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[time-freq] RefLock II behavior

Steven Bible n7hpr at tapr.org
Wed Jun 21 14:53:48 UTC 2006


Mike,

Luis brings up a good point about the GPS lock.  Is the GPS you are using a
timing quality GPS?  Have you done a self survey and lock its position?

I am using a M12 Timing unit that is self survey and locked.  I don't have
the best antenna up, and every once in a while I don't get good satellite
coverage.  Then I can see the frequency wonder slightly.

If someone uses a location GPS and just lets the 1PPS be where it will be, I
am sure you will see excursions.


73,

- Steve, N7HPR
 (n7hpr at tapr.org)




> -----Original Message-----
> From: time-freq-bounces at lists.tapr.org
> [mailto:time-freq-bounces at lists.tapr.org]On Behalf Of Luis Cupido
> Sent: Wednesday, June 21, 2006 2:00 AM
> To: TAPR time and frequency projects
> Subject: Re: [time-freq] RefLock II behavior
>
>
> Hi John,
> Hi Michael,
>
> John, I don't know what is the range of Michael's VCXO span,
> assuming it to be something like 50Hz or similar, and considering a dac
> size of 11bits that makes the quantization step to be 0.024 Hz
> so 1 Hz change should have a completely different origin.
>
> Also the loop filter should take care of that dithering by integrating
> many seconds, we can make the calculations to see how long we should
> integrate for example to get a resolution of 1/10 the dac size...
>
> Or the VCXO range is extremely large for the application (like 1KHz or
> so...)
> Or I would suspect of the 1pps quality, some GPS engines have quite bad
> pps jitter and this looks like changes when switching satellites
> or reduced
> satellite visibility (calculating with just 3 satellites for a
> short period
> , for example)
> and a non optimum GPS engine software.
>
> Just my impression... not enough info to make a more in deep judgment :(
>
> Luis Cupido.
> CT1DMK
>
> ----- Original Message -----
> From: "John Ackermann N8UR" <jra at febo.com>
> To: "TAPR time and frequency projects" <time-freq at lists.tapr.org>
> Sent: Wednesday, June 21, 2006 1:25 AM
> Subject: Re: [time-freq] RefLock II behavior
>
>
> > This looks similar to, but is orders of magnitude larger than,
> what I saw
> > when using the Reflock II to control a 10MHz TCXO from GPS.
> >
> > We concluded what was happening there was that the Reflock D/A was
> > dithering between two discrete steps, causing the noisy state
> for a while,
> > then the loop would move for a while to a stable state where
> the voltage
> > wasn't dithering, then it would drift off again.  Not sure if you're
> > seeing a magnified version of the same thing.
> >
> > John
> > ----
> >
> > Owen, Michael wrote:
> >> Dear friends,
> >>
> >> Thanks to Steve Bible, I got my brain un-stuck and figured out how to
> >> set the 0-ohm jumpers (I'll summarize everything in a couple of days
> >> when it's all finished and my shame has faded).
> >>
> >> For right now, I have a question.  RefLock plus my pretty good OCXO are
> >> trying to settle at 100 MHz but there are sharp spikes every few
> >> minutes.  Here's an image:
> >>
> >>  The time span is about 40 minutes.  Even after 3+ hours, the
> spikes are
> >> still there (although more rarely).  Does anyone have an idea
> how to get
> >> rid of them?
> >>
> >> 73, W9IP
> >>
> >> ------
> >> Michael R. Owen, Ph.D.
> >> Senior System Engineer
> >> Sensis Corporation
> >> (315)
> >> 634-3066
> ------------------------------------------------------------------------
> >>
> >> _______________________________________________
> >> time-freq mailing list
> >> time-freq at lists.tapr.org
> >> https://lists.tapr.org/cgi-bin/mailman/listinfo/time-freq
> >
> >
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