This is the Review Notes 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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