[time-nuts] Question on crystal jumps

Jim Palfreyman jim77742 at gmail.com
Fri Oct 24 00:15:39 UTC 2008

This discussion has come at an interesting time.

I've hooked up an LPRO-101 from ebay to an AVR micro-controller - basically
using it to clock the processor directly.

I've written code so the AVR is a clock and I've been comparing my clock's 1
PPS to the GPS.

Over a few minutes it hops back and forward a few hundred nsec. All quite
acceptable given the clock speed.

When I come back after a few hours it will suddenly be 10-20 usec slow. I
did see it jump over a few seconds from 200nsec to 17 usec.

At first I put this down to interference because it coincide with me
switching off a light. So I put the whole lot into a metal box, shorter
wires and tried again.

It still has jumps but this time it is *gaining*.

Until this post started I'd assumed it was maybe my code and was about to
dive in and check it.

Could these crystal "jumps" account for my issues?



2008/10/24 Steve Rooke <sar10538 at gmail.com>

> Hi,
> I believe it was pointed out earlier that the output of a LPRO uses
> some form of xtal oscillator as the output of the rubidium stage is
> quite noisy. Considering the general consensus is that xtal
> oscillators have these jumps, I wonder if the output of the rubidium
> stage could be just passed directly through a multi-stage xtal lattice
> filter to clean it up and use that directly and that may circumvent
> the xtal jumps people are seeing.
> 73 - steve
> --
> Steve Rooke - ZL3TUV & G8KVD
> Omnium finis imminet
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