Path: utzoo!utgpu!water!watmath!clyde!bellcore!rutgers!cmcl2!nrl-cmf!ames!pasteur!ucbvax!agate!saturn!eshop From: eshop@saturn.ucsc.edu (Jim Warner) Newsgroups: comp.protocols.appletalk Subject: Re: PhoneNet cabling Message-ID: <3611@saturn.ucsc.edu> Date: 4 Jun 88 17:10:10 GMT References:<614@mtxinu.UUCP> Reply-To: eshop@saturn.ucsc.edu (Jim Warner) Organization: University of California, Santa Cruz Lines: 30 In article <614@mtxinu.UUCP> ed@mtxinu.UUCP (Ed Gould) writes: > >As I think more, though, I remember that the cable that PhoneNet uses >is flat, untwisted telephone cable. So it might work better to use >two pairs, selecting one conductor from each for the PhoneNet, and >grounding the other. > No. Apple's LocalTalk is RS-422 balanced differential signalling. The two wires should be twisted together for the maximum noise immunity. You can read about it in EIA-422-A, available from the Electronic Industries Association (Dec 1978). Furthermore, "grounding the other [wire]" has little meaning in an interbuilding connection. It is not safe to assume that ground will be the same in different buildings. My reading of RS-422 does not lead to the conclusion that Farallon's distance limits are conservative. But whatever works works. The rules appear to be empirical rather than based on engineering analysis. I have peeled open a Farallon transformer and looked at the measures they have taken to guard against transients. They use the same transient suppression components that are used to protect 120 VAC circuits. I honestly can't imagine how these are at all appropriate to protecting the attached equipment. Jim Warner Univ of Cal Santa Cruz