[time-nuts] 4046 experiment for gpsdo

[Chuck Harris]

You missed the part about the 10MHz being divided by 10 million
to produce a 1PPS signal that is compared to the second 1PPS signal...

-Chuck Harris

Will wrote:
> Hi,
>
> I'm new and trying to get to grips with things.
>
> If I understand correctly, please forgive if I have it wrong,  This
> locks a 10MHz signal  to a 1Hz (1pps) signal.  What makes it lock to 10
> 000 000Hz instead of 999 999Hz or 10 000 001Hz?  Just the hope that the
> 10MHz is exactly that?
>
> Cheers,
> Will
>
> On 26/09/15 08:32, Jim Harman wrote:
>> To further demonstrate the Diode - R- C- approach, here  (hopefully) is a
>> screenshot of the raw DAC output vs time on my Arduino Micro (32u4) based
>> system. For this test the oscillator is free running with an error of about
>> 1 usec per 460 sec or 2.17x10^-9. The horizontal scale is 125 sec/div (1000
>> sec total) and the vertical is 1024  DAC counts (0-2.56 V) which
>> corresponds to 1 usec of offset between the oscillator and the reference.
>>
>> You can see that there is some curvature because the capacitor is being
>> charged through a resistor and not a true current source, but as I
>> mentioned earlier this does not affect the system's ability to lock the
>> oscillator to the pps reference. When locked with a time constant of 1000
>> sec, the phase detector output is almost always less than +/- 100 counts
>> from the setpoint of 500.
>>
>> The noise is due mostly to jitter in my PPS reference, which is generated
>> by an Adafruit GPS module. Presumably it would be less if I had a real
>> timing receiver.
>>
>>
>> ​.
>> If the inserted image does not come through, I will re-send as an
>> attachment.
>>
>>> --
>> --Jim Harman