WHOLE 1ST SEM - PRINCIPLES OF COMMUNICATION
signal-to-noise ratio
indicates the relative strengths of the signal and the noise in a communication system.
bit rate
information capacity of a system is expressed as ____________________.
binary digit/bit
information is represented as __________________.
PSK/phase shift keying
input binary information is encoded into groups of bits before modulating the carrier.
pulse-amplitude modulation/PAM
interference of noise is maximum in a PAM signal because of its pulse amplitude variation.
capture effect
interfering signals on the same frequency are effectively rejected in FM.
antenna
radiates or senses an electromagnetic field.
baud
rate of change of a signal on the transmission medium after encoding and modulation have occurred.
bandwidth efficiency
ratio of the transmission bit rate to the minimum bandwidth required for a particular modulation scheme.
mixer
receives the output of the RF amplifier and the frequency synthesizer from the local oscillator.
demodulator
recovers the original modulating information, may be a diode detector (for AM), a quadrature detector (for FM), or product detector (for SSB).
reflector
refers to a straight aluminum rod approximately 5% longer than the dipole.
transmit-time noise
refers to how long it takes for a current carrier such as a hole or electron to move from the input to the output.
directivity
refers to the ability of an antenna to send or receive signals over a narrow horizontal directional range.
refraction
refers to the bending of a wave due to the physical makeup of the medium through which the wave passes.
diffraction
refers to the bending of waves around an object.
permittivity
refers to the dielectric constant of the material between two conductors.
attenuation
refers to the loss of power of a signal; unitless or expressed in dB.
polarization
refers to the orientation of magnetic and electric fields with respect to the earth.
total gain/attenuation
refers to the product of all gain and attenuation factors.
baud
refers to the rate of change of a digital information signal.
1
the ideal shape factor value.
message signal
the information or intelligence in electrical form.
information source
the information or intelligence to be sent.
16-QAM
the input data are acted on in groups of four (2*2*2*2 = 16)
physical layer
the lowest level of the OSI hierarchy and is responsible for the actual propagation of unstructured data bits (1s and 0s) through a transmission medium.
noise immunity
the main benefit of FM over AM. FM can nevertheless tolerate a much higher noise level than AM for a given carrier amplitude.
channel/medium
the material in which electronic signal is sent.
fidelity
the measure of the ability of a communication system to produce, at the output of the receiver, an exact replica of the original source information.
selectivity
the measure of the ability of a receiver to accept a given band of frequencies and rejects all other.
shape factor
the measure of the steepness of the skirts, or the skirt selectivity of a receiver.
pulse-code modulation/PCM
the most widely used technique for digitizing information signals for electronic data transmission.
OSI/open systems interconnection
the name for a set of standards for communicating among computers.
fiber optics
the newest and probably the most promising type of guided transmission medium for virtually all forms of digital and data communications applications.
noise figure
the noise factor expressed in decibels (dB).
bit rate
the number of bits transmitted during one second and is expressed in bits per second (bps).
frequency
the number of cycles of a repetitive wave; measured in cycles per second (cps) or in Hertz (Hz).
intermediate frequency signal
the output of the mixer containing the same modulation that appeared on the input RF signal.
channel/medium
the pathway of signals.
directivity curve
the physical orientation of the antenna gives it a highly directional response or __________________.
pulse modulation
the process of changing a binary pulse signal to represent the information to be transmitted.
baseband transmission
the process of putting the baseband signal directly into a medium.
noise factor/noise ratio
the ratio of the Input SNR Power to the Output SNR Power.
information consumer
the recipient of information or intelligence.
AGC circuit
the recovered signal, which usually is AC (alternating current), is rectified and filtered into a DC (direct current) by the _____________________.
AM wave
the resulting signal from the process of amplitude modulation.
modulating signal
the signal containing intelligence or information to be transmitted.
IF amplifier
the signal from the mixer's output is amplified by this, and most of the receiver gain is obtained in these stages.
bus topology
the simplest and most common method of interconnecting computers.
tuned radio frequency receiver
the simplest radio receiver.
