Communication Receivers Quiz
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Questions and Answers

What does the designation 'A8F' represent in the context of ITU emissions?

  • Phase modulation with 8 channels
  • Amplitude-modulated, Digital TV with 10 channels
  • Amplitude-modulated, Analog TV with 8 channels
  • Amplitude-modulated, Analog TV with 10 channels (correct)

What does the 'G' in the designation 'G7W' signify?

  • Frequency modulation
  • Phase modulation (correct)
  • Digital modulation
  • Amplitude modulation

Which type of information is transmitted using the designation 'G7W'?

  • Continuous wave signals
  • Quantized or digital information (correct)
  • Amplitude-modulated TV channels
  • Analog information

In the ITU emissions designation '3k24', what does '3.24 kHz' indicate?

<p>Frequency of an amplitude-modulated signal (A)</p> Signup and view all the answers

How many channels are specified in the designation '3k24'?

<p>10 (A)</p> Signup and view all the answers

What does the letter 'A' represent in the AM voice signal code A3?

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

Which code designation indicates a DSB two sidebands suppressed carrier telephony?

<p>A3b (C)</p> Signup and view all the answers

What does '3' represent in the code A3?

<p>Information type as telephony (D)</p> Signup and view all the answers

In the ITU emission designation system, what is the purpose of the codes?

<p>To describe modulation and format easily (D)</p> Signup and view all the answers

Which of the following represents a SSB vestigial single sideband with a 30% pilot carrier?

<p>A5a (D)</p> Signup and view all the answers

What is selectivity in a communication receiver?

<p>The ability to identify and select a desired signal from others (D)</p> Signup and view all the answers

How is selectivity achieved in a receiver?

<p>Using tuned circuits like LC-tuned circuits (A)</p> Signup and view all the answers

What happens if the bandwidth of a tuned circuit becomes too narrow?

<p>It leads to information loss due to attenuation of sidebands (C)</p> Signup and view all the answers

What does the quality factor (Q) in a tuned circuit influence?

<p>The steepness of signal attenuation and bandwidth (B)</p> Signup and view all the answers

What is the formula for the bandwidth (BW) of a tuned circuit?

<p>$BW = \frac{f_r}{Q}$ (D)</p> Signup and view all the answers

What is the role of sensitivity in communication receivers?

<p>To pick up weak signals and allow for sufficient amplification (B)</p> Signup and view all the answers

What could happen if a radio receiver is too sensitive?

<p>It might pick up too much noise along with signals (A)</p> Signup and view all the answers

The ideal bandwidth of a selectivity curve in a receiver should be:

<p>Narrow enough to pass the main signal but wide enough to include all sidebands (D)</p> Signup and view all the answers

What does MDS stand for in relation to signal level?

<p>Minimum Discernible Signal (D)</p> Signup and view all the answers

In what unit is MDS expressed?

<p>Decibels (dBm) (C)</p> Signup and view all the answers

What does the formula $P_{dBm} = 10 \log_{10} \frac{P}{1 mW}$ calculate?

<p>Power level in dBm (C)</p> Signup and view all the answers

If a signal with 1 µV produces a power across 50 Ω, what is the power in watts?

<p>$2 \times 10^{-14} W$ (B)</p> Signup and view all the answers

How is power expressed in dB for $2 \times 10^{-14} W$?

<p>$-106.99 dBm$ (B)</p> Signup and view all the answers

What is the first part of the radio emission code designation?

<p>A capital letter defining modulation type (D)</p> Signup and view all the answers

What do the numbers in the radio emission code designation signify?

<p>The transmitted information type (C)</p> Signup and view all the answers

What is the significance of lower subscript letters in radio emission codes?

<p>Provide more specific definitions (D)</p> Signup and view all the answers

What is the purpose of cascading circuits or using filters in electronic communication systems?

<p>To achieve improved selectivity in the receiver. (D)</p> Signup and view all the answers

How is the shape factor expressed in the context of receiver bandwidth?

<p>As the ratio of the 60-dB bandwidth to the 6-dB bandwidth. (A)</p> Signup and view all the answers

What happens to the shape factor as the skirts of a tuned circuit response curve become steeper?

<p>The shape factor decreases. (C)</p> Signup and view all the answers

Which of the following represents how sensitivity in a receiver is mainly described?

<p>By the minimum discernible signal (MDS). (D)</p> Signup and view all the answers

If a receiver has a shape factor of 2.25, what can be inferred about its skirt selectivity?

