Teletype services

Chris Elmquist chrise at
Thu Nov 5 18:13:46 CST 2015

On Thursday (11/05/2015 at 04:03PM -0800), Brent Hilpert wrote:
> Curious as to the setup you are attempting this with, i.e. exactly what modem are you using?
> One in the base of the 33 or some common external one?
> I'm not familiar with all the possible modem variations one might find in a 33, but AIUI the modem for the 33 at the standard 110 bps was Bell 101 standard.
> There's not going to be a lot to talk to out there using the old parameters.
> Even if someone had an auto-baud dial-in setup out there somewhere, I wouldn't anticipate it being compatible.
> We have a 101-standard modem (in the base of a 33) around here, but have never tried it or tried connecting it to a phone line, I'm also not familiar with it enough to know how originate/answer issues are dealt with (whether it can do both) for such 33 to 33 communication.

Highest likelihood it is a Bell 103 which is AFSK at 300 baud or less.

The problem you have with Teletype to Teletype with telephone modems is
that both ends are likely to be originate modems--  meaning they will
have the same tone pairs for transmitting and receiving and thus cannot
talk to each other.

One end needs to be Originate (which is the Teletype) and the other end
needs to be Answer with the opposite tone pairs--  so that the transmit
tones are received by the other side and vise-versa.

Some very old acoustic couplers did have a way to reverse the tone pairs
but they were not very common.

Chris Elmquist

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