Figure 8 (Was: Variations in the Eumetcast signal)

Ernst Lobsiger


I had a closer look at the diurnal changes of signal quality
with respect to the figure 8 movement of Eutelsat 10A. As a
first approximation we can expect variations in elevation of
+/- i (inclination) which is +/- 0.062 ° in my latest keps.

I installed good old command line tool predict on one ob my
GNU/Linux boxes and found a figure 8 of +/- 0.07° in azimuth
and +/- 0.08° in elevation as seen from here in Switzerland.

Our dishes used have half power beamwidths of 1.0 to 1.5°.
So it's very unlikely that diurnal variations can be caused
by the figure 8 movement. And as usual I forgot that this
discussion is not new. Alan Sewards pointed that out in
message 20659 with more discussions following on that list.


---In, <geojohnt@...> wrote :

In a message dated 16/07/2017 19:35:25 GMT Summer Time, writes:

If the orbital plane of a geostationary sat is not 100% identical with
the equator plane of the earth we see the sat moving in a small figure 8 once
per day. You should point your antenna to the center intersection of this 8. If your
elevation is too high or too low (and you have a big dish) you will see diurnal
variations of signal strength and SNR.

Hello Ernst,

Genau - aber .......

I have tried two official agencies to obtain the inclination data for
EUTELSAT-10A to find out the equator crossing point, but failed.

I have checked, with updated keps on WXtrack EUTELSAT-10A's movements.
The satellite is over the equator between 04:29 to 04:57 UTC.
And between 16:30 to 16:58.

Now, I cannot guarantee those times are correct, they are purely from
'watching the inclination on WXtrack.


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