[time-nuts] Dephasing WWVB
Charles Steinmetz
csteinmetz at yandex.com
Sat Jun 28 21:38:34 UTC 2014
John wrote:
>I discovered an article on the web that uses an AD835 multiplier
>chip to square the WWVB signal * * *. I built a five section
>synchronous filter tuned to 60 KHz to get rid of interference and
>its output feeds the 835 chip. This all works fine. * * * the
>599J won't tune that high so I have to divide this 120 KHz frequency
>by 2. * * * I've tried to generate a pulse train from the 120
>KHz signal and then use a flip-flop to divide the frequency. This
>does not work well. Apparently generating the pulse train picks up
>noise and I end up with a 60 KHz signal with fluctuating phase. Now
>I'm trying to get a Miller frequency divider working
Why are you trying to generate pulses, rather than just squaring
(clipping) the output of the 835 in a saturated amplifier? Pulses
have less energy and therefore higher noise. All you need is a
signal-conditioning squarer matched to the level coming out of the
835 (see Bruce Griffith's pages at <ko4bb.com> for ideas, as well as
the Wenzel site and any number of illustrations in Experimental
Methods in RF Design -- for example, both Figures 5-46 and 4-45 show
complete simple squarers with FF dividers). Even a CMOS gate biased
to half-voltage should work fine. I like the NC7SZ74 Dflop for the
divider. Half of a 74HC74 works fine, too.
This should be the kind of thing you throw together in 15 minutes and
it works first time.
Best regards,
Charles
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