This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “Non Linear Device”.
1. Who originated the theory of radio waves?
Explanation: Maxwell was the first person who came up with the concept of electromagnetic theory and from there, the theory of radio waves was deduced. After some years, it was Hertz who applied Maxwell theories to the production and reception of waves.
2. Which effect is characteristic of FM reception in a noisy environment?
a) threshold effect
b) capture effect
c) bessel effect
d) carson’s effect
Explanation: Signal to Noise ratio is the measure of signal present with respect to the surrounding noise. Threshold effect has low output signal to noise ratio. It contains large noise as compared to input signal in envelope detector. In threshold effect, detection of message signal is difficult.
3. Mathematically, the number of sidebands in frequency modulated system is _________
Explanation: Wideband frequency modulated system has modulation index greater than 1. Thus, if we consider the number of sidebands in wideband frequency modulated system, we find it to be infinite, mathematically speaking.
4. Which statement is true about an SCA signal?
a) it can use amplitude modulation
b) it can use frequency modulation
c) is monaural
d) it can use amplitude as well as frequency modulation and is also monaural
Explanation: STC stands for Subsidiary Communication Authority. SCA is a separated data channel which is transmitted along with the main signal over a broadcast station. It can either be amplitude modulated or frequency modulated. It being monaural means that multiples audio signals are mixed and then passed through a single channel.
5. What is the use of pre-emphasis?
a) to increase the signal to noise ratio for higher audio frequencies
b) to allow stereo audio to be carried by FM stations
c) to increase the signal to noise ratio for all audio frequencies
d) to increase the signal to noise ratio for lower audio frequencies
Explanation: Pre-emphasis is applied in communication systems to improve signal strength before transmission. It refers to boosting the amplitudes of the weak modulating voltages for high audio frequencies. It is also helpful in increasing S/N ratio but for lower audio frequencies only.
6. In FM system, capture effect is observed when an FM receiver switching suddenly between two stations having nearby frequencies.
Explanation: Capture effect is related with FM reception. In capture effect, only the stronger of two signals at, or near, the same frequency will be demodulated.
7. What is the full form of NBFM?
a) Narrow band frequency modulation
b) National broadcast frequency modulation
c) Near band frequency modulation
d) Non broadcast frequency modulation
Explanation: NBFM stands for Narrow band frequency modulation. For NBFM, modulation index should be less than equal to 1.
8. Why the bandwidth of an FM signal is considered to be limited?
a) because there can only be a finite number of sidebands
b) because it is equal to the frequency deviation
c) because it is band-limited at the receiver
d) because the power in the outer sidebands is negligible
Explanation: In frequency modulation system, frequency of the carrier wave is varied in proportion with the instantaneous amplitude of the message signal, which is to be transmitted. IN Wideband FM, the number of sidebands are infinite. Thus, using Carson’s rule, the bandwidth of FM signal is kept limited considering the power impact of other sidebands negligible.
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