MCQ in Transmission Fundamentals Part 12 | ECE Board Exam

This is the Multiple Choice Questions Part 12 of the Series in Transmission Fundamentals as one of the Communications Engineering topics. In Preparation for the ECE Board Exam, make sure to expose yourself and familiarize yourself with each and every question compiled here taken from various sources, including but not limited to past Board Examination Questions in Electronic Systems and Technologies, Communications Books, Journals, and other Communications References.

MCQ Topic Outline included in ECE Board Exam Syllabi

• MCQ in Transmission System
• MCQ in Transmission Medium
• MCQ in Velocity and Line Wavelength
• MCQ in Characteristics Impedance
• MCQ in Primary Line Constants and Propagation Constants
• MCQ in Standing Waves
• MCQ in Voltage Standing Wave Ratio
• MCQ in Telephone Lines and Cables
• MCQ in Wave Guides
• MCQ in Balanced and Unbalanced Lines
• MCQ in Twisted pair wire, Coaxial Cable
• MCQ in Decibel
• MCQ in Signal and Noise Fundamentals

Continue Practice Exam Test Questions Part 12 of the Series

⇐ MCQ in Transmission Fundamentals Part 11 | ECE Board Exam

Choose the letter of the best answer in each questions.

551. The input impedance measured at infinite length of a transmission line

A.        Characteristic Impedance

B.        Reflection Coefficient

C.        Standing wave ratio

D.        All of the above

552. There is an improper impedance match between a 30 W transmitter and the antenna and 5 watts is reflected. How much power is actually transmitted?

A.        35 watts

B.        20 watts

C.        25 watts

D.        30 watts

553. What is the actual length in feet of a one quarter-wavelength of a coax with a velocity factor of 0.69 at 40 MHz?

A.        5.904

B.        16.974

C.        6.15

D.        4.244

554. A quarter-wave line is connected to an RF generator and is shorted out at the far end. What is the input impedance to the line at the generator?

A.        a low value of resistance

B.        a value of resistance equal to the characteristic impedance of the line

C.        a high value of resistance

D.        a capacitive reactance which is equal in value to the line’s surge impedance

555. A coaxial cable has a capacitance of 90 pF/m and a characteristic impedance of 75 ohms. Find the inductance of a 2 m length.

A.        1.013 uH

B.        450 nH

C.        506.25 nH

D.        225 nH

556. If the SWR on a transmission line has high value, the reason could be

A.        an impedance mismatch between the line and the load

B.        a reflection coefficient of zero at the load

C.        a high degree of attenuation between the load and the position where the SWR is measured

D.        that the line is nonresonant

557. Calculate the velocity factor of a coaxial cable used as a transmission line with the characteristic impedance of 50 ohms; capacitance is 40 pF/m and inductance is equal to 50 microH/m.

A.        0.7504

B.        0.0745

C.        0.7450

D.        0.0475

558. If a quarter-wave transmission line is shorted at one end

A.        there is minimum current at the shorted end

B.        the line behaves as a series-tuned circuit in relation to the generator

C.        there is a maximum voltage at the shorted end

D.        the line behaves as a parallel-tuned circuit in relation to the generator

559. What is the velocity factor for a cable with a Teflon dielectric (relative permittivity = 2.1).

A.        0.69

B.        1.449

C.        0.476

D.        2.1

560. A 50-ohm transmission line is feeding an antenna which represents a 50-ohm resistive load. To shorten the line, the length must be

