Path: utzoo!utgpu!water!watmath!clyde!att!rutgers!mailrus!ames!umd5!purdue!decwrl!ucbvax!agate!saturn!eshop From: eshop@saturn.ucsc.edu (Jim Warner) Newsgroups: comp.dcom.lans Subject: Re: Using 48.? ohm RG 62A/U cable for Thin Ethernet? Keywords: IBM COAX, Thin Ethernet, Cheapernet, Thinnet... Message-ID: <3496@saturn.ucsc.edu> Date: 29 May 88 00:18:27 GMT References: <2471@ritcsh.UUCP> <2631@ritcsh.UUCP> <22226@tis.llnl.gov> <875@ucsd.EDU> Reply-To: eshop@saturn.ucsc.edu (Jim Warner) Organization: University of California, Santa Cruz Lines: 23 Brian is right. What is important is the impedance of the cable. The only thing that is magic about 50 ohms is that's what all the transceivers in the world expect to see. If you are willing to make your own transceivers you can use any strange impedance cable that you happen to have installed in your buildings. To be sure, what you'll have won't be Ethernet, but it will work. The details of how to do such a foolish thing are in National Semi's publication 550083-001 "Advanced Peripherals IEEE 802.3 Local Area Network Guide." We have successfully used 110 ohm balanced video cable for an underground Ethernet link. This cable is sometimes called twinax because it has two center conductors surrounded by a shield. We found that by attaching the two center conductors together at both ends and treating it as coax, the actual impedance was 47 ohms. The slight shortfall in impedance is OK as long the cable isn't too short. (The DC loop resistance adds to the terminator resistance so that collision detection can still be guaranteed.) jim warner Sr Dev Engineer Divison of Natural Sciences University of California, Santa Cruz