Explore topic-wise InterviewSolutions in .

The correct OPTION is (a) Voltage series feedback

Easy EXPLANATION: The feedback used in HARTLEY OSCILLATOR is Voltage series feedback.

The correct answer is (c) Inductance

For EXPLANATION I would say: Lower FREQUENCIES are theoretically POSSIBLE in Hartley OSCILLATOR however in practice, the achievement of REQUIRED inductive value is a problem.

Right choice is (C) Inductive voltage divider

For EXPLANATION: Inductive voltage divider BIAS is used, wherein a center tapped inductor in PARALLEL to a capacitor is in the feedback network to the base of the transistor/amplifying element.

Right CHOICE is (a) 1

Explanation: There is only one CAPACITOR is used in the tank circuit of Hartley OSCILLATOR.

Correct OPTION is (a) Inductor

Explanation: Center tapped inductors are used in Hartley oscillator to ensure feedback. These are OFTEN in PARALLEL to a variable CAPACITOR, and feedback is sent into the base of the transistor.

The correct choice is (b) 2

To elaborate: There are two inductors in the tank CIRCUIT and one capacitor, in the HARTLEY OSCILLATOR. Often THOUGH, we USE a center tapped inductor instead of two inductors.

The CORRECT ANSWER is (d) Transistor

Best explanation: Active element USED in the Hartley oscillator is Transistor for AMPLIFICATION purposes.

Correct answer is (c) L1+L2

Easiest explanation: INDUCTANCE L1 and L2 are SERIES and hence effective inductance WITHOUT MUTUAL inductance will be L1+L2.

Correct OPTION is (b) Positive feedback

The EXPLANATION: As NORMAL oscillators, Hartley oscillator also uses positive feedback for sustained oscillation.

The CORRECT CHOICE is (a) Common emitter amplifier

To EXPLAIN I WOULD say: Common emitter transistor configuration is used in HARTLEY oscillator to ensure good oscillation.

The correct answer is (c) Band pass filter

To elaborate: The GAIN device in HARTLEY OSCILLATOR ACT as a band pass filter.

Right CHOICE is (C) 180 degree

To EXPLAIN: Phase shift provided by the tank circuit is 180 degrees to obey BARKHAUSEN’s criteria for SUSTAINED oscillation.

The correct answer is (b) 180 degree

Explanation: The COIL has a tap such that the proper PHASE is AVAILABLE to the base of the transistor. Value of L and C are adjusted to give a phase shift of 180°. The transistor itself CREATES a 180° phase shift and hence total shift is 360°/0.

The correct answer is (C) Class C

The explanation: HARTLEY OSCILLATOR MAKE use of class C amplifiers because it can amplify signals less than 180 degrees and provide output of full cycle.

Correct ANSWER is (B) 29KHz

To explain: L1 = 1mH

L2 = 2mH

Effective inductance L = L1+L2 = 1+2 = 3mH

C = 10nF

Oscillator frequency .

Frequency = 29kHz.

Correct option is (a) Hartley oscillator

To EXPLAIN I WOULD SAY: LC oscillators are also CALLED self-limiting oscillators.

Correct choice is (a) Voltage SERIES feedback

To explain I would SAY: Voltage series feedback is used in Colpitts oscillator. In voltage series feedback a part of output voltage is FED back to INPUT.

The correct answer is (c) High FREQUENCY region

Easy explanation: The Hartley OSCILLATOR is less PREFERRED than due to Colpitts oscillator’s performance in high frequency regions due to stability. Colpitt’s oscillator uses a capacitive voltage divider setup which PROVIDES better stability than an inductive voltage divider as in Hartley oscillator.

Correct answer is (a) INDUCTOR

The EXPLANATION: A capacitor with a center tap or simply two capacitors in parallel to an inductor, acting as a voltage divider, acts as the feedback system, providing feedback to the base of the amplifying transistor. Oscillations across the capacitor are applied at the base-emitter junction and appear across the COLLECTOR as an amplified output.

Correct answer is (d) Capacitive voltage DIVIDER

The explanation is: Capacitive voltage divider network is used for GIVING positive FEEDBACK in Colpitts oscillator. OSCILLATIONS across the capacitor are applied at the base-emitter junction and appear across the collector as an AMPLIFIED output. The amount of feedback depends on the ratio of the two capacitors being used.

Correct ANSWER is (b) 2

Best EXPLANATION: There are two capacitors in the tank circuit of Colpitts OSCILLATOR and it is GIVEN for VOLTAGE division.

Correct choice is (b) Frequency stability

Best explanation: Capacitive circuit in the COLPITT oscillator improves frequency stability. An additional 180° phase shift is provided by the capacitive tank circuit, PROVIDING no phase shift to the output. By changing tap POSITION or the VALUE of capacitors in the tank circuit, we can change feedback amount.

The correct option is (d) TRANSISTOR

For explanation: The ACTIVE ELEMENT USED in Colpitts OSCILLATOR is transistor and it is used for amplification of weak oscillator signals.

The correct answer is (a) High reactance to oscillation

For explanation: RFC choke PRESENT in Colpitts OSCILLATOR is to provide high reactance to AC oscillation and LOW reactance to DC SUPPLY to improve performance.

