[GPS_Standard] Self Test experiment with strange result

[Dimitri.p]

Calculating the Average offset manually sounds like a good idea.
I was hoping to do that from the logged serial data,
I started logging the serial data, and my eye cought the two lines i 
pasted below:

D|U|0201E|.|.|6805|000C|0000|0CA8|00
D|U|0201E|.|.|6800|000D|0000|0CA9|00

The sample frequency is 6805 and 6800
but the respective Frequency difference reported is 0000

Now as far as average offsets go, I'm pretty sure I don't know which 
values to use to calculate the  average offset.












At 07:28 AM 11/4/2015, Bert, VE2ZAZ wrote:
>Hi Dimitri.
>
>My first thoughts are that this might be caused be the way the 
>built-in 16-bit counter works. It is plausible that the counter 
>could mis-behave when everything is absolutely synchronous. This is 
>a condition that should not occur in real life, and averaging will 
>do the work to clean this up...
>
>You should try something else. Turn off the FLL. Do manual computing 
>of the average offset and see whether it correlates with the 
>described behavior. This will isolate it to the counter behavior.
>
>Cheers,
>
>Bert, VE2ZAZ
>
>
> > Date: Wed, 4 Nov 2015 00:22:17 -0800
> > To: gps_standard at mailman.qth.net
> > From: dimitri at dotp.com
> > Subject: Re: [GPS_Standard] Self Test experiment with strange result
> >
> > I took the 10 Mhz output from the board, run it through a divider
> > chain (74HC390s) to end up with 1Hz and used that to feed the 1PPS input .
> >
> > Montrol reports
> > Avg frequency offset -3.29e-10
> > Std Dev 1.46e-08
> > Min -3.12e-08
> > Max 2.50e-08
> >
> > These values are in the same neighborhood of what I get using the
> > 1PPS from the GPS.
> >
> > On frequency counters when you measure the counter's own timebase you
> > end up with 10 and as many zeroes as can fit on the display.
> >
> > I was expecting values in the e-12 (or better) neighborhood.
> >
> > The idea that there is a frequency "offset" when the 1PPS is derived
> > from the same 10MHz being measured doesn't make much sense at the moment.
> >
> > Can anyone shed any light on this ?
> >
> >
> > Dimitri
> >
> >
> > Dimitri
> >
> >
> >
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