Deck 7: Microwave Network Noise Figure, Oscillator Circuits, and Negative Resistance Devices

Question 1

Noise figure can be defined for any microwave network irrespective of any other constraints.

A) true
B) false

Answer 1

false

Question 2

Expression for noise of a two port network considering the noise due to transmission line and other lossy components is:

A)gktb + gnadded
B)gktb
C)gnadded
D)none of the mentioned

Answer 2

gktb + gnadded

Question 3

Noise equivalent temperature of a 2 stage cascade network is given by:

A)te1 + te2/ g1
B)te1 + te1
C)te1 / te1
D)none of the mentioned

Answer 3

te1 + te2/ g1

Question 4

For a Wilkinson power divider of insertion loss L and the coupler is matched to the external circuitry, and then the gain of the coupler in terms of insertion loss is:

A)2L
B)1/2L
C)l
D)1/l

Question 5

Noise equivalent temperature of Wilkinson coupler having a gain of 1/2L is given as:

A)t (2L-1)
B)t (2L+1)
C)t (2L*1)
D)t / (2L-1)

Question 6

Expression for over all noise figure of a mismatched amplifier is:

A)1+ (f-1)/ (1 -???2)
B)1
C)1+ (f-1)
D)(f-1)/ (1 -???2)

Question 7

One condition to be satisfied in an oscillator circuit so that stable oscillations are produced is:

A)positive feedback is to be achieved
B)negative feedback is to be achieved
C)1800 phase shift is required between the transistor input and output.
D)none of the mentioned

Question 8

In an oscillator, the resonant feedback circuit must have must have a low Q in order to achieve stable oscillation.

Question 9

Quartz crystal and tourmaline used in oscillators work on the principle of:

A)photo electric effect
B)piezo electric effect
C)raman effect
D)black body radiation

Question 10

A quartz crystals equivalent circuit is a series LCR circuit and has a series resonant frequency.

Question 11

In the plot of reactance v/s frequency of a crystal oscillator, the reactance between series resonant frequency and parallel resonant frequency is:

A)capacitive
B)inductive
C)both capacitive and inductive
D)none of the mentioned

Question 12

In the equivalent circuit of a quartz crystal, LCR arm has an inductance of 4 mH and capacitor has a value of 4nF, then the series resonant frequency of the oscillator is:

A)0.25 mhz
B)2.5 mhz
C)25 mhz
D)5 mhz

Question 13

Parallel resonant frequency of quartz crystal is given by:

A)1/ ?(lc?c/(c?+c))
B)1/?lc
C)1/?lc?
D)1/ ?(l(c?+c) )

Question 14

The equivalent circuit of a quartz crystal has LCR arm capacitance of 12nF and inductance of 3mH and parallel arm capacitance of 4nF. Parallel resonant frequency for the circuit is:

A)3 mhz
B)0.3 mhz
C)6 mhz
D)9 mhz

Question 15

In microwave oscillators, negative resistance transistors and diodes are used in order to generate oscillations in the circuit.

Question 16

Any device with negative impedance as its characteristic property can be called:

A)energy source
B)energy sink
C)oscillator
D)none of the mentioned

Question 17

In a microwave oscillator, a load of 50+50j is connected across a negative resistance device of impedance -50-50j. Steady state oscillation is not achieved in the oscillator.

Question 18

For achieving steady state oscillation, the condition to be satisfied in terms of reflection coefficients is:

A)?in=?l
B)?in=-?l
C)?in=1/?l
D)none of the mentioned

Question 19

To achieve stable oscillation, Zin + ZL=0 is the only necessary and sufficient condition to be satisfied by the microwave oscillator.

Question 20

In transistor oscillators, the requirement of a negative resistance device is satisfied using a varactor diode.

Question 21

In transistor oscillators, FET and BJT are used. Instability is achieved by:

A)giving a negative feedback
B)giving a positive feedback
C)using a tank circuit
D)none of the mentioned