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

Chris Albertson albertson.chris at gmail.com
Sat Feb 11 00:35:26 UTC 2012

On Fri, Feb 10, 2012 at 3:52 PM, Bob Camp <lists at rtty.us> wrote:
> Hi
> I think you will need some sort of analog detector to get what you are looking for.

I don't think it needs to be analog.   For example you can xor the two
10MHz signals and then sample the digital xor output then deduce its
duty cycle by counting how many samples are 1 and how many are 0.
You'd expect an equal number if there is a phase lock.   Might be best
to sample a-periodically at random.

Many designs put a low pass filter on the XOR but I think random
polling allows the software to adjust the time constant and is cheaper
to implement.  I think you'd have the latch the xor in a flipflop as
it would move to fast for a uP to read.

Chris Albertson
Redondo Beach, California

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