Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!lll-crg!mordor!sri-spam!sri-unix!hplabs!decwrl!sun!imagen!atari!portal!cupertino.pcc!Phil_CW_Sih From: Phil_CW_Sih@cupertino.pcc Newsgroups: comp.dcom.modems Subject: Re: An interesting modem problem Message-ID: <63@pcc.portal.uucp> Date: Thu, 13-Nov-86 16:09:37 EST Article-I.D.: pcc.63 Posted: Thu Nov 13 16:09:37 1986 Date-Received: Sun, 16-Nov-86 00:01:03 EST References: <128@gaia.UUCP> Distribution: world Organization: The Portal System (TM) Lines: 43 Jonathan Corbet {hao | nbires}!gaia!jon writes: I have had a recurring problem trying to communicate between two machines using Hayes-compatible (actually, one IS a Hayes) 1200 baud modems. Both modems work great; we both talk to a wide variety of machines with our respective modems. However, when we try to talk to each other, there appears to be a real line noise problem. In particular, the junk characters "~r" and "}i" appear repeatedly. ----- I've noticed this problem too in using my modem to call somewhere between 100 and 200 different systems each month. I am not sure of this answer, but I think it has to do with some internal adjustments of the modems in question. If we assume that this adjustment has a somewhat normal looking distribtion about a calibrated standard, then modems on either end of the distribution could have this problem. As an experiment (this is a real BS hack) I opened up one of my units because I was having this problem a lot. It started to happen after I had gotten it back from warranty repair. Inside I found one potentiometer which was still set at its original setting. Since this was the only adjustment in the whole thing, I decided to go online to some of the modems I was having noise problems with and play with it. After carefully marking its original position, I started to diddle it. What I found, not too surprisingly, was that I could dramatically influence the rate at which spurious characters came out of the receive end of the modem. This appeared to be a receiver only adjustment. I found that the acceptable range for this setting was different for each of the "problem" modems I called and there was a small (very small) overlap in the range acceptable to the majority of them. I also found that which junk characters you got depended on which side of the adjustment you were on. I ended up setting this potentiometer in this small range of maximum acceptance or compatibility and the problem has all but vanished. Mind you, I don't recommend anyone go and hack their modems. Phil Sih 408/973-9111 (voice) The Portal System: "Phil Sih" 408/725-0561 (data) UUCP: ucbvax!sun!portal!phil_sih%cupertino.pcc Internet: portal!phil_sih%cupertino.pcc@sun.com "Coming to you through the Portal-Usenet Gateway"