# Draw circuit diagram of transistor reactance modulator. Explain its working.

Draw circuit diagram of transistor reactance modulator. Explain its working.

## 1 Answer Explanation- A reactance modulator is illustrated in figure. It is basically a standard commonemitter class A amplifier. Resistors R1 and R2 from a voltage divider to bias the transistor into the linear region. R3 is an emitter bias resistor. The oscillator signal from the RC phase-shift circuit made up of Cs and Rs. The value of Cs is chosen so that its reactance at the oscillator frequency is about 10 or more times of the value of Rs. if the reactance is much greater than the resistance, the circuit will appear predominantly capacitive; therefore the current through the capacitor and Rs will lead the applied voltage by about 90◦. Since the collector current is in phase with the base current, which in turn is in phase with the base voltage, the collector current in Q1 leads the oscillator voltage V0 by 90 ◦. Of course, any circuit whose current leads its applied voltage by 90◦ looks capacitive to the source voltage. The modulating signal is applied to the modulator circuit through C1 and RFC1. The RFC helps keep the RF signal from the oscillator out of the audio circuit from the modulating signal usually comes. The audio modulating signal will vary the base voltage and current of Q1 according to the intelligence to be transmitted. The collector current will also vary in proportion. As the collector current amplitude varies, the phase shift angle changes with respect to the oscillator, voltage, which is interpreted by the oscillator as a change in the capacitance. So as the modulating signal changes, the effective capacitance of the circuit varies and the oscillator frequency is varied accordingly An increase in capacitance lowers the frequency, whereas a lower capacitance increases the frequency. The circuit produces direct frequency modulations.

## Related questions

Description : Draw the circuit diagram of varactor diode FM modulator and explain its working.

Answer : 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 ... the magnitude of frequency change is proportional to the amplitude of the modulating signal voltage.

Description : Draw the circuit diagram of practical diode detector and explain its working.

Answer : Circuit diagram of practical diode detector:  Explanation- The circuit operates in the following manner- The diode has been reversed so that now the negative envelope is demodulated. Due to this ... to produce AGC voltage. The DC AGC voltage is proportional to the amplitude of AM signal.

Description : Draw the circuit diagram of limiter and explain its working.

Answer : Circuit diagram of amplitude limiter:- Explanation:- 1. In frequency modulation, the signal amplitude is held constant while the carrier frequency is varied. 2. Any noise that contaminates ... V p-p instead of the alternately driven into saturation and cutoff, it limits the signal amplitude

Description : Explain reactance modulator for FM generation.

Answer : Explanation :- Audio modulating signal is applied to Q1 which varies the base voltage and current of Q1 according to the input information to be transmitted. The collector current ... lower the frequency & decrease capacitance increase the frequency and thus produce direct FM at output.

Description : Draw the TRF receiver block diagram and explain its working.

Answer : Explanation:- 1. TRF receivers are simple and having high sensitivity. The AM transmission takes place in MW band and SW band. MW frequency range is 540KHz to 1640KHz. 2. ... power level to drive the loudspeaker. 7. The loudspeaker converts electrical signal into original sound information.

Description : Draw the diagram for PAM generation using transistors. Explain its working.

Answer : Explanation:-1. Transistor Q1 is used in the active region so it has been provided with DC biasing to its base. 2. Modulating signal is applied to the base of transistor Q1 3. In the emitter of ... . 7. In the time interval between sampling pulses output is zero. Thus we get the output as PAM.

Description : Draw the circuit diagram of PWM using IC555. State its operation.

Answer : Operation: i. The timer IC555 is operated in monostable mode. ii. The negative going carrier pulses are to the differentiator formed by R1 & C1. The differentiator produces sharp negative ... . Thus PWM signal is generated at the output pin (3) of IC555 as monostablemultivibrator.

Description : Explain the working of amplitude limiter in FM receiver with circuit diagram.

Answer : Amplitude limiter: The function of amplitude limiter is to remove all amplitude variation of FM carrier voltage that may occur due to atmospheric disturbances. Use of amplitude limiter makes the system less noisy  Circuit Diagram:

Description : Draw block diagram of FM receiver and explain the use of limiter circuit.

