[GreenKeys] Tone frequency history?

[Jim Haynes]

The Bell 101 and 103 modems all used the same frequencies.  They were
full duplex, using different tone pairs in opposite directions.  They
did not use the frequencies based on a multiple of 85 Hz.

As I recall when the modem answers it puts out a tone that is supposed
to disable the echo suppressors.  That is necessary since the modem is
full duplex.

The 103 modems had strapping options to set which tone pair was for the
answering station and which was for the calling station.  And for each
tone pair there were options which tone was mark and which wa space.
Hence it was possible by strapping to set up modems for up to eight
different non-interoperable services.  There was TWX, and then there was
Dataphone, and then there were going to be Wide Area Data Service WADS
and something else WADS-prime, and that still leaves four combinations
for things they hadn't thought of yet.

 	---

 	"Ya can argue all ya wanna, but it's dif'rent than it was."
 	"No it ain't! No it ain't!  But ya gotta know the territory."
 		Meredith Willson, The Music Man