Path: utzoo!censor!geac!torsqnt!lethe!yunexus!ists!helios.physics.utoronto.ca!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!rpi!uwm.edu!bionet!hayes.ims.alaska.edu!floyd From: floyd@ims.alaska.edu (Floyd Davidson) Newsgroups: comp.dcom.modems Subject: Re: INFO-MODEMS Digest V91 #103 Message-ID: <1991Feb28.124121.29644@ims.alaska.edu> Date: 28 Feb 91 12:41:21 GMT References: Organization: University of Alaska, Institute of Marine Science Lines: 47 In article WILLIAMS@GAMMA.IS.TCU.EDU writes: [...] > > o USR says "modem is fine, we used the modem killer on it, no prob." > o modem returns false RING only on one line > o with modem on-hook, taking line off-hook then on-hook with type2500 > set causes false RING > o false RING doesn't occur on every on-hook command, just one in five > >Any clues? > >Mark Williams >williams@gamma.is.tcu.edu Well if the modem is OK, and it seems to be, then the modem is getting hit with something that can be mistaken for a ring. I haven't ever looked at what modems use as a ring detector, but telco equipment usually just has some form of a full wave bridge rectifier hung on the line. Basically any AC, or a significant spike, with enough voltage will look like ringing current. There are too many possible causes to guess at. Inductive spikes, capacitive discharges, sheesh, I don't know. But there are a couple things you can do. One is take every other thing off the line (phones, answering machines, fax, etc.). See if it still does it. If you have a voltmeter, measure the DC and then the AC across the line as you hang it up. Then go measure it across another line the same way (even using the same phone if you can), and see what the difference is. An analog meter movement would be required. A look at it with a scope would be interesting too, but if you can do that kind of thing just remember that it is a balanced line. Readings to ground don't mean anything, and grounding one side is trouble. Simple scopes don't look at tel lines very well. One thing that might help when talking to the telco is refering to it as the "ring detection" having a problem, rather than as a false ring. If the tech is a modem user it won't bother him either way, but if he isn't into modems the "ring detection" will ding bells (in his head) that are different than "false ring" does. Floyd -- Floyd L. Davidson | floyd@ims.alaska.edu | Alascom, Inc. pays me Salcha, AK 99714 | Univ. of Alaska | but not for opinions.