[time-nuts] Ublox neo-7M GPS

[SAIDJACK at aol.com]

Hi Tony,
 
that's consistent with what I remember. Do you have the capability to count 
 the number of 10MHz pulses per second to see if it is phase-coherent with 
the  UTC 1PPS pulse?
 
I am thinking that the software may be using statistics to approximate 10  
million cycles per second, which would mean they may or may not be exactly 
10  million cycles..

thanks,
Said
 
 
In a message dated 8/20/2014 11:07:59 Pacific Daylight Time,  
tnuts at toneh.demon.co.uk writes:

On  19/08/2014 16:11, Ed Palmer wrote:
> Does anyone have a neo-7M and an HP  5371A or a 5372A Analyzer?  Use 
> the Histogram Time Interval  function to measure a block of samples. 
> That will show the length of  the samples with a resolution of 200 ps.  
> That's what I did a  couple of years ago when I analyzed the Navsync 
> CW-12 with the old  and new firmware.

FWIW, I just had a look at the timepulse on a NEO-7M.  I configured it to 
10MHz, 50:50 duty cycle when locked, disabled when out  of lock. I don't 
have any of those Analyzers so I used an HP 54615B  digital scope. The 
period of the majority of cycles was 104ns with  'random' cycles being 
84ns. I did not observe any other cycle periods. I  don't know how 
accurate the time measurements are on the scope, but it  looks like the 
timing is derived from an approx 48MHz clock, and the  timing 
phase/frequency adjusted by periodically deleting 48MHz clock  cycles.

Although I said random, I couldn't make any observations as to  the 
statistics of the short and long cycles or their distribution - I  guess 
I'll have to write some software for my STM32F4 discovery board for  that.

If I get time, I'll do the same with a Reyax RYN25AI receiver  which has 
a UBLOX MAX-7C  module.

Tony
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