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

Magnus Danielson magnus at rubidium.dyndns.org
Fri Apr 23 06:16:21 UTC 2010

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:

(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.


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