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Solution Communication Mid Exam – Second Stage What happens when the amplitude of the modulating signal is greater than the amplitude of the carrier? a) Decay b) Distortion c) Amplification d) Attenuation The ratio between the modulating signal voltage and the carrier v...

Solution Communication Mid Exam – Second Stage What happens when the amplitude of the modulating signal is greater than the amplitude of the carrier? a) Decay b) Distortion c) Amplification d) Attenuation The ratio between the modulating signal voltage and the carrier voltage is called? a) Amplitude modulation b) Modulation frequency c) Modulation index d) Ratio of modulation VCO is used to generate a) Direct FM b) Indirect FM c) SSB-SC d) DSB-SC When does over-modulation occur? a) Modulating signal voltage < Carrier voltage b) Modulating signal voltage > Carrier voltage c) Modulating signal voltage = Carrier voltage d) Modulating signal voltage =0 What is the modulating signal voltage if the maximum and the minimum voltages on the wave was observed to be 10v and 5v respectively? a) 2.5v b) 7.5v c) 2.25v d) 3.21v What is the circuit used for producing DSB-SC called? a) Modulator b) Transmitter c) Receiver d) Duplexer If the modulating frequency of a carrier wave varies between 900kHz and 1100KHz, find it’s bandwidth? a) 1000KHz b) 100KHz c) 200KHz d) 1010KHz  Which of the following is indirect FM generation? a) varactor diode b) reactance modulator c) Crosby modulator d) Armstrong modulator The two types of angle modulation are: a) amplitude and frequency modulation. b) phase and frequency modulation. c) pulse and frequency modulation. d)phase and amplitude modulation Phase modulation is an indirect form of: a)amplitude modulation. b)pulse modulation. c)frequency modulation. d) angle modulation. The amount of frequency deviation is proportional to the amplitude of the intelligence signal in: a) an FM signal. b) a PM signal. c)both FM and PM signals. d) neither FM nor PM signals What is the effect on the deviation d of an FM signal when it is passed through a mixer? a) Doubles b) Reduces c)Becomes half d) Remains unchanged The output signal from an DSB-SC modulator is: Find total power a) 10w. b) 5w. c) 12.5w. d) 25w. Amplitude limiter in FM receivers are used to a) Remove amplitude variations due to noise b) Filteration c) Demodulation d) Amplification A sinusoidal modulating waveform of amplitude 5 V and a frequency of 2 KHz is applied to FM generator, which has a frequency sensitivity of 40 Hz/volt. Calculate the bandwidth. a) 2,000 Hz b) 2,000 KHz c) 4KHz d) 4Hz An FM wave is given by s(t)=20cos(8π×106t+9sin(2π×103t)). Calculate the modulation index. a) 103 b) 9 c) 20 d) 18 In Frequency Modulation a)Amplitude of the carrier remains same b) Frequency of the carrier varies in accordance with the modulating signal c) The number of side bands are infinite d) All of the above The amount of frequency deviation in FM signal depends on a) Amplitude of the modulating signal b) Carrier frequency c) Modulating frequency d) Transmitter amplifier The modulation index of FM is given by a) μ = frequency deviation/ modulating frequency b) μ = modulating frequency /frequency deviation c) μ = modulating frequency/ carrier frequency d) μ = carrier frequency / modulating frequency According to Carson’s rule, Bandwidth B and modulating frequency fm are related as a)B = 2(Δf + fm) Hz b) B = fm Hz c) B < 2fm Hz d) B > 2fm Hz After passing the FM signal through mixer, what is the change in the frequency deviation Δ when the modulating frequency is doubled? a) Becomes 2 Δ b) Becomes Δ /2 c) Becomes Δ2 d) Remains unchanged What are the disadvantages of PCM? a) Encoding, decoding and quantizing circuitry of PCM is complex. b)PCM require large bandwidth as compared to the other systems. c) a&b d) most of power is lost The modulation techniques used to convert analog signal into digital signal are a) Pulse code modulation b) AM modulation c) FM modulation d) All of the above The expression for bandwidth BW of a PCM system, where n is the number of bits per sample and fm is the modulating frequency, is given by a) BW> = nfm b) BW< = nfm c) BW> = 2 nfm d) BW> = 1/2nfm In uniform quantization process a)The step size remains same b) Step size varies according to the values of the input signal c) The quantizer has linear characteristics d) Both a and c are correct A PCM system uses a uniform quantizer followed by a 7 bit binary encoder. The bit rate of the system is equal to 49*106bps. what is the maximum bandwidth of message. a) 3Mbps b) 3.5Mbps c) 49Mkbps d) 7Mkbps In pulse amplitude modulation, a. Amplitude of the pulse train is varied b. Width of the pulse train is varied c. Frequency of the pulse train is varied d. None of the above A signal has the highest frequency component of 3.2MHz and peak to peak value 6 volt is transmitted using PCM. The number of quantization level is 512. calculate signal to quantization noise ratio a) 5dB b) 9.7dB c) 36.98dB d. None of the above In Pulse Position Modulation, the drawbacks are a)Synchronization is required between transmitter and receiver b) Large bandwidth is required as compared to PAM c) None of the above d)Both a and b The spectrum of the sampled signal may be obtained without overlapping only if a) fs ≥ 2fm b) fs < 2fm c) fs > fm d) fs < fm A low pass filter is a) Passes the frequencies lower than the specified cut off frequency b) Rejects higher frequencies c) Is used to recover signal from sampled signal d) All of the above Types of analog pulse modulation systems are a) Pulse amplitude modulation b) Pulse time modulation c) Frequency modulation d) Both a and b Aliasing refers to a) Sampling of signals less than at Nyquist rate b) Sampling of signals greater than at Nyquist rate c) Sampling of signals at Nyquist rate d) None of the above The modulation technique that uses the minimum channel bandwidth and transmitted power is a) FM b) DSB-SC c) VSB d)SSB