Satellite Communication: Active and Passive Satellite

What is 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 by creating a channel between the transmitter and the receiver located at different locations on the Earth.

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Satellite communication

Telephone, radio, television, internet, and military applications use satellite communications. Believe it or not, more than 2000 artificial satellites are hurtling around in space right above your heads.

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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 the 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 re-transmitting it back to Earth, ensuring excellent signal strength. 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 specific frequency for transmitting it. The International Telecommunication Union does this frequency allocation. Geosynchronous satellites are of note here. Geostationary orbit is present at the height of 35786 km above Earth’s surface. If you can spot such a satellite with a telescope from Earth, it will appear stationary to you. The orbital period of satellite and the rotational rate of the Earth is in sync.

Have A Look At This GIF About Geostationary Orbits

These were some of the typical orbits. Apart from these we also have orbits that address particular problems. The Russians faced one such issue. 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.

Advantages of Satellite Communication

Following are the advantages of satellite communication:

  • Installments of circuits are easy.
  • The elasticity of these circuits are excellent.
  • With the help of satellite communication, every corner of the earth can be covered.
  • The user fully controls the network.

Disadvantages of Satellite Communication

Following are the disadvantages of satellite communication:

  • Initial expenditure is expensive.
  • There are chances of blockage of frequencies.
  • Propagation and interference.

Applications of Satellite Communication

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

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