[time-nuts] Question about precise frequency / phase measurement

skywatcher skywatcher at web.de
Thu Apr 19 21:39:32 UTC 2012


Hi Bert

I want to monitor the frequency deviation continuously (that means: i 
don't want to look at a scope ;)
and log the data several times per second. The goal is not to make a 
'quality test' of the oscillator,
but to look for frequency deviations which are caused by external 
influences of various kind.

I have a digital 500 MS scope, so i can use this for circuit 
development, but i don't want to use it
for the actual measurements. Time measurements with microsecond accuracy 
can be done
with a microcontroller, that's not a problem.  BTW i'm using the 
Parallax 'Propeller' controller
which has 8 cores running at 80 MHz each, and can measure time intervals 
with 12.5 ns resolution.
It has also some very interesting timing circuitry, and can even 
generate VGA video signals with
user-defined timing without any external special components. May be of 
interest for one or the other
here on the list.  :)
For those who are interested:  
http://www.parallax.com/Portals/0/Downloads/docs/prod/prop/Propeller-P8X32A-Datasheet-v1.4.0.pdf

I think the DDMTD could be a good solution.  The question is, if 74HCxx 
parts would be good enough
to get < 1 mHz resolution for a 10 MHz frequency with an update rate of 
< 1 sec.
Can i use a 74HCT4046 PLL for the 'helper PLL' or is this one not good 
enough ?

Maybe i will do some tests next weekend to see what i can achieve with 
these 74HC parts, before
looking for better ones...

Regards,
   Wolfgang


Am 19.04.2012 23:14, schrieb EWKehren at aol.com:
> Wolfgang
> It would help if you would let us know what equipment other than a scope
> you have. Also what resolution you would want to achieve. One time set up  or
> want to use repeatedly.
> Bert Kehren
>
>




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