On 6/26/2011 6:03 PM, Tom Van Baak wrote:
Alberto,
That's a cute plot. I see 53 x 50 = 2650. What is the x axis scale?
Tom,
that capture was taken a few months ago, from memory it should cover about
15 or 20 minutes.
But I'm curious -- the pending issue with 60 Hz in the US is more about
uncorrected long-term accumulated time drift and less about short-term
frequency stability.
So it seems like you would have to integrate all the wiggles in the 53rd
harmonic of your waterfall plot in order to compute time drift, yes?
Yes, if what you are interested in is the potential drift of a line-controlled
clock, just integrating
the signed deltas from the nominal value will give that info. In any case, I
have near to my bed
such a clock. Thanks God the power line failures are very rare where I live
(let's say once every
three months), and that clock keeps admirably the time. I would guess just a
few seconds per month.
It doesn't have a crystal oscillator inside, it relies just on the 50 Hz.
Is there any chance you could run both the waterfall frequency monitor
and also a 50 Hz phase comparator for a couple of days to see how
well (or how poorly) one can compute the net long-term mains time drift
from a set of independent short-term frequency deviation measurements?
I don't have a 50 Hz phase comparator, but I can arrange for a long waterfall
capture, a day long,
if that can be of help.
73 Alberto I2PHD
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