[time-nuts] 60 Hz line quirks, anybody recognize this stuff?

[Bob Smither]

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.

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