[time-nuts] TIC resolution impact on GPSDO's performance

[Magnus Danielson]

From: Dr Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Subject: Re: [time-nuts] TIC resolution impact on GPSDO's performance
Date: Tue, 26 Dec 2006 23:35:28 +1300
Message-ID: <4590FAF0.2070001 at xtra.co.nz>

> Poul-Henning Kamp wrote:
> > In message <4590BB56.5070809 at xtra.co.nz>, Dr Bruce Griffiths writes:
> >   
> >> Poul-Henning Kamp wrote:
> >>
> >>     
> >>> I think what you are trying to express is that the frequency from
> >>> the internal Xtal (at times) is in an overtone of the 1Hz PPS, which
> >>> gives rise to hanging bridges.
> >>>
> >>>   
> >>>       
> >> Poul-Henning
> >>
> >> Surely you mean harmonic? An overtone is not necessarily a harmonic.
> >>     
> >
> > I meant overtone, becuase they are not in any harmonic relationship,
> > the XO is wandering around whereas the (ideal) PPS is, supposedly,
> > rock stable.
> >
> >   
> Poul-Henning
> 
> Perhaps you should explain what you mean by overtone as it is at odds 
> with both my understanding of the term as a vibrational mode of an 
> object (as in acoustics) higher than the fundamental or lowest frequency 
> vibrational mode and the definition given in Webster's dictionary (My 
> Oxford dictionary is buried somewhere) which insists that overtone is 
> synonomous with harmonic.
> 
> My understanding is that the phrase "an overtone of a 1Hz" has no real 
> meaning.

coherent
4) said esp of electromagnetic waves: having a definite relationship to each
   other: coherent light

harmonic(2)
1a) a tone in a harmonic series
2) in physics, a component frequency of a harmonic motion that is an integral
   multiple of the fundamental frequency

overtone
1b) Harmonic(2)

These expressions does not express well what is happening with the XO in
relation to the UTC(GPS)/UTC(USNO) or if you so like PPS_GPS. Only coherent
refers to the case of two signals where as harmonic and overtone (really just
refering to the same meaning) is refering to properties within one signal
mainly (you need special wordings such as "lock <foo> to a harmonic of <bar>",
but then again harmonic only refers to a property of <bar> where as lock is the
word tying <foo> to <bar>).

synchronous
1) happening, existing or arising at precisely the same time
2a) going on or operating together at exactly the same rate
 b) recurring together
3) involving or indicating synchronism
4) in physics, having the same period or having the same period and phase

asynchronous
not synchronous, proceeding at its own pace; esp relating to or denoting a
computing operation which does not wait for a communication to complete before
processing.

These give indication on the behaviour between two (or more) signals. I beleive
that it is best to point out that the XO is asynchronous to PPS_GPS. However,
both XO and PPS_GPS is isochronous:

isochronous (via isochronal)
1) having equal duration
2) recurring at regular intervals

This relates to a property of a single signal again. We consider all clocks of
being essentially isochronous except for the perturbations that we as time-nuts
spends endless discussions over how to measure and improve.

The "asynchronous" serial line is actually anisochronous BTW.

The above wordings comes out of my "The New Penguin English Dictionary" but
where applicable coincide with the ITU-T Rec. G.700. Let's use these terms
which have been found usefull by our colleages in the past.

Cheers,
Magnus