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*Answer can only contain numeric values

QUESTION: 1

** **An AM signal is represented in the domain as S (-c) = 4 cos 1800T + 10 cos 20002 + 4cos2200T then the bandwidth of the AM signal is _____ Hz

Solution:

QUESTION: 2

A 100MHz carrier is frequency modulated by 10 KHz wave. For a frequency deviation of 50 KHz, calculate the modulation index of the FM signal.

Solution:

Carrier frequency f_{c} = 100MHz

Modulating frequency f_{m} = 10 KHz

Frequency deviation Δf = 500 KHz

Modulation index of FM signal is given by

m_{f} = Δf/f_{m}

= 500 * 10^{3}/ 10 * 10^{3}

= 50

QUESTION: 3

Consider a system shown in the figure-1. Let X(f) and Y(f) represent the Fourier transforms of x(t) and y(t) respectively. The ideal HPF has cutoff frequency of 10 KHZ. X(f) is shown in the figure-2. The positive frequency where Y(f) has spectral peaks are

Solution:

2 KHz S. 24 KHz

QUESTION: 4

Three message signals each band limited to 10 kHz, 10 kHz, and 5 KHz are transmitted through a channel using frequency division multiplexing. The modulation techniques used are any, D513-SC, SSB respectively. The guard band is 2 KHz. Band width of the channel is

Solution:

BW after AM modulation = *2 x *10 = 20 KHz

BW after DSS-SC modulation = 2 x10 = 20 KHz BW after SSB modulation = 5 KHz

Guard band width = 2 x 2k=4 k

∴ Total BW after frequency multiplexing = 49 KHz

QUESTION: 5

A signal '4 t is band limited to the frequency range 0 to f_{n}. The signal frequency is translated by multiplying it by the signal V, t —cos2πf_{c}t . The value of f_{c} such that the bandwidth of the translated signal is 1% of the carrier frequency f_{c} will be

Solution:

BW after multiplexing =

*Answer can only contain numeric values

QUESTION: 6

The peak amplitude of an AM signal for tone modulation with carrier having maximum amplitude as 5 V, varies from 2 to 8 V then the sideband power is _________________________ (W)

Solution:

QUESTION: 7

Consider a frequency multiplier shown in the figure below.ss

A NBFM signal*X Mal t *with f, *= *200KHz and *f, *ranges 50 **Hz **to 150 KHz is given as an input to frequency multiplier. The Maximum Frequency deviation of the NBFM is 25 **Hz. **The maximum frequency deviation at the output is 75 KHz.

**Q.** The required frequency multiplication n is

Solution:

QUESTION: 8

Consider a frequency multiplier shown in the figure below.ss

A NBFM signal*X Mal t *with f, *= *200KHz and *f, *ranges 50 **Hz **to 150 KHz is given as an input to frequency multiplier. The Maximum Frequency deviation of the NBFM is 25 **Hz. **The maximum frequency deviation at the output is 75 KHz.

**Q. **The carrier frequency at the output is

Solution:

QUESTION: 9

SSB modulation may be viewed as a hybrid form of amplitude modulation and frequency modulation. Assuming a message signal m(t) = sin t and a carrier frequency 'f_{c}', the instantaneous frequency for the lower side band is

Solution:

For SSB modulation, the modulated wave is

QUESTION: 10

Given

**In a certain experimental conducted with f**_{m}** = 1 kHz and increasing A**_{m}**(starting ****from 0 volts), it is found that the carrier component of the FM signal is reduced to zero for the first time when A**_{m}** = 2 volts.**

The frequency sensitivity of the modulator is

Solution:

When A_{m} = 2V, carrier component = 0

ie. J_{0} (03) = 0 for the 1^{st} time

From the curve, corresponding (3=2.44

*Answer can only contain numeric values

QUESTION: 11

**If E**_{x}** and E**** _{y} represent the energies of m(t) and y(t) respectively, then **_______________

Solution:

M_{h} (ω) = -jM (6)) sgn(ω), (The given system is a Hilbert transformer) The *π *of a Hilbert transformer is

**H (**ω**) = -jsgn (**ω**)**

QUESTION: 12

**Determine the spectrum of y(t) in the system shown below.**

Solution:

Output of AM Modulator

QUESTION: 13

**Consider the scheme shown**

**If x (t) = m (t) cos (co _{c}t) then y (t) is**

Solution:

QUESTION: 14

**The above schematic generates FM signal as a wideband frequency modulator**

**using the indirect method. The output FM signal is characterized by ****f**** _{c} = 100 MHz, Δf = 75kHz (min). If the phase modulator has a modulation index of **β=

Solution:

**The lowest modulation frequency i.e., **

**Produces a frequency deviation**

**The highest modulation frequency ie.**

**Produces a frequency deviation of**

**Let us take the case of 100Hz **** as the worst case **

**Solving (1) & (2) we get,**

**n _{1}=75 , n_{2} =50**

QUESTION: 15

What is the standard IF frequency for AM receivers?

Solution:

In AM receivers, the standard intermediate frequency is approximately 455 KHz.

QUESTION: 16

**Consider a message signal m(t) = 2sin(10007t)**

**Phase sensitivity constant Kp=5rad/V**

**Frequency sensitivity constant K**_{f}**=75KHz/V**

**Q. If amplitude of message signal is doubled, then bandwidth for FM and PM will be**

Solution:

**Δf = 75x 4 = 300KHz ,**

**B _{FM }= 2(300 + 0.5) = 601KHz, Δ f= 2 x K_{p} x 2 x 500 = 10KHz,B_{pm }= 2(10 + 0.5) = 21KHz**

QUESTION: 17

**A 20 KW and 1 MHz carrier is frequency modulated by a sinusoidal signal so that the maximum frequency deviation is 50 KHz and the message signal is band limited to 500 KHz. The generated FM signal is amplitude modulated using carrier of 1 GHz.**

**Q. The bandwidth of the generated signal is**

Solution:

It is a narrow band FM

QUESTION: 18

**A 20 KW and 1 MHz carrier is frequency modulated by a sinusoidal signal so that the maximum frequency deviation is 50 KHz and the message signal is band limited to 500 KHz. The generated FM signal is amplitude modulated using carrier of 1 GHz.**

**Q. The bandwidth of the generated AM signal is**

Solution:

Taking above spectrum as message signal and generate AM signal using carrier 1GHZ

BW = 2 1,5 MHz = 3MHz

QUESTION: 19

**The input x(t) and the output y(t) of a certain nonlinear channel are related as ****y(t) = x(t) + 0.001 x ^{2}(t)**

**If frequency spectrum of input signal is**

**Q. ****The bandwidth of the output signal is**

Solution:

QUESTION: 20

**The input x(t) and the output y(t) of a certain nonlinear channel are related as ****y(t) = x(t) + 0.001 x ^{2}(t)**

**If frequency spectrum of input signal is**

**Q. Spectrum of the received signal after appropriate low pass filtering is **

Solution:

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