SatSig topic:

Signal strength difference day and night?

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Mar 27^th, 2006 at 3:01pm

Hi All ,
Could any one please tell me : is there is differences between signal strenght I can get at night and the one I can get during the day ?
I pointed my dish successfully in the night to the satellite, and next morning the signal was gone !
is it because of that ?, or it's just my dish has moved durng the night ?

Regards

Mar 27^th, 2006 at 3:19pm

Sounds like you have a "center of box" issue. Due to a wobble in the earth's axis, satellites in otherwise synchronous orbit look from the ground as if they're scribing a small horizontal figure 8 in the sky. Now draw an imaginary rectangle around this path, and you have "the box". Ideally, you want your dish pointed directly in the center of the box - at the waistline of the figure 8. What may have happened is that you initially found the satellite at one end of the box at night, and lose it when it reaches the other end of the box during the day.

Check the website of the company that owns the satellite. Some are good about posting COB data. The best actually post an actual time when the specific satellite is due to cross the center of it's own box. That's the ideal time to fine tune your pointing angles. There may be other reasons behind your issue, but I think that antenna pointing should be marked off the list before you move on.

//greg//

Mar 27^th, 2006 at 5:35pm

I visited the site of the SAT owner company (PAS 10) , and I got the time table of the center of the box.
Now I want to know , if I successfully pointed my dish to the satellite when it is at the center of the box , what will happen when the SAT moves to the edges again , am I going to get a low signal again ? how this thing is going to work as long as the SAT location to the earth will keep changing ?

Mar 27^th, 2006 at 9:30pm

Quote:

if I successfully pointed my dish to the satellite when it is at the center of the box , what will happen when the SAT moves to the edges again , am I going to get a low signal again ?

It's a one time thing, "the box" isn't that big. But if you start off on the wrong side , you're in trouble. Pointing dead center will give you the most consistent performance, plus/minus a little bit every 12 hours. But you won't have the 24 hour extreme that way.

//greg//

Apr 25^th, 2006 at 5:26pm

The “figure 8” of an inclined orbit may not always be vertical or an “oval”. It may have a pronounced slant based upon its eccentricity and argument of perigee. Eccentricity and argument of perigee may also cause the longitude of ascending and descending nodes (center of station) to shift to the east and/or west of mean longitude.

An inclination of the satellite orbit, however, causes the sub-satellite point (the point on the equator directly under the satellite orbital location) to move in a figure 8 pattern. The source of this figure 8, called the analemma, is the motion of the satellite along the inclined orbit, which will alternately fall behind and then catch up to the uniform rotation of the Earth on its axis.
[Remember – inclination is the N-S movement of the satellite as it completes an orbit. Nonzero eccentricity is the second factor that may cause a non-uniform apparent motion. (Remember, this is in an E-W direction.) In general, the inclination and eccentricity motions will be superimposed upon each other, resulting in two possible shapes for the motion of the geosynchronous satellite as seen from the Earth. If the nonzero inclination dominates, then the satellite will appear to move in a figure 8. If the eccentricity is larger than the inclination effect, the the apparent motion will be a single open oval