Communication Systems 12 Notes Physics Chapter 15

Chapter at a Glance

1. The attenuation in the case of ground wave propagation increases as the frequency of the wave and the distance increases. For space wave propagation direct field of view is required. Waves of frequency greater than 30 Mega Hertz penetrate through the ionosphere.

2. Ground wave propagation can be sustained only at low frequencies 500 kHz to 1500 kHz.

3. Bandwidth for amplitude modulation= 2 x frequency modulation.

7. The energy of a wave is directly proportional to its frequency. This permits modulated waves to carry the signals to long distances.

8. In amplitude modulation (AM), the amplitude of high frequency wave is changed in accordance with the intensity of the signal.

9. In A.M., the signal is contained in the sidebands.

10. The disadvantages of AM are noisy reception, low efficiency, and small operating range.

11. In frequency modulation (FM), the frequency of a high-frequency wave (carrier) is changed in accordance with the intensity of the signal

12. Lower and upper side frequency are roe- cos and roe + cos respectively.

13. A communication satellite is a spacecraft around the earth that carries on board microwave receiving and transmitting equipment capable of relaying signals from one point on each to other points.

14. Optical fibers are hair-thin glass strands and use the principle of total internal reflection for the transmission of light through them.

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