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Questions and Answers
Resistance is measured in volts.
Resistance is measured in volts.
False
A Voltage Standing Wave Ratio (VSWR) of 1:1 indicates a perfect impedance match.
A Voltage Standing Wave Ratio (VSWR) of 1:1 indicates a perfect impedance match.
True
The equivalent isotropically radiated power (EIRP) measures the power output at the transmitter.
The equivalent isotropically radiated power (EIRP) measures the power output at the transmitter.
False
In the USA, the maximum EIRP for devices that transmit radio signals is ten watts.
In the USA, the maximum EIRP for devices that transmit radio signals is ten watts.
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The watt is a unit of power that was established in 1889.
The watt is a unit of power that was established in 1889.
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The power level at the last connector before the antenna is not important for calculating EIRP.
The power level at the last connector before the antenna is not important for calculating EIRP.
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Impedance includes resistance and also accounts for the effects of AC's magnetic field.
Impedance includes resistance and also accounts for the effects of AC's magnetic field.
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One watt equals one ampere multiplied by one ohm.
One watt equals one ampere multiplied by one ohm.
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A light bulb consuming 0.5 A at 120 V uses 60 watts of power.
A light bulb consuming 0.5 A at 120 V uses 60 watts of power.
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One bel is a logarithmic unit that indicates a fixed value rather than a difference between two values.
One bel is a logarithmic unit that indicates a fixed value rather than a difference between two values.
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Radio frequency signals are electromagnetic signals generated by a direct current applied to an antenna.
Radio frequency signals are electromagnetic signals generated by a direct current applied to an antenna.
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Amplitude is a measurement of the distance between the peak of a wave and the trough.
Amplitude is a measurement of the distance between the peak of a wave and the trough.
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100 mW is equivalent to 10 dBm.
100 mW is equivalent to 10 dBm.
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In the context of decibels, logarithms are used to express the ratio between two power levels.
In the context of decibels, logarithms are used to express the ratio between two power levels.
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Frequency is measured in decibels (dB).
Frequency is measured in decibels (dB).
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In a wireless network, high amplitude generally indicates a weak signal.
In a wireless network, high amplitude generally indicates a weak signal.
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The variable A in the logarithm notation represents the logarithm of the number.
The variable A in the logarithm notation represents the logarithm of the number.
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Electromagnetic energy travels at approximately 300,000 kilometers per second in a vacuum.
Electromagnetic energy travels at approximately 300,000 kilometers per second in a vacuum.
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Decibels measure fixed values in power levels.
Decibels measure fixed values in power levels.
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The wavelength of a radio signal can be calculated by dividing the speed of light by its frequency.
The wavelength of a radio signal can be calculated by dividing the speed of light by its frequency.
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An isotropic radiator is a theoretical antenna that disperses energy unevenly.
An isotropic radiator is a theoretical antenna that disperses energy unevenly.
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A signal maintains the same frequency but can have a shorter wavelength when affected by obstacles.
A signal maintains the same frequency but can have a shorter wavelength when affected by obstacles.
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The base of the logarithm used in this context is specifically the decimal numbering system.
The base of the logarithm used in this context is specifically the decimal numbering system.
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Phase of electromagnetic waves is measured in radians.
Phase of electromagnetic waves is measured in radians.
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The received amplitude is always greater than the transmit amplitude.
The received amplitude is always greater than the transmit amplitude.
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Vertical and horizontal polarisation allows maximum signal reception between antennas.
Vertical and horizontal polarisation allows maximum signal reception between antennas.
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The effect known as gain refers to the decrease in amplitude of an electromagnetic wave.
The effect known as gain refers to the decrease in amplitude of an electromagnetic wave.
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Combining out-of-phase waves can lead to signal loss.
Combining out-of-phase waves can lead to signal loss.
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Signals in a wireless network are affected by the sensitivity level of each device.
Signals in a wireless network are affected by the sensitivity level of each device.
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Reflection of radio frequency signals does not depend on the texture of the surface.
Reflection of radio frequency signals does not depend on the texture of the surface.
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Active gain is solely a result of combining in-phase waves.
Active gain is solely a result of combining in-phase waves.
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Too much signal strength can help devices detect signals more easily.
Too much signal strength can help devices detect signals more easily.
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Multipath can cause significant signal loss in buildings.
Multipath can cause significant signal loss in buildings.
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Scattering involves a signal passing through a denser material.
Scattering involves a signal passing through a denser material.
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Higher voltage in a wire indicates stronger forces pushing electrons.
Higher voltage in a wire indicates stronger forces pushing electrons.
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Direct Current (DC) is characterized by electrons flowing back and forth.
Direct Current (DC) is characterized by electrons flowing back and forth.
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Absorption occurs when RF signals are completely obstructed by concrete.
Absorption occurs when RF signals are completely obstructed by concrete.
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Diffraction happens when waves bend around large obstacles.
Diffraction happens when waves bend around large obstacles.
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Good conductors have high resistance to electron flow.
Good conductors have high resistance to electron flow.
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Refraction causes an RF signal to bend when passing through a less dense material.
Refraction causes an RF signal to bend when passing through a less dense material.
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Antenna gain can have negative values.
Antenna gain can have negative values.
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An antenna with a gain of 3 dBi produces a weaker signal than an isotropic radiator.
An antenna with a gain of 3 dBi produces a weaker signal than an isotropic radiator.
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The Received Signal Strength Indicator (RSSI) is defined as an integer value between 0 and 256.
The Received Signal Strength Indicator (RSSI) is defined as an integer value between 0 and 256.
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Different manufacturers may measure RSSI differently, leading to inconsistencies in power level representation.
Different manufacturers may measure RSSI differently, leading to inconsistencies in power level representation.
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An RSSI value of 10 always indicates the same power level in milliwatts across all manufacturers.
An RSSI value of 10 always indicates the same power level in milliwatts across all manufacturers.
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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
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Radio signals can be degraded or changed as they travel.
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Gain increases the amplitude of the signal.
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Loss decreases the signal's amplitude.
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Gain can be passive (e.g., in phase waves) or active.
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Loss can be caused by out-of-phase waves, depending on the phase variations.
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Wireless devices have sensitivity levels to detect signals from background noise.
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Too much signal loss can cause errors
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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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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!
