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    Doubts: Communication Systems 
These are the problems where I am facing problems, Kindly give explanation for the probs. Source – Brilliant’s notes 2001. 

1. AM wave is given by e = 25( 1 + 0.7 cos 5000t – 0.3 cos 10000t) * sin 5 * 10^ 5t. evaluate the degree of modulation for the peaks and troughs. ( Ans : 0.03, 0.01 for both) 

2. A wave is frequency modulated with an index of Mf. If its frequency is multiplied by x times, then what will be its modulation index. ( Ans = Mf * x) 

3. The tuning range required for the variable capacitor for the MW band 550 kHz to 1650 kHz with IF of 455 kHz is (Ans: 4.39) 

4. An FM is modulated 60%. The modulating frequency at which the carrier has no energy is (Ans: 18.75 kHz) 

5. Zero mean white noise is passed through an ideal low pass filter with cut off at W Hz. The filter output will be uncorrelated at the time instants spaced ( Ans = m/2W sec apart; m = 1,2,3……) 

6. A FM carrier is sinusoid ally modulated. The modulation index B at which all the power is in the sidebands and no power in carrier is (Ans 2) 

7. The bit stream 01001 is differentially encoded using ‘Delay and EX OR’ scheme for DPSK transmission. Assuming the reference bit as ‘1’ and assigning phase of ‘0’ and ‘pi’ for 1’s and 0’s, respectively, in the encoded sequence, the transmitted phase sequence becomes (Ans: pi pi 0 pi pi) 

8. In a VSB system, the power contained in the sidebands due to a modulating frequency of 4 MHz is 50 watts. The power in the sidebands due to a modulating frequency of 0.5 MHz ( Ans – 100 watts) 

9. In Super Hetro dyne Receiver, mixer translates the carrier frequency (F1) to a fixed 455 kHz by using a local oscillator frequency (F2). The broad cast frequency range is from 540 – 1600 kHz. The range of tuning that must be provided in the local oscillator when F1 > F2 (Ans – 85 – 1145 kHz) (Source Gate Forum Test 5) 

10. The Fourier transform of x(t) = exp (- pi*t^2). 

11. Problem in digital transmission techniques (ASK, BPSK etc.) 

12. Need ready SNR formulas. For AM, FM, PM, ASK,BPSK etc
_________________
JuSt RoCkS ! 

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balu Senior Member Joined: 20Feb2007 Online Status: Offline Posts: 236	Topic: Communication Systems Posted: 22Feb2007 at 3:07pm
	Doubts: Communication Systems These are the problems where I am facing problems, Kindly give explanation for the probs. Source – Brilliant’s notes 2001. 1. AM wave is given by e = 25( 1 + 0.7 cos 5000t – 0.3 cos 10000t) * sin 5 * 10^ 5t. evaluate the degree of modulation for the peaks and troughs. ( Ans : 0.03, 0.01 for both) 2. A wave is frequency modulated with an index of Mf. If its frequency is multiplied by x times, then what will be its modulation index. ( Ans = Mf * x) 3. The tuning range required for the variable capacitor for the MW band 550 kHz to 1650 kHz with IF of 455 kHz is (Ans: 4.39) 4. An FM is modulated 60%. The modulating frequency at which the carrier has no energy is (Ans: 18.75 kHz) 5. Zero mean white noise is passed through an ideal low pass filter with cut off at W Hz. The filter output will be uncorrelated at the time instants spaced ( Ans = m/2W sec apart; m = 1,2,3……) 6. A FM carrier is sinusoid ally modulated. The modulation index B at which all the power is in the sidebands and no power in carrier is (Ans 2) 7. The bit stream 01001 is differentially encoded using ‘Delay and EX OR’ scheme for DPSK transmission. Assuming the reference bit as ‘1’ and assigning phase of ‘0’ and ‘pi’ for 1’s and 0’s, respectively, in the encoded sequence, the transmitted phase sequence becomes (Ans: pi pi 0 pi pi) 8. In a VSB system, the power contained in the sidebands due to a modulating frequency of 4 MHz is 50 watts. The power in the sidebands due to a modulating frequency of 0.5 MHz ( Ans – 100 watts) 9. In Super Hetro dyne Receiver, mixer translates the carrier frequency (F1) to a fixed 455 kHz by using a local oscillator frequency (F2). The broad cast frequency range is from 540 – 1600 kHz. The range of tuning that must be provided in the local oscillator when F1 > F2 (Ans – 85 – 1145 kHz) (Source Gate Forum Test 5) 10. The Fourier transform of x(t) = exp (- pit^2). 11. Problem in digital transmission techniques (ASK, BPSK etc.) 12. Need ready SNR formulas. For AM, FM, PM, ASK,BPSK etc _________________ JuSt RoCkS ! Post Resume:* Click here to Upload your Resume & Apply for Jobs

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