[time-nuts] LPRO-101 with Brooks Shera's GPS locking circuit
Didier Juges
didier at cox.net
Wed Dec 20 15:13:29 EST 2006
In the matter of lifetime (outside of MTBF issues), is it correct that
Rb has a built-in life limiting mechanism (the lamp wears out), where Qz
does not? If so, Rb oscillators will eventually fail but one might hope
a Qz oscillator may not.
Didier
Tom Van Baak wrote:
>> Hello folks,
>>
>> i like to play the bad boy again: My claim is
>>
>> a) that for most of us a GPSD Rb is of little to no
>> use compared to a good GPSD xtal oscillator
>>
>
> Ulrich,
>
> That's a rather general statement, but I understand what
> you mean. Consider, instead of a bold general assertion
> which can be disproved with a single counter-example,
> a simple list of advantages of quartz vs. rubidium. Then
> let the user decide which is appropriate for their unique
> application.
>
> There's more to a GPSDO than its ADEV. For example,
>
> Warm-up time --
> Many Rb will lock in 5 minutes, typically. Some Qz
> take much longer to get on-frequency from cold start.
> This can simplify the initial loop locking algorithm.
>
> Power consumption --
> Probably Qz-based GPSDO have much lower power
> consumption than Rb.
>
> Physical size --
> I would guess most Qz GPSDO are smaller than Rb
> GPSDO. One could argue that the Casio GPS wrist
> watches are a type of miniature GPSDO!
>
> Hold-over performance --
> For mid- to long-term, Rb is vastly superior to Qz;
> most Rb have daily drift rates 100x better than Qz.
>
> Stand-along performance --
> Without GPS lock, a free-running Rb can be trusted
> to be orders of magnitude more accurate than Qz.
>
> Environmental --
> Is it the case that Rb is less sensitive than Qz to
> extreme environments?
>
> Cost --
> As a rule, Qz-based GPSDO are cheaper than Rb.
>
> Phase noise --
> I'd guess that Qz-based GPSDO could have better
> short-term stability and phase noise than Rb.
>
> Tuning range --
> Could it be that Rb will run for many more years without
> coarse adjust than Qz?
>
> Lock indicator --
> Most Rb give you a signal when frequency lock has
> been achieved.
>
> Mechanical sensitivity --
> Rb GPSDO are much less sensitive to movement and
> shock than Qz. If you don't believe me watch what
> happens if you simply take your GPSDO and bump it,
> or turn it over on your desk. This is especially important
> during hold-over when no external correction is present.
>
> Lifetime --
> Is the MTBF of Qz much longer than Rb due to fewer
> parts and simpler design?
>
> Surplus --
> There are so many cheap telecom Rb out there it is
> near irresistible to make a GPSDO out of them.
>
> You get the idea; feel free to add the ones I missed.
>
> /tvb
>
>
>
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