Path: utzoo!censor!geac!torsqnt!lethe!yunexus!ists!helios.physics.utoronto.ca!news-server.csri.toronto.edu!cs.utexas.edu!samsung!usc!elroy.jpl.nasa.gov!sdd.hp.com!hplabs!hpfcso!hpfcbig!bame
From: bame@hpfcbig.SDE.HP.COM (Paul Bame)
Newsgroups: sci.electronics
Subject: Re: Getting timing from line cycles (was Re: Sidereal Time Clock)
Message-ID: <6560004@hpfcbig.SDE.HP.COM>
Date: 8 Jan 91 20:38:42 GMT
References: <1990Dec13.043046.14036@zoo.toronto.edu>
Organization: HP SESD, Fort Collins, CO
Lines: 19

> From what I understand, using the 60Hz line as a reference for timing is not
> a good practice if you want any accuracy.

Interesting article in '73 magazine this month about using TV horizontal
sync as a frequency standard.  Seems the networks use expensive, stable and
accurate sources to generate their (nationwide) timebase.  The '73 circuit
uses an inductive coupling to a TV to grab the sync and then a PLL-based
circuit to turn it into a useful frequency.  This could be
adapted to the sidereal clock problem.  You can also use the colorburst
but it requires connection to the TV.

Note, that local cable companies may re-generate colorburst and/or
Hsync of dubious accuracy.  Satellite and air-wave reception seems like
the best chance for a stable source.  Also note that local material
(read: commercials) inserted by affiliates may be of dubious accuracy.
The article mentions (I think) that PBS is a good choice.

			-Paul "Spice is the Variety of Life"
			bame@hpfcbig.sde.hp.com	N0KCL