Test: Communication Systems - 1 - CUET Humanities MCQ

Let the height of TV antenna be h and radius of earth be R and R >> h.
Let M be the receiving station when h << R, then NM may be assumed as tangent to the surface of earth, so
∠NMC = 90º

∴ NC² = NM² + MC²
(R + h)² = NM² + R²
⇒ NM² = R² +h² + 2RH - R²
= 2RH + h²
Since h << R, therefore
h² may be neglected. Hence, NM² = 2Rh
_^⇒ NM ∝ h^1/2

Optical communication is always preferred over microwave communication beacuase optical communication provides large number of channels and band-width.

Using the relation v = , we get v = 
≈ 1590 × 10³ Hz = 1590 kHz
Side band frequencies = 1590  2
= 1592 kHz and 1588 kHz.

The correct choice is (2). In fax and e-mail, the information signal is in the form of digital signal.

The correct choice is (3). Above 30 MHz, the ionosphere does not reflect the waves. Waves of frequency greater than 30 MHz are transmitted through the ionosphere.

 f_s = 100 × 10⁶ Hz, E_s = 100 V
 f_c = 300 × 10⁹ Hz, E_c = 400 V
Modulation index, m = E_s/E_c = 100/400 = 0.25 
Side band ΔF = F_max - F_min
= (F_s + F_c) - (F_c - F_s)
= 10⁸ [(3000 + 1) - (3000 - 1)]
= 10⁸ (2) = 2 × 10⁸

The physical sizes of the antennas of receiver and transmitter are both inversely proportional to carrier frequency. To achieve small antenna or transmitter dimensions and high gain, the use of a high carrier frequency is required, which may not penetrate the material to sufficient depth.

In radio and television broadcast, the information signal is in the form of analogue signals. The two most common modes of transmission are AM and FM, which in turn are analogue signals only.

Space wave propagation is employed to transmit very high frequency (VHF) and ultra high frequency (UHF) signal. Space wave propagation is defined as the radio waves that occur within the 20 km of the atmosphere.

To transmit an audio signal to a large distance, modulation of signal is done.