In message <33C673A3.6EA5(a)rain.org> classiccmp(a)u.washington.edu writes: I've got a few (I'm interested in telegraph and telephone history as well as computers, but my main collection is computer-related). It's not a large part of my collection, though. In the UK, modems were _rented_ from the GPO (== post office, who also ran the telephone system) at one time, like all other telephone equipment. Some of these modems are interesting technically - the earlier ones were about 14" square and 6" high, and contained plug-in modules for the PSU, modulator, demodulator, and controller. It was all discrete components (no chips), and some of the control used PO 3000-style relays (similar to the ones used in telephone exchanges). The demodulator was strange. It filtered the incoming signal (a multi-stage LC filter housed in a tobacco-tin sized box!), and then mixed it with a local oscillator to shift the frequency up. The output of that was filtered again, and fed to a 2-diode discriminator. The output of that was buffered and became the data output. It was basically a superhet FM receiver modified to work at the right frequency. Another strange GPO modem was the 13A. It's a 1" (approx) high plinth that was fitted under a Type 746 'phone that had extra 'voice' and 'data' buttons fitted. I know nothing about the circuitry in that one, but it's a rather neat unit. There were also things called 'isolation boxes' that were used to prevent faults in the user's equipment damaging the modem (or worse still the 'phone line). Typically they contained a number of zener diodes from each line of the RS232 connector to ground (2 diodes in inverse series per line), and some 50mA fuses in series with each line that would blow if there was overvoltage on that line. Such things are probably useless now, but I like to have all the bits of a classic setup, including little details such as this. The term 'modem eliminator' normally meant 'null modem cable', and was a passive device. -tony