Subject: Re: Better than 2ppm TCXO for <$25?
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Date: Mon, 28 Oct 2002 17:36:39 GMT
NNTP-Posting-Date: Mon, 28 Oct 2002 12:36:39 EST
Organization: Cox Communications
"Chris Carlen" wrote in message
> Hi folks:
> I also am aware that one could use other methods, like interfacing to a
> radio controlled clock, GPS, the internet time RFC, etc. Those things
> are very interesting, but I'd like to have a clock on my desk before the
> end of the decade. Even with a basic Xtal, that will be a challenge for
> my slow-going self.
Actually, it might be worth your while to consider WWV. There are chips
available from several suppliers that perform virtually all of the clock
functions. The frequencies used are around 60kHz. I don't recall that
interfacing them would have been very difficult, although our application
didn't require a time display.
I used to have a list of the part vendors, but have long since lost it. On
the other hand, I don't remember them being too difficult to track down (I'm
sure I googled). It's worth a quick look, even if you decide to go with
As an aside, if you're after long term accuracy, specs like 2ppm don't
really provide enough information. Clock errors accumulate over time, and in
general white noise effects will dominate in the short term, and low
frequency noise effects will dominate in the long term. Short and long term
are somewhat subjective, and depend on the type of clock. In high
performance frequency standards, low frequency effects may not become
apparent for days or weeks. The point is that although you might be
expecting an accuracy of 2 seconds every 11.6 days (1 million seconds), you
may find that your actual clock performance is significantly worse. On the
other hand, if you compared your clock to a reference standard over a
relatively short time period (say, less than an hour), it might be
significantly better than 2ppm.
-- Mike --