Electromagnetic Waves and Power Measurements
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Questions and Answers

Resistance is measured in volts.

False (B)

A Voltage Standing Wave Ratio (VSWR) of 1:1 indicates a perfect impedance match.

True (A)

The equivalent isotropically radiated power (EIRP) measures the power output at the transmitter.

False (B)

In the USA, the maximum EIRP for devices that transmit radio signals is ten watts.

<p>False (B)</p> Signup and view all the answers

The watt is a unit of power that was established in 1889.

<p>True (A)</p> Signup and view all the answers

The power level at the last connector before the antenna is not important for calculating EIRP.

<p>False (B)</p> Signup and view all the answers

Impedance includes resistance and also accounts for the effects of AC's magnetic field.

<p>True (A)</p> Signup and view all the answers

One watt equals one ampere multiplied by one ohm.

<p>False (B)</p> Signup and view all the answers

A light bulb consuming 0.5 A at 120 V uses 60 watts of power.

<p>True (A)</p> Signup and view all the answers

One bel is a logarithmic unit that indicates a fixed value rather than a difference between two values.

<p>False (B)</p> Signup and view all the answers

Radio frequency signals are electromagnetic signals generated by a direct current applied to an antenna.

<p>False (B)</p> Signup and view all the answers

Amplitude is a measurement of the distance between the peak of a wave and the trough.

<p>True (A)</p> Signup and view all the answers

100 mW is equivalent to 10 dBm.

<p>False (B)</p> Signup and view all the answers

In the context of decibels, logarithms are used to express the ratio between two power levels.

<p>True (A)</p> Signup and view all the answers

Frequency is measured in decibels (dB).

<p>False (B)</p> Signup and view all the answers

In a wireless network, high amplitude generally indicates a weak signal.

<p>False (B)</p> Signup and view all the answers

The variable A in the logarithm notation represents the logarithm of the number.

<p>False (B)</p> Signup and view all the answers

Electromagnetic energy travels at approximately 300,000 kilometers per second in a vacuum.

<p>True (A)</p> Signup and view all the answers

Decibels measure fixed values in power levels.

<p>False (B)</p> Signup and view all the answers

The wavelength of a radio signal can be calculated by dividing the speed of light by its frequency.

<p>True (A)</p> Signup and view all the answers

An isotropic radiator is a theoretical antenna that disperses energy unevenly.

<p>False (B)</p> Signup and view all the answers

A signal maintains the same frequency but can have a shorter wavelength when affected by obstacles.

<p>True (A)</p> Signup and view all the answers

The base of the logarithm used in this context is specifically the decimal numbering system.

<p>True (A)</p> Signup and view all the answers

Phase of electromagnetic waves is measured in radians.

<p>False (B)</p> Signup and view all the answers

The received amplitude is always greater than the transmit amplitude.

<p>False (B)</p> Signup and view all the answers

Vertical and horizontal polarisation allows maximum signal reception between antennas.

<p>False (B)</p> Signup and view all the answers

The effect known as gain refers to the decrease in amplitude of an electromagnetic wave.

<p>False (B)</p> Signup and view all the answers

Combining out-of-phase waves can lead to signal loss.

<p>True (A)</p> Signup and view all the answers

Signals in a wireless network are affected by the sensitivity level of each device.

<p>True (A)</p> Signup and view all the answers

Reflection of radio frequency signals does not depend on the texture of the surface.

<p>False (B)</p> Signup and view all the answers

Active gain is solely a result of combining in-phase waves.

<p>False (B)</p> Signup and view all the answers

Too much signal strength can help devices detect signals more easily.

<p>False (B)</p> Signup and view all the answers

Multipath can cause significant signal loss in buildings.

<p>True (A)</p> Signup and view all the answers

Scattering involves a signal passing through a denser material.

<p>False (B)</p> Signup and view all the answers

Higher voltage in a wire indicates stronger forces pushing electrons.

<p>True (A)</p> Signup and view all the answers

Direct Current (DC) is characterized by electrons flowing back and forth.

<p>False (B)</p> Signup and view all the answers

Absorption occurs when RF signals are completely obstructed by concrete.

<p>False (B)</p> Signup and view all the answers

Diffraction happens when waves bend around large obstacles.

<p>True (A)</p> Signup and view all the answers

Good conductors have high resistance to electron flow.

<p>False (B)</p> Signup and view all the answers

Refraction causes an RF signal to bend when passing through a less dense material.

<p>False (B)</p> Signup and view all the answers

Antenna gain can have negative values.

<p>False (B)</p> Signup and view all the answers

An antenna with a gain of 3 dBi produces a weaker signal than an isotropic radiator.

<p>False (B)</p> Signup and view all the answers

The Received Signal Strength Indicator (RSSI) is defined as an integer value between 0 and 256.

