Communication Systems — DU B. Sc. (Hons) Electronics Previous Year Question Papers

Under NEP UGCF Mode Semester VI Instruction for Candidates Ques. 1 (a) What is Internal Noise. Give any two examples. 3 Ques. 2 Ques. 3 (b) (c) (d) (e) (a) (b) (a) Why is modulation necessary for the transmission of signals? 3 What is over-modulation. Draw an over-modulated Amplitude Modulated Signal in the time domain. Also, draw the corresponding trapezoid. List two advantages and two disadvantages of Frequency Modulation over Amplitude Modulation. An amplitude modulated signal is being transmitted at a frequency of 650 KHz. What is the frequency of the image signal that must be rejected by the receiver? What is the VHF range? Give any application that utilizes this range of frequencies. What are the channels that can be used for the propagation of this frequency range. What is shot noise. Calculate the shot noise component of current present on a direct current of 1mA flowing across an abrupt semiconductor junction, given that the effective noise bandwidth is 1 A sinusoidal carrier wave has an amplitude of 10V and frequency of 30 KHz. It is amplitude modulated by a sinusoidal voltage of amplitude 3V and frequency 1KHz. The modulated voltage is developed across 50Ω resistance. (i) Write the equation for the modulated wave. (ii) Plot the modulated wave showing maxima and minima of waveform. (iii) Determine the modulation index. (iv) Draw the spectrum of the modulated wave. Ques. 4 Ques. 5 Ques. 6 (b) Describe vestigial sideband transmission. Give its applications. 7 (c) Explain the working of a collector modulator circuit for generation of an amplitude modulated wave. Also find the expression of modulator output power. (a) (b) (c) Determine the condition to avoid diagonal peak clipping in diode detector. An amplitude modulated wave 10[1 + 0.6 cos 2𝜋103 𝑡]𝑐𝑜𝑠2𝜋106𝑡 is to be detected by a linear diode detector. Find (a) the time constant τ, (b) the value of R if capacitor used is 100pF. List the three methods that can be used for the generation of Single Side Band Suppressed Carrier Signals. Draw the block diagram of the phase cancellation SSB generator and explain how the carrier and unwanted sideband are suppressed. (a) (b) (c) (a) (b) Is it possible to achieve FM via PM (Phase Modulation)? Draw the block diagram and explain the underlying principle. Encode the data stream’ 11010010 into RZ, BRZ, NRZ and split phase Manchester code What determines the bandwidth used by any given FM communication system? A modulating signal 5 cos 2𝜋(15 × 103)𝑡 angle modulates a carrier 𝐴 cos 𝜔𝐶 𝑡 (i) If 𝐾 𝑓 = 15 KHz/V and 𝐾𝑃=15 rad/V, find the modulation index and bandwidth for I. The FM system II. The PM system (ii) Determine the change in the bandwidth for both FM and PM if 𝑓𝑚 is reduced to 5 KHz. What are Pre-emphasis and De-emphasis circuits? Where and why are they used? In a Frequency Modulated signal, the total carrier power is redistributed between all components of the spectrum. Explain.