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

paul swed paulswedb at gmail.com
Sat Feb 11 00:48:08 UTC 2012


Hang on here. If the signal was 10 MHz for ref and RB its easy as suggested
here XOR gates and such.

But the GPS is a 1 second interval and the RB is 10 Mhz. So the GPS 1
second is the reference. Thats much harder then dealing with 100 Hz or up.
So the answer I have seen which seems to fit is Bobs comments earlier.
That is the numbers/thinking are right and it would take a really long gate
time to become more accurate.
I may get a slight improvement by using the better reciever that has a
tighter 1 PPS. I do see what I am betting is a jitter on the Novatel. But
its not a timing receiver.

Regards
Paul.

On Fri, 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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