[time-nuts] Different Thunderbolt versions

[Hal Murray]

> I actually want to work at frequencies below 50Mhz where a 50 degree
> phase error corresponds to about 3ns.

What is interesting to listen to below 50 MHz?  Are there any handy strong 
signals you can use for debugging/calibration?


> Also at these low frequencies the required accuracy approaches that
> claimed by some GPS receivers (4ns for the M12+ ?) so might it be
> possible to build a system which is accurate for arbitrary integration
> times? 

If you haven't seen it yet, this is wonderful background:
  http://www.gpstime.com/files/PTTI/PTTI_2006.pdf
In particular, be sure to check out the hanging bridges.

How far apart are your antennas?  Things might get a lot simpler if you can 
see the same GPS satellites.

If your runs are short enough, you might get better results by letting the 
oscillator coast during the run.  That is unplug the antennas or turn the 
feedback off in software.


This could be all wrong....

There are two things you need.   One is frequency, the other is time (PPS).

If the time is slightly off, that's equivalent to pointing your antenna in a 
different direction.  You get the same sort of error if the location of an 
antenna is slightly off.

I think the Earth's rotation introduces an error that's equivalent to the 
frequency being slightly off.



-- 
These are my opinions, not necessarily my employer's.  I hate spam.