Answer : Diagram Explanation Amplitude limiter: The function of amplitude limiter is to remove all amplitude variation of FM carrier voltage that may occur due to atmospheric disturbances. Use of amplitude limiter makes the system less noisy.

Description : Draw the block diagram of AM transmitter, explain its operation.

Answer : AM transmitter is of two types i)High Level AM Transmitter ii)Low Level AM Transmitter i) RF crystal oscillator: It is a source of carrier signal of desired frequency. The circuit is ... AM signal is then applied to the transmitting antenna which radiates this AM signal into air or space.

Description : Draw and label the circuit diagram of ratio detector

Answer : Draw and label the circuit diagram of ratio detector

Description : Draw the block diagram of PWM. List its advantages

Answer : Block diagram of PWM:- Advantages of PWM:- 1. More immune to noise. 2. Synchronization between transmitter and receiver is not required. 3. Possible to separate out signal from noise.

Description : Define pre-emphasis. State its need. Draw the circuit of pre-emphasis.

Answer : Definition- The artificial boosting of higher modulating frequencies to reduce the effect of noise is called as pre-emphasis. Need:- The artificial boosting of higher audio modulating ... by increasing the amplitude of modulating signal at higher frequencies. Circuit diagram

Description : Explain working of envelope detector with suitable diagram and waveform.

Answer : Envelope Detector: An Envelope Detector is an electronic circuit that takes a high frequency signal as input and provides an output which is as envelopes of the original signal. The capacitor ... decreases the responsiveness thus, real-world designs must be optimized for the application.

Description : With the help of neat diagram, explain the working of phase discriminator.

Answer : Explanation:- This discriminator is also known as the center tuned discriminator or the Foster Seeley discriminator after its inventors. It is possible to obtain the same S- Shape response curve from a circuit in ... fin = fc, fin > fc + Δf and fin<fc- Δf should be given marks

Description : Draw and explain block diagram of electronic communication system.

Answer : Block diagram of electronic communication system. Explanation Transducer: A transducer is usually required to convert the output of a source into an electrical signal that is suitable for ... etc. Output Transducer: The output transducer converts electrical signal in to sound signal.

Description : Explain loop antenna with neat sketch. Draw radiation pattern. State its advantages and applications.

Answer : Loop antenna:-The single turn coil carrying RF current through it having length less than the wavelength.   Advantages:- 1. highly directive 2. Small size Applications:- 1. For direction finding 2. In portable receivers 3. In navigation

Description : Draw the circuit diagram of Bootstrap’s time base generator and explain its working.

Answer : Circuit Diagram Waveform: Here transistor Q1 acts as a switch and transistor Q2 acts as an emitter follower (i.e. a unit gain amplifier).  Circuit Operation: Initially transistor ... The circuit pulls itself up by its own bootstrap and hence it is known as bootstrap sweep circuit.

Description : Draw circuit diagram for π filter and explain its working with waveforms.

Answer : Working of a Pi filter: In this circuit, we have a capacitor in parallel, then an inductor in series, followed by another capacitor in parallel. Capacitor C1 − This filter capacitor ... any ac component present in the signal to pass through it, which the inductor has failed to block.

Description : Draw the circuit diagram of battery charger using SCR and explain it’s working.

Answer : Battery charger circuit using SCR: The figure shows the battery charger circuit using SCR. A 12V discharged battery is connected in the circuit and switch SW is closed. The singlephase 230V ... not fired. In this way, after full charging, further charging is automatically stopped.

Description : Draw circuit diagram of Bistable multivibrator using IC-555 and explain its working.

Answer : Definition – A multivibrator which has two stable states, one can be change to other when trigger pulse is applied, known as bistable multivibrator. Circuit diagram of Bistable multivibrator using IC555

Description : Draw the circuit diagram of crystal oscillator and explain its working.

Answer : To excite a crystal for operation in the series-resonant mode it may be connected as a series element in a feedback path, the crystal impedance is the smallest and the amount of positive feedback is the largest. ... which is good.  The resonant frequency is given as  Fo = 1/( 2 π √LC )

Description : Draw block diagram of basic electronic communication system and state the function of each block.

