Amplitude modulation, more popularly known in its abbreviated form as “AM”, is a method of communication used mostly in the form of radio waves. Amplitude modulation is a form of modulation where the amplitude or displacement (“height”), of the wave’s signal varies based on the data being transmitted. The data is delivered as a whole based on the information encoded in the amplitude modulated wave signal.
How Amplitude Modulation Operates
Amplitude modulation works by altering the intensity or strength of the signal being transmitted in accordance to the data to be transmitted.
The History of Amplitude Modulation
Amplitude modulation was originally engineered for use with the electric telephone (modern-day telephone) to add audio to a receiver connected to a telephone transmitter.
Undulatory currents was the first technology to transmit audio signals via telephone wires (twisted pair). In 1906 Reginald Fessenden conducted an audio exhibition using amplitude modulation to broadcast audio signals using radio waves. From the exhibition in 1906 to modern day radio broadcasting, AM is still being used, referred to as the “AM Band”.
Improvements in Amplitude Modulation
The efficiency of AM transmissions can be improved by removing the carrier from the signal being transmitted. The removal of the carrier is referred to as a suppression of the carrier in the AM signal. With a suppressed carrier AM signal, the signal is up to three times more powerful and efficient than regular amplitude modulation transmissions. Further improvements can be made by increasing the complexity of delivery and reception of the AM transmission. The difficulty increases by the complete suppression of the carrier and one of the sidebands for transmission. This power efficient and transmission effective form of amplitude modulation is referred to as a single band amplitude modulation band transmission.
Uses of Amplitude Modulation
Single-band amplitude modulation band transmission signals were involved in the formulation of Morse codes. Morse code is an on-off broadcast of amplitude modulated signals. The signals are transmitted in a binary base, where on is a one, and off is a zero. Morse code to this day, is important in both emergency situations and basic but efficient communication between parties. Morse code or other on-off broadcasting is a part of continuous wave transmissions.
Amplitude modulation is, as aforementioned, a form of broadcasting radio signals. Established radio stations may use the AM band to conduct broadcasts for listeners using a certain radio wave receiver. Radio stations also maintain AM radio broadcasts for recurring messages or special announcements. Amplitude modulation, unlike frequency modulation (FM), is much easier to create and send. AM signals are also simple to receive.
Amplitude Modulation Circuitry
In order to create amplitude modulation signals, a circuit must be created. The simplest of the circuits available uses an anode (collector modulation) applied through the use of a transformer. The application of collector modulation is also referred to as low level modulation.
Using a vacuum tube, the radio frequency (RF) can be amplified. This is linear RF amplification. Linear RF amplification has an advantage over collector modulation as it requires a small audio amplifier to drive the modulator for generating AM signals. The disadvantages of linear RF amplification, however, are that it is less efficient than low level modulation.
Other circuitry for amplitude modulation include Class C power amplification and high level modulation.