Satellite Communication: Active and Passive Satellite

Satellite Communication

Satellite communication is the method of transporting information from one place to another using a communication satellite in orbit around the earth. Watching the English Premier League every weekend with your friends would have been impossible without this. A communication satellite is an artificial satellite that transmits the signal via a transponder. It does so by creating a channel of communication between the transmitter and the receiver located at different places on Earth.


Satellite communication

Satellite Communication

Satellite communications is used in telephone, radio, television, internet and military applications. Believe it or not, there are more than 2000 artificial satellites hurtling around in space right above your heads.


Satellites and other matter revolving around the planet

The Space Debris Consisting Of Satellites And Other Junk Revolving Around The Planet

The need for satellite communication becomes evident when we want to transmit signal to far off places, where the Earth’s curvature comes into play. This obstruction is overcome by putting communication satellites in space to transmit the signals across the curvature. Satellite communication uses two types of artificial satellites to transmit the signals:

  • Passive Satellites: If you put a hydrogen balloon which has a metallic coating over it, up in the air, it technically becomes a passive satellite. Such a balloon can reflect microwaves signals from one place to another. The passive satellites in space are similar. These satellites just reflect the signal back towards the earth without amplification. Since the satellites orbit height can range from 2000 to 35786 km, attenuation due to the atmosphere also comes into play and due to this, the received signal is often very weak.
  • Active Satellites: Active Satellites, unlike passive satellites, amplify the transmitted signals before retransmitting it back to Earth. This ensures excellent signal strength. Your home TV sets have a Set Top Box now. This is the Direct To Home (DTH) satellite communication. Although illegal in India, there are satellite mobile phones too. Imagine never being lost. You can go anywhere but you always have a guardian angel who knows exactly where you are. Passive satellites were the earliest communication satellite but now almost all the new ones are active satellites.

To avoid mixing up and interference of signals, every user is allocated a certain frequency to transmit in. This frequency allocation is done by the International Telecommunication Union. Geosynchronous satellites are of note here. Geosynchronous satellites have a geostationary orbit at a height of 35786 km above the Earth’s surface. If you can spot such a satellite with a telescope from Earth, it will appear stationary to you. The satellite’s orbital period has been synced with the rotational rate of the Earth.

Have A Look At This GIF About Geostationary Orbits

These were some of the common orbits. Apart from these we also have orbits that address very specific problems. One such problem was faced by the Russians. GEO satellites worked perfectly for the equatorial regions but it had a very weak coverage near the Poles. To address this problem, the Russians designed an orbit with a very high inclination. The inclination is the angle between the satellite’s orbit and the equator. This orbit was called the Molniya orbit. The orbit had excellent coverage of the North pole for a short time. Molniya had a period of 24 hours but out of that, it would be close to earth only for 6-9 hours. Russia launched some more satellites in the same orbit and soon they had uninterrupted coverage.

Applications of satellite communication are enormous

  • Telephone
  • Television
  • Digital cinema
  • Radio broadcasting
  • Amateur radio
  • Internet access
  • Military
  • Disaster Management

This article death with satellite communications, communication satellite, active and passive satellite. In the next article, we will discuss the various orbits that a satellite can have. To learn more about the fascinating world around you, visit BYJU’S

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Practise This Question

A cylindrical tank has a hole of 1 cm2 in its bottom. If the water is allowed to flow into the tank from a tube above it at the rate of 70 cm3/sec. then the maximum height up to which water can rise in the tank is