Basic Modulation in FE Electrical

Welcome to our FE study guide on Basic Modulation in FE Electrical. Whether you’re preparing for the FE Electrical and Computer exam or simply seeking to enhance your knowledge of communications and transmission, we will help you cover the basics and purpose of modulation along with its core elements per the NCEES® FE electrical exam guidelines.

Let’s begin with some fundamentals of Basic Modulation in FE Electrical.

What is Modulation, and Why is it Necessary?

Modulation is a fundamental concept in communication systems that plays a crucial role in transmitting information efficiently over long distances. The device or circuit that performs modulation modifies a carrier signal to carry information from a source to a destination.

In this discussion, we will cover the need for modulation, its technical depths, limitations of baseband signals, and real-world examples across various domains.

Case Study: Titanic’s Missed Signal – Importance of Modulation

titanic distress signal

Historical Background

On the fateful night of April 14-15, 1912, the RMS Titanic struck an iceberg and began to sink in the North Atlantic Ocean. As the ship faced impending disaster, the crew transmitted distress signals to nearby vessels, seeking assistance and rescue.

Communication Equipment on the Titanic

The Titanic was equipped with a Marconi wireless telegraph system, a cutting-edge technology. The wireless room was staffed by two operators, John Phillips and Harold Bride, who sent and received messages using Morse code over long-wave (300 meters) continuous wave (CW) transmissions.

Communication Challenges

  • CW Transmission – The Titanic’s wireless system used continuous wave (CW) transmission, essentially an on-off transmitter keying. This method was highly efficient for sending simple Morse code messages but had significant limitations for conveying voice or modulation signals. It did not make efficient use of the available bandwidth and could not carry voice or other modulation signals.
  • High-Frequency (Short Range) – The Titanic’s 300-meter wavelength transmission was on the higher end of the radio spectrum, limiting its range. While it could reach nearby ships, it couldn’t efficiently communicate over longer distances, such as to the closest rescue ship, the SS Californian, which was only about 10-19 miles away.
  • Interference and Prioritization – The Marconi operators onboard the Titanic were primarily focused on transmitting passenger messages rather than monitoring the distress frequency continuously. This delayed the recognition of the emergency.

The Missed Signals

communication error

As the Titanic began to sink, its wireless operators sent a series of distress signals (CQD and SOS) using CW transmission. Unfortunately, the nearby SS Californian’s radio operator, Cyril Evans, had already retired for the night, and the ship’s radio set was turned off. While the Californian was within range, it failed to receive the Titanic’s distress calls.

The SS Carpathia, over 50 miles away, picked up the Titanic’s distress signals and promptly responded to rescue survivors. The delay in communication and the missed signals by the Californian contributed to the loss of many lives.

Technical Analysis

The Titanic’s communication equipment, while state-of-the-art for its time, had several limitations that contributed to the tragedy:

  • CW Transmission – Continuous wave transmission made it challenging to effectively convey the situation’s urgency and pass on critical information.
  • Limited Range – The choice of a higher frequency (300 meters) limited the range of communication, especially at night when radio waves could travel further over the ocean.
  • Interference and Priority – The preoccupation of the radio operators with passenger messages rather than monitoring the distress frequency and the decision to retire for the night led to a significant delay in recognizing and responding to the emergency.

Modern Communication and Improved Modulation Techniques

In today’s world, the Titanic disaster serves as a historical lesson on the importance of effective communication and the limitations of early wireless technology.

Modern communication systems use more advanced modulation techniques like amplitude modulation (AM), frequency modulation (FM), and digital modulation to convey information efficiently and reliably.

  • AM and FM Radio – These modulation techniques are widely used for broadcasting, providing clear voice and audio signals over long distances.
  • Digital Modulation – In maritime and aviation communication cases, digital modulation techniques such as phase-shift keying (PSK) and quadrature amplitude modulation (QAM) transmit data more reliably, enabling accurate navigation, safety, and rescue operations.

Takeaways from Case Study

The Titanic’s missed distress signals highlight the critical role of modulation in communication and the historical limitations of early wireless technology.

Improved modulation techniques, alongside advanced communication systems and protocols, have since revolutionized our ability to transmit information, respond to emergencies, and save lives more effectively and efficiently.

If you are interested, you can learn more about this tragedy in detail here.

