I'm glad to hear that all is well and it is working but I don't really understand what is UNEXPECTED about the way the PTT output is implemented.?
It's clear on the schematic that what is essentially done is an open-drain MOSFET switch for the PTT. And there's a 220-ohm series protection resistor there, just to give some foolproofness to the situation... though - for those people who find that resistance value is too high, personally I wouldn't go building external circuits. If I was confident that the BSS123 would be within spec (170mA) in my application, I'd just remove the 220-ohm resistor and short its pads with a blob of solder!
Also - what other options would I have, for implementing a PTT output, than an open-drain MOSFET? Assuming?that I definitely want to steer clear of relays!
On Mon, Feb 26, 2024 at 12:56?AM Jim Bennett / K7TXA via <w6jhb=[email protected]> wrote:
Bojan, Roy, and Chris - thanks for the replies and tips on how to test that the PTT is in fact working. And surely enough, IT IS!! I metered between Tip and Ring and also between Ring and shield - 4.93 volts when I press the key. Most certainly not what most folks would have expected! But, now that I know PTT does function I'll feel safe connecting my SDR++ to the QMX through my MFJ-1708B-SDR box. Now I just need to get CAT-relay working so the QMX and SDR++ talk to each other!
?72/73 & many thanks guys. -- Jim / K7TXA Eagle, ID
