[time-nuts] C-Max Receiver Experiment
justin at fuzzythinking.com
Thu Nov 3 00:02:54 EDT 2011
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
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)
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
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.
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
>> fixed it. I'm going to attempt to capture the analog signal by probing
>> 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
>> 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.
> 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.
> SatSignal software - quality software written to your requirements
> Web: http://www.satsignal.eu
> Email: david-taylor at blueyonder.co.uk
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