Need for Modulation:

Limitations of Baseband Signals:

Baseband signals occupy a narrow frequency range around the zero-frequency (DC) point. These signals have several limitations, making them unsuitable for long-distance communication:

  • Bandwidth Limitation – Baseband signals require a wide bandwidth for transmission, which can be impractical for long-distance communication, where bandwidth is a precious resource.
  • Susceptibility to Noise – Baseband signals are more susceptible to noise and interference during transmission. They are often small and low-frequency, so they can be easily corrupted over long distances.
  • Attenuation – Signals traveling over long distances can experience attenuation, reducing their strength. This attenuation is more significant for baseband signals, limiting their reach.

How Modulation Addresses These Limitations

Modulation overcomes the limitations of baseband signals by superimposing the information signal onto a carrier signal. This process has several advantages:

  • Bandwidth Efficiency – Modulation signals have a higher frequency, allowing multiple signals to be transmitted simultaneously in different frequency bands, known as frequency-division multiplexing (FDM). This increases the efficiency of the communication channel.
  • Reduced Susceptibility to Noise – The increased frequency of the carrier signal makes modulation signals less susceptible to low-frequency noise, which is a common source of interference.
  • Improved Long-Distance Transmission – Modulation signals can travel longer distances without significant attenuation, carrying their energy over a more comprehensive frequency range.

Real-World Examples of Modulation:

AM (Amplitude Modulation)

AM is commonly used in the broadcasting industry, where the information signal varies the amplitude of the carrier signal. For instance, AM radio stations transmit audio signals by modulating the amplitude of a high-frequency carrier wave. Listeners can tune their radios to different carrier frequencies to receive different stations.

FM (Frequency Modulation)

FM is widely used in radio broadcasting, offering improved sound quality and noise resistance. In FM, the information signal varies the frequency of the carrier wave. FM is commonly used in radio broadcasting, where the audio signal modulates the carrier frequency.

PM (Phase Modulation)

PM is utilized in various applications, including satellite communication. In satellite communication, phase modulation encodes digital data onto carrier signals for long-range transmission. It offers good noise resistance and is essential for reliable satellite communication.

*We will discuss these modulations in more detail in the following sections.

Let’s look at practical use cases of different modulation methodologies in the real world.


In aviation, modulation is crucial for aircraft and air traffic control communication. AM and FM are used for voice communication, while digital modulation techniques like phase-shift keying (PSK) are employed for data transmission, ensuring safe and efficient air traffic management.

Satellite Communication:

Satellite communication systems use various forms of modulation to transmit signals from Earth to satellites and back. This includes AM and FM for audio signals, as well as more advanced digital modulation schemes for data transmission, ensuring reliable global connectivity.

Basics of Modulation

basic modulation

Basic Modulation in FE Electrical involves altering specific characteristics of a high-frequency carrier signal according to the variations in a lower-frequency modulating signal (information signal).

Here are key terms and concepts related to modulation:

  • Carrier Signal – The carrier signal is a high-frequency electromagnetic wave that carries no information but serves as a “vehicle” to transport the modulating signal. It is typically a continuous wave (CW) signal with a constant frequency and amplitude.
  • Modulating Signal (Information Signal) – The modulating signal is the lower-frequency signal that carries the information you want to transmit. It can be an audio signal (for voice or music), digital data, or any other type of information.
  • Modulation Depth (Modulation Index) – Modulation depth refers to the extent to which the modulating signal alters the carrier signal’s characteristics. It measures how much the carrier signal’s amplitude, frequency, or phase changes in response to the modulating signal.

How Modulation Works

Basic Modulation in FE Electrical is the process of embedding the information signal into the carrier signal to allow for efficient transmission over a communication channel. The modulation depth determines how much the carrier signal changes in response to the modulating signal. 

There are different modulation techniques, including amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM), each of which distinctly alters the carrier signal.

The Role of the Carrier Signal

The carrier signal provides the means for transmitting the information over long distances. It has a high frequency, which allows it to carry the information efficiently. 

However, without modulation, it carries no helpful information itself. The carrier signal is usually a high-frequency electromagnetic wave in the radio frequency (RF) or microwave range.

Superimposing the Modulating Signal

superimposition and interference of waves

The concept of superimposing signals is a fundamental principle in wave physics. According to the law of superimposition, when two or more waves occupy the same space simultaneously, their amplitudes at any given point add together. This means that the resulting wave at that point is the sum of the individual waves.

Mathematically, this can be expressed as follows for two waves A1sin(ω1t) and A2sin(ω2t):

Resultant wave = A1sin(ω1t) + A2sin(ω2t)

Types of Basic Modulation in FE Electrical

Let’s discuss the three primary types of Basic Modulation in FE Electrical.

