Low pass-below cutoff High pass-above cutoff Bandpass -narrow range Band reject -reject narrow range All pass - all frequency equally

Chapter - 1 Principles Of Communications Flashcards by Paul Castillo

It is the sending , processing and receiving information by Electrical or Electronic means

COMMUNICATION SYSTEM

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Basic Communication System

Transmitter
Transmission Channel
Receiver

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It is the source of information which must be delivered or transmitted to a particular destination over a channel

Converts signal to form more suitable for transmission

Performs ENCODING and MODULATION

Transmitter

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Basic Transmitter Components

Modulator
Amplifier
Oscillator

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It is the destination upon which information from the transmitter is delivered
It is a collection of electronic devices and circuits that accepts the transmitted signals from the trans.medium and coverts to original form

Performs DECODING and DEMODULATION

RECEIVER

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Basic Receiver Components

Demodulator
Amplifier
Output devices
(Speaker,Monitor,Printer)

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It is the path or mediun that the information Travels from the transmitter to the Receiver

ATTENUATION occurs at this point

Transmission Channel

Medium

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Classification of Transmission Media

Guided Media -provide conduit
(Transline , Optical Fiber , Waveguide)

Unguided Media -through Air
(Free space , Earth’s Atmosphere)

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It is electronic circuit which is capable of increasing the signal magnitude or amplitude without altering the signal waveform characteristics

Amplifier

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Q Point of Class A amplifier , Efficiency , Conduction Angle

Active (Linear)
25% or 50%
360deg

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Q Point of Class B amplifier , Efficiency , Conduction Angle

Cutoff
78.5%
180deg

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Q Point of Class AB amplifier

A little above cut-off
Between A and B
180-359 deg

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Q Point of Class C amplifier

Below Cut-off
More than 90%
Less than 180 deg

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Produces a periodic waveform on its output with only DC Supply voltage as input

Non rotating device for producing AC

Can be taught as an amplifier

OSCILLATOR

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Types of Oscillator

LC - for HF
•Hartley - Tapped Coil
•Colpitts - Split Capacitor
•Clapp - additional Capacitor
•Armstrong -tickler coil (transformer)

RC - for LF
•Wien Bridge -lead-Lag Circuit
•Phase Shift Oscillator - Series of RC sections
•Crystal Oscillator

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It is a Frequency Selective Circuit design to pass some frequency and reject others

Filter

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Basic Type of Filter

Low pass-below cutoff
High pass-above cutoff
Bandpass -narrow range
Band reject -reject narrow range
All pass - all frequency equally

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Effect has maximum Flatness response in pass band

Butterworth filter

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Have extremely good selectivity

Chebyshev Filter

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Produce even greater attenuation than chebyshev filter

Cauer Filter

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Provide desired frequency response but have a constant time delay in the pass band

Bessel (thompson) Filter

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The number of times a particular phenomenon occurs in a given period of time

Frequency

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It is the time required for one complete cycle of a repetitive waveform
Reciprocal of Frequency

Period or Time

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waves travel at characteristic speeds depending on the type of wave and the nature of the propagation of the medium

Propagation Velocity

Vp = Vf • C

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Distance between two similar points

Wavelength

Defined as a single valued function of time that conveys information

SIGNAL

These are time varying voltages or currents that are continuously changing such as sine wave and cosine wave

ANALOG SIGNAL

These are voltages or currents that change in discrete steps or levels

DIGITAL SIGNAL

It is the process of extracting information from signal, conditioning a signal from subsequent use. Signal transformation or altering a signal structure

SIGNAL PROCESSING

Simply describe the Frequency Content of the Signal

SPECTRA

The Signal Amplitude is plotted against Time like Oscilloscope

Time Domain Representation

The signal is plotted against frequency like in a Spectrum Analyzer

Frequency Domain Representation

It is also known as -3db bandwidth or half power bandwidth. Which indicated portion of electromagnetic spectrum

Bandwidth

Bandwidth formula

B=F(upper)-F(lower) F(upper) = fr+B/2 F(lower) =fr-B/2 fr=1/2pi(sqrtLC) B(effective) = (pi/2)(B)

These are also known as cutoff points , breakup points, -3dbpoints

Half Power Points

Transmission Modes

* Simplex - one way * Half-Duplex - two-way alternate * Full-Duplex - two-way Simultaneous * Full/Full Duplex - both direction at the same time but different station * Echoplex-more than half duplex but less that full duplex . Used in error detection scheme

