Difference Between AM and PM

During the early days when radio was greatly used, the radio stations uses a long, medium, and short-waves band to broadcast. After some time passes, high-frequency broadcast modes came into the picture. Amplitude Modulation (AM) and Phase Modulation (PM) are the two modulation techniques of analogue modulation that are used to transmit data from a place to faraway land in the form of radio waves. AM and PM both serve the same purpose with some differences.

AM v/s PM

The main difference between AM and PM is that AM is amplitude modulation with simple circuits in which the frequency and phase remain constant. On the other hand, PM is a phase modulation with a complex circuit in which the amplitude and frequency remain constant. The modulation index in AM ranges from 0 to 1, while the modulation index in PM is always greater than 1.

AM vs PM

Amplitude modulation or AM is an electronic communication technology that is most commonly used to transmit messages or signals through a radio wave. The carrier wave’s amplitude in the amplitude modulation varies corresponding to the amplitude of the message signal. Sometimes, AM is also called double-sideband amplitude modulation or DSBA; due to the sidebands being produced on the carrier frequency’s either side.

Phase modulation or PM is a pattern of modulation which for transmission, conditions the communication signals. In the local phase or known as the instantaneous phase of the carrier wave, phase modulation encrypts the signals of messages as variations. Phase modulation (PM) along with Frequency modulation (FM) are the two principal types of angular modulation.

Comparison Table Between AM and PM

Parameters of ComparisonAMPM
CircuitThe circuit used in amplitude modulation is simple.The circuit used in phase modulation is complex.
IndexThe index modulation of amplitude modulation varies from 0 to 1.The index modulation of phase modulation is always more than 1.
Immunity of noiseThe noise immunity in AM is poor.The noise immunity in PM is better than in AM.
Quality of soundAmplitude modulation sound quality is better.Phase modulation sound quality is poor.
Quality of signals The quality of signals received is low.The quality of signals received is high.

What is AM?

Amplitude modulation is one of the oldest types of modulation which is used even today, especially for the long, medium, or small broadcasting of waves and for aeronautical communication purposes. The main reason for the amplitude modulation being used is because of its ease in using it. The carrier amplitude should be modulated which is required by the system, but more importantly, the detector which is required in the receiver should be a simple circuit that is diode-based, which means that the radios of amplitude modulation do not require complex demodulators, due to which the costs were reduced.

The minimum cost spent was the key requirement for using radio technology on a large scale, especially when the ICs were not in the picture. The concussion of the sound waves on the microphone diversified its resistance which led to the diversification of the transmission intensity. The harsh or raspy sound was caused by the spark and very unrefined signals were able to be listened to over a few hundred meters.

Reginald Fessenden, a Canadian engineer was the first person ever to transmit the first amplitude modulation signal in the year 1901 by placing a carbon microphone in the antenna of a continuous spark transmission. AM is simple to carry out and can be easily demodulated with few components due to which the amplitude modulation receivers are cheap.

What is PM?

Phase modulation, as the name itself, implies that, for implementing the modulation, variations in phase are used by phase modulation. As both phase and frequency are linked to one another, this bind is carried forward to the phase modulation where they receive mutuality with FM or frequency modulation. Therefore, the term angle modulation is used to represent both PM and FM. For transmission of analogue, phase modulation is sometimes used, but it has become the fundamental point for the schemes of modulation that are used to carry data.

For data communication, phase shift keying is greatly used. Phase modulation is also the constituent element of a modulation names quadrature amplitude modulation, in which both phase and amplitude differ to deliver additional potentiality. Even though PM is used for analogue transmission, it is way more used as modulation in digital form where it is allowed to switch to various phases. This feature is known as phase shift keying, PSK, which has many different aspects. It is also possible to create Quadrature amplitude modulation (QAM) which is a form of modulation, by combining phase-shift keying and amplitude keying. Given below are some of the phase shift keying forms that are used:

  • PM- Phase Modulation.
  • PSK- Phase Shift Keying.
  • QPSK- Quadrature Phase Shift Keying.

These are some of the forms of a PM that are used today in radio communications. With today’s advanced technology of radio communication systems, it is possible to switch to any form of modulation which fits the current condition.

Main Differences Between AM and PM

  1. The frequency and phase in amplitude modulation stay the same. Whereas, the amplitude and frequency in phase modulation remain the same.
  2. The noise immunity of AM is poor whereas, the noise immunity of PM is way better than AM.
  3. Amplitude modulation is used on a large scale whereas, phase modulation is only used in mobile systems.
  4. The signals received by the amplitude modulation are of low quality whereas, the signals that the phase modulation receives are of high quality.
  5. The index of modulation in AM differs from 0 to 1 whereas, the index of modulation in PM is always greater than 1.
  6. The circuit used in amplitude modulation is simple whereas, the circuit used in phase modulation is complex.

Conclusion

In conclusion, AM and PM are both forms of modulation. Amplitude modulation is simple to implement and can be demodulated with few components, which makes it cheaper but not the most effective form to use. On the other hand, phase modulation provides the advantage of signal modulation as it allows high-speed communication for computers using a mobile system.

PM also can switch between different forms which is a great feature that fits today’s situations. The quality of signals that are received by the AM is low but the sound signals received as better. While the signals received by the PM receiver are of high quality but the sound quality is low.

References

  1. https://www.osapublishing.org/abstract.cfm?uri=josab-2-8-1320
  2. https://aip.scitation.org/doi/abs/10.1063/1.2745238
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