Difference Between AM and PM

During the early days when radio was greatly used, the radio stations used a long, medium, and short-wave band to broadcast. After some time passed, high-frequency broadcast modes came into the picture.


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Amplitude Modulation (AM) and Phase Modulation (PM) are the two modulation techniques of analogue modulation that 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.

Key Takeaways

  1. AM (ante meridiem) represents the time between midnight and noon, while PM (post meridiem) represents the time between noon and midnight.
  2. AM and PM help differentiate between morning and evening hours in the 12-hour format.
  3. The 24-hour time format doesn’t use AM or PM, as it distinguishes times of day using a 00:00 to 23:59 numbering system.

AM v/s PM

“AM stands for ante meridiem, Latin for””before noon”” It refers to the period of time from morning hours from midnight until noon or 12:00 PM “”P”” stands for””post meridiem”” which is Latin for””afternoon.” It refers to the period of time from noon, or 12:00 PM, until midnight.”AM stands for ante meridiem, Latin for “before noon.” It refers to the period from morning hours from midnight until noon or 12:00 PM.”PM” stands for “post meridiem,” which is Latin for “afternoon.” It refers to the period of time from noon, or 12:00 PM, until midnight.

AM vs PM

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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,, known as the instantaneous phase of the carrier wave, phase modulation encrypts the signals of messages as variations.

Phase modulation (PM) and Frequency modulation (FM) are the two principal types of angular modulation.

Comparison Table

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, 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 its ease of use.

The carrier amplitude should be modulated, which is required by the system, but more importantly, the detector, which is needed for the receiver, should be a simple circuit that is diode-based,

which means that the radios of amplitude modulation do not need complex demodulators, due to which the costs were reduced.

The minimum cost spent was the critical 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 spark caused the harsh or raspy sound and very unrefined signals could 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 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, for implementing the modulation, variations in phase are used by phase modulation.

As both phase and frequency are linked, this bind is carried forward to the phase modulation, where they receive mutuality with FM or frequency modulation.

Therefore, the term angle modulation represents both PM and FM.

For transmission of analogue, phase modulation is sometimes used, but it has become the fundamental point for the modulation schemes used to carry data.

For data communication, phase shift keying is extensively used.

Phase modulation is also the constituent element of quadrature amplitude modulation, in which both phase and amplitude differ to deliver other potentiality.

Even though PM is used for analogue transmission, it is way more used as modulation in digital form,, allowing it 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),, a form of modulation, by combining phase-shift 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 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. At the same time, 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.
  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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