[sdiy] oscillator jitter / phase noise

[Czech Martin]

Well, cold or not cold, a quartz stabilised DCO
will certainly have less jitter and verly low long
term drift.

In the case of a single vco it should make no difference.
Even the old circuit sare not that bad, they were no
intended as random generators, after all.

I think that the difference will only be audible
if two or more oscillators beat against each other.

DCOs tend to have very regular beating patterns,
but free running vcos tend to have complex phasing
patterns due to their drift. This seems to be a good
deal of the beauty.

Perhaps this implies also the measuring method:

compare a quartz oscillator with some vco.
There are circuits to compare the phase difference,
i.e. they put out a low frequency signal.
As long as the acumulated phase difference is only 
less than a cycle, this will work. In practise
it will be off and running, but there are phase comparators
which can deal with that, too.
Perhaps a simple way to do the measurement.
Using one of those HP jitter analyser boxes is certainly more straight
forward, the problem is that people who have access to such
an expensive machine have perhaps no access to vintage gear.

Anyway, using a reference frequency in this way will
take away the high bandwidth problems which the
direct pulse with measurement certainly has (logging the data
for every cycle).

m.c.



> -----Original Message-----
> From: René Schmitz [mailto:uzs159 at uni-bonn.de]
> Sent: Freitag, 4. Juni 2004 20:29
> To: Magnus Danielson
> Cc: Czech Martin; synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] oscillator jitter / phase noise
> 
> 
> 
> Hej Magnus et al.,
> 
> > That would be to over-interprent what I was saying. What I 
> mean to say is that
> > it is much harder to retrieve the phase modulation waveform 
> when digitized.
> > It is still encoded in the sampled waveform, but in a form 
> which is harder to
> > retrieve than having the raw waveform into a dedicated instrument.
> 
> What about waveforms that are generated digitally? By what 
> you're saying 
> they would inherently have that difficulty. You would need to 
> find a way 
> to process them, since one of the implicit questions is "why are 
> digitally generated waveforms 'cold'".
> 
> > The phase modulation is distributed throughout the full 
> cycle, but a high
> > resolution measurement is not possible by simple means as 
> we can do when we
> > have intact through-zero slopes.
> 
> Exactly.
> 
> Cheers,
>   René
> 
> -- 
> uzs159 at uni-bonn.de
> http://www.uni-bonn.de/~uzs159
> 
> 
>