Amplitude modulation Presented by aliv. Bangladesh Email: abujauad@gmail.com Cell: +8801672462007

1. Amplitude
Modulation

2. 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

3. Equipment Required
1. Module KL-93002
2. Oscilloscope
3. Spectrum Analyzer
4. RF Generators
5. Jumpers
6. Connectors

4. 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

5. • 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

6. Background
Modulating
Signal V(t), at
baseband(fB)
Action on carrier’s
amplitude, frequency
or phase
Modulated Signal
carrying the
information of
V(t), bandpass (fC)

7. Task to Do
1. 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%

8. 5. Using the spectrum analyzer,
observe and record of the
output signal spectrum
5. Using the results above and
calculate and record the
percentage modulation of
output signal
5. 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

9. Audio
Amplitude
Output Waveform Percentage
Modulation
250 mVp-p Emax= 1.3v
Emin=1v
{(Emax - Emin)/ Emax }* 100
= 23%
200 mVp-p Emax= 130mv
Emin=70mv
{(Emax - Emin)/ Emax }* 100
= 46%
150 mVp-p Emax=
Emin=
{(Emax - Emin)/ Emax }* 100
Records

10.  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

11. 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

12. 26 April 2014 12

13. • Amplitude modulation Presented by aliv.
Bangladesh
• Email: abujauad@gmail.com
• Cell: +8801672462007
26 April 2014 13