You might have already used an AM radio and still might be wondering what an AM radio actually is. If that’s you, you are in for an information feast. This article dwells on the AM radio receivers, different types of AM radios, and also uses of the AM radios.
AM radios make use of Amplitude modulation for information transmission. AM band uses radio signals and waves to transmit information, such as voice and music. This broadcasting service can be traced back to the 1870s and continued through the 20th century. It’s also dubbed as “medium-wave stations” in some countries. Its predecessor is the FM radio, which is quite popular, even today, for music. The two operate similarly but use different modulation methods. Read on to learn more about what AM is, its types, and its applications.
What is AM radio?
AM radios are those two-way radios which use Amplitude Modulation for broadcasting of service. Its ease of use made it a standard for voice transmissions. AM refers to the technique of encoding incoming audio information on the carrier wave. For a radio signal to carry audio, two-way, or any other broadcasting information, it must change or adapt. This process of change is known as modulation in telecommunication vocabulary. There are several ways a radio signal may be modulated; Amplitude Modulation is one of them. The signal changes its amplitude in proportion to the incoming sound.
Another way to look at it is, imagine radio waves. The height of a wave is its amplitude, and the way the amplitude varies according to the intensity’s instantaneous value is how it modulates. What this means is that the incoming radio signal has a sound wave encoded to it. Since the radio frequency signal “carries” the audio information, it’s known as the “carrier”.
The AM band frequency range is 535-1705 kHz, and it takes up 30 kHz of bandwidth for each signal. The Federal Communications Commission (FCC) divides the AM frequencies into three categories, which are Clear, Regional, and Local. These categories are further divided into classes: A, B, C, and D, depending on their frequencies.
Types of AM radio
The purpose of any radio receiver is to reproduce the input or modulated waves into sound waves. The receivers that serve this function of reproducing amplitude modulated signals are called AM radio receivers. There are two types of AM radio receivers:
1. Straight
The RF amplifier selects the desired radio wave and uses a tuned parallel circuit. The tuned RF amplifiers then amplify the selected radio wave and feed it to the detector circuit. Next, circuit draws out the audio signal from the carrier wave. The result is an amplified audio signal, which travels through a few more multiple audio-amplifications stages. The amplified audio signal is then output via the speaker. One drawback of the straight radio receiver is that there is interference from adjacent stations.
2. Superheterodyne
Major Edwin H. Armstrong aimed to overcome the limitations of straight radio receivers. Therefore, he invented the Superheterodyne receiver during World War I. The receivers that you see today use this circuitry. Superheterodyne receiver changes the desired radio frequency to an intermediate frequency (IM) through a special electronic circuit: mixed circuit. The radio’s oscillator generates high-frequency waves, which are combined with the selected radio frequency by the mixer circuit. During this procedure, the mixer creates frequencies that are equal to the difference between the radio wave frequency and oscillator. Therefore, the circuit and oscillator generate an intermediate frequency of 455 kHz over the desired radio frequency.
What is AM radio used for?
AM radio is used in a variety of settings, even today; although it’s not as popular as it was previously. Users tune into AM channels to seek information regarding weather, traffic, and news. There are plenty of talk shows, music stations, and you can also hear up-to-the-minute updates about your favorite baseball or football game. Some of the other AM radio applications include:
- Air band radio: Several airborne applications still use AM for ground to air transmissions at VHF. It also serves as a two-way radio service for ground staff.
- Single sideband: It continues to be used as single sideband for point-to-point HF radio links.
- Broadcast: Amplitude Modulation is still a popular choice for broadcast on the long, medium, and shortwave bands. That’s because it’s pretty simple to demodulate and cheap to manufacture. However, in recent times, users are moving to higher-quality transmission modes, such as FM and digital transmissions.
- Quadrature AM: One of the most common uses of AM is for the transmission of data, through short-range wireless links like Wi-Fi, cellular communications, and more.
Conclusion
AM has been widely popular among radio operators for broadcasting and two-way communication. However, it’s not as widely used today. This is because it’s not the most efficient in terms of the spectrum it takes up. Moreover, the AM band is more susceptible to interference, especially during a thunderstorm. Lightning generates electricity, which in turn causes noise spikes that users may pick up. Nonetheless, it still has plenty of applications even today, such as in airband radio and broadcast. This is because AM radio easily transmits over vast distances and has several stations in a frequency range.