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Questions and Answers
What does Johnson's Formula calculate?
What does Johnson's Formula calculate?
- Average noise power
- Voltage drop across a resistor
- Rms noise voltage (correct)
- Thermal resistance
Which of the following is NOT a variable in Johnson's Formula?
Which of the following is NOT a variable in Johnson's Formula?
- Boltzman's Constant
- Resistance
- Bandwidth
- Temperature in Celsius (correct)
What is the value of Boltzman's Constant used in noise calculations?
What is the value of Boltzman's Constant used in noise calculations?
- 1.38 x 10^-23 Kelvin (correct)
- 2.88 x 10^-23 Joule
- 1.60 x 10^-23 Joule
- 1.28 x 10^-23 Kelvin
How can you convert Celsius to Kelvin?
How can you convert Celsius to Kelvin?
Which formula expresses the relationship for averaging noise power?
Which formula expresses the relationship for averaging noise power?
Shot noise is directly proportional to which of the following?
Shot noise is directly proportional to which of the following?
What does the formula for the rms noise current 𝑰𝒏 represent?
What does the formula for the rms noise current 𝑰𝒏 represent?
Which of these temperature scales can directly impact noise calculations?
Which of these temperature scales can directly impact noise calculations?
What type of noise is characterized by its strength at lower frequencies, generally below a few kHz?
What type of noise is characterized by its strength at lower frequencies, generally below a few kHz?
What characteristic is true about shot noise?
What characteristic is true about shot noise?
In calculating the Signal-to-Noise Ratio (SNR), which of the following ratios may be used?
In calculating the Signal-to-Noise Ratio (SNR), which of the following ratios may be used?
What does Noise Figure (NF) express in terms of Noise Ratio (NR)?
What does Noise Figure (NF) express in terms of Noise Ratio (NR)?
Which factor is crucial for cascaded stages of amplifiers according to Friis' formula?
Which factor is crucial for cascaded stages of amplifiers according to Friis' formula?
What does a higher Signal-to-Noise Ratio (SNR) indicate about a communication system?
What does a higher Signal-to-Noise Ratio (SNR) indicate about a communication system?
In the formula for overall noise performance 𝑵𝑹𝑻, what do the denominators represent?
In the formula for overall noise performance 𝑵𝑹𝑻, what do the denominators represent?
Which component is NOT included in the calculation of the rms noise current 𝑰𝒏?
Which component is NOT included in the calculation of the rms noise current 𝑰𝒏?
What type of noise is classified as produced by sources in space?
What type of noise is classified as produced by sources in space?
Which of the following options is an example of industrial noise?
Which of the following options is an example of industrial noise?
Thermal noise is often referred to as what?
Thermal noise is often referred to as what?
What is the primary source of extraterrestrial noise?
What is the primary source of extraterrestrial noise?
Which type of noise comes from electrical disturbances in the earth's atmosphere?
Which type of noise comes from electrical disturbances in the earth's atmosphere?
What condition must be satisfied for proper amplitude modulation to occur?
What condition must be satisfied for proper amplitude modulation to occur?
What represents the instantaneous value of the information signal in amplitude modulation?
What represents the instantaneous value of the information signal in amplitude modulation?
What is the relationship between the carrier frequency and the modulating frequency in amplitude modulation?
What is the relationship between the carrier frequency and the modulating frequency in amplitude modulation?
What occurs if the amplitude of the modulating signal exceeds that of the carrier signal?
What occurs if the amplitude of the modulating signal exceeds that of the carrier signal?
In the equation $v_m = V_m ext{sin}(2 ext{pi} f_m t)$, what does $f_m$ represent?
In the equation $v_m = V_m ext{sin}(2 ext{pi} f_m t)$, what does $f_m$ represent?
What expression defines the instantaneous value of the carrier sine wave voltage?
What expression defines the instantaneous value of the carrier sine wave voltage?
Which parameter is NOT a part of the amplitude modulation process?
Which parameter is NOT a part of the amplitude modulation process?
What is a modulation technique that varies the amplitude of a carrier signal called?
What is a modulation technique that varies the amplitude of a carrier signal called?
What does the modulation index (m) represent when computed from Vmax and Vmin?
What does the modulation index (m) represent when computed from Vmax and Vmin?
Which formula correctly computes the upper sideband frequency (fUSB)?
Which formula correctly computes the upper sideband frequency (fUSB)?
How are sidebands related to the carrier frequency?
How are sidebands related to the carrier frequency?
What characteristic is essential for avoiding interference between signals using modulation?
What characteristic is essential for avoiding interference between signals using modulation?
Which statement accurately describes sidebands in the frequency domain?
Which statement accurately describes sidebands in the frequency domain?
What does the vertical axis of a frequency domain representation indicate?
What does the vertical axis of a frequency domain representation indicate?
Which of the following frequencies represents the lower sideband (fLSB)?
