Demystifying Modulation: Types of Radio Emissions Explained

Dive into the world of modulation and radio emissions, and learn about their crucial role in wireless communication devices.
a set of sinusoidal waves

As an expert in walkie-talkie technology, I often encounter questions about the underlying principles that make these devices work. One such essential concept is modulation, which plays a vital role in wireless communication.

In this guide, we’ll explore the different types of radio emissions and how they affect the performance of communication devices like walkie-talkies. Understanding these concepts is key to optimizing your device’s performance, so join me as we uncover the science behind one of the most critical aspects of radio communication: modulation.

Let’s dive in!

electronic circuit board radio communication

Basics of Modulation

Definition of Modulation

Modulation is the process of varying one or more properties of a carrier signal (usually a high-frequency sinusoidal waveform) to encode and transmit information. These properties can include the carrier wave’s amplitude, frequency, or phase. Modulation allows for efficient data transmission over long distances and enables multiple signals to share the same frequency band without interference.

Purpose of Modulation in Radio Communication

In radio communication, modulation serves several essential purposes:

  1. It allows for the efficient use of the frequency spectrum, enabling multiple users to share the same frequency band without causing interference.
  2. Modulation allows transmitting information over long distances while minimizing signal degradation.
  3. It ensures that the receiving device can easily detect and demodulate (decode) the transmitted signal.

Types of Modulation (brief overview)

There are two primary categories of modulation: analog and digital. Analog modulation techniques include amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM). Digital modulation techniques encompass various methods, such as Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), Quadrature Amplitude Modulation (QAM), and Orthogonal Frequency Division Multiplexing (OFDM).

In the following sections, we will delve deeper into these modulation types and their applications in radio communication.

Amplitude Modulation (AM)

Amplitude Modulation (AM) is an analog modulation technique in which the amplitude of the carrier wave is varied in proportion to the amplitude of the message signal while the frequency and phase remain constant. This method allows the information to be transmitted through the carrier wave, which the receiver can easily demodulate.

Advantages of AM:

  • Simple implementation: AM is relatively easy to implement in both the transmitter and receiver circuits, making it a cost-effective solution for radio communication..
  • Long-range transmission: Due to lower frequency bands, AM signals can travel long distances, which is advantageous for applications such as long-range broadcasting and aviation communication.

Disadvantages of AM

  • Lower bandwidth efficiency: AM requires a more extensive transmission bandwidth than other modulation techniques, such as FM or digital modulation.
  • Susceptible to noise: AM signals are more prone to interference from noise sources, which can degrade the quality of the received signal.

Applications of Amplitude Modulation in Radio Communication

AM is commonly used in various radio communication applications, including:

  • AM broadcasting: AM radio stations operate within the frequency range of 535 kHz to 1705 kHz, providing long-range transmission for news, talk shows, and music.
  • Aviation communication: Aircraft communication systems often use AM for air traffic control and pilot communication due to their long-range capabilities.
  • Shortwave radio: International broadcasters and amateur radio operators use shortwave AM to transmit signals over thousands of miles.

Frequency Modulation (FM)

Frequency Modulation (FM) is an analog modulation technique in which the frequency of the carrier wave is varied in accordance with the amplitude of the message signal while the amplitude and phase remain constant. This results in a less susceptible signal to noise and interference, providing improved audio quality compared to AM.

Advantages of FM

  • Improved audio quality: FM provides better audio quality than AM due to its reduced susceptibility to noise and interference.
  • Greater bandwidth efficiency: FM requires less bandwidth than AM for transmission, making it more efficient for certain applications.
  • Lower power consumption: FM transmitters generally consume less power than their AM counterparts.

Disadvantages of FM

  • More complex implementation: FM circuits are more complex than AM circuits, which can increase the cost of implementation.
  • Limited range: FM signals have a shorter range than AM signals due to their higher frequency, which may require more transmission infrastructure.

Applications of Frequency Modulation in Radio Communication

FM is widely used in various radio communication applications, including:

  • FM broadcasting: FM radio stations operate within the frequency range of 88 MHz to 108 MHz, providing high-quality audio for music, news, and talk shows.
  • Two-way radio communication: Walkie-talkies, police radios, and other two-way communication systems often use FM for clear and reliable communication.
  • Wireless audio systems: FM is commonly employed in wireless microphones, intercoms, and other audio transmission systems due to its superior audio quality.

Phase Modulation (PM)

Phase Modulation (PM) is an analog modulation technique in which the phase of the carrier wave is varied in accordance with the amplitude of the message signal while the amplitude and frequency remain constant. PM is closely related to FM, as frequency modulation can be mathematically derived from phase modulation and vice versa. In practice, FM is often used in place of PM due to its more straightforward implementation and better noise performance.

