Basics of Satellite Communication. ....... Satellite Communication fundamentals........

Let us start with a very basic question.  

What is satellite ?

Satellite is nothing but an object that moves around another large object.

For example: - Moon moves around the earth and earth is comparatively larger than moon, hence moon is a satellite of earth.

Now, next question which immediately comes I our mind, what is GSAT, INSAT satellite frequently in news.

So, to answer this. We will discuss categories of satellites.

Satellites can be divided into two categories.

1.    Natural satellites

2.    Artificial satellites like GSAT- 30 satellite and satellites of INSAT series.

Now we will discuss the importance of satellite communication.

1.    Wide coverage i.e. very large area of earth is visible from satellites and ideally with the help of 3 geo-stationary satellites the most of the parts of the earth is visible except polar region. We can say that the combination of 3 satellites, with the ability to relay message from one to other could inter connect virtually all of the earth except the polar region.

2.  In case of terrestrial communications due to curvature of earth LOS – line of sight communication is not possible beyond the horizon. With the help of satellite, it is possible and can be communicated beyond the line of sight.

3.  Satellite communications ignore geographical boundaries.

4.  Satellite can provide communication in moving flights, ships like in-flight connectivity.

5.    Satellites are used in Remote sensing that is satellite is used for detection of water pollution, oil fields, monitoring and reporting of weather conditions. 

If communication takes place between any two earth stations through a satellite, then it is called as Satellite Communication.

A communication satellite is nothing but a microwave repeater station in space. It is helpful in telecommunications, radio and television along with internet applications.

A repeater is a circuit, which increases the strength of the received signal and then transmits it. But this repeater works as a transponder. That means, it changes the frequency band of the transmitted signal from the received one.

The frequency with which, the signal is sent into the space is called as Uplink frequency. Similarly, the frequency with which, the signal is sent by the transponder is called as Downlink frequency. 

There are two basic segments of satellite communications:

1.  Space Segment

2.  Ground Segment

Space segment consists of satellite and satellite links- including solar panel, battery bank, power supply, payloads, antenna etc.

 The satellite signal which can be received at specific area or region of the earth is called satellite foot prints. Satellite footprints may be over a small area called spot beam. Over a regional area called regional beam and over a global area like Asia beam called global beam.

Ground segment consist of Ground station, control Centre and satellite launching facility.

Ground station may be transmitting or receiving earth station. Transmitting earth station consists of transmitter, TWT amplifier, LNA- low noise amplifier and dish antenna system. And receiving earth station consist of dish antenna to collect satellite signals like rain drop collection followed by LNA and LNB followed by, satellite receiver or set-top box and output of set-top box will be fed to the input of TV set for reception of TV channels.

Satellite should be properly placed in the corresponding orbit after launching it in the space. It revolves in a particular orbit and serves its purpose for scientific, military or commercial. The orbits, which are assigned to satellites with respect to earth are called Earth Orbits. The satellites present in those orbits are called as Earth Orbit Satellites.

We should choose an orbit properly for a satellite based on the requirement. There are three important types of satellite earth orbits.

• Geosynchronous Earth Orbit (GEO) Satellites
• Medium Earth Orbit (MEO) Satellites
• Low Earth Orbit (LEO) Satellites
  

Some important parameters of GEO, MEO and LEO satellites are:

Height of GEO satellites is about 36000 kms above the equatorial plane from earth surface. For MEO it ranges from 5000 to 12000 kilometers and in case of LEO it is 500-1500 kms.

The orbital rotational period for GEO is 24 hrs, for MEO is 2-8 hrs and in case of LEO 10-40 minutes.

To cover entire earth total no of satellites required in case of GEO 3, for MEO 8-20 and for LEO 40-80 satellites are required to cover entire earth.

 

Satellite Dish Antenna Tuning or Alignment:

To receive signal from any satellite, it is required to point your dish antenna towards that satellite. This is called antenna tuning. To tune or align a dish antenna three types of rotation is required.

Azimuth rotation – Azimuth Angle (horizontal rotation of dish antenna)

Elevation rotation- Elevation Angle (upward or downward movement of dish antenna)

Skew rotation- adjustment of LNB/LNA or rotation of LNB/LNA either in clockwise or anti-clockwise.

These rotations can be observed when a DTH installation engineer fix our dish antenna at the rooftop with the help of satellite meter. First, he fixes the antenna base and then connects the LNB (which is locally known as camera) at the focal point of the dish. Then he starts horizontal rotation to maximize signal strength in satellite meter. After getting maximum strength he fixes its horizontal position then he starts lifting up or down the dish to fix elevation and where  he gets maximum strength he fix it. Lastly the DTH engineer starts rotating LNB and fixes it.

This was a brief about Satellite basics. Thank you for watching HTB namaskar jai hind.