Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!mitel!sce!cognos!dgbt!gandalf!ml
From: ml@gandalf.UUCP (Marcus Leech)
Newsgroups: comp.dcom.lans
Subject: Re: Radio Time Clocks
Message-ID: <2515@gandalf.UUCP>
Date: 5 Jun 89 05:27:37 GMT
References: <895@osf.OSF.ORG> <3086@daisy.UUCP> <2767@csccat.UUCP> <16468@bellcore.bellcore.com>
Organization: Gandalf Data Ltd, Product Development
Lines: 34

In article <16468@bellcore.bellcore.com>, karn@jupiter (Phil R. Karn) writes:
> Has anybody built a clock that uses CHU's encoded time signals? CHU is
> generally much easier to receive in the northeastern US than WWV, but
Well, actually, yes.  We use one I designed to keep our VAXen synched to
  CHU to within abt 0.03sec.  The VAXen also synchronize other devices a couple
  of times a day.  I published an article in the April, 1988 issue of
  "The Canadian Amateur" [hey, Phil, are you a C.A.R.F. member? :-)] about
  the modem I designed and the software.
A regular 103-type modem won't work, because of some tight timing restrictions.
  My intention is to go commercial/semi-commercial with this thing.  If I
  get enough encouraging noises from people, I probably will.
If you build a modem based on my article, you can get the time-setting
  software from me for nothing.

I live and work only a few km away from the CHU transmitter site, so the
  signal is pretty good :-) ;-).  I've evaluated the signal in other parts
  of North America and concluded that a modem listening to the signal would
  be able to get a good "fix" at least several times per day, and usually
  several times per hour.  The problem with WWV isn't so much propagation, it's
  that you need an entire minute of ungarbled digital timecode to encode the
  current time of day.  The CHU format gives you nine bursts per minute, each
  encoding the entire T.O.D--that means that conditions can be pretty
  poor and still allow you to get one or two complete timecodes in a given
  minute.
Your average PC would need to get a fix about four times a day to stay within
  0.50sec of UTC.  Our VAX (785) drifts only about 0.2 seconds per day when
  left unattended, depending on phase-of-the-moon.  Many of the devices we
  periodically synchronize have drifts of up to 2 or three seconds per day.
  Why is a $5 Brand-X watch so much better than a $150 PC clock board?
-- 
"Better Living through modern chemistry" PaperMail: 130 Colonnade Rd, Nepean,ON
Marcus Leech                             E-mail:     ml@gandalf.UUCP
Gandalf Data Ltd                         PacketRadio: VE3MDL@VE3JF
"The opinions expressed herein are solely my own" So there