# Analog Communication Dec-2011

UNIT – I

1 (a) Explain the different types of noise in communication system. How we can reduce it ?

(b) A resistor 25 KQ is connected to input of amplifier. The amplifier is performing at the frequency range of 11 to 12 MHz. Determine the rms noise voltage at input of amplifier if ambient temperature is 25°C.                                              ,

OR

1 (a) Define the noise figure and noise temperature. Calculate noise figure and equivalent noise temperature of cascaded stage,.

(b) A receiver with 5 dB noise figure, 10 dB gain and 50 kHz noise band width is connected to an antenna that has noise temperature of 1050 K. Calculate the overall noise figure.

UNIT – II

2. (a) Derive the equation and power relation in AM system. Compare AM, DSBSC and SSB transmission.

(b)   A broad cast radio transmitter is 12 kW when modulation percentage is 65%. What will be the side band power ?

OR

2. (a) With the help of block diagram explain the AM Receiver. Also compare it with FM Receiver.

(b)   The antenna current of transmiter is 11.5 Amp when it is modulated to a depth 45% by audio sine wave. Determine unmodulated (carrier) current.

UNIT – III

3. (a) Compare AM, FM and PM.

(b) A FM voltage is given as

V = 15Sin (6.5 x 108t + 5.55sinl260 t)

Determine

(i)  Modulating and carrier frequency

(ii)  Modulation index and FM band width.

OR

3. (a)  Explain the principle of generation and detection of FM signal. Explain one method of FM detection in detail.

(b) Explain Preemphasis and Deemphasis.

UNIT – IV

4. (a) Calculate S/N ratio of square law demodulates and envelope detector.

(b) A FM broad cast system with max. deviation of = 75 kHz and band width B = 15 kHz. Assume power spectral density Sx – 1/2, find the output SNR and calculate improvement (IndB) over base band system.

OR

4.  Calculate the signal to noise ratio (S/N) in AM (DSBFC), FM and PM and compare it.

UNIT – V

5. Write short notes on followilig :

(a) Sampling

(b) Pulse amplitude modulation (PAM).

OR

5. Write short notes on following

(a) Pulse width modulation (PWM)

(b) Pulse position modulation (PPM).