[time-nuts] The VE2ZAZ GPSDO

tom w0kgw at citlink.net
Sat Oct 21 21:12:53 EDT 2006

thanks for volentering sounds like you know what it takes to make a good one 
and set up the webpage..............
tom w0kgw

----- Original Message ----- 
From: "Dr Bruce Griffiths" <bruce.griffiths at xtra.co.nz>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Saturday, October 21, 2006 7:20 PM
Subject: Re: [time-nuts] The VE2ZAZ GPSDO

> Tim Shoppa wrote:
>> "John Miles" <jmiles at pop.net> wrote:
>>> Some of the concerns may not be major issues (e.g., it seems safe to say
>>> that the FLL action will correct for drift caused by the 7805's tempco,
>>> unless you plan to dump a can of R134a on it), but others are worth 
>>> bringing
>>> to the magazine's attention.  If you'll forward your comments to Doug 
>>> Smith
>>> at kf6dx (at) arrl.org, he'll most likely print them in the Letters 
>>> column.
>> Having seen some bad vibes unfold through the channels of the
>> letters column and other communications with editors, I think that
>> BY FAR the most useful thing to do would be to contribute an
>> improvement (preferably with schematic) rather than a lengthy
>> textual or mathematical criticism.
>> Tim.
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> Since the disciplining technique is far from optimum, this may only
> serve to further sidetrack the less knowledgeable from the best
> engineering solution which can achieve a far better performance for a
> similar cost. A comparison of the performance of this method with the
> optimum method using similar receivers and crystal oscillators would
> have been helpful in assisting newcomers in selecting a more appropriate
> method.
> Perhaps someone should set up a webpage detailing how one should go
> about disciplining a high stability crystal oscillator.
> Allan deviation vs tau for various GPS receivers
> Allan deviation vs tau for various crystal oscillators.
> Various phase measurement techniques and associated tradeoffs
> Effect of various phase measurement techniques on the system Allan
> deviation vs tau.
> Filtering phase measurements and discarding outliers.
> Choosing the appropriate loop time constant.
> Miscellaneous:
> Use of synchronisers to reduce probability of generating runt pulses and
> metastability problems.
> Don't use same IC to buffer different frequencies
> Resynchronising divider chain outputs to reference frequency clock to
> reduce jitter.
> DAC requirements and tradeoffs
> Monotonicity
> Resolution
> Noise
> Short term stability
> Cost etc.
> Monotonic high resolution DAC techniques
> Multibit Audio DACs
> etc.
> Bruce
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