Path: utzoo!telecom-request Date: 20 Jun 91 04:14:23 GMT From: Geoff Steckel Newsgroups: comp.dcom.telecom Subject: Modem vs. Line-Powered 'In Use' Light Reply-To: gsteckel%Ecd@sun.com Message-ID: Organization: Omnivore Technology, Newton, Mass. (617)969-3448 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 473, Message 2 of 6 Lines: 29 Recently I bought a PP 9600-SA modem, and attempted to use it. No joy -- the best I could do was 4800 BPS. Mysteriously, only the incoming data were incorrect -- the remote system received my transmissions essentially perfectly. After a lot of futzing around, I disconnected a two-line phone with a line powered 'in-use' light. Voila! 9600 BPS V.32 worked with very low error rates. The culprit was a U.S. Tron # PL2125 two-line phone. It isn't a good phone -- I'm not sure how it passed the part 68 drop tests, and it had other problems. Still, it's the ONLY commercial example of a line-powered 'in use' light I've seen. My Panasonic and 'SW Bell' both use batteries to power the lights. Since the request for line-powered 'in use' indicators recurs frequently on at least two of these newsgroups, I'm posting this to suggest that they might not be a good idea. One could have the possibility of adding significant distortion to the phone signal, which for a V.32 modem could cause very bad interactions between outgoing and incoming data. Grossly simplified, one could easily present a nonlinear load on the line. Any phone engineers have any comment? geoff steckel (gwes@wjh12.harvard.EDU) (...!husc6!wjh12!omnivore!gws) Disclaimer: I am not affiliated with Sun Microsystems, despite the From: line. This posting is entirely the author's responsibility.