Satellite Communications MCQ || Satellite Communications Questions and Answers

21. What is the maximum theoretical data rate if a transponder is used for binary transmission and has a bandwidth of 36MHz?

  1. 32Mpbs
  2. 72Mpbs
  3. 36Mpbs
  4. 12Mpbs

Answer.2. 72Mpbs

Explanation

For binary transmission, the maximum theoretical data rate or channel capacity C for a given bandwidth B is

C = 2B

Where

B = Transmission Bandwidth

2(36) = 72Mpbs.

 

22. ISRO has established the _______, at Bharati Station, Antarctica, for receiving IRS data.

  1. NCAOR
  2. NRSC
  3. AGEOS
  4. IMGEOS

Answer.3. AGEOS

Explanation

  • ISRO has established the AGEOS, at Bharati Station, Antarctica, for receiving IRS data.
  • ISRO has established the Antarctica Ground Station for Earth Observation Satellites (AGEOS), at Bharati Station, Larsemann Hills, Antarctica, for receiving Indian Remote sensing Satellites (IRS) data.
  • The AGEOS is continuously operated and maintained by the Engineers of ISRO who are under deputation to Bharati Station, Antarctica on a regular basis.

 

23. An artificial satellite can be tracked very precisely from the earth by using?

  1. Zeeman effect
  2. Sonar
  3. Doppler effect
  4. Radar

Answer.3. Doppler effect

Explanation

An artificial satellite can be tracked very precisely from the earth by using the Doppler effect.

  • The Doppler effect, or Doppler shift, describes the changes in the frequency of any kind of sound or light wave produced by a moving source with respect to an observer.
  • Waves emitted by an object traveling toward an observer get compressed — prompting a higher frequency — as the source approaches the observer.
  • The reason for the Doppler effect is that when the source of the waves is moving towards the observer, each successive wave crest is emitted from a position closer to the observer than the crest of the previous wave.
  • The distance between successive wavefronts is then increased, so the waves “spread out”.

 

24. Why are techniques like frequency reuse and spatial isolation carried out?

  1. Reduce traffic load
  2. More gain
  3. High speed
  4. Error detection

Answer.1. Reduce traffic load

Explanation

In space when there is more traffic than there are transponders to handle it, therefore numerous techniques have been developed to effectively increase the bandwidth and signal-carrying capacity of the satellite. Such as frequency reuse and spatial isolation.

Techniques like frequency reuse and spatial isolation are carried out to Reduce traffic load.

The frequency reuse technique is widely used in cellular networks to mitigate the interference experienced by the users at the expense of lower spatial bandwidth efficiency.

 

25. India’s first satellite was named after _______.

  1. Varahamihira
  2. Ramanujam
  3. Bhaskara
  4. Aryabhatta

Answer.4. Aryabhatta

Explanation

  • India’s first indigenously-built satellite ‘Aryabhatta’ was launched on 19 April 1975.
  • The Aryabhatta was built by the Indian Space Research Organisation (ISRO). It was the country’s first artificial satellite.
  • It was named after Aryabhatta, the 5th-century Indian mathematician and astronomer.

 

26. The type of access used in GSM technology is ________

  1. FDMA
  2. TDMA
  3. FDMA/TDMA
  4. CDMA

Answer.3. FDMA/TDMA

Explanation

  • GSM stands for Global System for Mobile Communication. It is a digital cellular technology used for transmitting mobile voice and data services.
  • The GSM uses Gaussian Minimum Shift Keying (GMSK) modulation method.
  • GSM devised a combination of TDMA/FDMA as the method to divide the bandwidth among the users.
  • The FDMA part divides the total bandwidth into carrier frequencies.
  • GSM digitizes and compresses data and sends in the channel with two other streams of user data, each in its own time slot using TDMA.
  • It operates at either the 900 MHz or 1800 MHz frequency band.

