GROL - General Radiotelephone Operator License Amplifier and Oscillator Circuits Questions and Answers

Question 1

For an LC oscillator to begin and sustain oscillation, which condition must be met according to the Barkhausen criterion?

Accepted Answer

The total phase shift around the feedback loop must be 0° or 360°, and the loop gain must be slightly greater than 1.

Answer

The total phase shift around the feedback loop must be 180°, and the loop gain must be exactly 1.

Answer

The feedback signal must be negative, and the loop gain must be less than 1.

Answer

The amplifier must be biased for Class A operation, and the feedback network must have a 90° phase shift.

Question 2

A technician is designing an RF power amplifier for a continuous wave (CW) transmitter. To achieve the highest possible efficiency, which class of amplifier should be selected?

Accepted Answer

Class C

Answer

Class A

Answer

Class B

Answer

Class AB

Question 3

What is the primary distinguishing feature between a Hartley oscillator and a Colpitts oscillator?

Accepted Answer

A Hartley oscillator uses a tapped inductor for feedback, while a Colpitts oscillator uses a tapped capacitive divider.

Answer

A Hartley oscillator uses a tapped capacitor in its tank circuit, while a Colpitts uses a tapped inductor.

Answer

A Hartley oscillator is used for audio frequencies, while a Colpitts is exclusively for RF.

Answer

A Colpitts oscillator uses a resistive feedback network, while a Hartley uses a transformer.

Question 4

In an Armstrong oscillator circuit, how is the essential positive feedback provided to sustain oscillations?

Accepted Answer

Through magnetic coupling between a "tickler" coil in the output circuit and the tank coil in the input circuit.

Answer

Through a capacitive voltage divider connected between the collector and base.

Answer

Through an RC phase-shift network that provides a 180° phase shift.

Answer

Through a direct connection from the emitter output back to the base input.

Question 5

A technician observes that the output of a newly constructed oscillator has significant harmonic distortion and is not a pure sine wave. Which of the following is the most likely cause?

Accepted Answer

The loop gain of the oscillator is significantly greater than 1.

Answer

The resistance in the biasing network is too low.

Answer

The power supply voltage is too low, causing clipping.

Answer

The feedback network is providing negative feedback instead of positive.

Question 6

Which of the following describes the effect of negative feedback in an amplifier circuit, as opposed to the positive feedback used in an oscillator?

Accepted Answer

It reduces gain but improves stability and linearity.

Answer

It increases the overall gain and decreases stability.

Answer

It causes the amplifier to oscillate at a specific frequency.

Answer

It narrows the amplifier's bandwidth and increases distortion.