Amplitude Modulation

Objective Understanding the principle of amplitude modulation (AM) Understanding the waveform and the frequency spectrum of AM signal Calculating the percentage of modulation Measuring and adjusting an amplitude modulator circuit

Equipment Required

1. Module KL-93002 2. Oscilloscope 3. Spectrum Analyzer

4. RF Generators 5. Jumpers6. Connectors

Background• Modulation --Allow low frequency intelligence

signal onto a high frequency carrier signal

• AM -- A high frequency carrier signal is modulated by a low frequency modulating signal (usually an audio)

• Carrier -- A sinusoidal of high frequency

• In AM modulation the amplitude of the carrier is modified in proportion to the baseband signal

• The resulting band pass signal is the “Modulated” signal, which is a combination of the carrier and the original message

Background

BackgroundModulating Signal V(t), at baseband(fB)

Action on carrier’s amplitude, frequency or phase

Modulated Signal carrying the information of V(t), bandpass (fC)

Task to Do1. Locate AM modulator circuit on

Module KL -93002. Insert connect plugs in J1 and J3 to set R8 =1k and R 9 =6.8k

2. Connect a 250mVp-p, 1 kHz sine wave to the audio input (I/P2) and a 250 mVp-p, 100 kHz sine wave to the carrier input (I/P1).

3. Connect the vertical input of the oscilloscope to the AM output (O/P)

4. Observe the output waveform and adjust the VR 1 for the modulation index of 50%

5. Using the spectrum analyzer, observe and record of the output signal spectrum

6. Using the results above and calculate and record the percentage modulation of output signal

7. Using the oscilloscope, observe the output signals for the audio amplitudes of 200 mVp-p and 150 mVp-p and record the results

Task to Do

Audio Amplitude

Output Waveform Percentage Modulation

250 mVp-p Emax= 1.3vEmin=1v

{(Emax - Emin)/ Emax }* 100

= 23%

200 mVp-p Emax= 130mvEmin=70mv

{(Emax - Emin)/ Emax }* 100

= 46%

150 mVp-p Emax= Emin=

{(Emax - Emin)/ Emax }* 100

Records

Entertainment - AM Radio (music, talk radio) Business - CB Radio to relay shipment progress, conference

calls with other branches via telephone or speakerphone Government - Police officers keeping contact with the

station, or relaying the information and location of a suspect

Personal - Cell phones or walkie-talkies for chatting with friends

Military - Using undetectable radio signals to communicate with other soldiers, or voice commands to control weapons

Application of AM

Discussion Amplitude Modulation is the simplest and

earliest form of transmitters AM applications include broadcasting in

medium- and high frequency applications, CB radio and aircraft communications

AM is a nonlinear process Sum and difference frequencies are created

that carry the information

April 11, 2023 12

THANK YOU

April 11, 2023 13

• Amplitude modulation Presented by aliv. Bangladesh

• Email: abujauad@gmail.com• Cell: +8801672462007