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From: clements@bbn.com (Bob Clements)
Newsgroups: sci.electronics
Subject: Re: NBS time broadcast
Message-ID: <43666@bbn.COM>
Date: 2 Aug 89 14:34:11 GMT
References: <8720@kean.mun.ca> <2012@ubu.warwick.UUCP>
Sender: news@bbn.COM
Reply-To: clements@BBN.COM (Bob Clements)
Organization: Bolt Beranek and Newman Inc., Cambridge MA
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In article <2012@ubu.warwick.UUCP> pmj@cs.warwick.ac.uk (Paul Jaggard) writes:
>    In the UK, one source of accurate time information is the Rugby MSF
>transmitter on 60kHz (VLF). [...] Transmission range is in the
>order of a few hundred miles.

In the US, we have the same sort of thing. It's called WWVB and
it is also on 60 KHz.  The code is similar to that on the 100 Hz
subcarriers of WWV and WWVH, but not identical.

I have a small receiver board for 60 KHz stashed somewhere.  I
used it for a while before the Heathkit clock came out.  Since
I'm located in the Boston area, the signal from Fort Collins
Colorado and the signal from Rugby UK are about the same
strength.  Therefore the times when I can successfully receive
the time code are pretty rare.  I got a decent signal for a
couple of hours per day, not every day.  But in some parts of this
country, the WWVB signal is more reliable than the WWV signals.

As a matter of interest, WWVH in Hawaii synchronizes its time and
frequency with the NBS clocks on the mainland by listening to WWVB
on 60 KHz.  When I've visited there I've seen the chart recorder
showing phase differences between WWVB and a locally generated 60 KHz
from their local generators.  The difference was basically a 24-hour
sine wave, but they watch for long term drift.

The clocks at both WWV and WWVH are sets of three cesium clocks,
each with their own time/RF/tone generators, continually voting
among themselves.  This is all in a shielded, temperature
controlled room. The clocks are tweaked manually when necessary
to match higher authority. WWVH to match WWV, WWV to match the
big clocks in Boulder.

When I first visited WWVH their only external reference was WWVB.
More recently, they also compare against Loran C, Omega, and
something else I don't recall. Maybe GPS.  All the agencies watch
each other and cooperate keeping this accurate.

It's a neat place to visit.  It's on the southwest corner of Kauai.
In fact, it's a neat place even if you DON'T go to WWVH. :-)

>pmj@cs.warwick.ac.uk

Bob Clements, K1BC, clements@bbn.com