Student Name Student ID Last 4 digits only EE4330 Section 001 Fundamentals of Telecommunications Systems INSTRUCTOR Dr K R Rao Spring 2006 Test 1 Thursday 16 February 2006 3 30 4 50 pm 1 Hour and 20 minutes INSTRUCTIONS 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 2 Q1 In baseband communication baseband signals are transmitted A over a radio link B without any shift in the range of frequencies C along with the carrier signal D suppressing the carrier signal Q2 If signals g1 t and g2 t have bandwidths B1 and B2 Hz respectively the bandwidth of g1 t 2 g2 t 2 is A B1 B2 Hz B B1 B2 Hz C 2B1 2B2 Hz D B1 2 B2 2 Hz Q3 A baseband signal m t cos 3 000t 4sin 2 000t sin 1 000t modulates a carrier cos 10 000t The frequency components radians sec in the baseband signal are Baseband spectra rad sec A 1K B 1K 3K C 1K 2K 3K D 3K Q4 From Q3 the frequency components in the DSB SC spectra are DSB SC spectra rad sec A 9K 11K B 9K 11K 7K 13K C 9K 11K 8K 12K 7K 13K D 7K 13K Q5 Bandwidth of DSB SC signal modulated with baseband signal with bandwidth 200 Hz is A 100 Hz B 200 Hz C 300 Hz D 400 Hz 3 Q6 A DSB SC signal is given by m t cos ct where m t is a signal band limited to B Hz In order to avoid the overlap of the spectra what is the minimum usable value of c rad sec M 2 B 2 B A 4 B B 2 B C B D B 2 Q7 Consider a periodic signal m t shown below modulating a carrier signal Acos ct to obtain amplitude modulated signal A m t cos ct the modulation index is 0 5 Find A 6 v 2 ms t sec 0 4 ms 6 v 6 ms A 12 Volts B 15 Volts C 30 Volts D 60 Volts Q8 From Q7 find the power efficiency Hint Find average power of m t i e m2 t A 5 B 10 C 20 D 30 4 Q9 Given a baseband signal m t 2cos Lt sin Nt Find mh t mh t is Hilbert transform of m t A 2sin Lt cos Nt B 2cos Lt 90 sin Nt 90 C sin L N t 90 sin L N t 90 D cos L N t cos L N t Q10 Signal m1 t and m2 t band limited to 1 000 rad sec are transmitted over a channel by the multiplexing scheme shown below M1 1000 m1 t 0 1000 ii iii m2 t M2 1000 0 1000 2 cos 4 000t i 2 cos 2 000t What is the modulated signal spectrum at point iii A 7 4 2 1 0 1 2 4 7 7 4 2 1 0 1 2 4 7 4 2 1 0 1 2 4 4 2 1 0 1 2 4 B C 5 Krad sec Krad sec 5 D 7 Krad sec 7 Krad sec 5 Q11 From Q10 the bandwidth in rad sec of the channel must be at least A 7 K B 6 K C 5 K D 4 K Q12 In diode bridge modulator during positive half cycle of carrier signal diodes a D3 D1 c A cos ct D2 A cos ct d D4 t b A D1 D4 conduct but D2 D3 do not B D2 D3 conduct but D1 D4 do not C All the diodes conduct D All the diodes do not conduct Q13 For Amplitude modulation AM DSB with carrier A Envelope detection is always possible B Envelope detection is NOT possible when 1 C Envelope detection is NOT possible when 1 D Envelope detection cannot be applied Q14 For message signal m t cos3 1000t the baseband frequencies in rad sec are A 1K B 3K C 1K and 3K D 1K 2K and 3K 6 Q15 For synchronous demodulation scheme shown the lowpass filter suppresses spectrum centered at frequency A m t cos ct Low pass filter DC blocker Output cos ct A 3 c B 2 c C c D 0 DC Q16 Which of the following modulation schemes is used in color television to multiplex the chrominance signals A DSB with suppressed carrier B SSB C QAM D DM Q17 For 16 ary QAM A Bit rate and bandwidth are quadrupled B Bit rate and bandwidth are doubled C Bit rate is quadrupled but bandwidth remains the same D Bit rate is doubled but bandwidth remains the same Q18 The power efficiency for tone modulation under best condition is Here AM Signal is A m t cos ct and m t is a pure sinusoidal signal A 25 B 30 C 33 3 D 43 5 7 Q19 To demodulate DSB SC signal the type of demodulator used is A coherent B homodyne C synchronous D All the above Q20 For a broadcast system with a multitude of receivers for each transmitter it is more economical to have A AM with carrier B DSB with suppressed carrier C SSB D VSB