[GPS_Standard] GPSstd_PLL - what's next

[Bob Stewart]

Hi Jacques,

Here are a couple of plots regarding asymmetry on the 1PPS from the Adafruit.  On the first plot, notice the banding on the green 1PPS line on the left, and then the far right where two oscillators have obviously come into phase for a short while, leaving the 1PPS biased downward.

http://www.evoria.net/AE6RV/GPSstd_PLL/Plots/PPS%20Anomaly.png

This one is taken with a short timeframe.  Notice the problems from about 10:30 to 10:45 or so.  These two plots pretty much show why it is so hard to keep Bert's board in lock with frequency, much less phase.  And yet, the Adafruit is much more suitable for Bert's board than many others because of the narrow (10ns) phase jitter on the 1PPS.  I just wish it were always evenly distributed.  That would be perfect.

http://www.evoria.net/AE6RV/GPSstd_PLL/Plots/PPS%20Anomaly%202.png


Bob




>________________________________
> From: jacques audet <jaudet at hotmail.com>
>To: Bob Stewart <bob at evoria.net>; GPS Standard <gps_standard at mailman.qth.net> 
>Sent: Wednesday, December 11, 2013 9:57 AM
>Subject: RE: [GPS_Standard] GPSstd_PLL - what's next
> 
>
>
> 
>Hi Bob,
>I can only admire your determination for improving Bert's GPS standard using a PLL technique.
>You might be interested to look at the document, on my website:  ve2azx.net
>Modifications and Analysis of VE2ZAZ Frequency  Standard
>
>Unzip the file and look at the VCXO analysis file.
>My measurements show that the phase noise caused by PWM dithering is not an issue.
>Look at the last page, where I have measured the 1 pps output of my Trimble Ace-II GPS
>over 40 000 readings spaced 2 seconds apart and with 1 nSec resolution. 
>This experiment ran for almost a full day.
>It shows the distribution of the readings vs timing error.
>No reading ever occurred dead on with zero error !
>The distribution is completely asymetrical.
>I can only conclude that a lot of averaging on the 1 pps is required.
>Food for thinking !
>
>regards
>Jacques Audet
VE2AZX
>
>