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Radio Basics for Hackers, Part 2: Amplitude, Modulation, decibels and gain

Welcome back, my aspiring radio hackers!


As you know, radio hacking is the leading-edge of cybersecurity! Nearly everything digital around us emits, radiates or receives radio waves. These include our cellphones, computers, automobiles, remote controls, key fobs, GPS, and this list could go on and on. This is a little understood field of cybersecurity by our industry but well understood and exploited by the national security and intelligence units around the world. The advent of software defined radio has made this field reachable by the average cybersecurity professional.


In this series, Radio Basics for Hackers, I will try to buttress your basic understanding of radio signals and provide the prerequisite knowledge to advance to our SDR for Hackers series here at Hackers-Arise.


Amplitude

Amplitude in radio signals refers to the height of the wave, or the distance between the middle line of the wave and either its crest or through. In other words, amplitude is a measure of the power of a radio signal.




Amplitude modulation (AM) is a modulation technique in which the amplitude of a carrier wave is varied in accordance with the amplitude of the information signal. The information signal can be audio, video, or data.




In AM radio, the amplitude of the carrier wave is modulated by the audio signal. The audio signal is a low-frequency signal that cannot be transmitted over long distances. By modulating the carrier wave with the audio signal, the audio signal can be carried by the carrier wave and transmitted over long distances. The amplitude of a radio signal is measured in decibels (dB). The higher the amplitude, the stronger the signal. Amplitude is also measured in terms of its peak-to-peak value, which is the difference between the maximum and minimum values of the signal.

The amplitude of a radio signal is affected by a number of factors, including the power of the transmitter, the distance between the transmitter and the receiver, and the presence of noise. The higher the power of the transmitter, the greater the amplitude of the signal. The greater the distance between the transmitter and the receiver, the lower the amplitude of the signal. The presence of noise can also reduce the amplitude of the signal.

The amplitude of a radio signal is an important factor in determining the quality of the received signal. A higher amplitude signal will result in a better quality signal. However, a too high amplitude signal can also damage the receiver. Here are some additional points about amplitude in radio signals:

  • Amplitude is inversely proportional to wavelength: The higher the amplitude, the shorter the wavelength.

  • Amplitude is proportional to the power of the signal: The higher the amplitude, the greater the power of the signal.

  • Amplitude is affected by noise: Noise can reduce the amplitude of a signal.

  • Amplitude is important for determining the quality of the received signal: A higher amplitude signal will result in a better quality signal.


Modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a separate signal called the modulation signal that typically contains information to be transmitted. For example, the modulation signal might be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing a sequence of binary digits, a bitstream from a computer.

Modulation is essential in radio communications because it allows the information signal to be carried by the carrier wave. The carrier wave is a high-frequency signal that can be transmitted over long distances. The information signal is typically a low-frequency signal that cannot be transmitted over long distances. By modulating the carrier wave with the information signal, the information signal can be carried by the carrier wave and transmitted over long distances. There are many different modulation techniques, but some of the most common include:

  • Amplitude modulation (AM): In AM, the amplitude of the carrier wave is varied in accordance with the amplitude of the information signal.

  • Frequency modulation (FM): In FM, the frequency of the carrier wave is varied in accordance with the amplitude of the information signal.

  • Phase modulation (PM): In PM, the phase of the carrier wave is varied in accordance with the amplitude of the information signal.

  • Quadrature amplitude modulation (QAM): In QAM, both the amplitude and phase of the carrier wave are varied in accordance with the amplitude of the information signal.

The choice of modulation technique depends on a number of factors, including the type of information to be transmitted, the desired bandwidth, and the noise environment.

Here are some of the benefits of modulation:

  • Increased bandwidth: Modulation can increase the bandwidth of a signal, which allows more information to be transmitted.

  • Reduced interference: Modulation can reduce interference from other signals, which improves the quality of the received signal.

  • Increased range: Modulation can increase the range of a signal, which allows it to be transmitted over longer distances.

Modulation is a powerful technique that can be used to improve the performance of radio communications. It is a valuable tool for anyone who wants to transmit information over long distances.


Decibel


A decibel (dB) is a unit of measurement that is used to express the ratio of two values of a power or root-power quantity on a logarithmic scale. Decibels are used in a wide variety of applications, including acoustics, electronics, and telecommunications.

The decibel scale is a logarithmic scale, which means that a difference of 1 dB corresponds to a power ratio of 101/10 or root-power ratio of 10¹⁄²⁰. This means that a sound that is 10 dB louder than another sound is 10 times more powerful, and a sound that is 20 dB louder is 100 times more powerful. The decibel scale is also a relative scale, which means that the reference level is arbitrary. This means that the decibel level of a sound can only be meaningfully compared to the decibel level of another sound that is measured using the same reference level.

The most common reference level for sound measurements is 20 micropascals (μPa), which is the threshold of human hearing. This means that a sound that is 0 dB SPL is just barely audible to the human ear.

Other common reference levels for sound measurements include 1 pascal (Pa), which is the reference level for sound pressure level measurements in air, and 1 μW/cm2, which is the reference level for sound power level measurements in air. Decibels are a convenient unit of measurement for sound because they allow us to express the relative loudness of sounds in a way that is easy to understand. For example, a whisper is about 30 dB SPL, while a normal conversation is about 60 dB SPL, and a rock concert is about 120 dB SPL.

Decibels are also used to measure the power of other types of signals, such as electrical signals and optical signals. In these cases, the reference level is typically the power of a reference signal.

Decibels are a versatile unit of measurement that is used in a wide variety of applications. They are a convenient way to express the relative loudness of sounds, and they can also be used to measure the power of other types of signals.


Gain


In reference to radio signals, gain is a measure of the increase in power or amplitude of a signal. It is typically measured in decibels (dB).

Gain can be achieved through a variety of means, including:

  • Amplifiers: Amplifiers are electronic devices that increase the power of a signal.

  • Antennas: Antennas can increase the gain of a signal by focusing the signal in a particular direction.

  • Optics: Optics can increase the gain of a signal by using lenses or mirrors to focus the signal.



Gain is an important factor in radio communications, as it can improve the quality of the received signal. A higher gain signal will result in a better quality signal.

Here are some of the benefits of gain:

  • Improved signal quality: Gain can improve the signal quality by increasing the amplitude of the signal.

  • Increased range: Gain can increase the range of a signal by allowing it to be transmitted over longer distances.

  • Reduced noise: Gain can reduce noise by increasing the signal-to-noise ratio.

Gain is a powerful technique that can be used to improve the performance of radio communications. It is a valuable tool for anyone who wants to transmit signals over long distances or in noisy environments.


Here are some additional points about gain in reference to radio signals:

  • Gain is not the same as amplification: Amplification is the process of increasing the power of a signal, while gain is a measure of the increase in power or amplitude of a signal.

  • Gain can be expressed in decibels (dB) or linear units: When expressed in decibels, gain is the ratio of the output power to the input power, expressed in dB. When expressed in linear units, gain is the ratio of the output amplitude to the input amplitude.

  • Gain can be positive or negative: Positive gain indicates that the signal has been amplified, while negative gain indicates that the signal has been attenuated.


Summary


Hacking radio signals is the leading edge of cybersecurity! Nearly everything digital emits or receives radio signals. Hackers-Arise has initiated a training series called SDR for Hackers to train individual sin the cybersecurity community how to intercept, hack, and interfere with these signals.


This series on radio basics is intended to provide the aspiring cyberwarrior the prerequisite knowledge to be able to mak ethe most of this training.

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