Analog Communication. Assignment 4.

1. For a two stage frequency discriminator, the input is a voice signal occupying frequency band 0.3KHz to 3.4 KHz with the oscillators having frequencies f1=100KHz and 10MHz are used. Sketch the frequency spectrum at the input and output of each stage. Assume ban-pass filter used passes lower side-band only.

2. A SSB modulated wave is generated by modulating the carrier

c ( t )=100 cos (1600×103πt )by the signal, m( t )=cos (2000 πt )+2sin (2000πt ). Determine time-domain expression for the lower side-band of the SSB modulated signal and plot the magnitude spectrum of the same.

3. In an FM system, when the audio frequency is 500Hz and modulation voltage is 2.5V, the deviation produced is 5KHz. If the modulating voltage is now increased to 7.5V, calculate the new value of frequency deviation produced. If the AF voltage is raised to 10V while the modulating frequency dropped to 250Hz, what is the frequency deviation? Calculate the modulation index in each case.

4. Consider an angle-modulated signal, s( t )=10 cos (108 πt+5sin(2π 103 t )) . Find the maximum phase deviation and the maximum frequency deviation. (Clearly show the calculation steps).

5. A SSB signal with lower side-band is gives as,

s( t )=(A+m( t ))cos (ωct )+m̂( t )sin(ωc t ) . If the signal is received and demodulated by an envelope detector, determine the output of the envelope detector. What is the condition to be satisfied in order to faithfully demodulate the signal?