[ntp:questions] NTP phase lock loop inputs and outputs?

Uwe Klein uwe_klein_habertwedt at t-online.de
Mon May 19 19:25:13 UTC 2008


A simple algorithm I have used in the pastis

to measure phase offset.

in short intervals starting with an interval in
which under worst case errors phase changes
of less than 180 deg can happen.

correct the frequency error for that.
lengthen the interval, rinse and repeat.
until your phase offset is constant.

measure phase error from there.

then compute a frequency offset you need
to apply to have the phase change over this
error in a given timeframe
or
compute a time you have to shift frequency by
a given amount.

after the time has elapsed switch back to your
previously measured offset.

You should now have about zero frequency and phase error.
you will now have to fix the small errors in f and p
continuously.

I have used this ages ago (~1989) for a positioning system
that had to lock on the Stereo Pilot Tone or the RDS carrier of
multiple  FM Broadcast transmitter ( that ran in lockstep).

uwe




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