[time-nuts] Checking the Frequency of a Rubidium Oscillator

[Poul-Henning Kamp]

In message <491A210B.30401 at rubidium.dyndns.org>, Magnus Danielson writes:

> Once doppler bin and phase has been achieved for each PRN, [...]

Just a footnote to say that as soon as you start receiving ephemerides
from the first sat, the search-space can be significantly reduced
if you care to do the, rather longhaired, trignometric math.

>A sat based receiver must handle higher doppler offsets due to its 
>higher speed, [...]

While this is true for any non-geo-stationary satellite, it may not
be true for the project the initial poster talked about.

As I remember it, he said that the mission would be in an earth-following
orbit, ie: in the same orbit as the earth around the sun, but
trailing it by some distance.

Given that the distance in GPS terms is "vast" and furthermore that
the GPS orbits have a pretty steep angle relative to the earths
orbital path, I would expect the doppler offsets to be much smaller
than here on earth.

Obviously, getting a position fix will suck with the worst
DOP seen to date, but a frequency fix should not be out
of the question.

Obviously, the situation on the way to the final orbit is entirely
different, and there I would expect doppler to be totally out
of the lower end of the window.

Remember to figure out the relevant relativistic corrections.

Poul-Henning

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