-Let us get back to our common thread, satellite Internet access. We left it behind during week 1. We now have everything needed to access the satellite. We have the satellite box, the 75-centimeter dish and its head, we now only need to direct it towards the satellite. But which satellite are we talking about? For our subscription, we use the Astra 2E satellite. It is operated by SES and is positioned at 28.2 degrees east, that is to say east of the Greenwich meridian. This satellite was launched in 2013 by a Russian launcher, Proton. It has an estimated lifetime of 15 years. Onboard, it has 42 transponders for Europe and 12 transponders for the Middle-East. All these transponders are on the Ku band. But there are also 4 Ka-band transponders. We will use this Ka band for our satellite Internet access. The illustration here represents the service coverage for the Ka band. It is represented with concentric circles and values specified in small white discs. This time it is not the required antenna diameter in centimeters, it is the power transmitted by the satellite on each of these zones. It is interesting to note that the farther from the antenna center we go, its favorite direction, the less power we have. Where should we look to see the satellite? Let us now specify that unless we have a good telescope, we cannot see the satellite. But we can still wonder where we should look. In order to better rephrase this question, I would say: being located in Toulouse, which azimuth and elevation should I use to aim at the satellite? To answer this question, we need to have a look at the user manual of the connection kit. But we can also do a little trigonometry and calculate it ourselves. First, we specify the location of the terminal, shown here, 43 degrees 36 minutes 16 seconds north and 1 degree 26 minutes 38 seconds east. By looking at the map, we know that regarding the azimuth, since we are in Toulouse, we will have to look more or less south-east, that is to say to the left when facing south. Let us start with the azimuth calculation, that is to say the direction on the compass. We know that is it south-east. We consider Earth with the Greenwich meridian and the Equator. First observation, to calculate the azimuth, we are not really interested in the satellite but rather in its perpendicular projection on the ground. This is what we call the subsatellite point on the illustration. If we represent this point and the terminal's position as well as its meridian called M on a sphere, we get a spherical triangle. We will have a look at the theta angle which is the azimuth to the satellite. The good news is that, just as for a plane triangle, we can use trigonometry laws that make a relation between the angle and the length of the sides of the triangle. This formula is on the left. Once the calculation is done, we get a 143-degree azimuth angle between the terminal in Toulouse and the Astra 2E satellite I invite you to try this formula using your own town or, why not, by choosing another satellite. Now, let us calculate the elevation. In that case, we do not need a spherical triangle. We can work in the plane. We need to define what is called the central angle. The central angle is the angle between the straight line which links the Earth's center to the terminal and the straight line which links the Earth's center to the satellite. This is the definition of the central angle. You can also see the definition of the elevation. Trigonometry helps us calculate the value of this central angle, which will then allow us to calculate the elevation. The formula is represented here. We get a 33-degree elevation from Toulouse to look at Astra 2E. There are numerous applications on PC, tablets and smartphones to do these calculations for us. On smartphones, most of those also use the GPS to automatically locate the terminal. Now that we now the azimuth and the elevation to use, we can direct the antenna. But we will keep this activity for another week.