0.1 and 0.2
the spacing between elements is generally between _______ and _______ wavelength.
magnitude and direction
the strength and direction of the magnetic field depend upon the _____________ and _____________ of the current flow.
electromagnetic spectrum
the total span of frequencies and wavelengths used in communication systems.
flicker noise
the type of noise which is strongest at lower frequencies generally below a few kHz. the spectral density of this noise increases as the frequency decreases.
7 dB and 9 dB
the typical directivity for a Yagi is between ________ and ________.
modulation index
the value of _______________________ should be a number between zero (0) and one (1).
baseband signals
these are original information or intelligence.
skirts
these are the sides of a tuned circuit response curve.
parabolic reflector and feed mechanism
these are the two main parts of a parabolic reflector antenna.
near field
these fields are not radio wave, but they do contain any information transmitted.
near field
these fields weaken with the distance from the antenna, approximately by the quadruple power of the distance.
highly directional antenna
this antenna acts as a type of filter to provide selectivity based on the direction of the signal.
directional antenna
this antenna eliminates interference from other signals being received from all directions other than the direction of the desired signal.
receiving antenna
this antenna is pointed directly at the station to be received, thereby effectively rejecting signals from transmitters in all other directions.
omnidirectional antenna
this antenna radiates equally well in all directions.
carrier frequency
this frequency is greater than the modulating frequencies.
reflection
this happens if the metallic object is at least one-half wavelength at the frequency of operation.
director
this is cut approximately 5% shorter than the driven element.
diffraction
this radio wave propagation is explained by Huygen's principle.
marconi antenna
this type of antenna is commonly used at frequencies up to 2 MHz (such as standard AM broadcast).
yagi-uda antenna
this type of antenna is commonly used for VHF television (VHF TV band extends from 54 MHz to 216 MHz) reception because of its wide bandwidth.
8 bit word
this word must be transmitted serially before another sample is taken and another binary word is generated.
modulator
transforms the message signal into transmitted signal.
demodulator
translates the modulated signal back into the baseband signal (i.e. audio signal).
pulse-position modulation/PPM
transmission power of each pulse is same because of its constant pulse widths and amplitudes.
binary phase shift keying/BPSK
two phases are possible for the carrier, one phase represents a logic 1, and the other phase represents a logic 0.
noise
undesired current or voltages that occur in a circuit.
baud
unit of transmission rate, modulation rate or symbol rate and reciprocal of time of one output signaling element.
Carson's rule
bandwidth of FM signal can be determined using the ______________________.
pulse-amplitude modulation/PAM
bandwidth required for the transmission is very large in comparison to the maximum frequency present in the modulating signal.
quality factor
by controlling the__________________ of the resonant circuit, you can set the desired selectivity.
computer networks
can be classified in two different ways: broadcast and point to point.
IF amplifier
can provide a gain in the 10- to 30-dB range, they provide higher selectivity, require no tuning or adjustment and smaller compared to LC tuned circuits.
transceivers
circuits that can transmit and receive signals.
true
[TRUE OR FALSE] in free space, the speed of a radio wave is equal to the speed of light.
true
[TRUE OR FALSE] the change of air density causes refraction.
width
______________ of each pulse is made proportional to the amplitude of the signal at that instant.
position
_______________ of each pulse, in relation to the position of a recurrent reference pulse is varied by each instantaneous sampled value of the modulating wave
analog signal
__________________ is sampled and converted to a sequence of parallel binary words by an A/D (analog-todigital) converter.
antenna gain
____________________ is inversely proportional to beamwidth.
information bit
a basic unit of data/message used in digital communications.
AM signal
a composite of several signal, namely the carrier and the two sidebands, with each producing power in the antenna.
