[time-nuts] GPS lock of the FE5680. Current experiment and question

[Bob Camp]

Hi

Another way to build an analog phase detector...

Next layer on the onion is how to get the sawtooth correction out of the GPS and into your loop.

Bob



On Feb 11, 2012, at 12:05 AM, Chris Albertson <albertson.chris at gmail.com> wrote:

> All these different suggestions build down to one thing, the precision
> with which you measure the phase when you sample it each second.  The
> single flip flop will tell you which half cycle. a simple two bit
> counter made with two '74 FFs tells you which half cycle and with
> direction.
> 
> The "best" maybe  is if you let the PPS set a FF and the 10MHz reset
> it.  The FF's output gates a constant current to a capacitor and
> charges it to some voltage.  Then you measure that with a 10-bit ADC.
>  This measures the phase to maybe 1%, gives you direction and is
> pretty cheap to build
> 
> Let's see if I have the numbers right?  If you check a 10MHz signal
> once per second with just the FF then you have 1E-7.  You would need
> 1000 seconds for 1E-10.   But if you measure phase to 1/10th of a
> cycle you get to 1E-10   ten faster.  Right?
> 
> 
> Chris Albertson
> Redondo Beach, California
> 
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