Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 beta 3/9/83; site sdcrdcf.UUCP Path: utzoo!watmath!clyde!floyd!harpo!ihnp4!zehntel!hplabs!sdcrdcf!darrelj From: darrelj@sdcrdcf.UUCP (Darrel VanBuer) Newsgroups: net.lan Subject: Re: Ethernet cable length query - (nf) Message-ID: <944@sdcrdcf.UUCP> Date: Mon, 26-Mar-84 10:33:30 EST Article-I.D.: sdcrdcf.944 Posted: Mon Mar 26 10:33:30 1984 Date-Received: Wed, 28-Mar-84 01:22:15 EST References: <2832@fortune.UUCP> <1151@cbosgd.UUCP> Reply-To: darrelj@sdcrdcf.UUCP (Darrel VanBuer) Organization: System Development Corporation, Santa Monica Lines: 41 There are three distinct kinds of Ethernet tranceivers (not counting devices like a box to replace 8 tranceivers in a small region): Connectorized tranceivers (like 3-Com): a real pain to insert or remove since it partition your net for several minutes (especially if you have to install a pair of new connectors). Interlan vampires (also used by DEC): a big plastic box which is bolted to the side of the cable (with a rather expensive instalation kit) Xerox vampires (currently made by TCL): the cable tap is a small two-piece metal clamp which bolts to the cable and has a small threaded hole at right angles to the cable. The (cheaper) installation tools cut thru the insulation and braid under the hole (with a small circular saw), finally you screw the tranceiver (a metal box the size of two packs of cigarettes) into the hole. The tranceiver has a sharp stinger which pierces the insulation to make contact with the center. With great care in cleaning loose bits of braid from the bottom of the hole, these can be installed without disrupting the net. Also, extra clamps are only about $10 each, making it cheap to have "floating" tranceivers. My bias is toward these because this was the only kind on the old Experimental ethernet, and they're the least expensive. On "too tight": with the Xerox type, at least, the force needed to screw in a tranceiver goes up an order of magnitude when it bottoms out in the hole, so you can't miss it. One problem with the old taps was the rubber O-ring that came with the cable taps. The installation directions (from the tap manufacturer) say be sure to use it. The verbal directions from Xerox (confirmed in practice) is don't use it because it keeps you from screwing the tranceiver in far enough, resulting in poor center contact. This may not be a problem with the new stuff. On crashing a 750 by connecting a tranceiver to it: this is a previously reported problem. Basically, the Unibus in a 750 doesn't have enough +15 volt power to stand the starting inrush demanded by the tranceiver, and apparently doesn't depend on brand of tranceiver. -- Darrel J. Van Buer, PhD System Development Corp. 2500 Colorado Ave Santa Monica, CA 90406 (213)820-4111 x5449 ...{allegra,burdvax,cbosgd,hplabs,ihnp4,sdccsu3,trw-unix}!sdcrdcf!darrelj VANBUER@USC-ECL.ARPA