QAM/quadrature amplitude modulation
a form of digital modulation similar to PSK except the digital information is contained in both the amplitude and the phase of the transmitted carrier.
binary phase shift keying/BPSK
a form of square-wave modulation of a continuous wave (CW) signal.
carrier
a high-frequency signal, usually a sine-wave generated by an oscillator.
amplitude modulation
a modulation technique in which the modulating signal varies the amplitude of a sinusoidal carrier signal.
star topology
a multipoint circuit comprised of many two-point circuits where each remote station communicates directly with a centrally located computer.
bus topology
a multipoint data communications circuit that makes it relatively simple to control data flow between and among the computers because this configuration allows all stations to receive every transmission over the network.
ring topology
a multipoint data communications network where all stations are interconnected in tandem (series) to form a closed loop or circle.
reflector
a passive device that simply reflects the energy radiated by the feed mechanism into a concentrated highly directional emission in which the individual waves are all in phase with each other.
transmitting antenna
a takes a voltage from the transmitter and converts it to an electromagnetic signal.
loudspeaker
a transducer which changes electrical signal into sound signal.
full duplex
a two-way communication system where both parties can talk and listen simultaneously.
half duplex
a two-way communication system, but applies alternating direction.
decibels
a unit of measurement of the human hearing response.
marconi antenna
a very simple antenna which has uniform radiation in all directions is formed by a single vertical element insulated from ground.
receiver
accepts the transmitted signal from the medium and convert it back to a form understandable by human.
antenna
acts as the interface between a transmitter or receiver and free space.
hub
acts like a multipoint connector and also have store-and-forward capabilities, enabling them to handle more than one message at a time.
channel encoder
adds redundancy to facilitate error recovery after transmission.
broadcast
all stations and devices on the network share a single communications channel.
point to point
all transmissions from one station are intended for and received by the other station.
electric field
also an invisible force field produced by the presence of a potential difference between two conductors.
radio waves
also called an electromagnetic wave and made up of both electric and magnetic fields.
squelch circuit
also called muting circuit. it is used to keep the receiver audio turned off until an RF signal appears at the receiver input.
shape factor
also defined as the ratio of the 60-dB-down bandwidth to the 6-db-down bandwidth of a tuned circuit or filter.
dipole antenna
also formally known as the Hertz antenna.
digital amplitude modulation/DAM/on-off keying/OOK
also known as ASK/amplitude shift keying.
reflection
also produced by other partially conductive surfaces, such as the earth and bodies of water.
marconi antenna
also used as a whip antenna for mobile applications (police, taxi) because of its simplicity and omnidirectional pattern.
shot noise
also white noise in that is contains all frequencies and amplitudes over a very wide range.
AM signal
amplified by a power amplifier and is fed to the antenna.
pulse-position modulation/PPM
amplitude and width of the pulses is kept constant in this system.
PSK/phase shift keying
an M-ary digital modulation scheme similar to conventional phase modulation except with this, the input is binary digital signal and there are limited numbers of output phases possible.
modulation
an electronic method for transmitting information from a place to another.
magnetic field/magnetic flux
an invisible force field created by a magnet.
PSK/phase shift keying
another form of angle-modulated, constant amplitude digital modulation.
narrowband FM
any FM system in which the modulation index is less than 𝜋/2.
extraterrestrial noise
classified to as solar and cosmic which comes from the sources in space.
external noise
comes from sources which we have little or no control.
reflection
any metallic object on a transmission path, such as building parts, water towers, automobiles, airplanes, and even power lines, causes some ________________.
far field
approximately 10 wavelengths from the antenna is the radio wave with the composite electric and magnetic fields.
sidebands
are new signals at different frequencies generated whenever a carrier is modulated by an information signal.
data communications networks
are systems of interrelated computers and computer equipment.
180
as the input digital changes state, the phase of the output carrier shifts between two angles that are separated by _____ᵒ.
serial data
at the receiving end of the system, the ________________ is shifted into a shift register.
pulse modulation
consists essentially of sampling analog information signals and then converting those samples into discrete pulses and transporting the pulses from a source to a destination over a physical transmission medium.
dipole antenna
consists of two pieces of wire, rod, or tubing that are one-quarter wavelength long at the operating resonant frequency.
transport layer
controls and ensures the end-to-end integrity of the data message propagated through the network between two devices, which provides for the reliable, transparent transfer of data between two endpoints.
superheterodyne receivers
converts all incoming signals to a lower frequency, known as the intermediate frequency (IF) wherein the incoming signal is mixed with a local oscillator signal to produce the conversion.
transmitter
converts the electrical signal to a suitable signal for transmission over a medium.
source encoder
converts the message signal into a sequence of bits.
demodulator
converts the signal back to a form understandable by human.