<p>False (B)</p> Signup and view all the answers

Different manufacturers may measure RSSI differently, leading to inconsistencies in power level representation.

<p>True (A)</p> Signup and view all the answers

An RSSI value of 10 always indicates the same power level in milliwatts across all manufacturers.

<p>False (B)</p> Signup and view all the answers

Flashcards

Radio Frequency (RF) signals

Electromagnetic signals emitted from an antenna when alternating current is applied.

Amplitude

The strength of an RF signal, measured from peak or trough to the baseline.

Frequency

The number of waves per second, measured in Hertz (Hz).

Wavelength

The length of a single wave, calculated from frequency using the speed of light.

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Transmit amplitude

The amplitude of the signal at the time it is transmitted.

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Received amplitude

The amplitude of the signal when it reaches the receiver.

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Speed of light

The speed of light is approximately 300 million meters per second (m/s) in a vacuum.

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Signal Attenuation

The earth's atmosphere and obstacles can cause RF signals to slow down, reflect, refract, or absorb, affecting wavelength but not frequency.

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Multipath

When radio waves bounce off surfaces, creating areas with no signal.

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Scattering

Reflected waves bouncing off uneven surfaces or small objects, creating multiple signals.

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Refraction

Radio waves bending when passing through different densities, like air and water.

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Absorption

Materials absorbing radio waves, preventing them from reaching their target.

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Diffraction

Radio waves bending around obstacles, like buildings.

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Voltage

The difference in electrical charge between two points.

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Current

The flow of electrons through a conductor, measured in amps.

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Resistance

The opposition to the flow of electrons.

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Impedance

A broader term than resistance, encompassing the opposition to current flow in AC circuits, including factors like resistance, inductance, and capacitance.

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Voltage Standing Wave Ratio (VSWR)

A measure of how well impedances match in an AC circuit. A ratio of 1:1 signifies a perfect match, while a higher ratio indicates impedance mismatch.

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Equivalent Isotopically Radiated Power (EIRP)

The total power emitted by an antenna, considering its gain and the power supplied to it. It represents the actual power radiated into the air.

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Watt (W)

A unit of power, measuring the rate at which energy is used or converted. In wireless networks, it represents the power used to create radio signals.

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Signal Strength Difference

A fundamental concept in RF circuits. It describes how the difference in signal strength between the transmitted and received signals affects communication quality.

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Amplifier

A device used to amplify radio frequency signals, boosting their strength.

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Connector

A connector that joins different components in an RF circuit, allowing signal transmission and reception.

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Phase

The difference in position of two electromagnetic waves with the same frequency. It's measured in degrees.

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Antenna Polarization

The physical orientation of an antenna, affecting how efficiently it emits or receives signals.

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Radio Frequency Gain/Loss

The change in the amplitude of a radio signal. Gain increases the amplitude; loss decreases it.

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Passive Gain

The combination of in-phase waves, resulting in a stronger signal.

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Signal Loss (Out-of-Phase)

The decrease in signal strength caused by the combination of out-of-phase waves.

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Device Sensitivity

The ability of a device to pick up weak signals amidst background noise.

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Decibel (dB)

A logarithmic unit of measure used to express the ratio between two power levels.

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Logarithm

The exponent needed to raise a base to a specific number. For example, log10 1000 = 3 because 10 raised to the power of 3 equals 1000.

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Bel

A relative measurement that quantifies the difference between two values.

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Bel and Power

Each bel represents a tenfold increase in power. So a 1-bel difference means the power is 10 times greater.

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dBm (dB-milliwatt)

A unit of power measurement that uses 1 milliwatt (mW) as its reference point.

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Isotropic Radiator

A theoretical antenna that radiates energy evenly in all directions, like a spherical wave.

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Antenna Gain (dBi)

The measure of how well an antenna focuses its signal in a specific direction.

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dBi (decibel relative to isotropic)

A unit used to express antenna gain, relative to an isotropic radiator.

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Antenna Gain

The ability of an antenna to concentrate radio waves in a specific direction, resulting in a stronger signal in that direction compared to an isotropic radiator, which radiates equally in all directions.

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dBi (decibel-isotropic)

A unit of measurement for antenna gain, often expressed in decibels (dBi).

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Received Signal Strength Indicator (RSSI)

A method defined in the IEEE 802.11 standard for wireless network cards to measure the strength of radio frequency (RF) signals.

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RSSI Value

A value between 0 and 255 that represents the strength of a received radio signal, as defined by the IEEE 802.11 standard.

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RSSI Inconsistency

The inconsistency in how different manufacturers implement RSSI, leading to different interpretations of the same RSSI value in terms of actual signal power.

