Hi George --
You can feed frequency data into Stable32, but the documentation doesn't
clearly explain that you need to scale the readings into fractional
frequency using the scaling function in the File/Open dialog. To get
fractional frequency, you divide the results by the nominal frequency,
except that the scaling model in the Stable32 input box allows
multiplication only.
So, for a nominal 10 MHz (or 1e7 Hz) source where the data is in Hz
format (10,000,000.xxx Hz), you would multiply by 1e-7.
But if your counter outputs in MHz format, (10.xxx MHz), that's already
effectively scaled by 1e-6. So you end up using 1e-1 as the multiplier.
I have lost much hair trying to keep this straight; as wonderful as
Stable32 is, the documentation is aimed at people who already know what
they are doing. :-)
73,
John
----
On 12/14/2011 3:29 PM, George Dubovsky wrote:
List;
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
edges?
geo
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