 

27. Which technique uses two different antennas to reduce traffic on the same frequency?

  1. Spatial isolation
  2. Frequency reuse
  3. Multiplexing
  4. Modulation

Answer.2. Frequency reuse

Explanation

Frequency reuse is the process of using the same radio frequencies on radio transmitter sites within a geographic area. They are separated by sufficient distance to cause minimal interference with each other.

In the frequency reuse technique two systems use the same frequency, although operating on exactly the same frequencies, they are isolated from each other by the use of special antenna techniques.

For example, a vertically polarized antenna will not respond to a horizontally polarized signal and vice versa. Or a left-hand circularly polarized (LHCP) antenna will not respond to a right-hand circularly polarized (RHCP) signal and vice versa.

 

28. A satellite link uses different frequencies for receiving and transmitting in order to

  1. Avoid interference from terrestrial microwave link
  2. Minimize free space losses
  3. Maximize antenna gain
  4. Avoid interference between its powerful transmitted signal and the weak incoming signal

Answer.4. Avoid interference between its powerful transmitted signal and the weak incoming signal

Explanation

In satellite communication, uplink and downlink frequencies are kept different, i.e.

Uplink frequency > Downlink frequency

Explanation:

  • The transmission of a signal from the first earth station to a satellite through a channel is called uplink.
  • The transmission of a signal from the satellite to the second earth station through a channel is called the downlink.
  • Since the satellite cannot afford to deliver high powers because of battery power constraints, the downlink is sent at lower frequencies, while the station at earth can afford to transmit at high frequencies, so it transmits at higher frequencies.
  • This helps in avoiding interference between its powerful transmitted signal and the weak incoming signal.
  • The satellite transponder converts this signal into another frequency and sends it down to the second earth station.
  • This frequency is called the Downlink frequency. In a similar way, the second earth station can also communicate with the first one.

 

29. With reference to satellite orbit, Perigee is the

  1. Point in an intermediate orbit
  2. Highest point in the orbit
  3. Lowest point in the orbit
  4. None of these

Answer.3. Lowest point in the orbit

Explanation

The minimum distance of the planet or satellite from the earth is called perigee. With reference to satellite orbit, Perigee is the lowest point in the orbit

The point of the orbit where the satellite is farthest from the Earth is called the apogee.

 

30. Which technique uses spot beam antennas to divide the area covered by the satellite into smaller segments?

  1. Spatial isolation
  2. Frequency reuse
  3. Multiplexing
  4. Modulation

Answer.1. Spatial isolation

Explanation

  • The several techniques for electromagnetic isolation include orbital isolation, spatial isolation, geographic isolation, polarization isolation, and temporal isolation.
  • Increasing the space between satellites allows a ground station to see only one signal source in its range of vision or beamwidth. Orbital isolation, however, decreases the number of satellites that the GEO can accommodate and increases the difficulties of tracking moving satellites in lower orbits.
  • Spatial electromagnetic isolation is the result of concentrating transmission broadcast cones into narrow spot beams that reduce a satellite’s footprint. Using very high power to boost the effective isotropic radiated power (EIRP), large modern GEO satellites can carry up to 120,000 voice circuits in a near point-to-point mode. Creating many small, isolated zones, or spot beams, for wireless use of the same RF frequency allows reuse of RF frequencies and effectively increases the speed and effective capacity of a satellite broadcast system.
  • By using narrow beam or spot beam antennas, the area on the earth covered by the satellite can be divided up into smaller segments. Earth stations in each segment may actually use the same frequency, but because of the very narrow beam widths of the antennas, there is no interference between adjacent segments.

 

31. Where was the First experimental satellite telecommunication earth station set up in 1967 in India?

  1. Ahmednagar
  2. Allahabad
  3. Ahmedabad
  4. Aurangabad

Answer.3. Ahmedabad

Explanation

  • The first ‘Experimental Satellite Communication Earth Station (ESCES)’ was operationalized in Ahmedabad in 1967, and it also served as a training facility for Indian and international scientists and engineers.
  • ISRO was clear that it did not need to wait for its own satellites to begin application development, and that foreign satellites may be utilized in the early phases to demonstrate that a satellite system can contribute to national development.

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