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= A Reactance Modulator =

A reactance modulator changes the frequency of the tank circuit of the oscillator by changing its reactance. This is accomplished by a combination of a resistor, a condenser, and a vacuum tube (the modulator) connected across the tank circuit of the oscillator as in Fig. 33 A, and so adjusted as to act as a variable inductance or capacitance. Fig. 33 A. Principle of a reactance modulator The net result is to change the resonant frequency of the LC circuit by amounts proportional to the instantaneous a.f. voltages applied to the grid of the modulator tube, without changing the resistance of the LC circuit or the amplitude of the oscillations. A modulator circuit is shown in Fig. 33 B. Fig 33 B. A reactance modulator The voltages supplied to both the modulator and oscillator must be carefully stabilized to prevent undesired frequency changes. The speech amplifier (Fig. 33 A) does not have to deliver any power and need supply only a small output voltage, say 10 or 15 volts. A pentode and triode, R-C coupled, will be sufficient even with a sensitive microphone and a high-powered oscillator. The frequency change of LC per volt change on the a.f. grid of the modulator tube will be greater when C1,Fig. 33 B, is made smaller. The blocking condenser C2 has a comparatively high value, and hence offers but small reactance to r.f. currents. Fig. 19 H. An RC phase shifter In Fig. 33 B, the radio-frequency voltages which are developed across the tank in the oscillator circuit also appear across the RC1 circuit and across the parallel 6L7 modulator tube. Now look up the phase-shifting circuit of Fig. 19 H. The resistance r has been replaced by the internal resistance of the modulator tube of Fig. 33 B. The voltage drop across C1 is 90° out of phase with the tank voltage. It is applied to the control grid of the 6L7 whose r.f. plate current responds in the same phase. Thus this current is made to lag 90° behind the tank voltage. The r.f. plate current flows through the tank circuit and, combined with the current therein, is equivalent to a new current whose phase differs from the normal value just as though an additional reactance (not resistance) had been connected in with L and C. This, of course, changes the frequency of the LC circuit and hence of the transmitter. When a.f. is fed into the modulator tube, it causes proportionate changes in the r.f. plate current and hence in the equivalent reactance of the LC circuit.

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Difference between varactor modulator and reactance modulator?

A varactor modulator uses a varactor diode, which changes its capacitance with varying voltage, to modulate signals, typically in frequency modulation applications. In contrast, a reactance modulator alters the reactance of a circuit using various components (like capacitors or inductors) to achieve modulation, often in amplitude modulation schemes. While both techniques modify the reactive properties of a circuit to achieve modulation, the varactor modulator specifically relies on the tunable capacitance of the varactor diode for its operation.


What does capacitive reactance oppose?

Inductive reactance.


What is the symbol for inductive reactance?

Inductive reactance does NOT have it own sign or symbol. Rather, it uses Ohms as a quantifier. But Capacitive reactance ALSO uses Ohms as a quantifier. Fortunately, 1 Ohm of Inductive reactance is cancelled by 1 Ohm of Capacitive reactance at the same frequency of measurement.


What is the use of reactance relay?

reactance relay is used for distance protection of the transmission line....


What is the total formula for total reactance?

The total reactance (X) in an electrical circuit is the sum of inductive reactance (X_L) and capacitive reactance (X_C). It is expressed as ( X = X_L - X_C ), where inductive reactance is given by ( X_L = 2\pi f L ) and capacitive reactance is given by ( X_C = \frac{1}{2\pi f C} ). Here, ( f ) is the frequency of the AC signal, ( L ) is the inductance, and ( C ) is the capacitance. The total reactance determines how the circuit responds to alternating current.

Related Questions

Difference between varactor modulator and reactance modulator?

A varactor modulator uses a varactor diode, which changes its capacitance with varying voltage, to modulate signals, typically in frequency modulation applications. In contrast, a reactance modulator alters the reactance of a circuit using various components (like capacitors or inductors) to achieve modulation, often in amplitude modulation schemes. While both techniques modify the reactive properties of a circuit to achieve modulation, the varactor modulator specifically relies on the tunable capacitance of the varactor diode for its operation.


What is the unit of inductive reactance?

Inductive reactance, as well as capacitive reactance, is measured in ohms.


What does capacitive reactance oppose?

Inductive reactance.


What is a diode modulator?

A diode modulator is a type of AM modulator constructed using diodes. One type of diode modulator is the ring modulator shown in the image.


What is the Quantity Symbol for Reactance?

The quantity symbol for reactance is X.


What are the letters for Inductive Reactance?

The symbol for inductive reactance is XL.


What is the inverse of reactance?

The reciprocal of reactance is susceptance, expressed in siemens.


How is balanced modulator different from diode bridge modulator?

A diode bridge modulator is one kind of balanced modulator.


How does doubling the frequency effect the reactance of an inducter and capacitor?

for inductor, reactance XL = 2*pi* f *L, if frequency doubles then reactance increase. But for capacitor, reactance Xc = 1/(2*pi*f*C). In this case if frequency doubles the reactance decrease.


What is synchronous reactance in alternator?

The overall reactance of the armature winding is the sum of its leakage reactance plus fictitious reactance, which is known as synchronous reactance (Xs).Xs=XL+Xarwhere XL and Xar are in Ω/phase. Therefore, Xs is in Ω/phase.The impedance of armature winding is obtained by combining its resistance and its synchronous reactance.


What is the symbol for inductive reactance?

Inductive reactance does NOT have it own sign or symbol. Rather, it uses Ohms as a quantifier. But Capacitive reactance ALSO uses Ohms as a quantifier. Fortunately, 1 Ohm of Inductive reactance is cancelled by 1 Ohm of Capacitive reactance at the same frequency of measurement.


What is the reason that capacitive reactance measured in ohms?

Because it is. Capacitive reactance is a form of resistance, along with inductive reactance. All are measured in ohms.