[time-nuts] Noob question on measuring Allan Deviation on 10 MHz source

George Dubovsky n4ua.va at gmail.com
Wed Dec 14 15:29:04 EST 2011


OK, I need to measure the stability of a 10 MHz sine-wave source. After
reading a lot of background info on this list and some of the sources that
were referenced, I thought I could get away with a frequency measurement. I
now think I was wrong.

What I have is an Agilent 53230A counter (a pretty capable box - claims 20
ps one-shot resolution in TI mode), a Trimble Thunderbolt, the 10 MHz
oscillator to be measured,  and a copy of Stable32. My first effort
involved feeding the Trimble 10 MHz into the counter as its Ext Reference.
I then fed the Trimble 1pps into the Ext Trigger input of the counter and
fed the sinewave 10 MHz signal to be measured into Ch 1 of the counter. I
then captured the frequency reading of the counter every second and stuffed
those numbers into a file. I collected about 20 hours of frequency
readings, but when I imported that into Stable32 and attempted to do an
Allan Dev plot, it didn't look very good - specifically, the sigma numbers
were in the region of 10e-2 to 10e-4.

So, I grabbed another Thunderbolt and attempted to do the same measurement
on it, figuring that everyone (but me) has taken data on a T'bolt, so I
could just look on tvb's site or some such to find proper data on a Tbolt.
Again, the plot didn't look like it should.

Am I going to have to go to time interval measurements to do what I want?
And does this mean I will have to square up my 10 MHz signal to have real


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