Accurate frequency measurement using PXI 5142 Digitizer

[Helal]

I am Using PXI 5142 Digitizer to read the frequency of a 10 MHz atomic clock up to 8 decimal places. I am using single tone measurement block. But I can't get that accurate fix on the frequency because of the jitter.

Can someone help.

Thanks in Advance.

[BRennhofer]

Hi Helal,

How big is your jitter.
Up to 80 pseconds is ok.

Can you explain exactly how you connect your device and attached a screenshot from your VI?


best regards
Bernhard

[Helal]

Thanks For your reply; The device is connected to the digitizer through BNC connector.

Digitzer Scope Settings:  

Samples/seconds --> 2G S/s

Record Length      --> 800

Aqiusition mode   ---> N Samples              

Best Regards,

Helal

[johnsold]

Helal,

According to the PXI-5142 Specifications the timebase accuracy is +/-25 ppm.  That is between 4 and 5 significant digits of accuracy.  If you are phase referenced to an external clock, then the accuracy is determined by the external clock.

The timebase jitter of 2 ps represents 20 ppm at 10 MHz.

The "jitter" you are seeing may be due to non-synchronous sampling.  Getting good frequency measurements without synchrounous sampling can be quite challenging.

Your measurements appear to be within specifications for the Digitzer.

The normal procedure is to use an instrument which is much better (4 to 10 times) than the signal you are trying to measure. Your digitizer is likely several orders of magnitude LESS accurate than your atomic clock.  Why do you feel the need to make this measurement this way?

Lynn

[Helal]

Frankly, i am synchronizing another atomic clock to this one so it need to be precise

[johnsold]

Helal,

If you use one of the atomic clocks as a phase reference for the digitizer, you should be able to get a relative frequency with the accuracy limited by the accuracy of the reference clock and any sample jitter.

The random portion of the jitter can be reduced by averaging multiple measurements.

Lynn