EXPERIMENT NO. 03

DATE OF PERFORMANCE: GRADE:

DATE OF ASSESSMENT: SIGNATURE OF LECTURER/ TTA:

AIM: To get the demodulated signal form amplitude modulated signal using Diode.

CIRCUIT DIAGRAM:

APPARATUS:

SR.NO.

EQUIPMENT/DEVICE/ INSTRUMENT

SPECIFICATION/ RANGE

QTY. PURPOSE/ REMARKS

1.

2.

3.

4.

5.

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THEORY:

A number of methods can be used to demodulate AM, but the simplest is a diode detector.It operates by detecting the envelope of the incoming signal which it does by rectifying the signal.

Current is allowed to flow through the diode in only one direction, giving either the positive or negative half of the envelope at the output.

If the detector is to be used only for audio detection it does not matter which half of the envelope is used, either will work equally well. Only when the detector is also used to supply the automatic gain control (AGC) circuitry will the polarity of the diode matter.

The AM detector or demodulator includes a capacitor at the output. Its purpose is to remove any radiofrequency components of the signal at the output. The value is chosen so that it does not affect the audio base-band signal. There is also a leakage path to enable the capacitor to discharge, but this may be provided by the circuit into which the demodulator is connected.

This type of detector or demodulator is called a linear envelope detector because the output is Proportional to the input envelope.

Diode detector advantages & disadvantages:

The diode detector is widely sued, but it has several advantages and disadvantages:

Diode detector advantages:

Simplicity: The diode detector is very simple and is easy to construct. The circuit six veryStraight forward, consisting of a very few components.

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Low cost: Requiring so few components, and the fact that he components are not specialized, this form of detector is very cheap. Accordingly it is widely used in AM domestic radios.

Diode detector disadvantages:

Distortion: Although the diode detector is able to operate in a reasonably linear fashion over a reasonable range, outside this range high levels of distortion are introduced, and even within the more linear range, distortion levels are not particularly low. It is adequate for small low cost radios.

PROCEDURE:

1. Collect equipments/ devices/ instruments with the help of lab assistant & peon.2. Setup the instrument for am generation.3. Get the connected circuit checked by lecturer/ tta.4. Make the supply on only in the presence of lecturer/ tta.5. Now connect the generated am waveform to the input of am demodulator circuit.6. Now connect the cro channel after diode and observe the waveform.7. Now observe the demodulated output after the capacitor.8. Vary the potentiometer to observe the effect of it on demodulated output as

diagonal PEAK CLIPPING EFFECT.

GRAPH:

Draw the each observed waveform on the graph paper in the following sequence.

Modulating signal Carrier signal Amplitude Modulated waveform Waveform after diode Demodulated output after capacitor

CONCLUSION:

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