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Karnataka 2nd PUC Electronics Question Bank Chapter 7 Wireless Communications
2nd PUC Electronics Wireless Communications One Mark Questions and Answers
Name any two paths that a radio signal can take through space.
The paths that a radio signal can take through the space are:
- The ground wave
- The space wave
- The sky wave.
Name the two radio waves that propagate near to the surface of the earth.
- The ground wave
- The space wave
How are ground waves polarized?
The ground waves are vertically polarized.
What is the frequency range of signal that propagate best over the surface of the earth?
30 kHz to 3 MHz.
Identify the radio waves which are refracted by the ionosphere.
Very high-frequency VHF (30 MHz to 300 MHz).
Mention the range of frequency signals that porpagate best through ionosphere.
30 kHz to 3 MHz.
What is ionosphere?
Ionosphere is the upper portion of the atmosphere, which absorbs large quantities of radiant energy from the sun and becomes heated and ionised.
Which layer of the ionosphere has the greatest effect on a radio signal?
Which is the type of radio wave that propagates only over line-of-sight distance?
VHF (very high frequency) (30 MHz to 300MHz).
What is fading?
Fading is the fluctuation in the strength of the radio signal.
Define skip distance.
Skip distance is the minimum distance measured between transmitting antenna and the first receiving antenna measured along the surface of the earth after propagation through the ionosphere.
Define skip zone.
Skip zone or silent zone is the region around the receiving antenna, within the skip distance, where neither the ground wave nor sky wave is present.
Define critical angle.
Critical angle for a given layer is the maximum angle of incidence of a radio wave under ionospheric propagation that gets returned to the earth.
Define critical frequency.
Critical frequency for a given layer is the highest frequency of a beamed radio wave that will be returned to the earth.
Define electrical noise.
Noise is any unwanted electrical energy which interferes with the required signal.
Define signal to noise ratio.
Signal to noise ratio is the ratio of signal power to noise power.
Define noise ratio.
Noise ratio is the ratio of signal to noise ratio at the input to the signal to noise ratio at the output of the system.
Define noise figure.
Noise figure is the noise ratio expressed in decibel.
Mention the frequency of radio waves.
104 to 1014 Hz.
Define single hop distance.
Single hop distance is the maximum distance between transmitting antenna to first receiving antenna measured along the surface of the earth after propagation through the ionosphere.
2nd PUC Electronics Wireless Communications Two Marks Questions and Answers
Draw the block diagram of basic electronic communication system.
Write a short note on noise.
Noise is any unwanted electrical energy which interferes with the correct reception and reproduction of the required signal. Noise may be internal or external. Noise cannot be eliminated but can be minimized. Noise can be measured in a system using the parameters like signal to noise ratio, noise figure etc.
Mention the types of radio propagation.
- Ground waves.
- Space waves.
- Sky waves.
Mention the layers of ionosphere.
- l.D layer
- E layer.
- F layer.
Write a note on single hop distance.
The single hop distance is the maximum distance between the transmitting antenna to first receiving antenna measured along the surface of the earth after ionospheric propagation. For F2 layer, maximum single hop distance is 4000 km. As the average circumference of the earth is 20,000 km, the signal needs to undergo multiple hops, if it has to achieve round the globe communication.
What is fading? Explain.
Fading is fluctuations in the strength of radio signal. Fading occurs due to absorption in the layers of the atmosphere, loss during refraction, loss due to scattering of signals. Fading can be reduced by using repeater stations which boost up the signal strength satisfactorily to reach the receiving
2nd PUC Electronics Wireless Communications Three Marks Questions and Answers
Write frequency allocation table for different communication systems.
|Name of frequency band
|(VLF) Very low frequency
|Long distance communication
|30 kHz-300 kHz
|Low frequency (LF)
|300 kHz-3 MHz
|Medium frequency (MF)
|Radio broadcasting. Police walkie-talkie.
|3 MHz-30 MHz
|High Frequency (HF)
|30 MHz-300 MHz
|Very high frequency (VHF)
|Radar, TV, Fm broadcasting.
|300 MHz-3 GHz
|Ultra high Frequency (UHF)
|TV, Radar, Aviation
|3 GHz-30 GHz
|Super high frequency (SHF)
|Satellite communication Radar.
|30 GHz-300 GHz
|Extreme high frequency (EHF)
|Special purpose communication.
Explain in brief ground wave propagation.
Ground waves are the waves transmitted along or reflected from the surface of the earth. These can exist when the transmitting and receiving antennas are close to the surface of the earth.
The ground wave is vertically polarised and will transmit most effectively at a frequency less than 2 MHZ. The AM broad cast signals travel as ground waves. The strength of the ground wave is reduced due to energy absorption by the earths surface.
With relevant diagram, explain ionospheric propagation.
Ultraviolet radiation from the sun cause the upper atmosphere to ionize i.e. to become electrically charged. Hence a thick layer of ions formed at heights of 50 km to 400km. The ionosphere supports MF and HF wave propagation.
Its three layers are:
D layer: It is at a height of 70 km and has an average thickness of 10 km. It disappears in the night time. It reflects VLF and LF waves and absorbs MF and HF waves.
E layer: It is at a height of 100 km with a thickness of 25 km. This layer disappears at night. It helps in MF and HF wave propagation.
F layer: It is at a height of 150 km and extends upto 400 km. This layer exists during both day and night time. During day time, it splits into two layers F, and F2, and combines to form a single F layer during night time.
|F2 region. 250-400 km.
|F1 region. 160-250 km.
|E region. 95-130 km
|D region. 50-95 km.
Explain the concept of space wave propagation.
Space waves are the waves that travel from the transmitting to receiving antenna in the earths troposphere (first 18 km from earths surface). Space waves have two components.One of them is line of sight ray which travels directly from transmitting to receiving antenna.The other is ground reflected wave, which reaches the receiver due to reflection from the surface of the earth. Radio transmission at frequencies above 30 MHz, TV, FM, radar use space wave propagation.
2nd PUC Electronics Wireless Communications Five Marks Questions and Answers
Draw the block diagram of an electronic communication system and explain the function of each block in brief.
Define important terms used in ionospheric propagation. Define single hop distance. Answer:
Ionosphere is the layer of ions at a height of 50 km to 400 km formed due ionisation by ultraviolet radiations from the sun.
D layer of ionosphere is at a height of 70 km which has a thickness of 10 km. It disappears at night and reflects VLF and LF waves.
E layer of ionosphere is at a height of 100 km and has a thickness of 25 km. It disappears at night and helps MF and HF wave propagation.
F layer is at a height of 150 km and extends upto 400 km. It remains during both day and night . time. During day time, it splits into two layers Fj and F2 and combines to form a single F layer during night time.
F1 layer or kennelly-Heaviside layer is at a height of 200 km with a thickness of 20 km. Itreflects HF waves.
F2 layer or Appleton layer is at a height of 300 km and has a thickness of 20 km. It is usefull in HF wave propagation.