This set of Analog Communications Questions and Answers for Entrance exams focuses on “Generation of AM Using Amplifiers”.
1. Which of the following devices is used to generate AM waves?
a) Reactance modulator
b) Square law modulator
Explanation: AM signals are generated by Square-law modulators. The input for generating AM signal should be of type (A + m(t)) instead of m(t). Square-law modulator sums carrier and information signal, then passes it through a non-linear device.
2. Consider a wave, v = 15 sin (3πt + 5sin1300t), what is the carrier and signal frequency?
a) 2.5Hz and 200Hz
b) 1.5Hz and 100Hz
c) 1.5Hz and 207Hz
d) 5.5Hz and 500Hz
Explanation: Comparing with the general FM equation,
FM(t) = Ac sin( 2πfct + βsin(2πfmt)),
Signal and Carrier frequency are respectively
3. SWR is 1 for ________
a) Open or Short Circuit
b) Open circuit only
c) Short circuit only
d) Series or Parallel Circuit
Explanation: Standing Wave Ratio (SWR) is defined as the ratio of the maximum radio-frequency (RF) voltage to the minimum RF voltage along the line. If the line is open or short circuited, SWR is always 1.
4. The resonance frequency of an amplifier is 7MHz and it is having a bandwidth of 10KHz. What is its Q factor?
Explanation: Q factor = Frequency / Bandwidth
= 7MHz / 10KHz = 700.
5. Which chart is used for calculations of transmission lines?
a) Andre chart
b) Smith chart
c) Wilson chart
d) Federer chart
Explanation: Smith chart is highly used in radio frequency engineering. Because it is highly useful in solving problems related with transmission lines and matching circuits. It is highly useful for displaying multiple parameters like impedance, admittance etc simultaneously.
6. What is the effective power if the transmitted power of 5W is increased to 50dB?
Explanation: According to given problem, 10log10 (P/Pt) = 50,
10log10 (P/5) =50.
So, P = 500KW.
Where, P= Effective Power, Pt = Transmitted Power.
7. Field intensity follows ________
a) Bragg’s law
b) Inverse square law
c) Coulomb’s law
d) Gauss’s law
Explanation: Strength of an electric field due to a charge Q is inversely proportional to the square of the distance from the source. In electrostatics, inverse square law is also known as Coulomb’s Law.
8. If the power density at a given distance ‘R’ is one microwatt per square meter and the effective area of antenna is one square meter then the power captured by antenna is one microwatt.
Explanation: The above statement is true because power density is equal to
Power Density = 1 mW
Pt = Power captured by antenna,
Area of antenna = 4πR2 = 1m2.
9. The gain of antenna (G) is the ratio of power radiated in a particular direction to the power radiated from an isotropic antenna.
10. EM waves are attenuated as they travel.
Explanation: Electromagnetic radiation can travel through many forms of medium. They travel at the speed of light in air or free space, which are ideal media. However conductive media like metals form a barrier through which they do not travel. There are also some media through which when they travel, get attenuated. EM waves are attenuated as they travel because both field and power decrease as distance increases.
Sanfoundry Global Education & Learning Series – Analog Communications.
To practice all areas of Analog Communications for Entrance exams, here is complete set of 1000+ Multiple Choice Questions and Answers.