[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?

Regards,

Jim


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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