21-05-2013, 04:04 PM
PRE-EMPHASIS & DE-EMPHASIS
Aim:
1. To Observe the effects of pre-emphasis on given input signal.
2. To observe the effects of De-emphasis on given input signal.
Theory:
The noise has a effect on the higher modulating frequencies than on the lower ones. Thus, if the higher frequencies where artificially boosted at the transmitter and correspondingly cut at the receiver, an improvement in noise immunity could be expected, thereby increasing the SNR ratio. This boosting of the higher modulating frequencies at the transmitted is known as pre-emphasis and the compensation at the receiver is called de-emphasis.
Procedure:
1. Connect the circuit as per circuit diagram as shown in Fig.1.
2. Apply the sinusoidal signal of amplitude 20mV as input signal to pre emphasis circuit.
3. Then bty increasing the input signal frequency from 500Hz to 20KHz, observe the output voltage (Vo) and calculate gain (20log(Vo /Vi ) ).
4. Plot the graph between gain Vs frequency.
5. Repeat above steps 2 to 4 for de-emphasis circuit (shown in Fig: 2.) by applying the sinusoidal signal of 5V as input signal.