Telephony Abbreviations

Well as I remember, the directions were EAST and WEST they called them.

boB

I think you are confusing telephony with railroads. ;)

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Rick C

Yes, you are right.

2W vs 4W. The 2 wire (i.e. a single twisted pair) circuit uses hybrids at each end to achieve a bidirectional connection. The 4W circuit is two unidirectional 2W circuits, eliminating the hybrids and improving the (frequency response, quality, whatever).

TO vs E&M. TO "Transmission Only" means no handshaking. E&M "Ear and Mount" (also, possibly historically "Earth and Magneto") means handshaking.

[anecdote] This reminds of when I used to work in broadcast radio, and we used a 4W stereo pair leased from a carrier to get the programme from the studio to the transmitter. These were specially selected pairs, equalised for flatness, matched for phase and gain, and driven with a 40 ohm source impedance from our end (as opposed to the 600 ohm typically used for audio in those days).

One night I turned the radio on and it sounded a bit strange. I quickly figured out (just by listening) that one of the (left or right) channels had been inverted with respect to the other one. This has a distinctive "inside out" sound that is easy to recognise (and easy to recreate by swapping the speaker wiring polarity on one speaker only).

People had been ringing the station during the day, complaining about the long periods of silence (which turned out to be when an announcer had been speaking - these are panned exactly to the centre (L = R), so with the phase reversal (L = -R), receivers in mono mode would get something close to silence).

I checked the wiring at the station - nothing had changed, so it wasn't us.

Eventually we tracked it down to a technician at the phone company who had been swapping pairs around. So much for specially selected and matched.

Allan

s/Mount/Mouth/

Allan