[time-nuts] How to measure Allan Deviation?

Ulrich Bangert df6jb at ulrich-bangert.de
Mon Oct 23 13:28:11 EDT 2006


Didier,

> I need to find the best way to go from the 10 MHz sinewave to the 
> divider, probably through an LM119 comparator with modest 
> hysteresis.

the Datum LPRO User's Guide / Installation Guide discusses some methods
of sine to square wave conversion in terms of lowest phase noise. 

Since you were originally asking for Allan Deviation i would like to
advertise again my free PLOTTER software which does what ALAVAR does but
more nicely + many things more. Since it does not simply open the input
file but first makes a copy to a "working file" you may even work with
it on files in that a different program is currently sampling data, so
you don't have to wait to the end of data acquistion but may get
intermediate results at any time.

When you put forward your questions about measuring Allan deviation i
saw that it were all the right & intelligent questions and perhaps this
is the reason why so many people are willing to enlighten you. I wish I
had known time nuts when i was in the same state of mind as you. Would
have saved me years of learning it the hard way!

73 de Ulrich, DF6JB

> -----Ursprüngliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Didier Juges
> Gesendet: Montag, 23. Oktober 2006 06:03
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] How to measure Allan Deviation?
> 
> 
> Bruce,
> 
> Thanks for the reminder. That was my intention. I was 
> planning to use a 
> 74HC74, and whatever dividers I can get my hands on. I am not looking 
> forward to daisy chain seven 7490s, so I will probably try something 
> else. With the D flip-flop, the dividers don't really matter, 
> as long as 
> the delay is below 100nS.
> I need to find the best way to go from the 10 MHz sinewave to the 
> divider, probably through an LM119 comparator with modest 
> hysteresis. The need for a low jitter divider is the same for 
> the GPS disciplined 
> oscillator, so I should be able to reuse the divider for my frequency 
> standard.
> 
> Thanks
> 
> Didier
> 
> Dr Bruce Griffiths wrote:
> > Didier
> >
> > If you are going to use a PPS divider to divide the oscillator 
> > frequency
> > down to 1Hz, you will need to measure the inherent jitter 
> of the divider 
> > to ensure that it doesn't degrade the measurement 
> resolution. It may be 
> > necessary to resynchronise the divided output using a fast 
> D flipflop to 
> > reduce the inherent divider jitter to less than the 20ps 
> resolution of 
> > the 5370.
> >
> > Bruce
> >   
> 
> 
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