[time-nuts] C-Max Receiver Experiment

Justin Pinnix justin at fuzzythinking.com
Thu Nov 3 00:02:54 EDT 2011


Update -

I attempted to look at the analog signal.  I looked at the output of the
crystal.  With the scope's low-pass filter turned on I was able to see a
very weak sine wave with a period of roughly 15us.  It was too weak for any
analysis.

http://www.fuzzythinking.com/wordpress/wp-content/uploads/2011/11/60khz.png

I also looked at the demodulator out.  This is a much larger amplitude
signal, though it has already been rectified.  However, I was able to see
good correlation between it (blue) and the TCON output (yellow)

http://www.fuzzythinking.com/wordpress/wp-content/uploads/2011/11/dem_out.png

Most importantly, I've been reading up on the subject and have adjusted my
expectations.  I didn't realize that frequency measurements (like those
done by the HP117 and Fluke 207) don't actually use the timecode part of
the signal.

Page 11 of http://tf.nist.gov/general/pdf/1383.pdf tells me that WWVB is
3-4 orders of magnitude better than WWV for frequency measurements, but
that the two services' time uncertainties overlap and WWVB is at best 1
order better.  As a matter of fact, my measurements of the C-MAX line up
with the top end of that estimate (and Tom's :-)).

I'm still planning on capturing a long set of timings, but I need to do
some hardware mods first.

Thanks,
-Justin

On Mon, Oct 31, 2011 at 1:04 PM, David J Taylor <
david-taylor at blueyonder.co.uk> wrote:

>  Hi David,
>> Thanks for pointing out the problem with the figures in my webpage.  I
>> have
>> fixed it.  I'm going to attempt to capture the analog signal by probing
>> the
>> QOut pin.
>>
>
> The updated images make the effects clearer.  It will be interesting to
> see the image capture.
>
>
>  Good point about "precision" - it's all relative.  This is an extension of
>> a previous project of mine - a clock I built around an LPro.  Setting it
>> to
>> the Thunderbolt is a bit of a pain and I was hoping to build in the C-Max
>> to make it more "fire and forget".  I was hoping for a time signal within
>> several microseconds of UTC without the need of an outdoor antenna. Like
>> most of my projects, the journey is more interesting than the destination,
>> so even if I don't accomplish that goal I'm still having fun.  Embedding a
>> consumer GPS is probably the more practical solution.
>>
>> Thanks,
>> -Justin
>>
>
> Microseconds, no.  Milliseconds perhaps.  But sometimes nothing at all
> depending on the time of day and season of the year etc. etc.  Let's hear
> more about the project as it progresses.
>
>
> Cheers,
> David
> --
> SatSignal software - quality software written to your requirements
> Web:  http://www.satsignal.eu
> Email:  david-taylor at blueyonder.co.uk
>
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