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

EWKehren at aol.com EWKehren at aol.com
Thu Apr 19 22:18:24 UTC 2012


Wolfgang
I have quite a collection of equipment and have build Dual Mixer, PICTIC  
and what I think is best for you a circuit I call the Austron circuit. For 
less  than $ 50 you can have a standalone system that gives you a RS 232 
output with 1  E 12 resolution in 1 second, the PIC has 0.1, 1, 10 and 100 second 
gate  time. At 100 seconds you get 1 E 14. The circuit does use a two stage 
Xtal  filter which is the most difficult part of the circuit. How ever a 
DDS could be  used, but the DDS does not give you 1.000100 MHz with 14 digit 
accuracy so post  processing would be needed. If you have uProcessor 
expertise that would be  perfect way to eliminate the filter part, making it even 
lower cost and much  simpler. 
Never did a DDMTD so I do not know how it compares. If you are interested  
contact me off list and I send you all information.
Bert Kehren
 
 
In a message dated 4/19/2012 5:41:08 P.M. Eastern Daylight Time,  
skywatcher at web.de writes:

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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