AM Radio History: When and Who Invented AM Radios

Amplitude Modulation (AM) radio dates back to the early 1900s when it was used to transmit a signal to the ships at sea. But the beauty is that we still use this century-old technology. Any person who has a taste in history and technology will definitely be thinking two aspects of AM radio:

  • Who Invented AM radio?
  • When did AM radio start?

The AM radio history involves the creation of a practical device for sending and receiving signals and the development of laws and allocation of broadcast stations and frequencies. This was back during the Golden Age of Radio.

Today, despite being outdated, AM radio continues to be widely used. Although it’s not the best option for music, it’s still an excellent option for news, sports, and talk radio. This article discusses the past of AM radio. We will also drop a few hints on the future for AM radio going to be like? Read on!

AM Radio History

The AM radio came into the limelight after the discovery of electromagnetic waves and the invention of radio. The theoretical work of the AM technique is credited to Leblanc, Mayer, and Rayleigh. It was through their experimental works done in the 1800s that audio signals were transmitted over telephone lines through amplitude modulation. However, the inventors of the 20th century rediscovered these principles and developed these into practical devices. 

Lee de Forest is a well-known name in the world of radio because of his innovations like triode amplifier, audion, and vacuum tube. Forest, along with Reginald Fessenden, developed the amplitude modulation technique. This technique uses the wave’s strength to encode audio information.

When was AM Radio Invented and Who Invented the First AM Radio?

After years of hard work, Fessenden sent the first AM transmission (voice message) in 1906 from a garage in Brant Rock, Massachusetts. He used an Alexanderson alternator, along with a rotary spark-gap transmitter. Radio-equipped ships, within a range of a few hundred miles, heard the transmission.

Charles David Herrold established the first radio station, KQW, in San Jose, California, back in 1909. Its successor is the KCBS from San Francisco. Although AM usage was already relatively high, it exploded during the years before World War I. It was the primary source of news and entertainment for most households.

The creation of AM radio led to introducing new laws and regulations to prevent chaos over airwaves. For example, if multiple users tried broadcasting over the same frequency, the resulting audio would be incomprehensible. Therefore, they allocated the medium wave of the spectrum to commercial radio stations. The lower wave part of the spectrum was reserved for international transmissions.

Growth and Current stage

Radios based on the AM technique work to detect any changes in the amplitude. However, it is essential to note that these devices are also more susceptible to interference by anything that can cause variations (electrical noise) in amplitude. These include thunder and lightning, as well as any artificial electrical discharge. So, while AM remained the primary broadcasting method and radio communication up to WWII, it had severe drawbacks.

AM radio signals were also challenging to receive within buildings. The poor audio quality and the fact that users could only broadcast a single audio channel, other radio communication methods were introduced, such as Frequency Modulation (FM) radio. 

With listeners switching more to FM radio, most commercial AM radios changed their strategies. As a result, there was a rise in more news, sports, politics, weather, religion, and talk shows on the AM band around the 80s and 90s.

This is because of the atmospheric propagation of AM signals. Perhaps you’ve picked up a very distant AM radio station in your car at night. Once the sun sets, AM signals can bounce off the ionosphere and travel much farther. So if every AM station were to keep broadcasting at night, stations that were far apart would interfere with each other.

The AM radio broadcasts between 530 and 1710 kHz. All AM band stations use towers, so the polarization is vertical. During the daytime, propagation has a range of about 100 miles, depending on the power level. Those with greater power (50 kW) have more extensive range coverage. This propagation changes around nighttime because of atmospheric factors. As the ionized layers change, the signals travel at distances of a thousand miles or more.

If you use a decent AM radio receiver with a tall antenna, you would hear from stations across the country! For this reason, the Federal Communications Commission (FCC) has introduced regulations where only a few certain stations can broadcast all full power throughout the night. These are channels that will not cause chaos and are “clear channels.” 

What is AM radio used for now?

Although there are several limitations to AM radio, it continues to have a broad audience base. It’s a popular choice for local news and weather and serves as an essential communication tool in several industries, particularly aviation. Many people also use it for public safety purposes during emergency conditions. 

However, going forward, the future doesn’t look too bright for AM radio. According to current research predictions, most people will eventually switch to electric cars shortly. Although these cars are quiet and efficient, they generate electromagnetic waves that interfere with AM radio frequencies. Therefore, it’s almost impossible to listen to the AM band in an electric car. As a result, companies like BMW and Tesla have already eliminated AM radios from their vehicles. 

Furthermore, the internet and digital radio have also reduced the overall demand for radio. Today, you can easily find news, music, podcasts, and audio/video talk shows on the internet. Therefore, people are more likely to use online streaming services to access content from across the globe instead of listening to local stations. As a result, several medium-wave AM stations are shutting down across Europe, while other countries have eliminated AM radio.


The advent of AM radio can be traced back to the early 1900s. It has grown immensely since with millions of listeners throughout the years. Today, you can still find the AM technique in HAM and Citizen’s Band radios. It’s also the primary modulation used for communication between aircraft and control towers. 

While most people find the AM band dead, we find it to be surviving despite all odds. However, with electric cars eliminating AM radio from their models and Internet radio on the rise, it would be interesting to see how AM radio competes.