Fundamentals of Telecommunication Systems

EE4330

Lab Assignment 3

Project Assignment: Build and test an Envelope Detector with Full Carrier AM.

Detailed Instructions:

1. Set up the signal generator to produce an AM waveform

F_C = 1 MHz at 1.2V peak to peak

F_m = 1 KHz

Modulation Index: 100%

2. Build an envelope detector followed by a Low Pass Filter

C1 0.01 microfarad

C2 0.2 microfarad

D1 1N4148

R1 1000 ohms

R2 To Be Determined

R3 100 Kohms variable

R4 100 Kohms

U1A ¼ ST274

U1B ¼ ST274

2.1 Choose R2 so that the half power point of the RC network is at 5 KHz.

2.2 Use +10 for VCC⁺ and –10 for VCC^–

2.3 Set R3 so that the output of U1B is 0.8V p-p into the Speaker.

3. Connect a headphone or speaker (student supplied) to the output of U1B.

4. Repeat with F_C set to 100KHz, 50KHz, and 10KHz.

5. Take screen shots of the waveform and FFT of the waveform at the nodes in the signal path.

6. The report should contain the following sections:

a. The experiment performed,

b. The calculations made,

c. A Theory of Operation for each part of the circuit, and

d. Explanations for the waveforms observed.

· What is the significance of the waveforms produced by each value of F_C?

· It would be helpful to include a MatLab generated Bode plot showing the output of the Low Pass Filter.