A.        an odd multiple of three-quarters of a wavelength

B.        any convenient value

C.        an odd multiple of an eighth of a wavelength

D.        an even multiple of a quarter of a wavelength

561. A feature of an infinite transmission line is that

A.        the impedance varies at different positions on the line

B.        its input impedance at the generator is equal to the line’s surge impedance

C.        its phase velocity is greater than the velocity of light

D.        its input impedance is equivalent to a short circuit

562. The outer conductor of the coaxial cable is usually grounded

A.        only at the beginning of the cable

B.        the outer conductor must never be grounded

C.        only at the end of the cable

D.        at the beginning and at the end of the cable

563. Refers to a connector that normally connects RG-213 coaxial cable to an HF transceiver.

A.        PL-259

B.        F-type cable

C.        BNC

D.        N-type cable

564. An attenuator has a loss of 26 dB. If a power of 3 W is applied to the attenuator, find the output power.

A.        5.459 watts

B.        1.65 watts

C.        7.54 milliwatts

D.        1194 watts

565. When the surge impedance of a line is matched to a load, the line will

A.        have a VSWR equal to zero

B.        transfer maximum current to the load

C.        transfer maximum voltage to the load

D.        transfer maximum power to the load

566. A lossless line is terminated by a resistive load which is not equal to the surge impedance. If the value of the reflection coefficient is 0.5, the VSWR is

A.        5

B.        3

C.        2

D.        1.5

567. The best insulation at UHF is

A.        paper

B.        bakelite

C.        mica

D.        black rubber

568. Neglecting line losses, the RMS voltage along an RF transmission line having no standing waves

A.        is one-half of the surge impedance

B.        is equal to the impedance

C.        varies sinusoidally along the line

D.        is the product of the surge impedance and the line current

569. What length of standard RG-8/U coaxial cable would be required to obtain a 30 degree-phase shift at 250 MHz?

A.        0.99 m

B.        0.124 m

C.        0.066 m

D.        0.792 m

570. Nitrogen is placed in transmission lines to

A.        prevent moisture from entering the line

B.        improve the skin-effect of microwaves

C.        reduce the standing wave ratio of the line

D.        reduce arcing in the line

571. Referred to the fundamental frequency, a shorted stub line attached to the transmission line to absorb even harmonics could have a wavelength of

A.        1.41 wavelength

B.        1/2 wavelength

C.        1/6 wavelength

D.        1/4 wavelength

572. Nitrogen gas in concentric RF transmission lines is used to

A.        act as insulator

B.        prevent oxidation

C.        keep moisture out

D.       both a and b

573. If a transmission line has a power loss of 6 dB per 100 feet, what is the power at the feed point to the antenna at the end of a 200 foot-transmission line fed by a 100 watt transmitter?

A.        25 watts

B.        50 watts

C.        6 watts

D.        70 watts

574. Two adjacent minima on a slotted line are 20 cm apart. Find the wavelength assuming a velocity factor of 95%.

A.        43.7 m

B.        38 m

C.        46 cm

D.        40 cm

575. What would be the approximate series impedance of a quarter-wave matching line used to match a 600 ohm-feed to 70 ohm-antenna?

A.        25.88 ohms

B.        210 ohms

C.        205 ohms

D.        102.5 ohms

576. Which of the following represents the best SWR?

A.        1:1

B.        1:15

C.        1:2

D.        2:1

577. An optical time domain reflectometer display shows a discontinuity 1.4 microseconds from the start. If the line has a velocity factor of 0.92, how far is the fault from the reflectometer?

A.        193.2 m

B.        168 m

C.        386 m

D.        2210 m

578. A high SWR creates losses in a transmission line. A high standing wave ratio might be caused by

A.        an antenna electrically too long for its frequency

B.        improper turns ratio between primary and secondary in the plate tank transformer

C.        screen grid current flow

D.        an impedance mismatch

579. A properly connected transmission line

A.        has a standing wave ratio as near as 1:1 as possible

B.        is cut to an even harmonic of the carrier frequency

C.        is cut to a harmonic of the carrier frequency

D.        is grounded at the transmitter end

580. If a 3/4 wavelength transmission is shorted at one end, the impedance at the pen will be

A.        increased

B.        decreased

C.        infinite

D.        zero

581. The characteristic impedance of a transmission line does not depend upon its

A.        conductor spacing

B.        conductor diameter

C.        length

D.        none of the above

582. Which of the following is not a common transmission line impedance?

A.        50 ohms

B.        75 ohms

C.        120 ohms

D.        300 ohms

583. A ratio expressing the percentage of incident voltage reflected on a transmission line is known as the

A.        standing wave ratio

B.        line efficiency

C.        reflection coefficient

D.        velocity factor

584. A series tuned circuit operating at a frequency of 1 GHz is to be constructed from a shorted section of Teflon-dielectric coaxial cable. What length should be used?

