AM Antennas – What is Amplitude Modulation and How It Works

best am antenna reviews

Table of Contents

Types of AM Antennas

Loop AM Antenna

The loop AM antenna is the simplest kind of radio antenna, but it’s also the most versatile. You can use it for any frequency, from a few MHz to the microwave band.

The whole thing consists of two parts:

  1. A piece of wire with loops at each end
  2. An electric field generator inside that makes those loops act like antennas.

Cross Dipole Antenna

Antennas are not just different sizes, they are also different shapes.

The difference is the cross dipole antenna. Take a wire, bend it into a loop, then flatten out one side so it looks like a horseshoe, and you have your basic dipole antenna.

The loop has become four separate dipoles — two horizontal ones sticking out at the top and bottom of the loop, and two vertical ones sticking out at either end of the loop. This is the simplest kind of modern radio antenna but simply doesn’t mean easy to make.

Yagi Antenna

The Yagi antenna is a directional antenna with high gain.

It was invented in 1926 by Shintaro Uda, who published his invention in a Japanese scientific journal. The Yagi antenna is named after its inventor, Yagi.

A Yagi antenna consists of at least one driven element, one reflector, and one director. The driven element is the part of the antenna that must be connected to an external energy source such as a transmitter or amplifier.

AM Antenna Reviews

What is AM radio?

Amplitude Modulation AM is one of the simplest forms of modulation. It uses amplitude variation to carry information across a carrier wave and is a method of modulating an analog audio waveform onto or off a carrier wave of higher frequency.

AM set the stage for the more sophisticated and complex digital communications we build today: Frequency Modulation (FM) and Phase Modulation (PM).

Amplitude modulation (AM) history

The ability to modify the fundamental frequency of a signal or to convert electrical signals into other forms has been a closely guarded secret for decades.

The technology behind it dates back to the 1920s when Soviet scientists first demonstrated the feasibility of using simple amplifiers to simulate sounds. Since then, various pieces of information have emerged from governments and agencies outlining basic protocols and knowledge required to implement such systems into consumer products.

A Canadian named Reginald Fessenden was the first person who used amplitude-modulated radio transmission in 1901. He took an existing spark transmission and added a microphone to the antenna.

Amplitude modulation applications

Amplitude Modulation (AM) technology has been in use by the military and commercial operations for several years.

AM technology is an essential component of various surveillance systems. Users use it to detect both short and long-range airborne targets. They also use them to detect well-known amounts of explosive material and/or non-explosive materials like narcotics and weapons of mass destruction within transportation facilities, warehouses, industrial areas, and more. 

Broadcast transmissions

Broadcast transmissions are distorted due to digital signal reflections which are referred to as picture noise. Their receivers use Amplitude Modulation (AM) techniques to remove unwanted signals and to receive signals effectively by the broadcast equipment.

They developed this technique many years ago. The technology at that time had no standards to identify or remove such distortions while signal broadcasting. Instead, broadcasters relied upon their own abilities in detecting interference patterns generated by other signals present in the environment. 

Nevertheless, many people are moving to high-quality forms of transmission like frequency modulation, FM, or digital transmissions.

Airband radio

The propagation characteristics of AM radio make it suitable for both general use and military applications. Its primary function is for ground-to-air radio communications and for ground two-way radio links as well.

Quadrature amplitude modulation

It works by four channels of audio information, separated by a gap. Through the gap, an analog signal path is followed. This signal, with a low level of quantization and a high level of reflectivity, leads directly to the soundstage. The signal entering the transmitter moves through a high-level transformer connected to the speakers and then out into the room

These form some of the main uses of amplitude modulation. However, in its basic form, the form of modulation is used less as a result of its inefficient use of both spectrum and power.

What is amplitude modulation?

Amplitude modulation is the extraction of information from an analog or digital signal in a given set of frequencies.

The modulation occurs naturally in all audio information such as speech and music. It is increasingly becoming relevant in digital audio sources such as phone conversations, internet radio, or computer networks. This means users can represent data in more than two places at once and/or stretched across more than one frequency spectrum. They can also be digitally applied to signals coming from many different sources.

Amplitude demodulation

Is the process of extracting the frequency content of a modulation audio signal to be able to hear the original audio.

A simple AM detector consists of a diode configured to act as an envelope detector. A better-quality AM detector, the product detector, requires more parts but can have better performance.

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Advantages & disadvantages of amplitude modulation.

AM has advantages and disadvantages like any other technology. The summary below gives a highlight of the basic pro and cons.

Advantages of AM Radio

  • It’s simple to put together and maybe demodulated using a circuit with only a few components.
  • AM receivers are inexpensive since they do not require specialized components.

Disadvantages of AM Radio

  • It is inefficient in terms of power use.
  • It is inefficient in terms of bandwidth usage, requiring twice the bandwidth of the highest audio frequency.
  • Because AM detectors are susceptible to amplitude-based noise, noise is a concern with them.

In its basic form, AM is not as effective as other modes but is utilized in many fields, such as broadcasting, due to its large user base.


Amplitude modulation is a technique to convert sinusoids into sine-like signals. It provides an interesting alternative to the traditional sinewave signal processing architecture and applying to audio signals both for amplitude and frequency content. The idea is to process the signals in some way that preserves their fundamental frequency but transforms them in a way that yields new information.

AM antennas use the AM technology and can be hard to come by, as more modern technology is more often used now, such as FM Radio.