In amplitude modulation communication system ,speech or music is converted into electrical signal by using a device like microphone. The electrical signal is called message or baseband signal. The message signal is then used to electrically vary the amplitude of a pure sine-wave called the carrier. The carrier usually has frequency much greater than message frequency. While in amplitude modulation we made a dc shift because our signal lies in both cycles we want our message signal only in one cycle.
If we cover the boundaries of AM signal with dotted lines then it will become an envelope. If you look at envelopes closely you will notice that the upper envelope is the same shape as the message. The lower is also the same shape but inverted.
AM is defines as
AM = (DC + message) × carrier —-(1)
Complex signals such as speech and music are made up of thousands sinewaves so the AM signal includes thousands of pairs of sinewaves straddling carrier. These two groups of sinewaves are called the sidebands so the AM signal is known as Double-Side Band Full Carrier (DSBFC).
Generating an AM signal using a simple message:
For generating an AM signal use trainer called Emona trainer given block diagram is first part is eq-1 (2kHz is message + Variable DCV is 1V DC)
now we multiply it with high frequency carrier which is about 100kHz so the block diagram is
applied circuit on emona trainer:
After implementing all this circuit on trainer the output we got on oscilloscope is