[time-nuts] Lucent KS-24361/Z3812A GPSDO initial setup

Bob Stewart bob at evoria.net
Sat Oct 25 11:24:50 EDT 2014

Hi Bob,
During the first hour it reported poor geometry a number of times.  Then it seemed to get its act together and was solidly into survey mode.  A few hours later and it was satisfied with life and went into hold mode, with TFOM=3, FFOM=0.
This morning, I see that there is some phase tracking difference of opinion between my GPSDO and this one WRT the 10MHz signal out from REF-0.

The green is the phase difference plot, and the red is the ADEV.  Given this is the first time I have done this against another GPSDO, I don't know whether this is good or bad.  Looking at the phase plot on my unit, it wanders around a bit but not 100ns.
Sorry the plot is so busy with debug traces.  You can easily spot the same phase difference line as in the one above.  The blue squiggle is my phase error.  The red is my DAC.  The phase in this plot is in hundreds of ps.  I have shut the unit down numerous times recently, and the OXCO has been subjected to different thermal environments.  Right now the case is closed, there are no vent holes, and the temperature in the box on my PCB is just a bit over 99 degrees F.


      From: Bob Camp <kb8tq at n1k.org>
 To: Bob Stewart <bob at evoria.net>; Discussion of precise time and frequency measurement <time-nuts at febo.com> 
 Sent: Saturday, October 25, 2014 7:09 AM
 Subject: Re: [time-nuts] Lucent KS-24361/Z3812A GPSDO initial setup

One of the interesting things about these little receiver modules is that they don’t all report the same survey location. There are NIST papers with examples. You could probably spend a lot of time on the “why”. 

If you are getting “poor geometry” errors, either you have an antenna issue, or your receiver is in trouble some other way. It should go into survey mode and stick there. It should be solidly into the survey after about 10 minutes power on. 


> On Oct 24, 2014, at 9:46 PM, Bob Stewart <bob at evoria.net> wrote:
> Sorry if these comments are a bit naive, but this is my first exposure to a Z38xx.
> I've got mine powered on and connected to the antenna.  After referring to Stewart's original post (once again) I've managed to download HP's SATSTAT and get it running.  When I connected to the REF-1 unit (with the receiver) all I get is comms errors.  But when I connect to REF-0, Satstat seems quite happy.  It's reporting the unit as a Z3812A.  Is REF-0 the only one you can connect to, or is REF-1 mute till it's happy with the GPS receiver?
> The mode says "Power-Up: GPS Acquisition", so I guess that's OK.  I think things are progressing.  It's attempting to survey, but reporting "Suspended: poor geometry".  I suppose with a little more time this will work itself out?  It seems to be slowly tracking more sats, as it's now up to 5.
> I wonder if there's a way to shortcut the survey process using Satstat?  I've got a 48 hour survey done on this antenna with the LEA-6T, so I should be able to input those figures, right?  I'll see if I can find anything in a Satstat manual I found.
> Bob - AE6RV
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