This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “Heterodyne Receiver”.
1. What is the bandwidth required in SSB signal?
c) > 2fm
d) < 2fm
Explanation: In an AM modulated system, total bandwidth required is from fc + fm to fc – fm i.e. bandwidth is equal to 2fm. In SSB-SC transmission, one of the sideband gets suppressed so the bandwidth becomes fm only.
2. One of the advantage of using a high frequency carrier wave is that it dissipates very small power.
Explanation: The main advantage of using high frequency signals is that the signal gets transmitted over very long distances and thus dissipates very less power. The antenna height required for transmission also gets reduced at high frequencies. This is the reason for sending the audio signals at high frequency carrier signals for communication purpose.
3. What is the function of RF mixer?
a) Addition of two signals
b) Multiplication of two signals
c) Subtraction of two signals
d) To reduce the amount of noise
Explanation: RF mixer translates the frequencies of the two incoming signals from band to another by multiplying them.
4. The antenna current is 10A. Find the percentage of modulation when the antenna current increases to 10.4A?
5. All the output pulses are at full transmitter power for a strong signal in all of the following except ________
Explanation: Pulse amplitude modulation varies amplitude of pulses for transmission of data. Its output pulses are not at full transmitter power for a strong signal and thus it is a exception.
6. In pulse transmitter, the ratio of time on to time off is called ________
c) duty cycle
Explanation: Duty cycle is the fraction of one period in which the system is active. It can also be defined as the ratio of time on to time off of a system.
7. What is the carrier power of an un-modulated carrier signal when it is transmitted through an antenna having an impedance of 50ῼ and it produces a current of 5.4A?
Explanation: PC=I2 R = (5.4)2 X (50) = 1458 W.
8. Signal to quantization noise ratio in PCM system depends on _________
a) sampling rate
b) signal bandwidth
c) number of quantization levels
d) nature of carrier wave
Explanation: Pulse code modulation (PCM) is a digital form of communication. For demodulation of PCM, it is necessary to convert it into PAM. Quantization noise occurs in PCM only. Signal to quantization noise ratio depends on number of quantization levels.
9. Find the total power, if the carrier of an AM transmitter is 800W and it is modulated to 50%?
Explanation: PT=PC (1+m2⁄2), according to the problem PC = 800W and m = 0.5. On substituting values in the equation we get PT=800(1+ 0.52⁄2) = 900W.
10. Aliasing refers to ________
a) Sampling of signals less than at Nyquist rate
b) Sampling of signals at Nyquist rate
c) Sampling of signals greater than at Nyquist rate
d) Unsampled the already sampled signal
Explanation: Aliasing refers to the sampling of signals less than at Nyquist rate. Nyquist rate states that the rate of sampling of signals should be greater than or equal to twice the bandwidth of modulating signal. It gets reduced if sampling is done at a higher rate than nyquist rate of sampling.
Sanfoundry Global Education & Learning Series – Analog Communications.
To practice all areas of Analog Communications, here is complete set of 1000+ Multiple Choice Questions and Answers.