May FSK signals be used to receive a signal about when the called party answers?
I don't know much about FSK, but the need of a detection of answer are still there since polarity reversal are history.
An advanced payphone controller should be able to do a lot with this information, Start the collecting, break the line when the other ends hanging up etc.
dsk
PS USA/Europe use different frequencies for FSK ???
The only Frequency Shift Keying (FSK) signals currently used in the U.S. PSTN are for Caller ID (CID) signaling.
FSK signaling is also used to activate/deactivate Visual Message Waiting on POTS lines.
http://tesmw.com/
Assuming you aren't on a POTS line, I'd recommend doing this signaling outside the voice band or disabling the transmitter until this signal is received combined with disabling the FSK detector until disconnect or forward disconnect is received.
Now obviously this isn't going to be a public pay phone, but the last thing you want is to try demonstrating acoustic coupler modems and cause interference with your supervision system.
The topic you replied to is over 5 years old.
Lol, better late than never..
But, unlike many new posts to very OLD topics, this time the OP (dsk) is still here actively on the forum.
Terry