EE4330 Fundamentals of Telecommunication Systems Instructor Dr K R Rao Test 2 October 27 05 Thursday 2 00 3 20pm 1 Closed books and closed notes 2 Any additional information required is attached to the test you can only use the four page cheat sheet handout 3 Choose only one answer from the options given 4 Please print your name and last four digits of your ID 5 Once the test is returned to you please do not make any corrections we will keep copies of all your tests Student Name Student ID 1 1 Which part is not included in superheterodyne AM receiver 5 points a IF amplifier b Envelope detector c Frequency converter d Hard limiter 2 Selectivity of an FM radio channel in super heterodyne receiver is realized in which section 5 points a RF section b Mixer section c LO section d IF section 3 Fill in the function names in the blank blocks 5 points m t m t Integrator FM signal Frequency modulator PM signal 2 4 An angle modulated signal is given by EM t 10 cos15000t Carrier frequency c 10000 10 points a If this were a PM signal with k p 1000 determine m t b If this were a FM signal with k f 1000 determine m t 5 E t is the angle modulated signal E t 10 cos c t 0 1sin 2000 t here c 2 100000 0 15 points a Find the power of the modulated signal b Find the frequency deviation f in Hz c Find the deviation ratio d Find the phase deviation e Estimate the bandwidth of E t in Hz 6 The primary reason for using angle modulation in microwave radio relay system is 5 points a b c d Easy to implement the modulating circuit Low bandwidth Immunity to nonlinearity High bandwidth 7 Which of the following is not practical frequency demodulator 5 points a b c d Balanced discriminator Rectifier demodulator Zero crossing detector PLL 8 If m t 2 cos 8 t and Kf 8 determine for an FM signal points 15 a peak frequency deviation in Hz 3 b modulation index The FM modulated signal for above m t is E t 10 cos 200 t t If it is passed through filter with gain 1 centered at frequency 100 Hz and following characteristic H f 90 110 f Hz d Find the power at the output of the filter use Bessel function 9 The amplitude variations of the angle modulated carrier can be eliminated by 5 points a b c d Differentiator Integrator Band pass filter Band pass limiter 10 We are using Phase Locked Loop PLL as a FM demodulator Fill in the function name in the blank block to convert FM demodulator into PM demodulor 5 points PM signal m t Loop filter H s VoltageControlled oscillator 4 11 The channel noise acts as interference in an angle modulated signal In the interference is constant 5 points a b c d FM PM FM with preemphasis deemphasis None of the above 12 At intermediate frequencies pre emphasizer behaves like a 5 points a b c d Adder Differentiator Integrator Subtractor 13 What is the main purpose of using PDE in FM broadcasting 5 points a b c d To reduce interference by channel noise at higher frequencies To attenuate the lower frequency components of the message signal To reduce the bandwidth of the modulated signal None of the above 14 Which bandwith is independent of the spectrum of message signal m t 5 points a WBFM b WBPM 15 Consider a signal g t whose spectrum is band limited to B Hz what is bandwidth for signal g2 t 5 points a B Hz b 2B Hz c B 2 Hz d 4B Hz 5