[time-nuts] Re: New design for a GPS disciplined OCXO or Rubidium

[Poul-Henning Kamp]

Andy Talbot via time-nuts writes:

> Hence the value of using an unstable or jittered clock in the processor.

That may look like it improves the situation, but it does not.

The fundamental problem with "hanging bridges" is that they do not
average to zero over any predictable time interval, not even the
12 hour orbital period, so there is no way to "filter them out".

You can make it look like you filtered them out, but you will find
that all you have done is to introduce noise at longer taus, probably
a LOT of noise.

Once you get to the level of precision where you can see the first
hints of the hanging bridges, you /have/ to start applying the "residual"
communicated by the receiver.

That has been attempted in "pure hardware" both with programmable
delay-lines and DAC + adder + Sample & Hold circuitry.  I have yet
to hear anybody praise the results, temperature stability or ease
of implementation.

Hanging bridges is where sane people switch to a software PLL.

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