Advantages of PM

  • Better noise performance: Similar to FM, PM offers improved noise performance compared to AM, resulting in better audio quality.
  • Constant envelope: PM signals maintain a constant amplitude, making them more resilient to amplitude-related distortion and allowing for more efficient amplification.

Disadvantages of PM

  • Complex implementation: PM circuits can be more complex than AM circuits, leading to increased costs.
  • Limited applications: Due to its similarities with FM, PM is less commonly used in radio communication systems, with FM often being the preferred choice.

Applications of Phase Modulation in Radio Communication

While the PM is less common in radio communication applications due to its similarities with FM, it is still used in specific scenarios, including:

  • Satellite communication: PM is sometimes used in satellite communication systems for its constant envelope property, which allows for more efficient amplification.
  • Digital modulation schemes: PM serves as the basis for several digital modulation techniques, such as Binary Phase Shift Keying (BPSK) and Quadrature Phase Shift Keying (QPSK).
difference between phase, frequency and amplitude modulation
Difference Between Phase, Frequency, and Amplitude Modulation

Digital Modulation Techniques

Digital modulation is the process of encoding digital information into an analog carrier signal, allowing for the transmission of digital data over radio communication systems. Digital modulation offers several advantages over analog modulation, including improved noise performance, increased bandwidth efficiency, and better data security. In this section, we will briefly introduce some common digital modulation techniques.

differences between analog signal and digital signal
Differences Between Analog Signal and Digital Signal

Types of Digital Modulation (brief introduction)

  • Binary Phase Shift Keying (BPSK): BPSK is a digital modulation technique in which the phase of the carrier wave is shifted between two discrete values to represent binary data (0 and 1).
  • Quadrature Phase Shift Keying (QPSK): QPSK is an extension of BPSK in which the phase of the carrier wave is shifted between four discrete values, allowing for the transmission of two bits of data per symbol, resulting in increased bandwidth efficiency.
  • Quadrature Amplitude Modulation (QAM): QAM is a digital modulation technique that combines both amplitude and phase modulation to encode multiple bits of data per symbol, further increasing bandwidth efficiency.
  • Orthogonal Frequency Division Multiplexing (OFDM): OFDM is a digital modulation technique that divides the available frequency band into multiple orthogonal subcarriers, each modulated with a low data rate, allowing efficient transmission of high data rate signals in a multipath environment.

Advantages of Digital Modulation over Analog Modulation

Digital modulation offers several benefits over analog modulation techniques, including:

  • Improved noise performance: Digital modulation techniques are less susceptible to noise and interference, resulting in better overall signal quality.
  • Increased bandwidth efficiency: Digital modulation methods can transmit more data per unit of bandwidth, allowing for more efficient use of the available frequency spectrum.
  • Better data security: Digital modulation techniques can incorporate data encryption and error-correction coding, enhancing the security and reliability of the transmitted data.

Radio Emission Types

Radio emission classifications are used to categorize different types of radio signals based on their modulation characteristics, such as the type of modulation used, the nature of the transmitted information, and the bandwidth occupied by the signal. These classifications help standardize and regulate the use of radio frequencies, ensuring efficient and interference-free communication.

International Telecommunication Union (ITU) Designations

The International Telecommunication Union (ITU) designations for radio emissions consist of three symbols, each representing a specific aspect of the radio emission. Here is a complete list of the ITU symbols:

First Symbol – Type of Modulation:

SymbolModulation Type
AAmplitude modulation (double-sideband)
HAmplitude modulation (single-sideband, full carrier)
JAmplitude modulation (single-sideband, suppressed carrier)
RAmplitude modulation (single-sideband, reduced or variable level carrier)
BIndependent sidebands
CVestigial sideband modulation
DCarrier, unmodulated
FFrequency modulation
GPhase modulation
PPulse modulation
KPulse amplitude modulation (PAM)
LPulse width modulation (PWM) or Pulse length modulation (PLM)
MPulse position modulation (PPM)
QThe sequence of pulses, phase, or frequency modulation within each group
VCombination of pulse modulation methods
WCombination of any of the above
XModulation or methods not covered by the above categories
First Symbol and Its Meaning of Modulation Type

Second Symbol – Nature of the Signal Modulating the Main Carrier:

SymbolNature of the Signal/Main Carrier
0No modulating signal
1Digital signal, one channel, no subcarrier
2Digital signal, one channel, with subcarrier
3Analog signal, one channel
4Digital signal, two or more channels
5Analog signal, two or more channels
6Digital and analog signals combined
7Digital signal, two or more channels with subcarrier
8Analog signal, two or more channels with subcarrier
9The composite system, signals of various types
Second Symbol and Its Nature of Signal Modulating and Main Carrier

