[time-nuts] Frequency from telco
billj at ieee.org
Sun Sep 24 19:54:07 EDT 2006
Hal Murray wrote:
>Has anybody tried using the phone company as a frequency reference?
>Are the telco master clocks locked to GPS or national frequency sources? Or
>do they just use their own Cesium box?
Yes to all of the above. It depends on the telco. All of them "should"
meet the 10E-11 requirement
over a "long" interval
>Is that a useful way to get a good clock without a GPS antenna?
Probably, if you filter the jitter and wander with a reasonably good
>I worked with T1 many years ago. It wouldn't be hard to extract a signal to
>feed to a PLL.
You could lock an oscillator to the T1 rate and then divide that down to
something like 8 or 4 KHz
and use that to discipline you "precision" oscillator
>Has anybody done that and collected data? I'd expect lots of short term
>jitter and wander but the long term should be pretty good.
The telco's do that all the time. The worst wander I have seen was about
200 NanoSeconds over
a few minuets time. There was a lot of data available at one time. SONET
(fiber optics) had
a problem with step changes in phase on the payload.. Don't know how
that was resolved
>Does anybody know how DSL works? If I poke around with a scope in my DSL
>modem/router, will I find a clock locked to the telco's master clock?
>How many different versions of DSL are there?
I haven't worked in this field for about 16 years so anything I type is
from that time frame.
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