1.The intermediate frequency of a superheterodyne receiver is 500KHz. What is the image frequency at 1200KHz?
a) 600KHz
b) 500KHz
c) 700KHz
d) 200KHz
Explanation: The image frequency is an undesired input frequency which is demodulated by superheterodyne receivers along with the desired incoming signal. This results in two stations being received at the same time, thus producing interference. In the given problem, Image frequency is equal to (1200 – 500) which is equal to 700KHz.
2. Which of these amplifiers is used for impedance matching?
a) Common Base
b) Common Emitter
c) Common Collector
d) Common Base & Emitter
Explanation: An amplifier is an electronic circuit that is used to amplify the voltage signal or a current signal. Output impedance of common collector amplifier is low and thus it is suitable for impedance matching.
3. Discone antenna is mainly used in UHF range.
a) True
b) False
Explanation: A discone antenna is a version of a biconical antenna in which one of the cones is replaced by a disc. It is usually mounted vertically, with the disc at the top and the cone beneath. Discone antenna is a combination of disc and cone. Discone antenna is omnidirectional so it is mainly used in UHF range. It is especially used in airports.
4. Squelch circuit is normally inserted in receiver ________
a) after detector
b) before detector
c) before mixer
d) after power amplifier
Explanation: Squelch is a circuit that acts to suppress the audio (or video) output of a receiver in the absence of a sufficiently strong desired input signal. Squelch is added to suppress noise. It is added after detector when there is no carrier.
5. Each frequency gives rise to four side bands.
a) True
b) False
Explanation: Each frequency in communication gives rise to two side bands, Upper Sideband and Lower Sideband.
6. Field strength (E) is directly proportional to the square of transmission power.
a) True
b) False
Explanation: Field Strength is the intensity of an electric or magnetic field. Actually the Field strength (E) is directly proportional to the square root of transmission power i.e. E ∝ √Pt.
7. If the transmitted power is 100KW then the field at a distance ‘R’ is 60mV/m. Suppose if the transmitted power is reduced to 50KW then the field at same distance ‘R’ will be equal to ________
a) 50mV/m
b) 42mV/m
c) 45mV/m
d) 55mV/m
Explanation: Since, Field strength (E) is directly proportional to the square root of transmission power i.e. E ∝ √Pt. Therefore
which gives x = 42mV/m
8. If the value of resistor becomes 16 times than its previous value then its noise voltage will become ________
a) 16 times
b) 8 times
c) 4 times
d) 2 times
Explanation: Since the noise voltage is directly proportional to square root of resistance so if the value of resistor increased to 16 times then its noise voltage will become 4 times.
9. What is the modulation index for a single tone modulation, given that positive peak of AM wave is 20V and minimum value is 2V?
a) 0.81
b) 0.91
c) 0.73
d) 1
Explanation: Modulation Index (u) = (Vmax – Vmin)/(Vmax + Vmin)
= (20-2)/(20+2) = 9/11 = 0.81.
10. TV remote control used ultra violet light.
a) True
b) False
Explanation: The infrared (IR) and the ultraviolet(UV) rays represent the two extremities of the visible spectrum (400-700nm). While IR represents electromagnetic radiation with wavelengths longer than those of visible light, UV represents wavelengths shorter than visible light. Each time we press any button of TV remote, it sends a beam of infrared rays. For different commands, it sends out different beams that are detected by a microchip lying inside TV.