Answer : i) Input signal: - The information can be in the form of sound, picture or data coming from computer. ii) Input transducer: - it converts original information into equivalent electrical ... back to suitable form. vii) Output transducer: - It converts electrical signal into original form.

Description : Draw the block diagram of FM super heterodyne radio receiver with waveforms.

Answer : block diagram of FM super heterodyne radio receiver

Description : Define the transmission line? Draw it‟s general equivalent circuit.

Answer : Transmission line: A conductor or conductors designed to carry electricity or an electrical signal over large distances with minimum losses and distortion.  Equivalent circuit:

Description : Draw general equivalent circuit of transmission line.

Answer : Fig. General Equivalent circuit of transmission line

Description : Draw Yagiuda antenna with its radiation pattern.

Answer : Construction of Yagi-Uda Antenna Radiation Pattern of Yagi-Uda Antenna

Description : Draw the structure of horn antenna and its radiation pattern. List its any two applications.

Answer : The structure of horn antenna Radiation pattern of Horn Antenna Application:- i) Used at microwave frequency. ii) Used in satellite tracking

Description : Draw the circuit diagram and describe the working principle of full wave bridge rectifier. Draw its waveforms.

Answer : During the first half cycle : During the first half cycle of the input voltage, the upper end of the transformer secondary winding is positive with respect to the lower end. Thus during the first ... , terminal D, diode D4, and terminal A back to transformer and output will positive half cycle.

Description : Draw the circuit diagram of multi range AC voltmeter and describe its working

Answer : The above circuit looks like a multi range AC voltmeter. We know that, we will get AC voltmeter just by placing rectifier in series (cascade) with DC voltmeter. The above circuit was created ... any two points of an electric circuit, by connecting the switch, S to the desired voltage range.

Description : Draw the circuit diagram of complementary symmetry Class B push-pull amplifier and describe its working.

Answer : Diagram of complementary symmetry Class B push-pull amplifier: Working: The above circuit employs a NPN transistor and a PNP transistor connected in push pull configuration. When the input ... of class B, this circuit is termed as Complementary symmetry push pull class B amplifier.

Description : Draw the circuit diagram of class AB power amplifier and describe its working.

Answer : Circuit diagram: Circuit Description: The circuit consists of two center-tapped transformers T1 and T2, two identical transistors Q1 and Q2 , Resistor R and diode D. The DC voltage ... and Q2 conduct, as soon as input cross zero, negative sinusoidal voltage will appear across load.

Description : Draw practical set-up and explain the procedure to measure selectivity of radio receiver.

Answer : Procedure to measure selectivity of radio receiver: Throughout the measurement the receiver is kept tuned to desired frequency 950 Khz. Now the generator output frequency is deviated below ... the generator output voltage is adjusted to get a standard 50 miliwatt receiver output power.

Description : Draw construction of Yagi-Uda antenna and explain.

Answer : Explanation A Yagi-Uda antenna, commonly known as a Yagi antenna, is a directional antenna consisting of multiple parallel elements in a line, usually half-wave dipoles made of ... receiver with a transmission line and additional parasitic elements called reflector and one or more directors.

Description : Draw and explain PLL as an FM demodulator.

Answer : Explanation:- FM signal which is to be demodulated is applied to input of PLL.VCO output must be identical to input signal if PLL is to remain locked. As PLL is locked, VCO ... error voltage represents the modulating signal. Thus at the error amplifier output we get demodulated FM output.

Description : Explain with a neat diagram of ratio detector. Why limiter stage is not used before ratio detector.

Answer : With diode D2 reversed , O is positive with respect to b, so that Vab is a sum voltage rather than the difference it was in the discriminator it is now possible to connect a large capacitor ... of limiter stage due to large capacitor C5 .Hence, limiter stage is not used in ratio detector.

Description : Explain with block diagram of Armstrong method of FM generation.

Answer : Explanation:- The crystal oscillator generates the carrier at low frequency typically at 1 MHz this is applied to the combining network and a 90o phase shifter. The modulating signal is passed through an ... power amplifier to raise the power level of the FM signal.  Phasor Diagram:-

Description : Explain skip zone and skip distance with neat diagram.

