Amplitude Modulated Waveform

Various factors restrict the transmittance of the original low-frequency communication signal over lengthy ranges. As a result, at the transmitter, the low-frequency message signal’s data superimposes on a high-frequency wave, which serves as a carrier of the data. This behaviour is modulation. We can classify modulation into three types:

• Amplitude Modulation (AM)
• Frequency Modulation (FM)
• Phase Modulation (PM)

Amplitude modulation is the method of transmitting a wave signal by varying its amplitude. AM is often helpful for delivering data via a radio carrier wave and is commonly employed in electronic communication.  

Amplitude Modulation

Amplitude modulation (AM) is a method used in electronic communication, most notably for the radio wave transmission of messages. In amplitude modulation, we can modify the amplitude (signal intensity) of the wave per that of the message signal, such as an audio signal.

Amplitude Modulated Waveform

In AM, the amplitude of the carrier varies according to the voltage or power level of the information stream. The AM carrier is sent without any modulation. The carrier amplitude increases and falls in line with the modulating information stream (a sine wave). During AM, the carrier frequency remains constant. The amplitude-modulated waveform is important as it helps efficiently transmit signals at a low cost.

There is a fluctuation in the amplitude of the carrier wave whenever we utilise amplitude modulation. As a result, the amplitude of the carrier varies as the voltage or power level of the information signal varies. The carrier wave in amplitude modulation doesn’t fluctuate in amplitude. 

On the other hand, the modulating data takes the shape of signal components with frequencies that are either higher or lower than the carrier’s. We call the signal elements sidebands, and the sideband power is attributable to differences in the signal’s total amplitude.

Let us consider a carrier signal c(t)= Ac sin wct and m(t)= Am sin wmt as a message signal. So the modulated signal is given as:

 cm(t)= (Ac + Am sin wmt)sin wct 

=>  cm(t) = Ac(1 + Am/Ac sin wmt)sin wct 

μ = Am/Ac is the modulation index.

Amplitude Modulated Waveform Production and Detection

Assume that we create our base or message signal as described above. To generate an amplitude modulated wave, we must superimpose this signal with a higher frequency signal. This signal is known as the ‘carrier signal.’ It varies from one carrier to the next.

A radio transmission, for example, has a different carrier signal than a TV broadcast, and so on. Assume this carrier signal is represented as: 

c(t)= Ac sin wct

As a result, the carrier signal has a different amplitude and frequency than the message signal. Both of these signals superimpose on one other. We utilise a basic triode to superimpose these signals to execute this purpose.

We can form the modulated signal ‘B’ by superimposing the message signal ‘c’ and the carrier signal ‘A.’ However, the obtained signal ‘B’ is only in one phase. To solve this difficulty, we utilise a square-law device in the circuit to square the resulting waveform. The square-law device is non-linear and results in the output.

Then, subject this square waveform to a bandpass filter. As its name indicates, the bandpass filter is a device that filters out undesired frequencies.

However, the procedure is not complete. The resultant modulated signal is relatively weak and cannot withstand attenuation over a long distance. It necessitates the amplification of the signal. 

We do this by amplifying the signal with an amplifier diode. The signal’s quality does not change; the amplifier (the circuit’s last component) only increases its strength.

Finally, the amplified and modulated signal is transmitted to a transmitter or antenna for emission at a certain bandwidth frequency. This antenna broadcasts the signal across long distances using radiation. 

However, this does not guarantee that the signal will reach its target. We duplicate the signal at periodic intervals utilising repeaters to decrease attenuation and noise.

Advantages

The following are the benefits of amplitude modulation:

• Amplitude modulation is cost-effective and conveniently accessible.
• The implementation of amplitude modulation is straightforward.
• It is simple to demodulate by employing a circuit with fewer components.
• Amplitude modulation receivers are cheap and affordable since they do not require any specialist components to continue the operation.

Disadvantages

The following are the drawbacks of amplitude modulation:

• Amplitude modulation consumes a lot of energy, hence reducing its efficiency.
• In this procedure, we employ amplitude-frequency numerous times to modulate the signal by a carrier signal.
• The receiving end’s initial signal quality is poor, generating a variety of issues.
• They produce a lot of noise, which might be bothersome.
• It is only feasible in one-on-one communication, which is a significant disadvantage.

Conclusion

Amplitude modulation is the method of transmitting wave signals by changing the signal’s amplitude. Amplitude modulation (AM) is another name for amplitude modulation. It has frequent application in data transmission over a radio carrier wave and has typical use in electronic communication. 

A variety of communication applications utilise amplitude modification. Portable two-way radios, citizens band radio, and VHF aviation radio are examples of such modes of communication. Amplitude modulation is also utilised in computer modems when referring to medium-wave AM radio broadcasts.