[time-nuts] Ublox neo-7M GPS

Tom Van Baak (lab) tvb at leapsecond.com
Tue Aug 19 16:01:49 EDT 2014


Hal, as long as you maintain long-term phase lock it's a disciplined oscillator. So, yes, a carrier tracking WWVB receiver with sufficiently stable flywheel LO is a WWVBDO.

Said, too-short or too-long 100 ns cycles is one thing. Still ok for many applications. But tell me more about extra or missing pulses in the ublox-7. That sounds like a show stopper to me.

/tvb (i5s)

> On Aug 19, 2014, at 2:05 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
> 
> 
> SAIDJACK at aol.com said:
>> its not a GPSDO though, not even a simple one :)
>>  It does not discipline an oscillator. It generates the output by
>> mathematically calculating how many phases it has to add/drop in a second,
>> then   digitally adds/drops/extends/retards the phase of the output clock to
>> achieve an average of number of desired clock cycles.
> 
> Is there something about the term GPSDO that says I have to do the "D" in the 
> analog domain rather than the digital domain?
> 
> I agree that current technology doesn't give results that are useful for many 
> applications that currently use GPSDOs.  What if the clock ran at a GHz?  10 
> GHz?  Sure, it would have spurs, but would it be useful for some applications?
> 
> Is a GPSDO still a GPSDO if the D/A driving the VCXO only has a few bits?  
> How many bits does it need to be a real GPSDO?
> 
> Is a battery powered wall clock listening to WWVB at 2 AM a WWVDO?  It's got 
> a pretty good ADEV if you go out far enough.
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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