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Questions and Answers
What is the purpose of the local oscillator (LO) in a superheterodyne receiver?
What is the purpose of the local oscillator (LO) in a superheterodyne receiver?
- To filter out unwanted frequencies
- To demodulate the incoming signal
- To amplify the incoming signal
- To convert the incoming signal to a fixed intermediate frequency (IF) (correct)
Which type of detector is commonly used for demodulating frequency modulated (FM) signals?
Which type of detector is commonly used for demodulating frequency modulated (FM) signals?
- Synchronous detector
- Ratio detector (correct)
- Envelope detector
- Slope detector
What is the purpose of ganged tuning in a superheterodyne receiver?
What is the purpose of ganged tuning in a superheterodyne receiver?
- To demodulate the incoming signal
- To filter out unwanted frequencies
- To ensure a fixed intermediate frequency (IF) by changing the variable capacitors together (correct)
- To adjust the sensitivity of the receiver
Which type of detector is commonly used for demodulating amplitude modulated (AM) signals?
Which type of detector is commonly used for demodulating amplitude modulated (AM) signals?
What is the advantage of using a superheterodyne receiver over a tuned radio-frequency (TRF) receiver?
What is the advantage of using a superheterodyne receiver over a tuned radio-frequency (TRF) receiver?
In a synchronous detector, what is the purpose of synchronizing the local oscillator with the carrier frequency?
In a synchronous detector, what is the purpose of synchronizing the local oscillator with the carrier frequency?
What are the two main types of AM detectors described in the text?
What are the two main types of AM detectors described in the text?
What is the main advantage of the envelope detector over the synchronous detector?
What is the main advantage of the envelope detector over the synchronous detector?
Which type of modulation signal is the synchronous detector typically used for?
Which type of modulation signal is the synchronous detector typically used for?
What is the key requirement for the synchronous detector to operate correctly?
What is the key requirement for the synchronous detector to operate correctly?
What is the purpose of the capacitor C1 in the envelope detector circuit?
What is the purpose of the capacitor C1 in the envelope detector circuit?
What is the relationship between the RC time constant and the modulating signal frequency in the envelope detector?
What is the relationship between the RC time constant and the modulating signal frequency in the envelope detector?
In the given text, what is the purpose of the diode arrangement?
In the given text, what is the purpose of the diode arrangement?
Which of the following statements is true about the output of the ring modulator?
Which of the following statements is true about the output of the ring modulator?
What is the primary function of a radio receiver mentioned in the text?
What is the primary function of a radio receiver mentioned in the text?
Which type of modulation is described in the given text?
Which type of modulation is described in the given text?
What is the purpose of the carrier wave in the modulation process described in the text?
What is the purpose of the carrier wave in the modulation process described in the text?
What is the major difference between different types of radio receivers?
What is the major difference between different types of radio receivers?
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Study Notes
Receiver Types
- There are two main types of receivers: Tuned Radio-Frequency (TRF) Receiver and Superhetrodyne Receiver.
TRF Receiver
- Used in old radio receivers
- Very simple and high sensitivity receiver
- Difficulties arise at higher frequencies, in the Tuning amplifiers
- Quality factor (Q) affects the bandwidth and selectivity of the receiver
- Example: If Rx is used with a bandwidth of 10 KHz at Tuning frequency 535 KHz, Q = 53.5, but for practical purposes, Q = 120, which increases the bandwidth to 13.7 KHz and decreases the selectivity of the receiver.
Superhetrodyne Receiver
- Signal voltage is combined with Local Oscillator (LO) voltage and converted into a signal of a lower, generally fixed frequency (Intermediate Frequency, IF)
- The signal at this frequency contains the same modulation as the original carrier and is amplified and detected to reproduce the original signal
- Ganged Tuning is used to ensure fixed IF by changing the variable capacitors together in the LO, mixer, and RF
Receiver Parameters
Sensitivity
- Ability of the receiver to amplify weak signals
- Two types of AM detectors: non-coherent (Envelope detector) and coherent (Synchronous detector)
Envelope Detector
- Used for speech, music, and video
- Diode is used to detect the envelope of the AM wave
- Diode operates as a half-wave rectifier and the capacitor charge time constant is equal to (RC)
- Output is proportional to the input
- Condition for RC: RC ≤ 1 - m² / (mW)
Synchronous Detector
- Used for DSB-SC or SSB-SC signals
- Multiplicative mixer where two signals multiply in a non-linear device
- Regenerates the carrier
- Output contains audio signal and two sideband frequencies, but no carrier
Ring Modulator
- Carrier is applied to the midpoint of the input and output transformer
- Rectifiers construct a ring shape across the network
- Output contains audio signal and two sideband frequencies, but no carrier
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