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

George Dubovsky n4ua.va at gmail.com
Thu Dec 15 09:02:49 EST 2011


John,

I believe the scaling factor was the key. Thanks.

I have v 1.58 of Stable32 and the scaling function now has its own button
and is not in the Open dialog. I'm sure I'm nowhere near out of the woods
yet, so I'm gonna keep your e-mail addy on speed dial ;-)


geo

On Wed, Dec 14, 2011 at 4:19 PM, John Ackermann N8UR <jra at febo.com> wrote:

> 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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