Amplitude modulation

Radio waves carry sounds to us.

One way to do this is called amplitude modulation.

This makes the wave taller or shorter. The wave changes its size to match a sound. This lets the wave carry a voice or music.

People used this to send the first radio news. It is still used for many types of radio today. It is a very old and useful way to talk.

Do you like to listen to the radio?

Radio waves carry messages through the air. One way to do this is called amplitude modulation, or AM.

In AM, a radio wave acts like a carrier. A carrier wave is a steady signal that carries information. To send a sound, the wave changes its height. This height is called amplitude.

The wave gets taller or shorter to match the sound. This creates a shape that holds the message.

AM was the first way to send audio by radio. Researchers like Reginald Fessenden worked on this in the early 1900s.

He helped make the first continuous waves. Before this, radio used sparks that made loud buzzing noises. These sparks could not carry clear voices. AM is still used today for many things. It is used for shortwave radio and aircraft radio. It is also used in some computer modems.

One downside is that AM can pick up noise. This makes the sound less clear than other types of radio. Because of this, AM is often used for talking instead of music.

Amplitude modulation, often called AM, is a way to send information through radio waves.

It works by changing the height of a steady radio wave. This steady wave is known as a carrier wave. The carrier wave has a much higher frequency than the sound it carries. By changing the height, or amplitude, of the wave, we can hide a message inside it.

This height follows the shape of the sound or data being sent. The resulting shape is called an envelope. This method is very important for many types of communication today.

To understand how it works, imagine a carrier wave as a smooth, repeating pattern.

When we use AM, we change the strength of that wave to match a message. If the message is a voice, the wave gets taller or shorter to match the sound. This process is called modulation. In the radio spectrum, this creates a central carrier frequency and two sidebands. These sidebands are mirror images of each other.

Some systems use single-sideband modulation to save power. This method uses filters to remove one sideband and the carrier. This makes the transmission more efficient for things like amateur radio.

AM was the very first method used to broadcast audio over the radio.

Before this, people used spark gap transmitters to send Morse code. Those sparks made loud, buzzing noises that could not carry clear voices. In 1900, a researcher named Reginald Fessenden made the first AM transmission. He sent a message from Cobb Island, Maryland, to a person named Mr. Thiessen.

Fessenden also helped create the Alexanderson alternator. This machine helped make the first public entertainment broadcast on Christmas Eve, 1906. Other pioneers like Roberto Landell de Moura also worked on early radiotelephone experiments.

There are many specific ways AM is used in our world.

Standard AM is used for shortwave radio and news broadcasts. It is also used in aircraft radio and citizens band radio. For digital data, computers use a version called quadrature amplitude modulation, or QAM.

Some simple digital signals use on-off keying to represent ones and zeros. One downside of AM is that it picks up electrical noise easily. This noise is amplified along with the signal. Because of this, AM is better for talking than for high-quality music.

Even though AM is an older technology, it connects to many modern tools.

You might hear AM radio when listening to sports or talk shows. It is also used by radio amateurs to communicate over long distances. The way we use signals today is a direct path from those early experiments. Even old telephone lines used a simple form of amplitude modulation. They used a direct current as a carrier to send speech.

Understanding AM helps us see how we learned to send voices through the air.

Amplitude modulation, commonly known as AM, is a fundamental technique in electronic communication. It is used to transmit information, such as audio or data, by varying the strength of a continuous wave. This wave is called a carrier signal. The carrier signal has a much higher frequency than the message signal it carries. By changing the instantaneous amplitude of the carrier, the information is embedded into the wave.

This process allows us to send voices, music, and digital data across long distances through the air.

To understand the mechanism, we must look at how the carrier and message interact. In AM, the amplitude of the carrier wave changes in proportion to the message signal. This message signal creates what is known as an envelope. The envelope is the outer shape of the transmitted waveform that follows the message.

In the frequency domain, this process produces a signal with power at the carrier frequency. It also creates two adjacent sidebands. These sidebands are mirror images of each other and have a bandwidth equal to the message.

At a receiving station, the process is reversed through demodulation to extract the original message.

There are several distinct types of amplitude modulation used for different purposes. Standard AM is often called double-sideband amplitude modulation (DSBAM) because it uses both sidebands. Some systems use single-sideband modulation (SSB) to improve efficiency. This method uses bandpass filters to eliminate one sideband and sometimes the carrier itself. This reduces the total transmission power required and allows for better bandwidth utilization.

Another version is amplitude-shift keying (ASK), which is used for digital signals. A simple form of ASK is on-off keying, where ones and zeros are represented by the presence or absence of a carrier. More complex digital systems use quadrature amplitude modulation (QAM) to use bandwidth more efficiently.

History shows that AM was the earliest method for transmitting audio in radio broadcasting. Before this, spark gap transmitters were used for wireless telegraphy. These transmitters used pulses of radio waves to send Morse code, but they could not carry clear audio. They produced damped waves that sounded like a loud buzz.

The shift toward practical radiotelephone transmission happened between 1900 and 1920. Researchers like Roberto Landell de Moura and Reginald Fessenden led these early experiments. Fessenden realized that a new kind of transmitter was needed to produce continuous waves rather than impulsive sparks.

Reginald Fessenden made history on December 23, 1900. He performed the first AM transmission from Cobb Island, Maryland. He used a spark gap transmitter with a 10 kHz interrupter to send a voice message.

Later, he helped develop the Alexanderson alternator to create continuous waves. This led to the first public entertainment broadcast on Christmas Eve, 1906. Fessenden also discovered heterodyning and invented the electrolytic detector, also called a liquid baretter, in 1902. These inventions helped overcome the technological hurdles of generating and receiving AM signals.

While AM is useful, it has specific limitations regarding power and noise. AM is considered inefficient in power usage because at least two-thirds of the transmitting power goes into the carrier signal. The carrier itself contains no actual information like voice or data.

Furthermore, AM receivers amplify noise and electromagnetic interference along with the signal. To improve the signal-to-noise ratio by a factor of 10, a transmitter must increase its power by a factor of 10. Because of this, AM is often used for voice, such as news or sports, rather than high-fidelity music.

Despite these challenges, AM remains vital in many modern communication systems. It is still used in shortwave radio, amateur radio, and two-way radios. It is also found in VHF aircraft radio and citizens band radio. Even traditional analog telephony used a simple form of AM. In those systems, a direct current acted as a carrier with a frequency of 0 Hz.

Understanding these principles helps us see how we moved from simple sparks to complex digital data transmission.