Right option is (c) Low resistance to DC

For EXPLANATION: RFC choke present in Colpitts oscillator is to provide high REACTANCE to AC oscillation and low reactance to DC supply to improve performance. If resistor is USED there will be some POWER loss in DC biasing which is unnecessary.

Right CHOICE is (b) Positive feedback

Explanation: Colpitts OSCILLATOR uses positive feedback for oscillation. The feedback is provided through a capacitor VOLTAGE divider tank circuit to the AMPLIFYING element.

Correct choice is (a) Gang tuning

Easy explanation: FREQUENCY of oscillation is determined by the tank circuit and is varied by the gang tuning of two capacitors/center TAPPED capacitors. As they are TUNED, thus as tuning is varied then VALUES of both capacitors varies, and the ratio of both capacitors remains same.

Right option is (c) 180 degree

Explanation: The overall PHASE shift provided by tank circuit is 180 degrees. Since the active ELEMENT produces a phase shift of 180 degrees the tank circuit should CREATE 180 degrees to obey Barkhausen’s criteria.

Right choice is (c) Band PASS FILTER

The explanation is: The gain device in Colpitts oscillator act as a band pass filter and thus LIMITS frequency of OSCILLATION to a certain RANGE.

Correct choice is (a) Common emitter amplifier

Easy EXPLANATION: Common emitter CONFIGURATION is used for amplifying distorted oscillatory signal to a PERFECT oscillation. The transistor PROVIDES a 180° phase shift and tank circuit another 180°, a total of 0 phase shift.

The CORRECT ANSWER is (d) 2ICRL C2/C1+C2

The explanation: Amplitude of oscillation in Colpitts OSCILLATOR using describing FUNCTION method is egual to

V=(2IC RL C2)/C1.

The correct option is (c) HIGH FREQUENCY region

Best explanation: Colpitts OSCILLATOR shows BETTER frequency STABILITY in high frequencies than Hartley oscillator.

Right OPTION is (a) Capacitive

Explanation: COLPITTS oscillator provides more PERFORMANCE than HARTLEY oscillator because of its capacitive feedback elements. Due to less self and mutual inductance in the circuit, frequency stability of the oscillator is improved along with a more simple DESIGN.

Correct answer is (d) Frequency depends EXTERNAL resistors and capacitors

Explanation: The crystal OSCILLATOR is highly STABLE with time, highly stable with temperature, highly selective. The frequency of crystal is a constant REGARDLESS of output circuits. The frequency is dependent on the crystal shape which does not differ much at all.

Correct choice is (b) One INDUCTORS and two capacitors

To EXPLAIN: There is one inductor in series with a resistor and a CAPACITOR, which are all in parallel to a second capacitor. The WHOLE SETUP acts like a crystal oscillator and the values of these components determine the resonant frequency.

Correct OPTION is (a) Inter electrode CAPACITANCE

To EXPLAIN: The parallel capacitor of the equivalent circuit of crystal oscillator constitute for electrostatic capacitance between TWO parallel plates of crystal. That is, it is inter electrode capacitance. It represents the capacitance formed due to mechanical moulding of the crystal.

The correct CHOICE is (d) MASS

For EXPLANATION: Inductance of the CRYSTAL oscillator physically refer to mass of the oscillator.

Right choice is (c) VISCOUS factor

The best I can explain: The resistance in the equivalent CIRCUIT REPRESENTS the friction of the crystal’s internal STRUCTURE, or we can say the viscous factor of the crystal.

The CORRECT answer is (b) Infinity

To explain: The oscillator has two resonant FREQUENCIES, parallel and series. Parallel resonance OCCURS when the reactance of series leg becomes equal to that of the parallel capacitor, and during this TIME, impedance offered is very high, almost INFINITE.

Correct choice is (B) Compliance

The EXPLANATION is: The SERIES capacitance of the oscillator PHYSICALLY represents the compliance of the oscillator.

Correct choice is (b) Capacitor

For explanation I WOULD say: When the frequency of oscillation of crystal becomes LESS than that of wS the OSCILLATOR becomes capacitive and in between wS and wP it becomes inductive.

The correct option is (a) CRYSTAL oven

The BEST I can explain: For critical applications, the quartz oscillator is mounted in a temperature-controlled container. It is called a crystal oven, and can also be mounted on SHOCK absorbers to PREVENT PERTURBATION.

The correct option is (b) COLPITTS oscillator

Best EXPLANATION: Crystal oscillator operating between WS and wP is inductive and HENCE we can replace it with INDUCTOR in colpitts oscillator.

Right choice is (b) Piezo ELECTRIC effect

To explain: When a voltage source is applied to a quartz CRYSTAL, it begins to produce a CHARACTERISTIC known as the Piezo electric effect. It is a property of a crystal by which an ELECTRICAL charge produces a MECHANICAL force by changing the shape of the crystal and vice versa, a mechanical force applied to the crystal produces an electrical charge.

Correct answer is (c) More accurate

Explanation: Quartz(crystal) oscillators are able to OSCILLATE with DESIRED frequency, with LITTLE needed power to operate it. The frequency is stable for a WIDE range of TEMPERATURE with minimal frequency change around 0.001% while the same is 0.5% for a ceramic oscillator. The phenomenon of operation is almost the same though.

Right answer is (c) Shape of crystal

For explanation I would say: The crystal FREQUENCY will only depend on INTERNAL characteristics of the crystal and hence it DEPENDS on shape or ’CUT’ of the crystal.