AM Stereo History

Early Stereo

Koss Stereo headphones, 1950s Stereo sound reproduction was first experimented with in the early 1900s, and was put into use in motion pictures in the 1930s. However, Stereo sound did not gain much widespread popularity until the introduction of the Stereo LP phonograph record in 1957, which suddenly added a whole new dimension to music listening.

Early experiments with Stereo radio broadcasting involved two separate stations, often one on AM and the other on FM, broadcasting the Left and Right audio channels. However, this was not a satisfactory solution as it required two separate radios, or one radio with two independent tuner sections. Also, listeners tuning in just one of the pair of stations would be missing out on half of the audio content.

AM vs. FM

Engineers worked on methods of putting both Stereo audio channels onto a single radio station -- or "Multiplexing", as it is called. We all know about multiplex FM Stereo; it was introduced in the USA in 1961 and became especially popular in the 1970s. Today, virtually all radios have FM Stereo capability.

However, the untold story is that multiplex AM Stereo was being developed at the same time as FM Stereo. Engineers such as Leonard Kahn developed and tested AM Stereo systems in the late 1950s that worked very well and would have made a very satisfactory solution for AM Stereo broadcasting at the time.

But, things were different back then. AM was still the most popular band for radio listening. Most people did not even have an FM radio, and FM stations were struggling to gain listeners. Because of this, the FCC (Federal Communications Commission) thought of adding Stereo sound to FM -- and FM only -- as a way to help it gain popularity. So, the FCC approved use of FM Stereo, but did not allow AM Stereo to be used, since it would have given AM even more of an advantage in listenership over FM.

National AM Stereophonic Radio Committee handbook, December 1977 Well, as well all know, by a few decades later, things had definitely changed. By the 1970s, the FM band was becoming the preferred place for music listening, and the monaural audio of AM radio sounded inferior in comparison. Many AM stations still offered attractive programming and had high ratings, but listeners were no longer turning to AM as their primary source for musical entertainment on the radio.

AM Stereo Finally Arrives

Meanwhile, AM Stereo had not been forgotten. Engineers continued to work on it and perfect its performance and sound quality. Various companies, including Motorola, developed their own systems for transmitting AM Stereo.

As the 1980s approached, the FCC had finally decided to take another look at AM Stereo, because it was one way to help AM radio stay competitive with FM. There were five different AM Stereo systems being proposed to the FCC, and the FCC struggled with the decision of which one to choose as the single standard for AM Stereo broadcasting.

At first, the FCC decided to select one of the systems, designed by Magnavox, as the standard. As you can imagine, the proponents of the four other systems complained, saying that their systems worked better than Magnavox and that the FCC's research which led to this decision was flawed and incomplete.

The Marketplace Wars

Sony's line of multi-system AM STEREO radios The FCC was going to choose another system, designed by Harris, as the single standard, but by this time the popular opinion was becoming that they should simply allow all of the systems to be used, and that the preferences and competitive forces of broadcasters and radio listeners would eventually converge toward one of the systems as the single "de facto" standard.

So, on March 4, 1982, that is exactly what the FCC did. There were now four AM Stereo systems to choose from, designed by Motorola, Magnavox, Kahn/Hazeltine, and Harris. For the first few years, except for Magnavox, all of the systems were about equally competitive. Many "multi-system" AM Stereo radios were sold so that listeners could tune in all of the systems.

The AM Stereo Challenge on 1260 WWWW, a Kahn/Hazeltine station But out of this group, Motorola was the largest company, and was already a parts supplier for many car radio manufacturers such as Delco (GM's car radio brand). So, by 1986, the majority of AM Stereo radios that were available only supported the Motorola system, named "C-Quam" (Compatible Quadrature AM), and other countries like Australia, Mexico, and Canada were choosing the Motorola C-Quam system as their single standard for AM Stereo. By this time, Harris had also given up on their own AM Stereo system, and put their support behind the C-Quam system as well.

But in the USA, Leonard Kahn, creator of the Kahn/Hazeltine AM Stereo system, was very vocal about the advantages of his system over Motorola's, and he managed to convince enough stations to stay with his system. This confused listeners, because a radio designed for the Motorola system would not be able to receive a Kahn signal in stereo. And many radio manufacturers and radio stations were reluctant to adopt AM Stereo without knowing which system was going to be the winner. It was becoming clear that a single system had to be chosen, if AM Stereo was going to survive at all.

C-Quam as the Standard

Finally, in 1993, the FCC did choose a single system for AM Stereo. Looking at its overwheming popularity over the Kahn system, they chose the Motorola system as the single standard, which was also the standard for all other countries in the world with AM Stereo broadcasting.

People who supported the Kahn system were upset because they thought the Kahn system had better performance than Motorola's C-Quam system. They were quick to point out some problems with the Motorola system, such as "platform motion", a condition in which an unstable signal can cause the audio "platform" to fluctuate between the Left and Right channels, as if somebody was turning the Balance knob on the radio.

Aiwa radio tuned to WJR 760 AM STEREO

Today's AM Stereo

However, Motorola wasn't satisfied just because their system had "won" and was the standard. They listened to the complaints and worked to reduce or eliminate most of the past problems with the C-Quam system. By the early 1990s, they introduced new circuit designs which offered better audio fidelity and featured methods which greatly reduced the occurence of "platform motion".

Unfortunately, since then, people haven't paid much attention to AM Stereo. In fact, many people think it doesn't even exist anymore. But it does exist, and it is used by hundreds of stations all around the world. And new AM Stereo radios continue to be manufactured and sold every year. AM Stereo even remains competitive against digital AM broadcasting systems, such as iBiquity's "HD Radio", which are plagued with problems and will actually reduce the sound quality that AM radio has to offer.

AM Stereo has been on the air for over three decades. And because of advocacy on Internet sites like this one, it remains a popular and well-known technology. People are still interested in getting high-fidelity Stereo audio from the AM radio band. AM Stereo is an established standard, it works very well, and it is affordable to both stations and listeners. That is the AM Stereo Advantage!