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.
<<attachment: smither.vcf>>
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