What is varactor diode modulator?
Varactor diode modulator is the direct method of FM generation wherein the carrier frequency is directly varied by the modulating signal. A varactor diode is a semiconductor diode whose junction capacitance varies linearly with applied voltage when the diode is reverse biased.
Which of the following diode is used in FM modulator?
Varactor diodes are certainly employed frequently, together with a reactance modulator, to provide automatic frequency correction for an FM transmitter.
What are the types of FM modulators?
There are two different types of frequency modulation used in telecommunications: analog frequency modulation and digital frequency modulation.
What is FM modulator circuit?
The FM modulator circuit (frequency modulation) is built with a Motorola MC1648P oscillator. Two varactors, Motorola MV-209 are used to frequency modulate the oscillator. The 5000 Ω potentiometer is used to bias the varactors for the best linearity.
What is a varactor diode used for?
A varactor diode is a simple variable capacitor that allows oscillator circuits and other circuits to be easily tuned by applying a voltage. These diodes have a similar structure as a p-n diode; the structure of a varactor diode is rather simple and illustrates its power as a component with nonlinear reactance.
What is the key feature of a varactor diode?
Important characteristics are capacitance when designated bias voltage is applied (ex. C3V where VR=3V), capacitance variation when applied voltage changes (capacitance ratio) and series resistance that affects Q index when used in oscillators or filters.
How is varactor used?
Varactor or varicap diodes are used mainly in radio frequency or RF circuits to provide voltage controlled variable capacitance. These electronic componenta can be used in a whole variety of ways where a capacitance level needs to be controlled by a voltage.
What does a varactor do?
How does a modulator work?
Modulation is what takes a signal from low frequencies (the message) and pulls it up to a higher frequency (the carrier). The idea is simple: Multiply your message by a high frequency carrier, such as 680 kHz. Voila, that’s AM radio!
What are different types of FM generation?
Methods of FM Generation.
Why is modulation necessary?
Modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted. It is necessary because of following reasons: Reduction in the height of antenna. Avoids mixing of signals.
What is the need of modulation?
Modulation is simply a widely used process in communication systems in which a very high-frequency carrier wave is used to transmit the low-frequency message signal so that the transmitted signal continues to have all the information contained in the original message signal.
How does a varactor diode modulator work?
Varactor Diode Modulator The capacitance of D 1, of course, is controlled by two factors: a fixed dc bias and the modulating signal. In Fig b, the bias on D 1 is set by the voltage divider which is made up of R 1 and R 2. Usually either R 1 or R 2 is made variable so that the center carrier frequency can be adjusted over a narrow range.
What is a varactor FM modulator?
Varactor FM Modulator.—Another fm modulator which is widely used in transistorized circuitry uses a voltage-variable capacitor (VARACTOR). The varactor is simply a diode, or pn junction, that is designed to have a certain amount of capacitance between junctions. View (A) of figure 2-15 shows the varactor schematic symbol.
How to improve frequency stability of FM system?
Figure 2-14.—Method for improving frequency stability of fm system. Varactor FM Modulator.—Another fm modulator which is widely used in transistorized circuitry uses a voltage-variable capacitor (VARACTOR). The varactor is simply a diode, or pn junction, that is designed to have a certain amount of capacitance between junctions.
What is the effect of external modulating AF voltage on diode?
The external modulating AF voltage adds to and subtracts from the dc bias, which changes the capacitance of the diode and thus the frequency of oscillation. Positive alternations of the modulating signal increase the reverse bias on the varactor diode, which decreases its capacitance and increases the frequency of oscillation.