larry@uunet.uu.net (Larry Lippman) (08/06/90)
In article <10349@accuvax.nwu.edu> david@cs.uow.edu.au (David E A Wilson) writes: > Here in Australia, I have noticed that with my parents phone, the ring > sound that the caller gets depends on the phone plugged into the > socket (phones that chirp and phones that ring a bell sound different > to the caller). > Would this tend to indicate the vintage of their exchange? Yup. It is old *and* electromechanical. In BOC areas, there is still No. 1 XBAR and SxS in service which have unmodified intraoffice trunks which obtain ringback tone from the superimposed ringing supply. Listening to a call placed to a party with some electronic ringers will result in a distinctive sound from spurious oscillations created by the ringer circuit. Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?" {boulder||decvax||rutgers||watmath}!acsu.buffalo.edu!kitty!larry VOICE: 716/688-1231 || FAX: 716/741-9635 {utzoo||uunet}!/ \aerion!larry
John Higdon <john@bovine.ati.com> (08/07/90)
Larry Lippman <kitty!larry@uunet.uu.net> writes: > Yup. It is old *and* electromechanical. In BOC areas, there > is still No. 1 XBAR and SxS in service which have unmodified > intraoffice trunks which obtain ringback tone from the superimposed > ringing supply. Listening to a call placed to a party with some > electronic ringers will result in a distinctive sound from spurious > oscillations created by the ringer circuit. Boy, does this bring back childhood memories. Much to the consternation of my parents I had a habit of building gobs of gadgetry to hook up to the phone line in the house. It got so bad that at the tender age of fourteen, I was ordered to get my own line in my own name so that when the "phone police" came out, the family phone could remain on the wall. Anyway, it always seemed that my "ring detectors" put trash back into the line such that when my number was called, the tone sounded "gurgly". The exchange was a #5 crossbar. The most ambitious of my projects was the building from scratch of a KSU for some key phones that had been rescued from an old building. To get the common audible to ring and the lights to flash required some way of detecting incoming ring. The circuit consisted of a series capacitor, full-wave bridge rectifier, and a sensitive relay. There was a large cap across the relay coil that would charge during the ring cycle and hold the relay closed between rings -- keeping the lights flashing and the bell ringing. Apparently, the non-linearity of the rectifiers reflected back into the phone line, and it sounded much like there was answering service equipment on the line to the caller. I hated this because I was sure that this would be instantly apparent to the phone company and that someone would investigate. Never happened. But then, whenever there was line trouble, all of this stuff was removed before that call to 611 was ever made. Ah, the good old days. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@bovine.ati.com | San Jose, CA 95150 | M o o !