[time-nuts] Measuring 10 MHz accurately.

Ulrich Bangert df6jb at ulrich-bangert.de
Wed May 7 13:20:02 EDT 2008


Martyn,

2 parts in 10E-12 in a second's gate time would require to measure the
time interval with an 2 ps resolution. Since the SR620 (at least mine)
features a 20 ps single shot resolution, i fear your number is more
likely "20 parts in 10E-12". Or what you are doing is to make >= 10
measurements / s of phase and computing the arithmetic mean of them.  

There are not really many companies to offer you direct sub-picosecond
measurement resolution and if at all the devices may in the same price
reigion as your company's boxes. There ARE some measurement schemes that
enable you kind of "artificial magnification" of the time differences to
be measured, for example the Dual Mixer Time Difference Method. In
principle they all look VERY EASY and may give you the impression that
you can make measurements with that on the kitchen table. I have tried
out a few of them just to find out that they do indeed work (in
principle) but that their technical realisation has some strange
requirements that are not too easily given on standard workbench.
Nevertheless I am still working on the problem using a not so well known
proposal.   

Best regards
Ulrich Bangert

> -----Ursprungliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Martyn Smith
> Gesendet: Mittwoch, 7. Mai 2008 18:52
> An: time-nuts at febo.com
> Betreff: [time-nuts] Measuring 10 MHz accurately.
> 
> 
> Hi,
> 
> Two questions for all of you today.
> 
> 1st Question
> 
> I can measure 10 MHz frequency to an accuracy of about 2 
> parts in 10E-12 in 
> a one second gate time.
> 
> I use a SR620 time interval counter and make a timeAB measurement.
> 
> I make two measurements of phase (between my UUT and my 
> reference)  and then 
> calculate the frequency.
> 
> I have some nice software that controls the SR620 and does 
> all the math.
> 
> I'm sure most of you understand my measurement technique, 
> since it's as old 
> as the hills.
> 
> Does anyone have a good application note explain this 
> standard procedure? 
> I'm trying to explain it to a friend, and can't find a nice 
> application note 
> with some diagrams, formulas etc.  I know HP did one and 
> Standard did as 
> well, but can't find any quickly.
> 
> 2nd Question.
> 
> I really need to measure 10 MHz to an accuracy of 1 part in 
> 10E-13 / second 
> (ignoring the accuracy of my workshop standard).  I've tried 
> multiplying the 
> 10 MHz to the GHz frequencies, but never manage to improve on 
> the technique 
> I mention in my first question.
> 
> Any ideas for a relatively cheap way of doing this.  I 
> actually represent a 
> company that can measure to parts in 10E-15 in one second, 
> but their boxes 
> costs $50k.
> 
> Best Regards
> 
> Martyn
> 
> 
> 
> 
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