FM waveform
created by a frequency deviation (fd) which is proportional to the voltage of the modulating signal at a given instant.
FSK/frequency shift keying
form of constant-amplitude angle modulation similar to standard frequency modulation (FM) except the modulating signal is a binary signal that varies between two discrete voltage levels rather than a continuously changing analog waveform.
information capacity
function of bandwidth and transmission time, where the carrier amplitude remains constant.
RF stage
generally contains two or three RF amplifiers. these amplifiers are tuned RF amplifiers, they have variable tuned circuit at the input and output sides.
magnetic field/magnetic flux
generated around a conductor when current flows through it.
receiving antenna
has a voltage induced into it by the electromagnetic signal that passes across it.
pulse-position modulation/PPM
has the advantage of requiring constant transmitter power output, but the disadvantage of depending on transmitter-receiver synchronization.
point to point
have only two stations and no addresses needed.
fiber optics
have the capacity to carry much more information than their metallic counterparts or, for that matter, even the most sophisticated wireless communications systems.
AGC circuit
help maintain a constant output voltage level over a wide range of RF input signal levels, they also help the receiver to function over a wide range so that strong signals do not produce performance-degrading distortion.
horizontally polarized
if an electric field is parallel to the earth, the electromagnetic wave is said to be _____________________.
shadow zone
if an obstacle appears between a transmitter and receiver, some of the signal is blocked, creating a _________________.
vertically polarized
if the electric field is perpendicular to the earth, the wave is ________________.
polarities
in any given time, the wires have opposite ________________.
pulse-code modulation/PCM
in this method of pulse modulation, pulses are of fixed length and fixed amplitude.
pulse-position modulation/PPM
in this method of pulse modulation, transmitter must send synchronizing pulses to operate timing circuits in the receiver.
16-QAM
in this method, both the phase and the amplitude of the transmit carrier are varied
ASK/amplitude shift keying
in this system, binary information signal directly modulates the amplitude of an analog carrier.
multidrop/linear bus
other terms for bus topology.
network architectures
outline the products and services necessary for the individual components within a data communications network to operate together.
shift register
parallel binary output is converted to a serial signal by a __________________.
demodulator
performs signal processing; produces bit estimates to be feed to the channel decoder.
antenna
picks up the weak radio signal and feeds it to the RF amplifier or also called low-noise amplifier (LNA).
bandwidth
portion of electromagnetic spectrum occupied by a signal.
source decoder
processes the estimated information bits to obtain an estimate of the message.
channel decoder
processes the imperfect bit estimates from the demodulator.
RF amplifier
processes the very weak input signals, increasing their amplitude prior to mixing. it also minimizes oscillator radiation.
internal noise
produced by electronic components in a receiver circuit such as resistors, diodes, transistors, etc.
industrial noise
produced by manufactured equipment, such as automotive ignition systems, electric motors and generators.
network layer
provides details that enable data to be routed between devices in an environment using multiple networks, subnetworks, or both.
parabolic reflector antenna
provides extremely high gain and directivity and are very popular for microwave radio and satellite communication links.
presentation layer
provides independence to the application processes by addressing any code or syntax conversion necessary to present the data to the network in a common communications format.
pulse-amplitude modulation/PAM
pulses are then sent by either wire or cable, or else are used to modulate a carrier.
transmitter efficiency
FM signals have constant amplitude, and it is therefore not necessary to use linear amplifiers to increase their power level.
RF stage
The desired signal is selected in the antenna but since it is very weak, it is amplified by the radio frequency (RF) amplifier in the ________________.
point to point
data are often transmitted in long, continuous messages, sometimes requiring several hours to send.
frames/blocks/packets
data are propagated through the network in relatively short messages sometimes called ________________.
antenna bandwidth
defined as the frequency range over which antenna operation is "satisfactory".
selectivity
defined as the measure of the extent to which a receiver can differentiate between the desired information signals and disturbances or information signal at other frequencies.
sensitivity
defined as the receiver's ability to amplify weak signals, defined in terms of voltage which must be applied at the receiver input terminals to provide a standard output power measured at the output terminals.
logical topology
describes how data actually flow through the network.
network topology
describes the layout or appearance of a network, and how the network is actually laid out.
near field
describes the region directly around the antenna where the electric and magnetic fields are distinct.
bandwidth
determines the maximum speed of data pulses the medium can handle; expressed in Hz.