(relative dielectric = 2.1)

A.        0.10 m

B.        0.143 m

C.        0.315 m

D.        0.217 m

585. A 75 ohm line is terminated in a 30 ohm resistance. Find the SWR.

A.        0.4

B.        0.6

C.        2.5

D.        0.429

586. A generator sends 50 mW down a 50 ohm line. The generator is matched to the line but the load is not. If the coefficient of reflection is 0.6, how much power is reflected?

A.        20 milliwatts

B.        30 milliwatts

C.        32 milliwatts

D.        18 milliwatts

587. At very high frequencies, transmission lines are used as

A.        tuned circuits

B.        resistors

C.        antennas

D.        insulators

588. Transmission line shielding is grounded

A.        at the input only

B.        if the antenna is a Marconi design

C.        at both input and output

D.        at the output only

589. A shorted quarter-wave line at the operating frequency acts like a(an)

A.        series resonant circuit

B.        capacitor

C.        inductor

D.       parallel resonant circuit

590. A transmitter is required to deliver 100 W to an antenna through 45 m of coaxial cable with a loss of 3 dB/100 m. What must be the output power of the transmitter, assuming the line is matched?

A.        136 W

B.        151 W

C.        116.815 W

D.        153 W

591. A generator sends 50 mW down a 50 ohm line. The generator is matched to the line but the load is not. If the coefficient of reflection is 0.25, how much power is dissipated in the load?

A.        37.5 milliwatts

B.        46.9 milliwatts

C.        12.5 milliwatts

D.        3.125 milliwatts

592. An indication in radio communication when the voltage standing wave ratio is equal to zero

A.        No input power

B.        Load is purely resistive

C.        Pure reactive load

D.        Open power

593. The main disadvantage of the two-hole directional coupler is

A.        narrow bandwidth

B.        poor directivity

C.        high SWR

D.        low directional coupling

594. A shorted half-wave line at the operating frequency acts like a(an)

A.        series resonant circuit

B.        capacitor

C.        parallel resonant circuit

D.        inductor

595. A load impedance of 100 + j25 ohms is normalized on a 100 ohm-line. The normalized value is

A.        0.25 – j1 ohms

B.        2 + j0.5 ohms

C.        1 + j0.25 ohms

D.        0.94 – j24 ohms

596. A pattern of voltage and current variations along a transmission line not terminated in its characteristic impedance is called

A.        radio waves

B.        magnetic field

C.        standing waves

D.        electric field

597. A 75 – j50 ohm load is connected to a coaxial transmission line of ZO = 75 ohms, at 10 GHz. The best method of matching consists in connecting

A.        a short-circuited stub at some specific distance from the load

B.        a short-circuited stub at the load

C.        a capacitance at some specific distance from the load

D.        an inductance at the load

598. Calculate the impedance seen looking into a 75 ohm line 1 m long terminated in a load impedance of 100 ohms, if the line has a velocity factor of 0.8 and operates at a frequency of 30 MHz.

A.        72 – j21 ohms

B.        75 – j25 ohms

C.        40 – j30 ohms

D.        50 – j25 ohms

599. The velocity factor of a transmission line

A.        increases the velocity along the transmission line

B.        depends on the dielectric of the material used

C.        is higher for a solid dielectric than for air

D.        is governed by the skin effect

600. A transmitter supplies 50 W to a load through a line with an SWR of 4:1. Find the power absorbed by the load.

A.        32 W

B.        18 W

C.        44.4 W

D.        5.6 W

Questions and Answers in Transmission Fundamentals Series

Following is the list of multiple choice questions in this brand new series:

Complete List of MCQ in Communications Engineering per topic