<p>The skirts are somewhat steep, indicating good selectivity. (C)</p> Signup and view all the answers

What is the relationship between gain and sensitivity in a receiver?

<p>Higher gain generally leads to improved sensitivity. (D)</p> Signup and view all the answers

What does a shape factor of 1 signify in terms of selectivity?

<p>The selectivity is excellent. (B)</p> Signup and view all the answers

Which factor primarily influences the ability of a receiver to discern weak signals?

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

What does the first part of the code 'BBBB' represent?

<p>Defines the bandwidth (C)</p> Signup and view all the answers

Which letter represents Frequency Modulation in the modulation type classification?

<p>F (D)</p> Signup and view all the answers

In the bandwidth designator list, what does 'M' stand for?

<p>Megahertz (C)</p> Signup and view all the answers

Which of the following modulation types indicates a combination of Amplitude Modulation and Frequency Modulation?

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

What does the digit '3' indicate in terms of modulating signal type?

<p>Analog, single channel (C)</p> Signup and view all the answers

Which information type is indicated by the letter 'E'?

<p>Telephony (human voice) (D)</p> Signup and view all the answers

What does the letter 'N' signify in the modulation types?

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

Which of the following indicates no modulation in modulating signal types?

<p>0 (A)</p> Signup and view all the answers

If a signal is classified as '2M25', what frequency does it represent?

<p>2.25 MHz (A)</p> Signup and view all the answers

What does the letter 'W' represent in modulation types?

<p>Some combination of any of the above types (B)</p> Signup and view all the answers

Flashcards

Selectivity (receiver)

The ability of a receiver to choose a desired signal from others in a complex frequency spectrum.

Sensitivity (receiver)

The receiver's ability to detect and amplify weak or faint signals.

LC-tuned circuit

An electronic circuit using an inductor (L) and capacitor (C) to select a specific frequency.

Quality factor (Q)

A measure of how well a tuned circuit selects a specific frequency.

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Bandwidth (selectivity curve)

The range of frequencies a tuned circuit allows to pass without significant attenuation.

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Bandwidth formula (tuned circuit)

Bandwidth = resonant frequency (fr) / quality factor (Q).

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Receiver Selectivity

The ability of a receiver to distinguish the desired signal from unwanted signals.

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Shape Factor

A measure of the steepness of the skirts of a receiver's response curve. It's calculated as the ratio of the bandwidth at a 60dB attenuation point to the bandwidth at a 6dB attenuation point.

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Skirts (Skirt Selectivity)

The sides of a tuned circuit response curve, showing how quickly the signal strength decreases away from the center frequency.

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60 dB Bandwidth

The width of the frequency range over which the signal is attenuated by 60 decibels compared to the peak.

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6 dB Bandwidth

The width of the frequency range over which the signal strength is reduced by 6 decibels compared to the peak signal.

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Receiver Sensitivity

The ability of a receiver to detect weak signals.

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Minimum Discernible Signal (MDS)

The smallest signal strength a receiver can detect reliably.

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Signal-to-Noise Ratio (SNR)

The ratio of the power of a desired signal to the power of the unwanted noise.

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Overall Gain

The total amplification of a receiver, the factor that multiplies the input signal to produce the output.

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Noise Floor

The internally generated noise value in a receiver.

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MDS

Minimum Detectable Signal, the input signal level close to the noise floor of a receiver.

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dBm

Decibels relative to one milliwatt (mW). A unit for expressing power levels.

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Power (dBm Calculation)

Calculate power in dBm using the formula: dBm = 10 log10 (P / 1 mW), where P is the power in watts.

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Receiver Sensitivity

The lowest power level a receiver can detect

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Input Impedance (50Ω)

Common impedance value for a receiver's antenna input, often used in radio frequency (RF) systems.

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Signal Power Calculation

Calculate signal power (P) using the formula: P = V^2 / R, where V is voltage and R is resistance.

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Radio Emission Code

A code (capital letter, number, and lowercase subscript letters) used to categorize types of radio signals.

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Modulation Type

The method used to encode information onto a radio wave.

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Transmitted Information Type

The form of information being carried by the radio wave, like voice, data, or images.

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Specific Definitions

Further details about radio emissions, using lowercase subscript letters in the code.

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AM voice signal code

The code A3 designates an Amplitude Modulation (AM) signal carrying voice (telephony) information.

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DSB telephony code

A variation of AM voice transmission using Double Sideband Suppressed Carrier (DSB), its code is A3b.

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SSB telephony code

Single Sideband (SSB) telephony, potentially with a pilot carrier, is coded using A5a or A3j.

