AM broadcasting

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AM broadcasting is a method of radio broadcasting using Amplitude Modulation (AM). It was the first method developed for making audio radio transmissions, and it is still used worldwide, primarily for medium wave (also known as AM band) transmissions, but also on the longwave and shortwave radio bands.

History

The history of AM broadcasting can be traced back to the early 20th century. The invention of amplitude modulation is attributed to Reginald Fessenden and Lee de Forest in the early 1900s. The first commercial AM radio station, KDKA in Pittsburgh, began broadcasting in 1920. This marked the beginning of the radio era, with AM radio becoming a vital means of communication, especially for long-distance audio transmission.

Technical Overview

AM broadcasting works by varying the strength (amplitude) of the transmitted signal in relation to the information being sent. For example, when broadcasting music or speech, the variations in amplitude correspond to the sound waves of the audio signal. This modulation technique contrasts with Frequency Modulation (FM), where the frequency of the carrier wave is varied.

Carrier Wave

In AM broadcasting, the carrier wave's amplitude is varied in proportion to that of the message signal, such as an audio signal. This carrier wave is generated at the radio station and is mixed with the audio signal to produce the AM signal, which is then transmitted through the airwaves.

Bandwidth and Frequency

The typical AM broadcast band ranges from 530 to 1700 kHz in the Americas, and from 531 to 1602 kHz in other parts of the world. Each station is assigned a specific frequency within this band. The bandwidth of an AM broadcast signal is determined by the highest frequency in the modulating audio signal. According to Carson's Rule, the total bandwidth required for AM broadcasting is twice the bandwidth of the modulating signal.

Advantages and Disadvantages

AM broadcasting has several advantages, including its simplicity and its ability to cover long distances, especially at night when AM signals can bounce off the ionosphere and travel thousands of kilometers. However, AM signals are more susceptible to noise and interference than FM signals. Noise from electrical equipment, atmospheric conditions, and other sources can degrade the quality of AM broadcasts.

Current Status and Future

Despite the rise of FM broadcasting, digital radio, and streaming services, AM broadcasting remains relevant, especially for news, talk radio, and sports broadcasting. In some regions, AM stations are an important source of information during emergencies. However, the future of AM broadcasting is uncertain, with some countries planning to phase out AM transmissions in favor of digital broadcasting technologies.

See Also

• FM broadcasting
• Shortwave radio
• Digital Audio Broadcasting (DAB)
• Radio broadcasting