AM and FM

In this article, we will discuss FM, AM, how they work, history of FM and AM, and the difference between AM and FM.

Radio signals are broadcast using AM (or Amplitude Modulation) and FM (or Frequency Modulation). Electromagnetic waves are used to transfer data in both cases. The amplitude of the signal or carrier delivered is modulated (changing) depending on the information being sent, but the frequency remains fixed. This is in contrast to FM technology, which encodes information (music) by altering the frequency of the wave while keeping the amplitude constant.

How does FM work?

Frequency modulation works by adjusting the intensity of the broadcast signal in response to the data being provided on a regular basis.

Frequency modulation is used in FM radio. Assume a signal with a low frequency and amplitude to understand frequency modulation. The frequency of the transmission remains constant or unmodulated as it passes. We discovered that a signal contains relatively little data.

As a result, when you supply information to this signal, the frequency changes in lockstep with the information. The carrier frequency also transmits music or voice when the frequency is modulated between low and high. As a consequence, we observe that the frequency fluctuates, but the amplitude remains constant throughout.

How does AM works?

An AM receiver detects amplitude fluctuations in radio waves at a certain frequency while receiving input signals. To run a loudspeaker or earphone, it amplifies fluctuations in the signal voltage.

In this case, a radio receiver sits in the opposite corner of a radio transmitter that captures radio waves via an antenna. It next filters the audio signals that were added to those waves, amplifies them, and eventually plays them on a speaker by processing those waves to extract only those waves that are vibrating at the required frequency.


The AM technique of audio transmission was successfully used for the first time in the mid-1870s to provide high-quality radio via telephone lines, and it was the first method utilised for audio and radio transmissions. In the 1930s, Edwin Armstrong was primarily responsible for the development of FM radio in the United States.

The Advantages and Disadvantages of AM vs. FM

AM radio has the benefit of being reasonably easy to detect with inexpensive equipment, even if the signal is weak. Another benefit is that it has a smaller bandwidth than FM radio and a greater coverage area. The transmission is influenced by electrical storms and other radio frequency interference, which is a major drawback of AM. Furthermore, whereas radio transmitters can send sound waves up to 15 kHz, most receivers can only reproduce frequencies of 5 kHz or less. Wideband FM was created to address the interference problem that plagued AM radio.

FM has a unique advantage over AM in that the sound quality of FM radio is superior to that of AM radio. The downside of FM signals is that they are more localised and cannot be broadcast over vast distances. As a result, additional FM radio stations may be required to cover a vast region. Furthermore, the coverage and quality of FM may be limited by the presence of towering structures or land masses. Third, an FM signal necessitates a more complex receiver and transmitter than an AM signal.

Difference between AM and FM

The abbreviation AM stands for Amplitude ModulationFrequency Modulation (FM) is the abbreviation for FM
In the mid-1870s, the AM technique of audio transmission was effectively implemented for the first timeFM radio was invented in the 1930s in the United States, mostly by Edwin Armstrong
The signal to be sent modulates the amplitude of a radio wave known as the “carrier” or “carrier wave” in AM. The frequency and phase of the signal remain unchangedThe signal to be sent modulates the frequency of a radio wave known as the “carrier” or “carrier wave” in FM. The amplitude and phase of the signal stay unchanged
AM has a lower sound quality than FM, but it is less expensive and can be broadcast over longer areas. Because it has a smaller bandwidth, it can accommodate more stations in any frequency rangeIn comparison to AM, FM is less susceptible to interference. Physical impediments, on the other hand, have an influence on FM transmissions. Due to its increased bandwidth, FM provides a superior sound quality
The frequency range for AM radio is 535 to 1705 KHz (OR) Up to 1200 bits per second are possibleFM radio operates at a greater frequency range of 88 to 108 MHz, 1200–2400 bits per second (OR)
The modulating frequency is twice as high as before. The modulating signal in AM radio transmission has a bandwidth of 15kHz, hence the bandwidth of an amplitude-modulated signal is 30kHzThe modulating signal frequency and the frequency variation are multiplied by two. The bandwidth required is 180kHz if the frequency variation is 75kHz and the modulating signal frequency is 15kHz
Because noise affects amplitude, which is where information is “stored” in an AM signal, AM is more vulnerable to noiseBecause information in an FM signal is transferred by modifying the frequency rather than the amplitude, it is less vulnerable to noise

Also See:


Using the process of changing a carrier signal, amplitude modulation and frequency modulation are utilised to convey data. The fundamental difference between the two modulations is that frequency modulation modifies the carrier wave’s frequency according to the transmit data, whereas amplitude modulation modifies the carrier wave according to the data. If multiple separate sets of data must be conveyed over the same media, for example, each set is delivered using a different frequency wave. This is the procedure for producing radio broadcasts.


Frequently asked questions

Get answers to the most common queries related to the JEE Examination Preparation.

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Answer. Modulation is an electrical technique for imprinting a piece of information, such as speech, music, an image...Read full

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Answer. In order to minimise interference with other AM radio stations, most AM radio stations are obliged by FCC gu...Read full