On 09/03/2012 11:11 PM, Bob Smither wrote:
On 09/03/2012 12:00 PM, Graham / KE9H wrote:
On 9/1/2012 1:35 AM, Hal Murray wrote:
The context is using the 60 Hz line for timing.
I'm feeding 60 Hz from a wall wart transformer into a modem control signal
that the kernel PPS stuff watches. Mostly, it works as expected, but
occasionally, it picks or drops a cycle.
In order to understand what was going on, I fed the same signal into the
audio input and setup a job to capture the audio. Here is an example of a
pick:
http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-09-a-pick.png
http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-09-a0.png
http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-09-a1.png
OK, that somewhat makes sense.
Something happened several days ago. I used to get picks/drops rarely, say
ballpark of 1 a month. Now I'm getting 10 or 20 per day. So I started
looking closer.
I'm now seeing stuff like this. I've got lots and lots of examples. I added
a second PC with different hardware. It sees the same stuff.
Does anybody recognize this?
http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-a0.png
http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-b0.png
http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-c0.png
http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-d0.png
http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-e0.png
Hal:
Two ideas:
1.) You could have some process in Windows that is causing aperiodic
blocking of the OS's ability to process real time data. Can be many,
many causes.
Hmmm - but wouldn't that result in missing samples and an abrupt phase jump?
The waveforms reported appear phase continuous (right number of samples) but the
sample values are somehow forced to a constant value. I would guess that the
waveform being sampled actually looks like that.
Indeed. What I was stroked by was the repetitive levels and their
tendency (except for one case) to strive towards zero with a small
slope. For me the source is in the analogue domain rather than digital
domain. Phase continuity and restoration of phase rather implies
disturbance of the analogue signal, and the fault behaviour looks like
some form of intermittent glitch and discharge mechanism. Try to see if
you can find some intermittent part of the design.
Cheers,
Magnus
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