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

[Bob Camp]

Hi

If your GPS puts out 1 pps, you get one sample per second out of your phase detector. If it's digital you get a one or a zero. Dead time between edges is 50 ns. You throw away a lot of the accuracy of GPS by doing it this way. With an analog detector you would know how early or late you are. With better data in, the average will be more accurate.

Bob



On Feb 10, 2012, at 7:35 PM, Chris Albertson <albertson.chris at gmail.com> wrote:

> 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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