FM Modulation Circuit

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Questions and Answers

What is the role of the FET reactance modulator in the frequency modulation circuit?

It acts as a current amplifier

It acts as a voltage amplifier

It acts as a variable resistor

It acts as a variable capacitor (correct)

What happens to the frequency of oscillations when the modulating voltage increases in an FET reactance modulator circuit?

It decreases

It becomes zero

It remains constant

It increases (correct)

What is the purpose of the oscillator tuned circuit in the frequency modulation circuit?

To generate a low-frequency modulating wave

To generate a high-frequency carrier wave (correct)

To amplify the FM signal

To demodulate the FM signal

What is the result of changing the effective capacitance between terminals 1-1 in the FET reactance modulator circuit?

The frequency of oscillations changes Signup and view all the answers

What is the role of the modulating signal in the frequency modulation circuit?

To vary the frequency of oscillations Signup and view all the answers

What type of modulation is achieved using the FET reactance modulator circuit?

Frequency modulation Signup and view all the answers

What is the effect of increasing the signal vg on the frequency of the FM output?

It increases the frequency Signup and view all the answers

What type of reactance is produced by the circuit in figure 4.25(c)?

Capacitive reactance Signup and view all the answers

What is the purpose of a reactance modulator in FM signal generation?

To modulate the frequency of the carrier wave Signup and view all the answers

What is the effect of decreasing the signal vg on the frequency of the FM output?

It decreases the frequency Signup and view all the answers

What is the advantage of using a FET reactance modulator in FM signal generation?

It provides a high degree of frequency modulation Signup and view all the answers

What is the relationship between the signal vg and the frequency of the FM output?

The frequency of the FM output increases as the signal vg increases Signup and view all the answers

What is the role of the variable capacitance or inductance in a FET reactance modulator?

To modulate the frequency of the carrier wave Signup and view all the answers

What is the purpose of figure 4.24(c) in the context of FM signal generation?

To illustrate the waveform of the FM output Signup and view all the answers

What is the purpose of the modulator in FM signal generation?

To vary the frequency of the carrier wave Signup and view all the answers

What is the advantage of using FM in communication systems?

It is more resistant to noise Signup and view all the answers

What is the role of the demodulator in FM demodulation?

To extract the information signal from the FM signal Signup and view all the answers

What is the type of FM modulation used in communication systems?

Wideband FM Signup and view all the answers

What is the significance of the modulation index in FM signal generation?

It determines the bandwidth of the FM signal Signup and view all the answers

What is the purpose of the oscillator in FM signal generation?

To generate the carrier wave Signup and view all the answers

What is the type of FM demodulation used in communication systems?

Frequency discriminator demodulation Signup and view all the answers

What is the advantage of using FM in audio broadcasting?

It has a higher signal-to-noise ratio Signup and view all the answers

What is the role of the phase modulator in FM signal generation?

To vary the phase of the carrier wave Signup and view all the answers

What is the application of FM in communication systems?

All of the above Signup and view all the answers

Study Notes

FET Reactance Modulator

The FET reactance modulator is used to generate Frequency Modulation (FM) waves.
The modulator acts as a variable capacitor, and its effective capacitance changes with the modulating voltage.
When the modulating voltage increases, the capacitance decreases, resulting in an increase in the frequency of oscillations.

Frequency Modulation using FET Reactance Modulator

The FM wave is generated by varying the capacitance of the FET reactance modulator.
The frequency of oscillations increases with an increase in the modulating voltage.
The equivalent circuit of the FET reactance modulator is shown in Fig. 4.24(b).

Methods of FM Generation

There are two methods of FM generation: Direct Method and Indirect Method.
The Direct Method uses a voltage-controlled oscillator (VCO) to generate the FM wave.
The Indirect Method uses a reactance modulator to generate the FM wave.

Indirect Method: Armstrong Method of FM Generation

The Armstrong Method uses a reactance modulator to generate the FM wave.
The reactance modulator is a FET-based circuit that varies its capacitance with the modulating voltage.
The FM wave is generated by varying the capacitance of the reactance modulator.

Non-Linear Reactance Modulator

The non-linear reactance modulator uses a diode to vary the capacitance of the reactance modulator.
The non-linear reactance modulator produces a non-linear FM wave.

Applications of FM

FM is used in various applications, including radio broadcasting, mobile communication, and satellite communication.
FM is used to transmit audio signals, and it provides a high signal-to-noise ratio.

Phase Modulation (PM)

PM is a type of modulation that varies the phase of the carrier wave.
PM is used in digital communication systems, such as Wi-Fi and cellular networks.
PM is more resistant to noise and interference than FM.

Comparison of FM and PM

FM is more susceptible to noise and interference than PM.
PM is more resistant to noise and interference than FM.
FM is used in analog communication systems, while PM is used in digital communication systems.

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Description

This quiz is about FM modulation circuit diagram, it covers oscillator tuned circuit, FET reactance, and modulation signal.