Which of the following frequencies represents the lower sideband (fLSB)?
What is the peak value of the modulating signal (Vm) used in calculating the modulation index?
What is the peak value of the modulating signal (Vm) used in calculating the modulation index?
Study Notes
Johnson's Formula for Noise Voltage
- Open-circuit noise voltage across a resistor calculated by Johnson's Formula: 𝑽𝒏 = √𝟒𝒌𝑻𝑩𝑹.
- Parameters:
- 𝑽𝒏 = rms noise voltage
- 𝑘 = Boltzmann’s Constant (1.38 x 10⁻²³ K)
- 𝑻 = temperature in Kelvin (ᵒC + 273)
- 𝑩 = bandwidth in Hertz
- 𝑹 = resistance in ohms (Ω).
Thermal Noise Power Calculation
- Thermal noise power given by: 𝑷𝒏 = 𝒌𝑻𝑩.
- Average noise power (𝑷𝒏) is essential for assessing thermal noise in circuits.
Temperature Conversion Formulas
- Common temperature scales: Fahrenheit (ᵒF), Celsius (ᵒC), Kelvin (K).
- Conversion formulas:
- Celsius from Fahrenheit: 𝑻𝒄 = 5(𝑻𝑭 - 32) / 9.
- Fahrenheit from Celsius: 𝑻𝑭 = (9𝑻𝒄 / 5) + 32.
- Kelvin from Celsius: 𝑻𝑲 = 𝑻𝒄 + 273.
Shot Noise Characteristics
- Shot noise is a type of white noise containing a wide range of frequencies.
- Proportional to the DC bias flowing in a device, leading to maximum output power and voltage with minimal distortion.
Modulation Index in AM Signals
- Modulation index (m) computed using AM signal values:
- 𝑚 = (𝑉𝑚𝑎𝑥 - 𝑉𝑚𝑖𝑛) / (𝑉𝑚𝑎𝑥 + 𝑉𝑚𝑖𝑛).
Sidebands and Modulation
- Sidebands are frequencies generated when a carrier is modulated, occurring above and below the carrier frequency.
- Upper sideband frequency: 𝒇𝑼𝑺𝑩 = 𝒇𝑐 + 𝒇𝒎; Lower sideband frequency: 𝒇𝑳𝑺𝑩 = 𝒇𝑐 − 𝒇𝒎.
- Modulation enables frequency translation, preventing signal interference.
rms Noise Current Calculation
- rms noise current (𝑰𝒏) calculated as: 𝑰𝒏 = √𝟐𝒒𝑰𝑩.
- 𝑞 = charge on an electron (1.6 x 10⁻¹⁹ C), 𝑰 = direct current in Amperes, 𝑩 = bandwidth in Hertz.
Types of Noise
- Transmit-time Noise: Delay of current carriers from input to output.
- Flicker Noise: Dominates at low frequencies (below a few kHz), increases spectral density as frequency decreases.
Signal-to-Noise Ratio (SNR)
- Measures the strength of signal in comparison to noise in communication systems.
- Computed using voltage or power values:
- 𝑆𝑁𝑅 = 𝑉𝑠 / 𝑉𝑛 or 𝑆𝑁𝑅 = 𝑃𝑠 / 𝑃𝑛.
Noise Factor and Noise Figure
- Noise Factor (NR): 𝑁𝑅 = 𝑆𝑁𝑅 𝑖𝑛𝑝𝑢𝑡 / 𝑆𝑁𝑅 𝑜𝑢𝑡𝑝𝑢𝑡.
- Noise Figure (NF): Expressed in dB as: 𝑁𝐹 = 10 log(𝑁𝑅).
- Overall Noise Performance for cascaded stages computed using Friis’ formula.
Amplitude Modulation Concepts
- Modulation is key for effective information transmission.
- Modulating signal represented as: 𝑣𝑚 = 𝑉𝑚 sin(2𝜋𝑓𝑚𝑡).
- Carrier frequency expressed as: 𝑣𝑐 = 𝑉𝑐 sin(2𝜋𝑓𝑐𝑡).
- Amplitude of the modulating signal must be less than the carrier amplitude to avoid distortion (𝑉𝑚 < 𝑉𝑐).
External Noise Sources
- External noise classifications: industrial, atmospheric, and extraterrestrial noise.
- Industrial noise emits from equipment like motors and generators.
- Atmospheric noise often results from environmental phenomena like lightning.
- Extraterrestrial noise encompasses signals from solar and cosmic sources.
Internal Noise Characteristics
- Generated by electronic components, such as resistors and transistors.
- Thermal noise arises from random motion of electrons due to heat, often referred to as white noise.
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Description
Explore Johnson's Formula for calculating noise voltage across a resistor. This quiz will test your understanding of the relationship between temperature, bandwidth, and noise in electronic circuits. Perfect for students of electrical engineering and physics.
