Question 1

A modern device that replaces a slotted line is:
A)digital cro
B)generators
C)network analyzers
D)computers

Accepted Answer

Network analyzers have largely replaced slotted lines in modern applications for measuring the characteristics of electrical networks, due to their ability to provide comprehensive and precise measurements of network parameters.

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

Accepted Answer

SWR=1.5, λ=4 cm, d=1.48 cmReflection coefficient, Γ = (SWR-1)/(SWR+1) = (1.5-1)/(1.5+1) = 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

Accepted Answer

C

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

Accepted Answer

Negative feedback in an amplifier helps to stabilize the gain, reduce distortion, and flatten the frequency response, making it more uniform across different frequencies.

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

Accepted Answer

Balanced amplifiers use a differential input stage to cancel out common-mode noise and distortion, resulting in a flat gain response without reducing gain.

Question 6

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

Accepted Answer

The bandwidth of a balanced amplifier is indeed limited by the bandwidth of the coupler used in its design, as the coupler's performance directly affects the overall frequency response and operational bandwidth of the amplifier.

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

Accepted Answer

The Lange coupler is commonly used in balanced amplifiers due to its ability to provide tight coupling and wide bandwidth, which are essential for achieving the desired performance in such applications.

Question 8

Distributed amplifiers offer very high
A)gain
B)bandwidth
C)attenuation
D)none of the mentioned

Accepted Answer

Distributed amplifiers are known for offering very high bandwidth, which is achieved by distributing the signal across multiple amplifying elements, each of which amplifies a portion of the bandwidth.

Question 9

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

Accepted Answer

In distributed amplifiers, the FET stages are not connected in series; instead, the active devices (FETs) are connected in parallel with the distributed circuit elements (inductors and capacitors) to form a distributed system.

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

Accepted Answer

A differential amplifier uses balanced input and output, meaning there are two signal lines with opposite polarity at each port, allowing it to amplify the difference between two input signals while rejecting any signals that are common to both inputs.

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

Accepted Answer

The answer of A major advantage of differential amplifiers is:
A)high...

Question 12

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

Accepted Answer

The 1800 hybrid is used both at the input and output of a differential amplifier to ensure balanced operation, providing isolation between the input and output ports while maintaining signal integrity.

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

Accepted Answer

An oscillator is a non-linear circuit that converts DC power into an AC waveform of a specific frequency, determined by the design of the oscillator itself. This is in contrast to attenuators and amplifiers, which do not inherently convert DC to AC nor determine the frequency of an output waveform based on their design.

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 (?))

Accepted Answer

The correct transfer function of an RF oscillator is given by A) a/ (1-ah(?)). This form represents a feedback system where "a" is the forward gain and "h(?)" is the feedback factor. The negative sign in the denominator indicates positive feedback, which is essential for oscillation.

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

Accepted Answer

The criterion on which oscillations are produced in an oscillator circuit is called the Barkhausen criterion. It states that the product of the gains around the loop must be equal to one and the sum of the phase shifts around the loop must be zero (or equivalently, a multiple of 2π) for sustained oscillations.

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

Accepted Answer

The necessary condition for oscillation in a Colpitts oscillator is that the ratio of the capacitors c2/c1 should equal the transconductance gm divided by the input conductance gi.

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

Accepted Answer

The Colpitts oscillator's frequency of oscillation is given by $f = \frac{1}{2\pi\sqrt{LC}}$, where $L$ is the inductance and $C$ is the effective capacitance given by $C = \frac{C_1C_2}{C_1 + C_2}$ for capacitors $C_1$ and $C_2$ in the feedback section. For $L = 0.10\mu H$ and $f = 50 MHz$, solving for $C$ gives an effective capacitance. Given $C_1 = C_2 = 100pf$ results in the correct effective capacitance for a 50 MHz oscillation, assuming the formula and the parallel combination of capacitors are applied correctly.

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 ?

Accepted Answer

The quality factor (Qo) is given by Qo = (2 * π * f * L) / R, where f is the frequency, L is the inductance, and R is the series resistance. Solving for R gives R = (2 * π * 50 * 10^6 * 0.1 * 10^-6) / 100 = 0.31 Ω.

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

Accepted Answer

The resonant frequency $f$ of a Hartley oscillator can be calculated using the formula $f = \frac{1}{2\pi\sqrt{L_{total}C}}$, where $L_{total}$ is the total inductance in the circuit and $C$ is the capacitance. For a Hartley oscillator, the total inductance $L_{total}$ is the sum of the individual inductances, so $L_{total} = 12\,mH + 4\,mH = 16\,mH = 16 \times 10^{-3}\,H$, and $C = 4\,nF = 4 \times 10^{-9}\,F$. Plugging these values into the formula gives $f = \frac{1}{2\pi\sqrt{16 \times 10^{-3} \times 4 \times 10^{-9}}}$, which calculates to approximately 19.89 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

Accepted Answer

The answer of Colpitts oscillator in the feedback section has...

Quiz 6: RF Devices and Circuits

A modern device that replaces a slotted line is:

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:

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

To flatten the gain response of a transistor:

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

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

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

Distributed amplifiers offer very high

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

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

A major advantage of differential amplifiers is:

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

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

The transfer function of an RF oscillator is given by:

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

The necessary condition for oscillation in a Colpitts oscillator is:

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:

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)

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:

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: