[time-nuts] Simulating Oscillator Noise: Difficulties SimulatingFlicker FM Noise

[Kyle Wesson]

Wow. Thanks Magnus, Tom, and Bob for all of the information you
provided to me about oscillator simulations and particular noise
types. I'm going to read and digest it and see if I can get some
better results. I'm also going to purchase stable32 since it seems to
be the gold standard for precise timing work and then compare it to
the output of my scripts.

Thanks again!
Kyle

On Fri, Apr 23, 2010 at 1:16 AM, Magnus Danielson
<magnus at rubidium.dyndns.org> wrote:
> Hi Bob,
>
> On 04/23/2010 04:10 AM, Bob Camp wrote:
>>
>> Hi
>>
>> Back in the late 70's HP was pushing their ADEV test setup to us. They
>> hauled one in (yes indeed
>> more than one box) for a demo. It took them most of the morning to get it
>> in from the parking lot
>> and set up / warmed up / running.
>
> To much amusement I am sure.
>
>> They ran us through a little presentation on how ADEV has two slopes (I
>> *wish* I'd kept a copy...).
>> We brought out some sample oscillators, and ran them through. *Surprise*
>> more than two slopes.
>> I then asked them "what do the other slopes mean?". No answer .... we'll
>> get back to you ....
>> mumble mumble .... They never did get back to me.
>
> Depending on the oscillator you expect to see white, 1/f and 1/f^3 phase
> modulation noise or white, 1/f^2 and 1/f^3 phase modulation noise. Looking
> at tabulated Allan variance:
>
> http://en.wikipedia.org/wiki/Allan_variance#Power-law_noise
> (see also Tom's PDF)
>
> We see that white and 1/f is weakly different such that they can be expected
> easilly be mistaken for having the same slope. The 1/f^3 noise has a flat
> Allan variance response. So, their oscillator during testing may simply have
> been of one kind and the oscillator you brought out of the other.
>
> The Allan variance unability to separeate the white and 1/f noise triggered
> the development of the modified Allan variance, but that only happend after
> that incident.
>
>> Needless to say they would have been a lot more likely to make the sale if
>> they had one of your
>> one page charts.
>
> A copy of Leesons paper (a two-page thing) in 1966 would have helped a lot.
>
> Cheers,
> Magnus
>
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