\endgroup$
    – wbg
    Commented Feb 14, 2022 at 5:36

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