[time-nuts] Re: GPSDO/GNSSDO project: STM32G4 + u-blox ZED-F9T + TDC7200

[John Ackermann N8UR]

On 8/6/22 20:03, Greg Troxel via time-nuts wrote:

> I've long heard "don't enable SBAS for timing" claims and I've never
> understood the full rationale.  In theory, the observed pseudoranges,
> after applying the pseudorange corrections, are then used in a
> navigation solution.  Everybody believes that one gets better XYZ out of
> that.  Time is trickier, as the reference stations have to steer their
> clocks as they get measured pseudoranges to diff with calculated
> pseudoranges (from satellite positions from the broadcast ephemeris and
> their surveyed ARP, with an antenna model).  But I would expect that the
> general reduction of errors would lead to a tighter solution in all 4
> unknowns.
> 
> So the obvious experiment is to take two indentical receivers, one of
> F9P, F9T, M8T, run them on a splitter both with SBAS off and compare
> each timepulse to a cesium clock or something, to verify that they
> behave the same, and then change so that one has SBAS and the other is
> still off and look at that.

I'll have hardware available to do that testing in hopefully a month or 
two, as well as trying the ZED-F9T time sync between two receivers.  I 
just need to add those measurements to the chore list...

John