[time-nuts] Dephasing WWVB

[John Reed]

Thanks Paul.  I thought that this would be a simple project.  But, I'm 
seeing that random phase jump problem on every method I've tried so far.  My 
first attempt was a 2N2222 that would go into saturation on the plus cycle, 
then into a flip-flop.  I ended up with the phase problem on the 60 KHz 
output.  Then I tried using a pulse generator into a flip-flop.  Same 
problem.  The puzzling thing is the 120 KHz output from the 2N2222 or pulse 
generator look fine, but the 50 KHz output of the flip-flop is not.

By the way, my 5 section synchronous filter is an LC with op-amps between 
each stage to bring the gain up for the squaring chip.  It has a 2 KHz -6 dB 
bandwidth at 60 KHz.

John

-----Original Message----- 
From: paul swed
Sent: Sunday, June 29, 2014 9:34 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Dephasing WWVB

John welcome to time nuts. This won't be a super long post have other
things to do.
Search for d-psk-r and you can see a few of my exploits. Summation. "It
ain't easy".
It appears to be really easy unless you are far away like the east coast.
Then the propagation gods enter into the picture along with the 60 KHz
station in England that shows up most nights.
The simplest of approaches was indeed the old doubling trick and the many
flavors of it. I built most along with regenerative dividers and other
trickery. Fact is it simply drops a count and that flips the phase quite
annoying.
I finally created two approaches. One specifically for spectracom devices
essentially adding a third mixer and checking for the flip. Works but
requires internal hacking of the spectracom.
The other pretty much a freestanding receiever using a classic costas loop
approach. All details were released to time nuts over a year ago.
My next stab is more of a digital approach using the STM discovery board.
Have to say I seem to get lost in some of the basics of getting all of the
crazy registers set.
However its value is it can run very very fast. So you can do some nice
sampling.
Regards
Paul
WB8TSL


On Sat, Jun 28, 2014 at 5:38 PM, Charles Steinmetz <csteinmetz at yandex.com>
wrote:

> 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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