[SI-LIST] Re: PPM measurement for reference clock
- From: Joseph.Schachner@xxxxxxxxxxxxxxxxxx
- To: lijun_hit@xxxxxxxxx
- Date: Tue, 8 Jan 2013 17:06:07 -0500
Frequency counter : arbitrarily high resolution of the mean frequency of
your clock
Spectrum analyzer: within limits, controllable frequency resolution; will
show sidebands if there is phase modulation or amplitude modulation of the
clock.
Real time scope of suitable bandwidth, with FFT: within limits (maximum
acquisition duration and maximum FFT size) can produce results similar to
that of a spectrum analyzer. Can probably produce a time domain "track"
showing wander of the clock using one of several techniques.
You didn't mention what kind of clock you're looking at. Is it meant to
be rock stable, like SONET? Or is it a Spread Spectrum clock, as for PCI
Express or SATA, and you're trying to make sure it stays between nominal
and 5000ppm lower? In the later case, I think you need the real time
scope to look at the SSC track - but I may be biased.
It is conceivable that some frequency counter could make measurements fast
enough that the stream of frequency values it produces would show the SSC
triangular frequency modulation (which is at about 30kHz) but I don't know
of one that is that fast; most counters waste many milliseconds between
gated measurements, so even if the measurement time is negligible the
update rate is not likely to be fast enough. If you found one that was
fast enough, you'd probably need an external computer to catch those
values and plot them or measure FM from them, unless that frequency
counter has a display and can do that internally (I don't know of one that
can do that, either).
It should also be possible to figure out the SSC amount from the magnitude
of the 30kHz FM sidebands shown in the spectrum analyzer, but I think that
is a very inconvenient technique.
Actually seeing the modulation shape and magnitude shown on a frequency
track on a real time scope is easier, and much more intuitive.
--- Joe S.
From: jun li <lijun_hit@xxxxxxxxx>
To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
Date: 01/08/2013 04:25 PM
Subject: [SI-LIST] PPM measurement for reference clock
Sent by: si-list-bounce@xxxxxxxxxxxxx
Hi experts,
Except frequency counter, is there any other equipment recommendation for
clock PPM measurement? Do you think center frequency of spectrum analyzer
can be utilized for ppm calculation?
Thanks
Jun
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
