Analog Communication (EC) Jan 2010

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EC5 O1

USN I 1 M

M S RAMAIAH INSTITUTE OF TECHNOLOGY(AUTONOMOUS INSTITUTE, AFFILIATED TO VTU)

BANGALORE - 560 054

SEMESTER END EXAMINATIONS - JANUARY 2010

Course & Branch : B.E (Electronics and Communication)

Subject : Analog Communication

Subject Code: EC 501

Instructions to Candidates:1. Answer one Full question from each unit.

Semester: V

Max. Marks: 100

Duration: 3 Hrs

UNIT-I

1 a) Define and explain the following:

i) Noise figureii) Equvalent Noise Temperature

b) Three amplifiers have the following specifications:Ampi f i er 1 F1=8dB G1=42dB

Ampi f i er 2 F2=9dB G2=38dB

Ampi f i er 3 F3=5dB G3=22dB

The amplifiers are connected in cascade. Find overall noise figure

( 6 )

( 6 )

c) Show that the Figure of Merit of an SSB system is equal to unity (8)

2 a) What is noise equivalent bandwidth? Derive an expression for the same. (5)

b) Calculate the output signal to noise ratio in dB for three links, the first two (3)of which have a signal to noise ratio of 60dB and the third has a signal tonoise ratio of 40dB.

c) Derive an expression for the Figure of (vierit of an FM receiver. (12)

UNIT-II

3 a) What is the need of moduation?

b) Define demodulation. Explain the method of demodulation using a square-law device.

c) A carrier of 5v(rms) at a frequency of 1MHz and a modulating voltage of0.2v(rms) at a frequency of 1kHz are applied in series to a suitably biased

rectifier which has a characteristic given by i=5+v+0.05v2 where 'v' is involts and 'i' is in µA. Compute the value of amplitudes, and frequencies ofvarious components of the signal at rectifier output and also the

modulation index.

( 3 )

( 8 )

( 9 )

4 a) Explain AM generation using switching modulator with relevant diagrams (7)-and analysis.

b) What is QAM ? Explain with relevant block diagram . Also mention its (8)advantages.

c) A non -coherent carrier Accos ( 2 1 T f t+ 0) is added to a DSBSC signal (5)

cos2nf,t . m(t). It is passed through an envelope detector . Evaluate the

output for i) 0 = 0 ii) 0 t0, Im(t)I <_ 2

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C )

UNIT - III

Define the Hilbert Transform and explain its properties.

With suitable block diagrams explain the phase discrimination method ofSSB generation.

( 6 )

( 7 )

Consider a two stage modulator as shown in Fig.5(c). The input signal (7)consists of a voice signal occupying the frequency band 0.3 to 3.4KHz. Thetwo oscillator frequencies have the values f1=100KHz, and f2= 1OMHz.Specify the following:

(i) Sidebands of DSBSC modulated wave appearing at the twoproduct modulator outputs.

(ii) Sidebands of SSB moduated wave appearing at the two BPF

outputs.

(iii) The pass bands and guard bands of the two BPFs.

LA)

I (1ciil t

r -law)

Fig .5 (c)6 . a ) Define the following:

(i) Pre-envelope

(ii) Complex-envelope

( 4 )

b ) Explain coherent detection of SSB. ( 8 )

c ) Find the Hilbert Transform of the following

i 8

( 8 )

) 2t) (ii) l+t

UNIT - IV

7. a) Show that a VSB modulated wave s(t) containing a vestige of LSB defined

b t = 2° (t 2 t i t- 2

(8)

) m ) cos ) r f^ m ( ) s n nfcs(

b) Explain with a neat block diagram the operation of a superheterodyne

receiver.

(8)

c) What is frequency translation? Briefly explain. ( 4 )

8. a) Explain FDM with suitable block diagrams. (8)b) How is an envelope detector used to detect VSB? Illustrate with suitableanalysis.

(8)

C ) What is the function of AVC in an AM receiver? ( 4 )

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UNIT - V

9. a) A carrier wave is frequency moduated with a sinusoidal frequency fn,=1KHz (6)

and an amplitude Am which is increased starting from zero volts. It is

found that the carrier components of FM wave is reduced to zero for thefirst time when Am=2 volts. Determine

(i) Sensitivity of the moduator

(ii) The value of Am for which the carrier component is reduced tozero for the second time.

Given Jo(0)=0 for 1S` time at 2.405Jo(R)=0 for 2nd time at p= 5.52

b) Expan FMdemoduation usng zero-cross ng detect or. (8)

c) Compa e AMand FMsys ems ( 6)

10a) Showthat FMhas i nfi ni te si debands. (12b) An FM signal is applied to a square law device with output voltage related (8).

to input voltage by vo=9v;2. Explain how such a device can be used to

obtain an FM signal with greater frequency deviation than that available at

input.

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Analog Communication (EC) Jan 2010

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