[time-nuts] Ublox neo-7M GPS

Tony tnuts at toneh.demon.co.uk
Thu Aug 21 01:56:21 UTC 2014


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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