[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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