[time-nuts] Re: Types of noise (was: Phase Station 53100A Questions)

[Magnus Danielson]

Dear Joe,

On 2022-02-13 23:31, Joseph Gwinn wrote:
> On Sun, 13 Feb 2022 03:30:30 -0500, time-nuts-request at lists.febo.com
> wrote:
> time-nuts Digest, Vol 214, Issue 15
>
> Attila,
>
>> Date: Sat, 12 Feb 2022 20:38:48 +0100
>> From: Attila Kinali <attila at kinali.ch>
>> Subject: [time-nuts] Types of noise (was: Phase Station 53100A
>> 	Questions)
>> To: Discussion of precise time and frequency measurement
>> 	<time-nuts at lists.febo.com>
>> Message-ID: <20220212203848.72783256d221001199dfd9cc at kinali.ch>
>>
>> On Fri, 11 Feb 2022 18:25:05 -0500
>> Joseph Gwinn <joegwinn at comcast.net> wrote:
>>
>>> May not realize that thermal noise (additive) and phase
>>> noise (multiplicative) are not the same, and do not behave the same.
>> It seems like you are mixing up here quite a few different concepts:
>> Phase noise vs amplitude noise, additive vs multiplicative noise,
>> thermal vs other noise sources, white noise vs 1/f^a-noise.
> You are right of course.  I was using shorthand.
>
> A better word than multiplicative is parametric, the varying
> parameters being path loss and path group delay.  This is as seen at
> the phase noise test set.
>
>
>> All these are orthogonal to each other and you can pick and match them.
>> I.e. Phase noise can be additive, 1/f^2-noise and thermal.
> At the generator, certainly.  But the downstream PN test set may not
> be able to tell.  More later.
>
>
>> Amplitude and phase noise are looking at noise from two different
>> perspective. One is how large the variation of the peak of a sine
>> wave is, the other is how much the zero crossing varies in time.
>> Note that all natural noise sources will be both amplitude and
>> phase noise.
> Hmm.  One case I'm interested in is where the path attenuation varies
> according to a random telegraph waveform, due to for instance a loose
> connector or cracked center conductor rattling under heavy
> vibration.  In this, the electrical length does not change.  While
> the source of the carrier whose PN is being measured will have some
> mixture of AM and PM characteristic of that source, the residual
> (added) PN will be characteristic of the transit damage encountered
> between source and PN test set.  So wouldn't this randomly varying
> attenuation yield mostly residual AM PN and little residual PM PN?

Actually, measure vibration inpact like this have a long tradition and 
is indeed possible.

It may or may not be an effective method thought. As suggested by 
others, TDR may very well be more effective method to locate impedance 
errors. Could be that they add good information for different errors.

Also, recall that errorenous connectors can create passive 
intermodulation distorsion (PIM), which is readilly measured using the 
two-tone method.

I would use a wealth of methods to attempt different techniques and see 
what they excell at and not.

I would not assume the random telegraph waveform variation. I would 
rather learn from reality the types of variations you see.

I think you should consider two different phases, detection of problem 
and location of problem. When it comes to location finding, TDR excell 
at that. AM measurements as well as PIM is relevant for detection of 
problem as well as verification.

I would recommend you to look at the updated IEEE Std 1193 when it comes 
out. There is improved examples and references in it that may be of 
interest to you.

It may be beenficial to stick accelerometers here and there to pick up 
the vibrations, so it can be correlated to the measured noise, at it 
could help to locate the source of the noise and thus help with locating 
where, more or less which engine that was causing it.

Cheers,
Magnus