OSI/open systems interconnection
developed to facilitate the intercommunications of data processing equipment by separating network responsibilities into seven distinct layers.
knife-edge diffraction
diffraction is sometimes called as _____________________.
A/D converter
each time a sample is taken, an 8 bit word is generated by the ______________________.
sensitivity
essentially determined by the noise level encountered in the receiver. can be expressed as signal-to-noise ratio (SNR), noise factor (NF), or SINAD. it can also be expressed as microvolt level of input signal.
mesh topology
every station has a direct two-point communications link to every other station on the circuit and sometimes called fully connected.
pulse-width modulation/PWM
fixed amplitude and starting time of each pulse.
reflection
follows the principles of light wave reflection; the angle of reflection is equal to the angle of incidence.
yagi-uda antenna
is a linear array consisting of a dipole and two or more parasitic elements: one reflector and one or more directors.
network architecture
is a set of equipment, transmission media, and procedures that ensures that a specific sequence of events occurs in a network in the proper order to produce the intended results.
data communications network
is any system of computers, computer terminals, or computer peripheral equipment used to transmit and/or receive information between two or more locations.
optical communications system
is one that uses light as the carrier of information.
session layer
is responsible for network availability (i.e., data storage and processor capacity). it provides the logical connection entities at the application layer.
total transmitted power
is simply the sum of the carrier power (Pc) and the two power in the two sidebands PUSB and PLSB.
application layer
is the highest layer in the hierarchy and is analogous to the general manager of the network by providing access to the OSI environment.
antenna
is where the signals from different sources such as stations are present.
sidebands
it is said that in any modulation process, __________________ are produced.
modulation
it is the process by which an information or intelligence is modified by the carrier.
far field
its strength also diminishes with distance but only at the square of the distance.
pulse-width modulation/PWM
less noise compared to PAM because of its constant amplitude and does not require synchronization between transmitter and receiver.
space
logic 0 frequency.
mark
logic 1 frequency.
glass/plastic
optical fiber communications systems use ______________ fiber cables to "contain" the light waves and guide them in a manner similar to the way electromagnetic waves are guided through a metallic transmission medium.
local oscillator
made tunable so that its frequency can be adjusted over a relatively wide range. as its frequency changed, the mixer translates a wide range of input frequencies to the fixed IF.
modulator
maps the coded bits to be sent to the channel.
pulse-position modulation/PPM
may be obtained from PWM.
antenna reciprocity
means that the characteristics and performance of an antenna are the same whether the antenna is radiating or intercepting an electromagnetic signal.
information capacity
measure of how much information can be propagated through a communications system.
point to point
most basic topology and used in data communications networks that transfer high-speed digital information between only two stations.
percentage of modulation
multiplying the modulation index (m) by 100 gives the __________________________.
star topology
multipoint data communications network where remote stations are connected by cable segments directly to a centrally located computer.
thermal noise
noise that are caused by random motion of free electrons in a conductor through heat.
sidebands
occur in the frequency spectrum directly above and directly below the carrier frequency.
distortion
occurs when the modulation index exceeds one (1) which results to garbled or harsh unnatural sounds in the speaker for voice, while scrambled and inaccurate picture on a TV screen for video.
antenna bandwidth
often expressed as a percentage of the antenna's optimum frequency of operation.
bandwidth efficiency
often used to compare the performance of one digital modulation technique to another.
