[Starlink] Microstate Accounting and the Nyquist problem

[Gary E. Miller]

Yo Mike!

On Sat, 12 Jun 2021 21:05:19 +0200
Mike Puchol <mike at starlink.sx> wrote:

> Duh… you are correct, I was still on the desktop-sizes ones… but
> would you need one? What I can find is not cheap. It would be
> interesting to work the math eg for Doppler shift compensation which
> could require better accuracy than a “normal” GPS synced timing
> source.

GNSS satellites have many atomic clocks.  Usually three, to start
with.  Some Ceasium, some Rubidium.  They know what time it is, but not
where they are.  Solar winds psuh them around by several meters.  So
ground stations bounce lasers off the sats to reduce the positiion
uncertainty.

After that, the Ionosphere and Troposphere uncertainty dominates.

The doppler can be +/- 10Khz, but the receiver bandwidth is about 250
hz.  So you need to know the doppler before you can lock on the signal
from the bird.

Starlink must have even greater doppler, compensated by a wider receiver
bandwidth.

No way you are improving on what the GNSS folks do.  A lot of black
magic invovled.

For well under $100 you can get a receiver solution that will asily
surpass the clock resolution in a Linux host (<50 ns).  The actual
PPS will be around 15ns.  That can be improved with a bit of external
hardware.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588

	    Veritas liberabit vos. -- Quid est veritas?
    "If you can't measure it, you can't improve it." - Lord Kelvin
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