Third Symbol – Type of Transmitted Information:

SymbolType of Transmitted Information
NNo transmitted information
ATelegraphy for aural reception (morse code)
BTelegraphy for automatic reception (e.g., RTTY)
DData transmission, telemetry, telecommand
ETelephony (voice communication)
FVideo (television)
GCombination of the above
WCombination of any of the above
XTransmitted information not covered by the above categories
Third Symbol and Its Types of Transmitted Information

This list provides an overview of the ITU designations for radio emissions, helping to categorize and standardize various types of radio signals based on their modulation characteristics.

Examples of Radio Emission Types and Their Applications

  • A3E: Amplitude-modulated (AM) voice communication, commonly used in AM radio broadcasting and aviation communication.
  • F3E: Frequency-modulated (FM) voice communication, typically used in FM radio broadcasting and two-way radio systems like walkie-talkies.
  • G7D: Phase-shift keying (PSK) digital communication, often employed in satellite communication and wireless data transmission.

The Role of Modulation in Walkie-Talkies

Common Modulation Techniques Used in Walkie-Talkies

Walkie-talkies commonly employ Frequency Modulation (FM) for voice communication, as it offers several advantages over Amplitude Modulation (AM), such as improved audio quality, better noise performance, and reduced power consumption. 

In addition, digital walkie-talkies may use digital modulation techniques like Binary Phase Shift Keying (BPSK) or Quadrature Phase Shift Keying (QPSK) to transmit digital data, such as text messages or GPS information.

Factors Affecting the Choice of Modulation Technique

Several factors can influence the choice of modulation technique for walkie-talkies:

  • Audio quality: FM offers superior audio quality compared to AM, making it the preferred choice for clear voice communication.
  • Range: While FM has a shorter range than AM, the improved audio quality and noise performance often outweigh the range limitations in many applications.
  • Power consumption: FM transmitters generally consume less power than AM transmitters, making them more suitable for battery-powered devices like walkie-talkies.
  • Bandwidth efficiency: Digital modulation techniques can provide higher bandwidth efficiency, allowing for the transmission of more data in the available frequency spectrum.

Impact of Modulation on Range, Clarity, and Battery Life

The choice of modulation technique directly impacts the performance of walkie-talkies in terms of range, clarity, and battery life:

  • Range: FM walkie-talkies may have a shorter range than AM walkie-talkies due to their higher frequency. However, the overall audio quality and noise performance are typically more important factors in most applications.
  • Clarity: FM provides clearer voice communication compared to AM, making it the preferred choice for walkie-talkies used in various professional and recreational settings.
  • Battery life: Since FM transmitters consume less power than AM transmitters, walkie-talkies using FM modulation generally have longer battery life, which is crucial for portable communication devices.


In this article, we discussed the importance of modulation in radio communication systems, including walkie-talkies. We covered the basics of Amplitude Modulation (AM), Frequency Modulation (FM), and Phase Modulation (PM), as well as common digital modulation techniques like Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), and Quadrature Amplitude Modulation (QAM). Additionally, we explored radio emission types and their applications, as well as the role of modulation in walkie-talkie performance.

Understanding modulation techniques is crucial for optimizing the performance of walkie-talkies, as it directly impacts factors such as range, clarity, and battery life. Users can ensure efficient communication in various environments and applications by selecting the appropriate modulation technique, from professional settings to recreational activities.

We hope this article has provided you with a solid foundation for understanding modulation and its role in radio communication systems like walkie-talkies. We encourage you to continue exploring and learning about radio communication technology, as it is a fascinating and ever-evolving field with numerous applications in our daily lives. By deepening your knowledge, you can make more informed decisions when selecting and using radio communication devices, ultimately enhancing your communication experience.

About The Arthur
Picture of Kenny Zhang
I've been running a factory that manufactures two-way radios & their accessories. We want to share some knowledge and news about Walkie-Talkie from the sight of the supplier.

4 Responses

  1. hallo,

    Ik ben in het bezit van de welbekende SEG-15d en zoek hierbij de modulatiesoorten van de symbolen.
    deze kent de A2J, A3H en A3J.
    Deze TRX is een SSB bak.
    via andere sites heb ik uitgevist dat A3J ssb met onderdrukte draaggolf is en A3H ssb met een volle draaggolf.
    Maar ik kan nergens vinden wat A2J inhoud…. telegrafie in ssb misschien ?

    73,s Patrick.

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