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

[Chris Albertson]

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