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[time-freq] Re: Febo.com's Z3801A Performance

Gregg Levine gregg.drwho8 at gmail.com
Sat Jun 30 02:40:21 UTC 2007


On 6/29/07, John Ackermann N8UR <jra at febo.com> wrote:
> Hi Keith --
>
> I've been wondering about these spikes myself.  My gut feeling is that
> they are probably the result of network or other queueing delays (what
> we're looking at is the offset of the Z3801A system as seen by another
> box across a 100mbit ethernet).  But why the system with the Z3801A is
> consistently the noisiest of the three, while the one using LORAN-C is
> the quietest, I'm not sure.  One possibility is that the LORAN-C system
> is getting only a PPS signal and doesn't have a serial timecode coming
> it; it's possible that somehow the jitter on the serial time marker
> could be influencing the results.  But I'm really only guessing...
>
> John
> ----
> K&J Aggett said the following on 06/29/2007 07:25 PM:
> > Hi John,
> >
> > I am curious about the regular, large jumps in offset shown in the
> > Current Day graph.  These jumps are much larger than others that are
> > present, suggesting that the minimum correction possible is of the order
> > of 5 microseconds or so.  Now, assuming that the Z801A is performing
> > well, we have a cosseted, high quality xtal oscillator which, apart from
> > the relatively rare jump, should just drift gently along, requiring the
> > occasional intervention of the controller to keep it on
> > frequency/phase.  A further observation is that positive jumps are
> > frequently followed by smaller negative jumps.  Over-correction
> > somewhere perhaps?
> >
> > Is there any indication as to what these jumps mean?  Are they
> > representative of actual changes in the Z3801A output or are they
> > introduced elsewhere else in the system?  I have been wondering about
> > strange spikes on some of my monitoring, too, but as yet lack sufficient
> > data to do more than wonder.
> >
> >
> > Keith Aggett
> >
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Hello!
John can you, ah, point out as to which unit the Z3801A system is?
Consider this folks, LORAN C is a form of radio, it was originally
created for the maritime trade for such issues as distance tracking of
ships and points on land. .

Isn't it possible that the LORAN C reception is being effected by
Jansky noise? What we consider to be static on those areas of the
radio spectrum that are not allocated could be that form of noise. It
could also be all sorts of everything else. However I shall leave out
the areas of reference that are straight out of science fiction for
this area of discussion.


Side trip back towards my first post and your responses, (because I
first saw what you replied to on this, John, as part of a digest with
them.): I have since found the PPS Kit for Linux on the kernel.org
site. I've built a kernel with the stuff applied. The next step is to
setup my hardware for those tests, and then work out how to generate
my graphs. John what methods did you use for that purpose?
-- 
Gregg C Levine gregg.drwho8 at gmail.com
"This signature was once found posting rude
messages in English in the Moscow subway."




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