[time-nuts] Simple solution for disciplining OCXO with 1 PPS

Bob Camp kb8tq at n1k.org
Sun May 22 21:35:45 EDT 2016


Hi

No, there is no purely analog way to access the sawtooth information. If you restrict yourself 
to “pure analog” then the PPS will be bopping around by +/- 10 to +/-20 ns each second. Put
another way, you start out with 1 to 2x10^-8 at 1 second. The same thing is true at 10 KHz or
at any other output frequency. 

To get down to the vicinity of 1x10^-10 with any sort of rational ADEV, you are going to need 
the equivalent of a very long time constant analog filter. It also needs to have *very* good 
DC characteristics and low noise. The simple answer is to use a *lot* of C and not much R
in the beast. That gets you into a boatload of high quality film capacitors. 

There is no getting around having a narrow / long time constant filter if you want a useful 
signal out of the OCXO...

Bob

> On May 22, 2016, at 8:24 PM, Chris Albertson <albertson.chris at gmail.com> wrote:
> 
> On Sun, May 22, 2016 at 3:52 PM, Attila Kinali <attila at kinali.ch> wrote:
> 
>> Judging from the ADEV plots of the M12 receiver from TvB[1], which hit
>> 10^-10 (w/ sawtooth) around 200s, I'd say that 10^-10 @1000s should be
>> easy.
> 
> Can a pure analog design access the sawtooth correction?  My GPS
> receivers send sawtooth as a digital message on a serial port.   I
> don't know if saw tooth correction is required to meet his spec.
> 
> I think what he needs if he wants to go 100% analog is a GPS receiver
> that outputs pulses at 10Hz not 1Hz.  But to program the pulse rate
> he'd need to send data to the serial control port.
> 
> -- 
> 
> Chris Albertson
> Redondo Beach, California
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