[time-nuts] Disciplining Rubidium

Jim Lux James.P.Lux at jpl.nasa.gov
Thu Apr 24 18:20:28 EDT 2008

At 02:29 PM 4/24/2008, SAIDJACK at aol.com wrote:
>Hi Tom,
>that Superstar receiver only has +/-50ns 1PPS timing accuracy (typical).
>That compares to an M12M claimed accuracy of +/-10ns corrected.
>I wonder why the receiver manufacturers don't do the math on the carrier
>phase, and generate very accurate 1PPS signals. Is it because they 
>don't have
>OCXO's? Or do they need the data from USNO to do the math?

Money?  There's not much demand for cheap receivers better than 50ns, 
so a mfr isn't going to spend the time and money to do it.

Other uncertainties (multipath, ionosphere, phase center movement 
with look angle, etc) are of that general magnitude as well, so even 
if your little receiver could put out a 1pps with 1ns accuracy, the 
other parts of the system are worse.

A bit of system engineering would show that there's not much market 
for a $100 receiver that has to be hooked up to a $4000 choke ring 
antenna, for instance.

Certainly, for the hacker market, one might see this (if for no other 
reason than you could build your own antenna, or at least, the chokes)

>Is there any public domain software that can take the carrier phase data,
>and give you a solution, at least a position fix with 1cm accuracy etc?

You might start here:

>As far as I know the M12+ was tested at USNO to within 2ns average over 300
>hours, and I have never seen a better timing receiver measurement. But that
>still is 2 Feet accuracy, a far cry from 1cm.

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