ELECTRIC OSCILLATORS – Air – DGCA Question Bank For Politics

#1. The purpose of a basic Oscillator is to:

amplify a signal

attenuate a signal

produce a sine wave from a DC input

increase the frequency of a sine wave

#2. A basic oscillator consists of 1. amplifier 2. positive feedback path 3. negative feedback path 4. frequency determining circuit 5. DC supply 6. AC supply

1, 3, 4, 5.

1, 2, 4, 5.

1, 3, 4, 6.

1, 2, 3.

#3. An electrical resonant circuit is constructed from:

esistors and inductors in series

inductors and resistors in series or parallel

nductors and resistors always in parallel

apacitor and inductor which may be in parallel or series

#4. When a parallel inductive capacitive circuit is operating at its resonant frequency:

capacitive reactance is greater than inductive reactance

inductive reactance is greater than capacitive reactance

inductive reactance equals capacitive reactance and a large circulating current exists

inductive reactance equals capacitive reactance and zero current flows in the circuit

#5. Capacitive reactance:

decreases as frequency increases

increases as frequency increases

remains constant with changes in frequency

remains constant up to approximately 30MHz and then decreases with increasing frequency

#6. Inductive reactance:

decreases as frequency increases

increases as frequency increases

remains constant with changes in frequency

effectively falls to zero at VHF and above

#7. In a LC circuit the frequency where XL = XC is called: Look at the circuit at annex A and answer the following 3 questions

Impedance (Z)

Cancellation point

Oscillation frequency (F0)

Resonant frequency (F0)

#8. Which components form the resonant circuit and control the frequency of operation: 1. C1 2. L1 3. TR1 4. L2 5. C2

1 and 2 only

1, 2, 3, 5.

2, 3, 4, 5.

3 only

#9. The NPN transistor TR1 is necessary to:

form the positive feedback path to maintain oscillations

act as the frequency controlling device

act as an amplifier and make up for losses in the circuit

form the negative feedback path to maintain oscillations

#10. Positive feedback in the circuit:

is provided by transistor TR1

is provided by transformer coupling between L1 and L2

is not necessary, the oscillations are maintained by negative feedback

is determined by the ratio of C1 to L1

#11. In the circuit at Annex A it is necessary to make the output frequency variable. This could be achieved by:

replacing C1 with a variable capacitor

placing a variable resistor in the emitter of TR1

increasing the turns ratio of L1 - L2

making the gain of transistor TR1 variable

#12. The Piezo electric effect is:

the resonation when XL = XC

the generation of sine waves by an oscillator

a quartz crystal vibrating at a frequency dependent on its thickness when an EMF is applied to it

a quartz crystal vibrating at a frequency dependent on the size of the EMF applied to it

#13. Look at the circuit at Annex B. This shows:

an audio frequency amplifier

a radio frequency amplifier

crystal controlled oscillator

a LC controlled oscillator

#14. The advantages of a crystal controlled oscillator over a LC controlled oscillator include: 1. cheapness of construction 2. precise stable frequency output 3. Very narrow bandwidth 4. frequency can easily be changed

2 and 3 only

1, 2, and 3

1, 3, and 4

there are no particular advantages

#15. The output frequency of a magnetron depends on:

the voltage applied to the cathode

the voltage applied to the anode

the size of the cavities

the material from which the cavities are constructed

#16. To produce frequencies in the SHF (microwave) band which of the following could be used: 1. LC oscillator 2. Crystal oscillator 3. Magnetron 4. Klystron

1 and 2 only

2, 3, and 4

3 and 4 only

3 only

#17. Oscillations in a magnetron are maintained by:

electrons under the influence of a magnetic field energising the cavities

electrons under the influence of an electrostatic field creating negative feedback to the cavities

electromagnetic coupling between anode and cathode

electromagnetic coupling between heater and cathode

#18. The high power pulse of a ground radar system is most likely to be produced by:

crystal oscillator

klystron

klystron followed by a power amplifier

magnetron

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