Communication Systems

Speech signals is in the range of

• 3700 Hz to 7000 $\stackrel{\circ }{\mathrm{A}}$ wavelength

• 20 Hz to 20 kHz frequency

• 300 Hz to 3100 Hz frequency

• 540 kHz to 1600 kHz frequency

To transmit a signal of frequency ω_m with a carrier frequency ω_c, in AM transmission, the bandwidth of the filter and amplifier is

• ω_m

• 2ω_m

• ω_c

• ω_c − ω_m

If the height of TV tower is increased by 21%, then the transmission range is enhanced by

• 10 %

• 5 %

• 15 %

• 25 %

The range of a communication system can be extended by a

• modulator

• transmitter

• repeater

• receiver

For commercial telephonic communication, the frequency  range for speech signals is

• 50 Hz to 1000 Hz

• 3000 Hz to 4500 Hz

• 300 Hz to 3100 Hz

• 5000 Hz to 6500 Hz

The role of envelope detector in an AM receiver is to

• retrieve the message signal

• rectify the AM signal

• modify the AM signal

• modulate the message signal

Identify the mismatched pair

• Noise  —  Unwanted signals

• Repeater  —  Communication satellite

• Attenuation  —  Srengthening of signal

• Demodulation  —  Retrieval of information 

Pick out the wrong statement.

• Analog signals provide a continuous set of values

• Digital signals represent values as discrete steps

• Analog signals utilise the binary system

• Digital signals can be processed by logic gates

A ground receiver receives a signal at 5 MHz, transmitted by a ground transmitter at a height of 320 m, which is 110 km away from it. Then it can communicate through (radius of the Earth, R = 6400 km)

• space waves

• ground waves

• sky waves

• both sky and ground waves

The power radiated by a linear antenna of length l at wavelength λ is

• directly proportional to l

• inversely proportional to λ

• inversely proportional to λ²

• directly proportional to λ²