Amplitude Modulation (AM)

In AM, the modulating signal varies the amplitude of the carrier signal. When the modulating signal is positive, it increases the carrier signal’s amplitude; when the modulating signal is negative, it decreases the amplitude.


  • Carrier Signal: AM involves varying the amplitude of the carrier signal in response to the modulating signal. The amplitude of the carrier wave is made to vary proportionally with the amplitude of the modulating signal.
  • Modulation Signal: The Modulation signal in AM is expressed as S(t)=[Ac+Am⋅m(t)]⋅cos(2πfct), where:
    • Ac is the carrier amplitude.
    • Am is the amplitude of the modulating signal.
    • m(t) is the modulating signal.
    • fc is the carrier frequency.

Pros: AM is relatively simple and widely used for broadcasting medium-frequency (MF) and high-frequency (HF) radio signals.

Cons: It is susceptible to amplitude variations due to interference and noise, making it less immune to disturbances.

Frequency Modulation (FM)

In FM, the modulating signal varies the frequency of the carrier signal. When the modulating signal has a higher amplitude, it produces a higher frequency carrier wave. When the modulating signal has a lower amplitude, it leads to a lower-frequency carrier wave.


  • Carrier Signal: In FM, the carrier signal’s frequency is altered by the modulating signal. When the modulating signal has a higher amplitude, it leads to a higher frequency carrier wave, and lower amplitude results in a lower frequency carrier wave.
  • Modulation Signal: The modulation signal in FM is expressed as S(t)=Ac⋅cos[2πfct+kf⋅m(t)], where:
    • Ac is the carrier amplitude.
    • kf is the frequency sensitivity constant.
    • m(t) is the modulating signal.
    • fc is the carrier frequency.

Pros: FM is known for its resistance to amplitude noise and interference, making it ideal for high-fidelity audio transmission.

Cons: It requires a broader bandwidth for transmission compared to AM.

Phase Modulation (PM)

In PM, the modulating signal alters the phase of the carrier signal. The modulating signal’s phase variations determine how the carrier signal’s phase changes over time.


  • Carrier Signal: PM involves varying the carrier signal phase based on the modulating signal. Changes in the modulating signal result in phase shifts in the carrier signal.
  • Modulation Signal: The Modulation signal in PM is expressed as S(t)=Ac⋅cos[2πfct+kp⋅m(t)], where:
    • Ac is the carrier amplitude.
    • kp is the phase sensitivity constant.
    • m(t) is the modulating signal.
    • fc is the carrier frequency.

Pros: PM is used in various applications, including certain types of data transmission and some analog modulation systems.

Cons: It is less commonly used in commercial broadcasting due to its complexity than AM and FM.

*The formula for Phase Modulation (PM) and Frequency Modulation (FM) are similar because both PM and FM are closely related forms of angular modulation. They both involve variations in the phase or frequency of the carrier signal in response to the modulating signal.

Technical/Mathematical Differences in AM and PM

  • PM (Phase Modulation): In PM, the modulating signal directly causes phase shifts in the carrier signal. The modulated signal’s phase is proportional to the instantaneous value of the modulating signal. The phase sensitivity constant, denoted as kp, determines the degree to which the phase changes in response to the modulating signal.
  • FM (Frequency Modulation): In FM, the modulating signal causes variations in the carrier signal’s instantaneous frequency. The instantaneous frequency is proportional to the modulating signal’s derivative (rate of change). The frequency sensitivity constant, denoted as kf, determines how the frequency varies with the modulating signal.

*The mathematical similarity arises because the phase 2πfct is common to both equations, representing the carrier signal’s phase at any given time t.

  • In FM, the frequency is directly determined by the integral of the modulating signal. The integral represents the cumulative effect of the modulating signal, which affects the carrier signal’s frequency.
  • In PM, the phase is directly determined by the modulating signal m(t). Changes in the modulating signal m(t) directly influence the phase of the carrier signal.


As we wrap up our exploration of “Basic Modulation in FE Electrical,” I hope you’ve found this study guide insightful. To further gear up for success, I recommend checking out “Study for FE,” your trusty resource for comprehensive FE Electrical exam prep. We offer practice exams, study materials, Electrical and Computer FE Exam Practice PDF, and more to boost your chances of acing the test.

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Licensed Professional Engineer in Texas (PE), Florida (PE) and Ontario (P. Eng) with consulting experience in design, commissioning and plant engineering for clients in Energy, Mining and Infrastructure.