Reviewer in Transmission Fundamentals | ECE Board Exam

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(Last Updated On: February 15, 2020)

Review Notes in Transmission Fundamentals

This is the Reviewer in Transmission Fundamentals as one topic in ECE Board Exam taken from various sources including but not limited to past Board Examination Questions in Electronic System and Technologies (EST), Communications Books, Journals and other Communications References. This particular Coaching Notes in Communications Engineering has random Questions and Answers in random topics. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.

Summary of Important Transmission Fundamentals Review Notes

Impedance is the opposition to the transfer of energy which is considered the dominant characteristics of a cable or circuit that emanates from its physical structure

When load impedance equals to Zo of the line, it means that the load absorbs all the power

4:1 – Impedance matching ratio of a coax balun

dBr stands for dB relative level

1000 Hz – Standard test tone used for audio measurement

When VSWR is equal to zero, this means that no power is applied


Reflection coefficient is the ratio of reflected voltage to the forward traveling voltage

Transmission line must be matched to the load to transfer maximum power to the load


Dissipation factor indicates the relative energy loss in a capacitor

0 dBm is the standard test tone

Standing waves – the energy that neither radiated into space nor completely transmitted

1 Angstrom (A°) is equal to 10^-10 m

It is impossible to use a waveguide at low radio frequencies because of the size of the waveguide


Communications is the transmission and reception of information

Transmission lines are either balanced or unbalanced with respect to ground


The standing wave ratio is equal to 1 if the load is properly matched with the transmission line

Low attenuation is the advantage of the balanced transmission line compared to unbalanced line

Spectral analysis is the method of determining the bandwidth of any processing system

Losses in the conducting walls of the guide causes the attenuation present in a waveguide

Balun – a device that converts a balanced line to an unbalanced line of a transmission line

The average power rating of RG-58 C/u is 50 W


RG-211A – a coaxial cable used for high temperatures

The velocity factor of a transmission line depends on the dielectric constant of the material used


Impedance inversion can be obtained by a quarter-wave line


Transmission lines when connected to antennas have resistive load at the resonant frequency


Characteristic impedance – the impedance measured at the input of the transmission line when its length is infinite

Complex propagation constant is not considered primary line constant

The dielectric constants of materials commonly used in transmission lines range from about 1.2 to 2.8


Typically, the velocity factor (Vf) of the materials used in transmission lines rage from 0.6 to 0.9


For an air dielectric two-wire line, the minimum characteristic impedance value is 83 ohms


When a quarter-wave section transmission line is terminated by a short circuit and is connected to an RF source at the other end, its input impedance is equivalent to a parallel resonant LC circuit


The concept used to make one Smith chart universal is called normalization


The basic elements of communication system are the transmitter, receiver, and transmission channel


Facsimile is the transmission of printed material over telephone lines

Call waiting tone is a continuous tone generated by the combination of two frequencies of 350 Hz and 440 Hz used in telephone sets

VF repeaters are unidirectional amplifiers having 20-25 decibel gain that are placed about 75 km apart used to compensate for losses along the telephone

Induction coil is a component in the telephone set that has the primary function of interfacing the handset to the local loop

Pulse dialing has 10 pulse/sec rate

Trunk line is a telephone wire that connects two central offices

MTSO – the central switching office coordinating element for all cell sites that has cellular processor and cellular switch. It interfaces with telephone company zone offices, control call processing and handle billing activities

Base station in a cellular system performs radio-related functions for cellular site.

Frequency re-use – a technology used to increase the capacity of a mobile phone system

If the grade of service of a telephone system indicated P = 0.05, it means lost call of 5%

3700 Hz is the Out-of-band signaling between Toll Central Offices (Bell System Standard)

If the SWR is infinite, the load transmission line is purely reactive

Not more than 12 digits make up an international telephone number as recommended by CCITT REC. E. 161

One (1) Erlang is equal to 36 CCS

WATS – standard tariff for flat rate telephone service beyond the normal flat rate in that area

The standard analog telephone channel bandwidth is 300-3400 Hz

Manual switching – type of switching in which a pair of wire from the telephone set terminates in a jack and the switch is supervised by an operator

Everytime when the telephone is idle, the handset is in the on-hook state.

Varistor is a component in the telephone set that has the primary function of compensating for the local loop length

Electromagnetic receiver is used in conventional telephone handset

A voice-grade circuit using PTN has an ideal passband of 0 to 4 kHz

Basic voice grade (VG) is the minimum-quality circuit available using the PTN

Direct distance dialing (DDD) network is called Dial-up network

The advantage of sidetone is it assures the customer that the telephone is working

Tie trunk is a special service circuit connected two private branch exchanges (PBX)

Tariff – the published rates, regulations, and descriptions governing the provision of communications service for public use

The power loss of a telephone hybrid is 3 dB

Telephone channel has a band-pass characteristic occupying the frequency range of 300-3400 Hz

The first strowger step-by-step switch was used in 1897

G.122 is the CCITT recommendation for a preparation of loss plan, a variable loss plans and a fixed loss plan

Umbrella cells is appropriate for load management, fast moving mobiles and low-usage areas

In cellular networks, standard base station antennas are replaced by adaptive array

Analogue cellular technology is the basis of the first generation wireless local loop

When the calling party hears a “busy” tone on his telephone, the call is considered completed

Short-circuited stubs are preferred to open circuited stubs because the latter are liable to radiate

Coefficient of reflection is the ratio of the reflected voltage to the incident voltage

Quarter-wave matching – one method of determining antenna impedance

Single-wire line is a single conductor running from the transmitter to the antenna

