Path: utzoo!telecom-request Date: 13 Jun 91 18:11:28 GMT From: Julian Macassey Newsgroups: comp.dcom.telecom Subject: Re: Rotary Dial Phones Forgotten But Not Gone Reply-To: Julian Macassey Message-ID: Organization: The Hole in the Wall Hollywood California U.S.A. Sender: Telecom@eecs.nwu.edu 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 452, Message 9 of 11 Lines: 44 In article John Higdon writes: X-Telecom-Digest: Volume 11, Issue 450, Message 3 of 11 > Julian Macassey writes: >> The voltage applied to the Tip and Ring to activate the light is >> usually 90V at 100Hz. This frequency is ignored by the frequency >> sensitive ringer that responds to 40 - 150V at 20 Hz. The neon is not >> frequency sensitive, so it flashes for message waiting or ring >> current. > ITT uses a similar, but much simpler method of lighting the message > waiting lamp. The System 3100 just sends 60 ipm pulses of 100VDC over > the line. The direct current is completely ignored by the ringer, but > lights the neon lamp. Unlike the 100Hz, there is no flow through any > circuitry except for the neon lamp. In addition to being much more > difficult to generate (than DC), some of the 100Hz will inevitably > leak through the L/C bell network creating a bit of inefficiency. The > DC supply is very simple and cheap. And of course what John doesn't mention is the best reason for using DC today is the dreaded Type B ringers. The telephone bell of old was frequency selective. 100 Hz would be out of the bandwidth of all types of mechanical ringer. Type B ringers are not the gong bells of old but the "crickets in heat" chirpers. According to FCC specs, a Type B ringer should respond from 15.3 to 68 Hz. In reality, these Type B ringers respond nicely to 100 Hz. This means in an office environemnt you can go nuts listening to a colleague's phone in the next pen (cubicle) chirp away every couple of seconds. DC from a good PBX will then save you the grief of a whole office sounding like a crickets orgy while the staff are out at a meeting and the voice mail is backing up. Julian Macassey, julian@bongo.info.com N6ARE@K6VE.#SOCAL.CA.USA.NA 742 1/2 North Hayworth Avenue Hollywood CA 90046-7142 voice (213) 653-4495