Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!usc!elroy.jpl.nasa.gov!swrinde!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!dsinc!telecom-request From: john@zygot.ati.com (John Higdon) Newsgroups: comp.dcom.telecom Subject: Re: Rotary Dial w/o Wire Connection Message-ID: Date: 15 Mar 91 19:20:00 GMT Sender: Telecom@eecs.nwu.edu Reply-To: John Higdon Organization: Green Hills and Cows Lines: 32 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 205, Message 8 of 11 "Ronald T. Crocker" writes: > Not being an expert on the subject, I seem to recall that MTS or IMTS > phones were rotary dial, and that they did, in fact, use some kind of > pulse dialing scheme. Yes, they did. All number transmission was "rotary" based on IMTS. When you would come "off hook" on your mobile unit, it would look for an idle channel that was in operation. With IMTS, there were not many. When the mobile found a channel with idle tone, it would key up and identify itself by "dialing" its assigned phone number for the base system. Dialing consisted of a tone that was frequency shifted once for each pulse. It sounded like a series of "tweedles". If your mobile number was valid, the system would return dial tone. Your call was placed using the rotary dial provided. However, instead of using hard wire to send DC pulses, it used that frequency shifted tone. The dial would come off home and the tone would begin. As the dial returned, each pulse would be represented by a shift in the tone's frequency. A person monitoring the line could easily determine the dialed number. For the record, there was another way calls could be rotary dialed without hard wire. Many LD tandems used to respond to pulses of 2600 Hz and would complete calls based on numbers "dialed" in this manner. Hence, 2600 Hz would serve as both supervisory and signaling carrier. It was called "SF" (single frequency). John Higdon | P. O. Box 7648 | +1 408 723 1395 john@zygot.ati.com | San Jose, CA 95150 | M o o !