Coaxial cable impedance is typically 50 to 75 ohms

Waveguide becomes compulsory above 3 GHz

Normal voice channel bandwidth is 4 kHz

Echo suppressors are used on all communications system when the round trip propagation time exceeds 50 ms

Quarter-wavelength line is used as impedance transformer

The transmission lines which can convey electromagnetic waves only in higher modes is usually called waveguide

Nitrogen gas is sometimes used in waveguide to keep the waveguide dry

It is impossible to use a waveguide at low radio frequencies because of the size of the waveguide

To couple in and out of a waveguide, insertion of an E-probe into the waveguide and insertion of an H-loop into the waveguide is done

A rectangular waveguide is operating in the dominant TE10 mode. The associated flux lines are established transversely across the narrow dimension of the waveguide

For dominant mode of a rectangular waveguide, the distance between two instantaneous consecutive positions of maximum field intensity is referred to as half of the guide wavelength

The guide wavelength, in a rectangular waveguide is greater than the free-space wavelength at the same signal frequency

Using the TE10 mode, microwave power can only be transmitted in free rectangular guide provided the wide dimension is greater than one-half of the wavelength in free space

If the signal frequency applied to a rectangular guide is increased and the dominant mode is employed, the group velocity is increased

The frequency range over which a rectangular waveguide is excited in the dominant mode is limited to the difference between the frequency at which the cutoff wavelength is twice the narrow dimension

If a rectangular waveguide is to be excited in the dominant mode, the E-probe should be inserted at a distance of one quarter-wavelength from the sealed end

A quarter-wave line is connected to an RF generator and is shorted out at the far end. The input impedance to the line generator is a high value of resistance

If the SWR on a transmission line has a high value, the reason could be an impedance mismatch between the line and the load

If a quarter-wave transmission line is shorted at one end the line behaves as a parallel-tuned circuit in relation to the generator

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

The outer conductor of the coaxial cable is usually grounded at the beginning and at the end of the cable

A feature of an infinite transmission line is that its input impedance at the generator is equal to the line’s surge impedance

When the surge impedance of a line is matched to a load, the line will transfer maximum power to the load

SWR – ratio of the mismatch between the antenna and the transmitter power

F3C and A3E – emission designation for a facsimile

AWG #19 – commonly used telephone wire

Wavelength is the distance traveled by a wave in the time of one cycle

The velocity factor is inversely proportional with respect to the square root of the dielectric constant

Balun circuit connects a balanced line to an unbalanced line

To connect a coaxial line to a parallel wire line, balun is used

Waveguides are transmission lines which can convey electromagnetic waves only in higher order modes

The amount of uncertainly in a system of symbols is also called entropy

The twists in twisted wire pairs reduced electromagnetic interference

Loading means to the addition of inductance

Coaxial is the most commonly used transmission line for high frequency application

The characteristic impedance of a transmission does not depend upon its length

For maximum absorption of power at the antenna, the relationship between the characteristic impedance of the line Zo and the load impedance Zl should be Zo = Zl

The mismatch between antenna and transmission line impedance cannot be corrected for by adjusting the length of transmission line

Standing waves is a pattern of voltage and current variations along a transmission line not terminated in its characteristic impedance

The desirable SWR on a transmission line is 1

The most desirable reflection coefficient is 0

Reflection coefficient is the ratio expressing the percentage of incident voltage reflected on a transmission line

At very high frequencies, transmission lines act as tuned circuits

A shorted quarter-wave line at the operating frequency acts like a parallel resonant circuit

A shorted half-wave line at the operating frequency acts like a series resonant circuit

Coaxial medium is least susceptible to noise

Twisted pair medium is most widely used in LANs

Coaxial cable is the most commonly used transmission line in television system

DC blocks are used in coaxial transmission line for the purpose of preventing AC power supply voltage from being shorted by a balun or band splitter

Adjacent channel interference is a type of interference caused by off-air TV channels 2 and 4, plus a satellite dish operating on channel 3

Dithering (in TVRO communications) is a process for reducing the effect of noise on the TVRO video signal

Frequency and voltage are important useful quantities describing waveforms

Halving the power means 3-dB loss

One neper (Np) is 8.686 decibels

Reflectometer is used to measure SWR

214-056 twin lead which is commonly used for TV lead-in has characteristics impedance of 300 ohm

A coaxial cable is a good example of a bounded medium

dNp is known as one-tenth of a neper

The input impedance of a quarterwave short-circuited transmission line at its resonant frequency is infinite or an open circuit

The ratio of the largest rms value to the smallest rms value of the voltage in the line is called VSWR

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

A power difference of -3 dB means a loss of one half of the power

Low attenuation is an advantage of the balance transmission line

Waveguides are used mainly for microwave transmission because no generators are powerful enough to excite them

The ratio of the smallest to the largest rms current value is called ISWR

A ten times power change in transmission system is equivalent to 10 dB

Parallel-wire line type transmission line is employed where balanced properties are required

To be properly matched the ratio of a maximum voltage along a transmission line should be equal to 1

Absorption coefficient – the ratio between the energy absorbed by a surface to the total energy received by the surface

When the diameter of the conductors of a 2 wire transmission line is held constant, the effect of decreasing the distance between the conductors is decrease the impedance

The higher the gauge number of a conductor the higher the resistance or the smaller the diameter

λ/4 transformer – a short length of transmission line used to reduce/eliminate standing wave in the main transmission line

Reflectance – ratio of reflected power to incident power

The SWR when a transmission line is terminated in a short circuit is infinite

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