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ITU Emission Designation

A system used to easily describe radio signal format and modulation, agreed upon by the International Telecommunication Union (ITU).

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Modulation Type

Specifies the method/technique used in modifying the carrier wave to transmit information, such as AM or SSB.

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Information Type

Classification of information being transmitted, like voice (telephony), or video.

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Specifics

Additional details of the radio transmission parameters.

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Radio emission code

A shorthand notation, used by entities like ITU, to precisely designate the technical characteristics of a radio transmission.

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Bandwidth Designator Format

Three digits representing significant figures, followed by a capital letter indicating the unit (e.g., kHz, MHz).

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BBBB 123 45 Structure

A system to categorize characteristics of transmitted signals: B=bandwidth, 1=modulation, 2=modulating signal type, 3=information type, 4=practical details, 5=multiplexing details (optional).

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Modulation Type (N)

Unmodulated Carrier signal, no additional modulation applied.

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Modulation Type (A)

Amplitude Modulation: the amplitude of the carrier wave varies according to the modulating signal's amplitude.

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Modulating Signal Type (0)

No modulating signal used. The carrier signal is unchanged.

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Modulating Signal Type (1)

Digital, single channel, no additional modulation applied.

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Modulation Type (F)

Frequency Modulation (FM): the frequency of the carrier wave varies according to the modulating signal's amplitude.

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Transmitted Information Type (A)

Telegraphy (human input).

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ITU Emission Designator

A code (capital letter, number, and lowercase letters) used to classify radio signals by their modulation type, modulating signal type, and transmitted information.

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Modulation Type

The method used to encode information onto a radio wave (e.g., amplitude, frequency, phase).

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Modulating Signal Type

The kind of signal used to modulate the radio wave (e.g., analog, digital, multi-channel).

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Transmitted Information Type

The form of information being carried by the wave (e.g., voice, data, television).

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3k24 Amplitude-modulated Analog TV

An example of an ITU emission designator for amplitude-modulated analog tv with 10 channels, using a 3.24 kHz bandwidth.

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Phase modulation multi-channel

An example of an ITU emission designator for phase modulation multi-channel with quantized or digital information.

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Study Notes

Communication Receivers

  • Transmitted signals weaken over long distances, picking up noise.
  • Receivers need selectivity and sensitivity to recover the original signal.
  • Selectivity is the ability to identify and select a desired signal from others.
  • Sensitivity is the ability to pick up weak signals and amplify them.

Selectivity

  • Achieved using tuned circuits (LC-tuned circuits).
  • LC-tuned circuits consist of an inductor and a capacitor.
  • Selectivity is controlled by the quality factor (Q) of the LC-tuned circuit.
  • Ideal bandwidth (BW) must be wide enough to pass the signal and its sidebands, but narrow enough to eliminate adjacent frequencies.
  • Bandwidth formula: BW = fr / Q
  • Increasing Q narrows the bandwidth, improving attenuation of unwanted signals.
  • However, too narrow a bandwidth can attenuate the signal's sidebands, causing information loss.

Sensitivity

  • Sensitivity is mainly determined by overall gain. Higher gain leads to better sensitivity.
  • Signal-to-noise ratio (SNR) also affects sensitivity. Higher SNR (signal compared to noise) improves sensitivity.

Minimum Discernible Signal (MDS)

  • MDS is a method for expressing receiver sensitivity.
  • It is the input signal level almost equal to the average noise floor of the receiver.
  • MDS is expressed in dBm (decibels relative to one milliwatt).
  • Formula: dBm = 10 log10 (P/1mW), where P is power in watts

Classification of Radio Emissions

  • Radio emission codes are used to identify types of signals.
  • The codes consist of a capital letter (modulation type), a number (information type), and lowercase letters (subscript details).
  • Examples include AM (amplitude modulation) and specific information types like voice or data.

ITU Emission Designations

  • A system for describing signals (more variations than previous system)
  • Used to easily describe format and modulation for radio transmissions
  • Format BBBB 123 45,
    • BBBB is the bandwidth.
    • First digit is the modulation type
    • Second digit is the modulation type (e.g., voice/data)
    • Third digit is the signal type (e.g., analog/digital)
  • Optional (possibly 4th or 5th digit) additional specifics about the signal.
  • Bandwidth measurements are often expressed with units like kHz, MHz, etc.

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Description

Test your knowledge on communication receivers, focusing on their selectivity and sensitivity. This quiz covers key concepts such as LC-tuned circuits, the quality factor, and bandwidth calculations, essential for understanding signal transmission and reception.

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