Pre-Emphasis & De-Emphasis Networks

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Aim:- 

To draw the frequency response of Pre-emphasis & De-emphasis networks.

Introduction:-

Educational trainer a useful kit for the demonstration of Pre-emphasis & De-emphasis at different time constants & plot the graph of the frequency response of Pre-emphasis and De-emphasis networks. The kit consists of 200 Hz-20 kHz audio oscillator 70µ sec & 50µ sec De-emphasis networks.

 Pre-Emphasis Circuit Diagram:-



DE-Emphasis Circuit Diagram:-



Theory:-

Pre-emphasis refers to boosting the relative amplitudes of the modulating voltage for higher audio frequencies from 2 to approximately 15 kHz .De-emphasis means attenuating those frequencies by the amount by which they are boosted. However, Pre-emphasis is done at the transmitter and De-emphasis is done in the receiver. The purpose is to improve the signal-to-noise ratio for FM reception. A time constant of 75µ sec is specified in the RC or L/Z network for Pre-emphasis and De-emphasis.

Tabular column:-

Pre-Emphasis and De-Emphasis (Tabular column is the same for both)

Sl. Number

Frequency in Hz

i/p voltage Vin

volts

o/p voltage Vo in volts

Gain=Vo/Vin

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 








Procedure:-

1) Check the apparatus properly.

2) Connections are made as shown from the circuit diagram for Pe-emphasis.

3) Switch on the power supply.

4) Set the i/p voltage for frequency 1 kHz & o/p for 4 volts.

5) Take the i/p & o/p voltage simultaneously for varying audio range frequency i.e. (20 Hz- 20 kHz).

6) First, take for the Pre-emphasis.

7)  Then calculate again & plot a grad of frequency vs. gain of a pre-emphasis.

8) For De-emphasis repeat the steps up to 5 using de-emphasis trainer kit.

9) Then calculate the gain.

10) Plot the graph of frequency vs. gain.

Pre- Emphasis Nature of graph:-

De-Emphasis nature of  Graph:-


Result: -  

We have studied the Pre-emphasis & De-emphasis circuit & plotted the frequency response of Pre-emphasis & De-emphasis network.


 


 

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