[GPS_Standard] Self Test experiment with strange result

[Bert, VE2ZAZ]

Dimitri,

Use the raw count hexadecimal 68xx. This is the counter reading for each 16 second window.

Cheers,

Bert, VE2ZAZ

> Date: Wed, 4 Nov 2015 11:45:06 -0800
> To: ve2zaz at sympatico.ca; gps_standard at mailman.qth.net
> From: dimitri at dotp.com
> Subject: RE: [GPS_Standard] Self Test  experiment with strange result
> 
> 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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