From owner-freebsd-hackers Thu Jan 8 21:28:46 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.7/8.8.7) id VAA13568 for hackers-outgoing; Thu, 8 Jan 1998 21:28:46 -0800 (PST) (envelope-from owner-freebsd-hackers@FreeBSD.ORG) Received: from shell.futuresouth.com (shell.futuresouth.com [207.141.254.20]) by hub.freebsd.org (8.8.7/8.8.7) with ESMTP id VAA13550 for ; Thu, 8 Jan 1998 21:28:24 -0800 (PST) (envelope-from tim@shell.futuresouth.com) Received: (from tim@localhost) by shell.futuresouth.com (8.8.8/8.8.8) id XAA24539; Thu, 8 Jan 1998 23:25:35 -0600 (CST) Message-ID: <19980108232535.39313@futuresouth.com> Date: Thu, 8 Jan 1998 23:25:35 -0600 From: Tim Tsai To: David Kelly Cc: FreeBSD Hackers Subject: Re: GPS for xntpd Stratum 1 servers References: <199801090340.VAA13302@nospam.hiwaay.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 0.88 In-Reply-To: <199801090340.VAA13302@nospam.hiwaay.net>; from David Kelly on Thu, Jan 08, 1998 at 09:40:48PM -0600 Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk > > On Wed, 7 Jan 1998, David Kelly wrote: > > > If you are on the 15th floor of a 30 floor building then you are going > > > to have troubles with the GPS in any case. Any view out the window will > > > have less than half the sky visible. Sometimes there may not be enough > > > satelites visible for a lock. > > > > Yeah, Mike Smith suggested RS-232 <==> Fiber <==> RS-232 to the roof, but > > unfortunately doing that costs an arm and a leg in this concrete jungle. > > Er, maybe just a leg these days. You only need three satellites to get a 2D position. I believe 1 satellite in view is all that is necessary to get the time. That is very practical nowadays [in Mississippi we easily get 8-10 satellites in clear view] even if you only have a clear view of the sky on one side of the building. If you can extend a small pole (say 3 feet) out the window then it would be more than enough. I've stuck GPS antenna mounted on a broom stick out of hotel windows enough times to know this works. :-) > So whatcha do is take that old 386sx16 and put it on ethernet, up on the > roof with the GPS, and let it be the timeserver. It'd be easier to use a couple of RS232<->RS422/RS485 converters. At the typical GPS baud rate (4800/9600 baud) you should be able to run the wire hundreds of meters if not more (RS422 spec escapes me at the moment). The converters run for about $30-$100 a piece. Tim