Deck 6: RF Devices and Circuits

Question 1

A modern device that replaces a slotted line is:

A)digital cro
B)generators
C)network analyzers
D)computers

Answer 1

network analyzers

Question 2

If SWR=1.5 with a wavelength of 4 cm and the distance between load and first minima is 1.48cm, then the reflection coefficient is:

A)0.0126+j0.1996
B)0.0128
C)0.26+j0.16
D)none of the mentioned

Answer 2

0.0126+j0.1996

Question 3

High gain is not achievable at microwave frequencies using BJT amplifiers because:

A)device construction
B)complex architecture
C)ports are not matched at high frequencies
D)none of the mentioned

Answer 3

ports are not matched at high frequencies

Question 4

To flatten the gain response of a transistor:

A)biasing current has to be increased
B)input signal level has to increased
C)increase the operational bandwidth
D)give negative feedback to the amplifier

Question 5

In conventional amplifiers, a flat gain response is achieved at the cost of reduced gain. But this drawback can be overcome by using:

A)balanced amplifiers
B)distributed amplifiers
C)differential amplifiers
D)none of the mentioned

Question 6

Bandwidth of balanced amplifier can be an octave or more, but is limited by the bandwidth of the coupler.

Question 7

Coupler that is mostly used in balanced amplifiers to achieve the required performance is:

A)branch line coupler
B)wilkinson coupler
C)lange coupler
D)waveguide coupler

Question 8

Distributed amplifiers offer very high

A)gain
B)bandwidth
C)attenuation
D)none of the mentioned

Question 9

In distributed amplifiers, all the FET stages in the amplifier are connected in series to one another.

Question 10

_________uses balanced input and output, meaning that there are 2 signal lines, with opposite polarity at each port.

A)differential amplifier
B)distributed amplifier
C)balanced amplifier
D)none of the mentioned

Question 11

A major advantage of differential amplifiers is:

A)high gain
B)low input impedance
C)higher output voltage swing
D)none of the mentioned

Question 12

Along with a differential amplifier, 1800 hybrid is used both at the input and output.

Question 13

__________is a non linear circuit that converts DC power to an AC waveform of desired frequency based on the oscillator design.

A)attenuator
B)amplifier
C)oscillator
D)none of the mentioned

Question 14

The transfer function of an RF oscillator is given by:

A)a/ (1-ah (?))
B)a/ (1+ah (?))
C)a/ (-1+ah (?))
D)1/ (1-ah (?))

Question 15

The criterion on which oscillations are produced in the oscillator circuit is called:

A)shannon's criteria
B)barkhausen criteria
C)colpitts criteria
D)none of the mentioned

Question 16

The necessary condition for oscillation in a Colpitts oscillator is:

A)c2/c1=gm/gi
B)c1/c2=gm/gi
C)c2/c1= gm*gi
D)none of the mentioned

Question 17

Colpitts oscillator operating at 50 MHz has an inductor in the feedback section of value 0.10µH. then the values of the capacitors in the feedback section is:

A)100 pf, 100 pf
B)100 pf, 50 pf
C)70 pf, 130 pf
D)80 pf, 60 pf

Question 18

An inductor is operating at frequency of 50 MHz. Its inductance is 0.1 µH, and then the series resistance associated with the inductor is: (Qo=100)

A)0.31 ?
B)1.32 ?
C)1 ?
D)1.561 ?

Question 19

Hartley oscillator has inductance values of 12 mH and 4 mH in the feedback section and a capacitor of 4 nF. Then the resonant frequency of the circuit is:

A)19.89 khz
B)25 khz
C)45 khz
D)12 khz

Question 20

Colpitts oscillator in the feedback section has an inductance of 4 mH and capacitors of 12 nH and 4 nH. Then the resonant frequency of Colpitts oscillator is:

A)50.4 khz
B)35.1 khz
C)45.9 khz
D)none of the mentioned

Question 21

For Colpitts oscillator, the capacitors C1 and C2 in the feedback network are 1 µF and 25 µF respectively. Then the ? value of the transistor is:

A)35
B)000.76
C)25
D)0.0025

Question 22

Amplifier efficiency is the ratio of RF output power to DC input power. This parameter determines the performance of an amplifier.

Question 23

__________is defined as the ratio of desired signal power to undesired noise power.

A)signal to noise ratio
B)noise to signal ratio
C)noise figure
D)noise temperature

Question 24

__________  is defined as the ratio of input signal to noise ratio to the output signal to noise ratio.

A)noise figure
B)noise temperature
C)snro
D)none of the mentioned

Question 25

The equivalent noise temperature of a network given the noise figure of the network or system is:

A)t₀(f-1)
B)t₀(f+1)
C)t₀(f)
D)t0/f