Answer : Skip distance:-Skip distance is defined as the shortest distance from a transmitter, measured along the surface of earth at which a sky wav of fixed frequency returns back to the earth. Skip zone: skip zone where signal is not detectable

Description : Explain half dipole antenna ( Resonant antenna ) with its radiation patteren.

Answer : Half wave dipole antenna Explanation:  1. It is a resonant antenna 2. It is exact half wavelength (λ /2) long & open circuited at one end. 3. The dipole antennas have ... pattern is bidirectional.  The radiation pattern of half wave dipole antenna is - The radiation pattern

Description : Draw block diagram of digital LCR –Q meter and explain its working.

Answer : Block diagram Working The output of LCR-Q meter is given to current to voltage converter, AC amplifier or DC amplifer depending upon position of switch Current to voltage ... /D converter. A/D converter converts analog signal into digital output andfinaaly displayed on display.

Description : Draw block diagram of AF sine and square wave generator and explain its working

Answer : The AF signal generator, which generates either sine wave or square wave in the range of audio frequencies based on the requirement is called AF Sine and Square wave generator. Its block diagram is shown ... can be used to produce either AF sine wave or AF square wave based on the requirement.

Description : Draw a flow sheet diagram of manufacturing of producer gas and explain its working.

Answer : Producer gas, It is a mixture of flammable gases (principally carbon monoxide and hydrogen) and nonflammable gases (mainly nitrogen and carbon dioxide) made by the partial combustion of carbonaceous substances, ... valve on the top. Producer gas is cooled by passing through waste heat boiler.

Description : Draw block diagram of OTDR and explain its working.

Answer : Block diagram of OTDR Working principle of OTDR: A light pulse is launched into the fiber in the forward direction from an injection laser using either a ... backscattered light is detected using avalanche photodiode receiver. Output of photodiode receiver drivers an integrator.

Description : Draw the block diagram of TDMA system and explain its working.

Answer : Block diagram of TDMA system:- OR Explanation:- In TDMA, each user has all the bandwidth, all the power and part of the time. It is frequently used with data and ... receives the bursts from all other earth stations and must select from them the traffic destined only for itself.

Description : Draw the block diagram of PCM receiver with the help of relevant wave form and explain its working

Answer : Block diagram of PCM receiver:- Explanation:- A PCM signal contaminated with noise is available at the receive input. The regeneration circuit at the receiver will separate PCM pulses from noise ... quantized PAM signal is passed through a low pass filter recovers the analog signal x (t).

Description : Draw the block diagram of function generator and explain its working.

Answer : Principle of operation of function generator: Function generator operates to produce different waveforms such as sine, square, triangular of adjustable frequency which is used to test ... whose frequency is determined by the magnitude of current supplied by constant current sources.

Description : Draw the constructional details diagram of Centrifugal clutch. Explain its working principle.

Answer : Working Principle of Centrifugal Clutch: The centrifugal clutch uses centrifugal force, instead of spring force for keeping it in engaged position. Also, it does not require clutch pedal for ... increase of speed causes the shoe to press harder and enables more torque to be transmitted.

Description : Draw block diagram for CNC drilling machine and explain its working.

Answer : Block diagram consist of the following points:  Machine tool with DC servo motor as feedback element. The transducer is added as adaptive control application.  The auxiliary controller ... line.  The interrupt pulses are generated by TBG and supplied to computer through inter

Description : Draw schematic diagram of welding transformer showing constructional features of a welding transformer. Also explain its working.

Answer : Constructional features of welding transformer: Working of welding transformer: i) It is a step down transformer that reduces the voltage from the source voltage to a voltage desired according to the demands of ... 230 V, 415 V Secondary voltage - 40 to 60 V Secondary current - 200 to 600 A

Description : Draw the diagram of zero crossing detector using op-amp and explain its working.

Answer : The zero crossing detector circuit is an important application of the op-amp comparator circuit. It can also be called as the sine to square wave converter. Anyone of the inverting or non-inverting ... the possibility of any false zero crossing due to noise voltages at the op-amp input.

← Prev Question Next Question →