[time-nuts] GPS W/10KHz

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Feb 10 17:41:03 EST 2014


Dennis Ferguson wrote:
> On 10 Feb, 2014, at 00:48 , Bruce Griffiths<bruce.griffiths at xtra.co.nz>  wrote:
>    
>> Instead of speculating try reading the specifications.
>> 1Hz phase modulation of the 10kHz output is present.
>> The receiver sawtooth error sample rate is 1Hz not 10kHz.
>> The 10kHz output signal phase is adjusted at a 1Hz rate by the receiver.
>>      
> Ah, as soon as I pressed send for the last note I realized what
> you were likely telling me.
>
> Yes, the LEA-6T only provides you with a quantization (sawtooth)
> correction for 1 pps and no higher rate.  At 1 pps you should
> pay attention to the digital correction (implying no analog-only
> implementation is possible; you minimally need the delay line
> thing) since the frequency of the saw tooth is often low enough
> to leak into the control response and the correction should make
> the sawtooth go away.
>
> All I was pointing out is that at a higher output frequency, like
> 10 kpps, the frequency of the quantization saw tooth error will
> almost always be much higher as well.  There's no need for the digital
> correction since averaging over a relatively short period, like in
> the loop filter of an appropriate analog PLL, will almost always be
> sufficient to smooth the sawtooth.
>
> Dennis Ferguson
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>    
The internal PLL will smooth out the quantisation error somewhat.
However the phase of the higher frequency outputs isnt adjusted on every 
edge by resampling the phase error wrt the GPS signal.

More detail on the internal PLL would be useful.
About all one can glean from the datasheet is that it has a bandwidth of 
somewhat less than 1Hz.

Bruce



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