Data communications over telegraph circuits 1941

Baudot hasn't been used for about a century. The five-bit code used by the deaf, radio hams, Telex, TWX, newsrooms, and the ASR-32 Teletype, is properly called Murray or IAT2. If you like, I can post code tables for both codes. They're as different as ASCII is from EBCDIC.

That's true, but irrelevant, since different frequencies are used.

Deaf TTY modems use 1400 and 1800 Hz. They are half duplex, meaning that the two sides take turns sending. The non-sending side is silent.

Bell 103 uses 1070 and 1270 in one direction, and simultaneously 2025 and 2225 in the other. Neither side is ever silent, until there is "NO CARRIER".

Of course nothing prevents someone from hooking up a Bell 103 modem to a ASR-32 Teletype. This should allow communication with anyone who has an identical setup. Good luck finding such a person, however.

As you said, Bell 103 modems had no knowledge of speed. They'd just as soon send 110 baud, or 10 baud, or 1, as 300 -- whatever they were fed through the serial cable. Given a good enough phone line, they can be run at higher speeds than 300.

The DEC VT100 terminal could be set as slow as 50 bps. I set someone's to that speed one April Fools' Day. I don't recall whether it went through a modem, though.

Of course it's possible that modern modems that emulate the Bell 103 have stronger opinions about speed, framing, etc., so you may be right.

I wish I understood the details of newer faster modems better. I've been playing with time-reversed modem signals. Is it possible to send a message which makes sense both forwards and backwards? A bit-wise palindrome? (Looking at just the data bits, not start, stop, or parity, ASCII does poorly at this, but Murray-IAT2 does astonishingly well, as does Morse code.) --