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Study Notes

Radio Frequency (RF) Basics

  • RF signals are electromagnetic signals radiated from an antenna when an alternating current is applied.
  • The theory states a time-varying electric field generates a magnetic field, and vice versa.

Learning Outcomes

  • Describe wireless communication concepts.
  • Manage wireless components.

Amplitude

  • Amplitude measures the distance between the peak (highest) or trough (lowest) and the base of a wave.
  • Higher amplitude corresponds to greater signal strength.
  • Transmit amplitude is the signal strength at transmission.
  • Received amplitude is the signal strength at reception.

Frequency

  • Frequency is the rate at which an event occurs in a given time unit.
  • For radio signals, it's the number of waves that occur each second.
  • Measured in Hertz (Hz).

Wavelength

  • Wavelength is the length of a wave, measured in meters.
  • It can be calculated from frequency using the speed of light (approximately 300,000,000 m/s).
  • Electromagnetic waves can be slowed, reflected, refracted, or absorbed by the atmosphere and other obstacles. These changes can affect the wavelength but not the frequency.

Phase

  • Phase compares two electromagnetic waves with the same frequency to determine if they're synchronized.
  • Phase is measured in degrees (angles).

Polarization

  • Polarization is the physical alignment of an object.
  • Important to ensure proper communication between wireless devices.
  • The magnetic field generated by an electric current passing through a conductor is always perpendicular to the electric field.

Radio Frequency Behavior

  • Radio signals can be degraded or changed as they travel.

  • Gain increases the amplitude of the signal.

  • Loss decreases the signal's amplitude.

  • Gain can be passive (e.g., in phase waves) or active.

  • Loss can be caused by out-of-phase waves, depending on the phase variations.

  • Wireless devices have sensitivity levels to detect signals from background noise.

  • Too much signal loss can cause errors

  • Too strong a signal can also increase noise levels, hindering signal detection

Reflection, Scattering, Refraction, Absorption, Diffraction

  • Issues affecting RF signals due to objects:
    • Reflection: signals bounce off objects (smooth surfaces better).
    • Scattering: signals reflect off uneven surfaces or small objects, creating multiple bounces.
    • Refraction: signals bending when passing through different materials.
    • Absorption: signals absorbed by materials like concrete.
    • Diffraction: signals bending around obstacles.

Voltage Standing Wave Ratio (VSWR)

  • Measures impedance match in a circuit.
  • A VSWR of 1:1 indicates no reflected power (perfect match).
  • A VSWR of 1.5:1 indicates some mismatch.
  • VSWR values close to 1:1 are beneficial to avoid power loss and protect equipment in wireless networks.

Intentional Radiators

  • Every country has regulations for radio technology use (e.g., FCC in the USA, ICASA in South Africa).
  • EIRP (Equivalent Isotropically Radiated Power) measures actual power output at the antenna.
  • Understanding EIRP and RF circuit power levels is vital for meeting local regulations.

Watts (W)

  • The watt is a unit of power, indicating the rate of energy use/conversion.
  • Used in wireless networks to represent the power devices use to create radio signals.
  • One Watt equals one Ampere multiplied by one Volt.

Decibel (dB)

  • A logarithmic unit of measure (named after Alexander Graham Bell).
  • Measures the difference between two values, not absolute values.
  • Log₁₀(A₂ / A₁) gives the difference in bels, where A₁ and A₂ are values being compared.

Decibels Relative to a Milliwatt (dBm)

  • Using dBm simplifies calculations by using a common reference point of 1 milliwatt (mW).
  • 100mW equals 20 dBm (since 100mW is 100 times 1mW).

Decibels Relative to an Isotropic Radiator (dBi)

  • Isotropic radiator (theoretical) spreads energy equally in all directions, acting as a reference point
  • Real antennas concentrate signals in specific directions (gain).
  • Gain (in dBi) is a positive value and represents how much stronger the signal is in a certain direction compared to an isotropic radiator.

Received Signal Strength Indicator (RSSI)

  • Wireless network cards measure RF signal strength to help decide when to switch connections.
  • IEEE 802.11 provides a method (RSSI) to report signal strength, yet implementation and reported values vary between hardware manufacturers.
  • RSSI values can be highly non-standard, meaning one manufacturer's 10 RSSI could actually correlate with another manufacturer's 60 mW power level.

Group Discussion

  • Students are to discuss factors affecting radio signals and their impact (e.g. signal interference, noise levels, reflection, scattering etc).

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ITNSA0 - Lesson 1 - Radio Frequency (RF) Basics PDF

Description

This quiz covers key concepts related to electromagnetic waves, power measurements, and impedance in electrical circuits. Participants will explore topics such as Voltage Standing Wave Ratio, equivalent isotropically radiated power, and the relationship between voltage, current, and resistance. Test your understanding of these fundamental concepts in electrical engineering!

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