D/A converter / digital-to-analog converter
once one 8-bit word is in the register, the ___________________ converts it to a proportional analog output.
parallel word
once the conversion is complete, the _______________ from the A/D converter is transferred to the shift register.
circuit complexity
one major disadvantage of FM in the past involved the complexity of the circuits used for frequency modulation and demodulation in comparison with the simple circuits used for AM.
dipole antenna
one of the most widely used antenna types is the half-wave dipole.
simplex
one-way communication; it can send information in one direction only.
pulse-code modulation/PCM
only digitally encoded modulation technique that is commonly used for digital transmission.
m
represents a digit that corresponds to the number of conditions, levels, or combinations possible for a given number of binary variables.
pulse-width modulation/PWM
requires larger bandwidth compared to PAM.
data-link layer
responsible for providing error-free communications across the physical link connecting primary and secondary stations (nodes) within a network (sometimes referred to as hop-tohop delivery).
loop
ring topology is sometimes called as _______________.
pulse-amplitude modulation/PAM
sampled at regular intervals, and each sample is made proportional to the amplitude of the signal at the instant of sampling.
OSI/open systems interconnection
serves as a structural guideline for exchanging information between computers, workstations, and networks.
network
set of devices (sometimes called nodes or stations) interconnected by media links.
transmitted signal
signals that are suitable for transmission.
FSK/frequency shift keying
simple, low-performance type of digital modulation.
ASK/amplitude shift keying
simplest digital modulation technique.
binary phase shift keying/BPSK
simplest form of PSK.
pulse-amplitude modulation/PAM
simplest form of pulse modulation.
hybrid topology
simply combining two or more of the traditional topologies to form a larger, more complex topology. sometimes called mixed topologies.
circular polarization
some antennas produce _______________ in which the electric and magnetic fields rotate as they leave the antenna.
huygen's principle
states that all electromagnetic waves, light as well as radio waves, radiate as spherical wave fronts from a source.
m-ary
term derived from the word binary.
strength and direction
the ____________ and ______________ of the magnetic field depend upon the magnitude and direction of the current flow.
clock and start conversion
the _______________ and __________________ signals are synchronized so that the resulting output signal is a continuous train of binary words.
clock signal
the __________________ is derived from the data to ensure exact synchronization with the transmitted data.
carrier center frequency
the _____________________ (fc) is shifted (deviated) up and down in the frequency domain by the binary input signal
start conversion signal
the _______________________ triggers the S/H (sample-and-hold) circuit to hold the sampled value and starts the A/D converter.
fidelity
the ability of a receiver to reproduce all the modulating frequencies equally and depends on the frequency response of the AF amplifier.
feed mechanism
the active element and houses the primary antenna, which radiates electromagnetic waves toward the reflector.
frequency deviation
the amount of change in carrier frequency produced.
gain
the amplification of a signal; unitless or expressed in dB.
angle of incidence
the angle between the incoming line of the wave and a perpendicular line to the reflecting surface.
angle of reflection
the angle between the reflected wave and the perpendicular line
antenna beamwidth
the angular separation between the two half-power (-3 dB) points on the major lobe of an antenna's plane radiation pattern, usually taken in one of the "principal" planes.
audio amplifier
the audio signal from the demodulator is amplified by the ____________________
audio power amplifier
the audio signal is further amplified by ____________________ up to the desired power level to drive the loudspeaker.
excessive spectrum use
the bandwidth of an FM signal is, in general considerably wider than that of an AM signal transmitting similar information.
modulator
the circuit used for producing AM.
one/1
the clock pulses start shifting the data out ____________ bit at a time.
bandwidth
the difference between the half-power frequencies (difference between the highest and lowest frequencies of operation).
dynamic range
the difference between the minimum input level necessary to discern a signal and the input that will overdrive the receiver and produce distortion.
opposite
the direction of current flow in one wire is always ______________ that in the other wire, therefore the magnetic fields combine
wavelength
the distance of a wave occupied by one cycle; usually expressed in meters or miles.
envelope
the dotted line in the modulated signal.
antenna
the electric field spreads out from conductor to conductor, which is the concept of ______________.
atmospheric noise
the electrical disturbances that occur in the earth's atmosphere, often referred to as static which usually comes from lightning.
multicasting
when messages are intended for a specific group of subscribers, it is called ___________________.
broadcasting
when messages are intended for all subscribers on the network, it is called ___________________.
yagi-uda antenna
widely used antenna that commonly uses a folded dipole as the driven element.
