Path: utzoo!attcan!uunet!pyrdc!netsys!vector!nobody From: mibte!jbh@umix.cc.umich.edu (James Harvey) Newsgroups: comp.dcom.telecom Subject: Re: Submission for comp.dcom.telecom Message-ID: Date: 3 Nov 88 13:28:32 GMT Sender: chip@vector.UUCP Lines: 48 Approved: telecom-request@vector.uucp X-Submissions-To: telecom@bu-cs.bu.edu (TELECOM Digest Coordinator) X-Administrivia-To: telecom-request@vector.uucp (USENET Telecom Moderator) X-TELECOM-Digest: volume 8, issue 171, message 4 {{{ Quoted text edited *severly* to pass inews. -chip }}} In article , kitty!larry@cs.buffalo.edu writes: > In article MCHARRY%BNR.CA@MITVMA.MIT.EDU (J.) > writes: > >> Some years ago I saw a nifty way of putting a 'busy light' {{{...}}} >> (Some systems fail to provide a ground reference.) > ALL telephone systems are designed to provide a "ground reference", > {{{...}}} The number Five ESS (AT&T) does NOT provide a ground reference while in the talking condition. Even for ground start lines! >> {{{...}}} > A loud hum, eh? What we have here is, ahem, a classic example > of what is properly called "longitudinal imbalance". You won't get > FCC Part 68 certification with that design! :-) Very true, Part 68 requires 60 db of balance for certification. > I would suggest not trying ANY variation of the above scheme. {{{...}}} > There are numerous ways to sense line status by means of > ISOLATED sensing of series loop current, or by high-impedance (> 100,000 > ohms) briding across tip and ring to sense loop voltage. No ground > reference is needed in either of these techniques. I believe the only solution is to buy a ground start line from your local telco. Might have to rig a special phone up to draw dial tone properly. This is the only way to ensure a ground on your line when in use. On the 5ESS, you have to sense the ground and remember it because it goes away as soon as the switch converts to the "Talking" state. > <> Larry Lippman @ Recognition Research Corp., Clarence, New York > <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry > <> VOICE: 716/688-1231 {att|hplabs|mtune|utzoo|uunet}!/ > <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?" -- Jim Harvey | "Ask not for whom the bell Michigan Bell Telephone | tolls and you will only pay 29777 Telegraph | Station-to-Station rates." Southfield, Mich. 48034 | ulysses!gamma!mibte!jbh