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

Magnus Danielson magnus at rubidium.dyndns.org
Sat Sep 1 21:17:08 UTC 2012


On 09/01/2012 08:35 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
>
>

It's interesting to notice that you have about the same distance from 
the middle in all 5 examples. It's like you trigger a diode drop for a 
while. Notice that there is a small slope towards zero.

Cheers,
Magnus




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