[time-nuts] crystal oscillators & TPLL

Steve Rooke sar10538 at gmail.com
Wed Jun 23 00:36:19 UTC 2010


Poul,

On 23 June 2010 06:55, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
> In message <0C4F750835264E13AB61D4B8C8448B68 at Warcon28Gz>, "WarrenS" writes:
>
>>> you have a very tough row to hoe when it comes to proving
>>> that your frequency samples represent the same signal as a sequence
>>> of zero deadtime period measurements would do.
>>
>>Sorry, I though that was obvious.
>
> Yes, you probably did.

If there was not a continuous zero dead-time connection around the
TPLL loop it would be impossible for it to keep lock and track the two
oscillators. As you can see from Warren's block schematic, there is a
100kHz filter in the loop to block 2f components from the mixer and a
gain block of 100x. From John Miles' tests you can see that the PLL
tracks from 0.1s, 10Hz, way out towards 100s, 0.01Hz, or the graphs
would not be coherent. As for measurement of ADEV much below 0.1s, it
is generally agreed that phase noise noise measurements be performed
here.

Steve

> Poul-Henning
>
> --
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.
>
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-- 
Steve Rooke - ZL3TUV & G8KVD
The only reason for time is so that everything doesn't happen at once.
- Einstein



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