[time-nuts] Z3801 lockin behaviour

Magnus Danielson cfmd at bredband.net
Mon Jul 24 06:13:39 EDT 2006


From: shoppa at trailing-edge.com (Tim Shoppa)
Subject: Re: [time-nuts] Z3801 lockin behaviour
Date: Sun, 23 Jul 2006 21:37:52 -0400
Message-ID: <20060724013752.6D199848056 at mini-me.trailing-edge.com>

> Magnus Danielson <cfmd at bredband.net> wrote:
> > > If it doesn't lock after a few hours, I'd suggest a full
> > > reset. Also check your signal levels, and elevation
> > > mask. Did it get your lat/lon/alt correct?
> >
> > Seems alright. Get SS values which seems good, occassionally above 200 but
> > rarely below 100. Usually track 5-6 satelites but if it had been a 12 channel
> > receiver I would have had 12 satellites tracked over the 10 degree elevation
> > mask.
> 
> Your GPS part seems to be working fine.
> 
> Have you logged the EFC values before/during/after unlock? Some Z3801A's
> have OCXO's that are remarkably steady with nice smooth EFC curves and
> hardly ever a jump, others jump around by hundreds or thousands of EFC
> units a few times a year, and others jump around by hundreds or thousands
> of EFC units multiple times a day (going out of lock at each jump.)

I haven't really made any real logs. I have checked the EFC values and it does
move around.

> During an EFC jump the TI can go to very large values for short periods
> of time.

Mine goes into holdover on a regular basis. During holdover it reaches 1.5 us.
After holdover it tracks in and has TI around 0 (+/- 6-7 ns) but then it starts
to drift out. It does that with a wobbely walk. It really looks like there is
too much noise going on so it won't maintain steady lock.

I'm pondering if it may not be something wrong with the running state of the
SmartClock stuff. Maybe reset that so it has to relearn. I had the same problem
as I am having now last time I had it powered, and then it didn't sort itself
out either.  It could also be a bad OCXO. It might be that it needs time to
heal itself. I didn't have this problem initially thought.

Hmm...

I need to setup some real logging. SatStat isn't making me that happy even if
it gives a good overview when sitting there.

Cheers,
Magnus



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