Columbia University Computing History   

Acoustically Coupled Modems

Acoustically coupled modems
Ven-Tel and Anderson-Jacobson acoustically coupled modems
Acoustic coupler in action
Acoustic coupler in action with DEC VT520 terminal
IBM PC/AT with Hayes Smartmodem
IBM PC/AT with Hayes Smartmodem
Ven-Tel and Anderson-Jacobson acoustically coupled Bell 103 modems, 1970s (we also used to have some A-J wooden models but they were thrown out before I could photograph them). To make a connection, you dial the number on the telephone, wait for the tone from answering modem, then mash the telephone receiver down into the rubber cups as shown at right, at which point the Carrier light should come on and you can start using your connection. There is no autodialer, no no error detection, no error correction, no compression. The 25-pin serial interface is at the rear and operates at 110 or 300 bits per second depending on the answering tone. Beginning in the 1980s, "smart" modems like the one shown at right dispensed with the rubber cubs, and were connected to the telephone's RJ45 jack.

Photos: Frank da Cruz, 2011.

Columbia University Computing History Frank da Cruz / This page created: January 2001 Revised: 31 March 2021