Electromagnetic Spectrum Mnemonics

Every Very Very Loving Mom Has Very Understanding Son Except I Inject V Until Xplosive Growth VHS at 3:30 kasi ma galing

Electromagnetic Spectrum Designation is based on the

ITU-R V.431-6: | Nomenclature of the Frequency and Wavelength Bands Used in Telecommunication

Voice Frequency Range

300hz to 3khz

Audio Frequency Range

20hz to 20khz

Electronics Communication System uses frequencies from

VLF to Light Frequencies

Frequencies that lies between VLF to EHF commonly used in wireless communications systems

Radiowaves

Secondary carrier that carry additional modulating signal and itself modulated onto the main carrier

Subcarrier

Too long wavelength to be seen

Infrared

Too short wavelength to be seen

Ultraviolet

A fundamental quantity representing the rate at which energy is used and it is more readily measurable since jt can be converted to heat

Power

One-tenth of a bel

Decibel

Decibel Computations

``` Bel = log(p2/p1) Pdb = 10log(p2/p1) Pdb = 20log(v2/v1) = 20log(I2/I1) Pdbm = 10log(p/1mW) in mili Pdbu = 10log(p/1uW) in micro PdbW = 10log(p/1W) in Watt ```

To convert dbu to dbm

Subtract 30

To convert dbm to db

Subtract 30

To convert dbu to db

Subtract 60

To convert db to dbm

Add 30

To convert dbm to dbu

Add 30

To convert db to dbu

Add 60

Random , Undesirable Electrical Energy that enters the communication system via communicating medium and interferes with the transmitted message

Noise

Is any waveform pertubatikn or deviation caused by imperfect response of the system to the desired signal

Distortion

Any contamination by extraneous or external signals from human sources

Interference

Two main Types of Noise

Uncorrelated and Correlated Noise

Noise is present regardless of wether there is signal present or not

Uncorrelated Noise

Noise is only present when there is a signal

Correlated Noise

Two Main Types of Uncorrelated Noise

External and Internal Noise

Noise coming from outside the environment

External Noise

Also known as Static Noise , caused by lightning discharges

Atmospheric Noise

Consist of electrical signals that originate from outside earth also know as space or deep space noise

Extraterrestrial Noise

It is generated directly from the sun's heat repeats every 11 years like corona and sunspots

Solar Noise

Also known as sky noise , stellar noise or black body noise . It is RF noise generated by distant stars

Cosmic Noise

It is noise other than solar noise and cosmic noise

Galactic Noise

It is also known as man made noise usually between 1-600mhz

Industrial Noise

It is an electrical noise generated within a device or circuit

Internal Noise

Noise associated with random movement of electrons within a conductor Brown si johnson White si gaussian

Thermal Noise

Noise Power

P = ktb

Noise Voltage

Vn = sqrt 4kTBR

Total noise Voltage and Current and Power

Vnt = sqrt (vn1^2 + vn2^2) Int = sqrt (in1^2 + in2^2) Pt = P1 + P2 ....

Random arrival of carriers (holes and electrons) happens in semiconductor

Shot Noise

Noise Current

In = sqrt(2qBI) In = sqrt(2qB(I+2Is))

Also Known as Transistor Noise since it is commonly found in Transistors

Partition Noise

Also Known as Modulation Noise , Flicker Noise , 1/f Noise. Noise Power varies inversely with frequency . Also known as pink noise and it is common in low frequencies

Excess Noise

It is an irregular,random variation produced by any modification to a stream pf carriers as they pass from input to output also known as HighFrequency Noise

Transit Time Noise

Also known as Popcorn Noise which is a low frequency noise found in transistors such as BJTs

Burst Noise

These are large noise spikes present in the avalanche current due to oscillation that result in the avalanching region

Avalanche Noise

Type of noise having a flat spectrum over a defined frequency band

White noise

Noise having a power density that decreases by 3 db per octave

Pink Noise

Noise having a power density that decreases by 6db per octave

Brown or Red Noise

Noise having a power density that increases by 3db per octave

Blue Noise

Noise having a power density that increases by 6db per octave

Violet Noise

It is a noise that sounds the same to the ears regardless of the frequency

Gray Noise

Clashing , displeasing noise

Orange Noise

Background noises of the world

Green Noise

It is a silent noise

Black Noise

Types of Correlated Noise

Harmonic Distortion Intermodulation Distortion Impulse Noise

It is also known as Amplitude Distortion

Harmonic Distortion

Power of a Signal Having Distortion

P=Po(1+THD^2) THD = total harmonic distortion , unitless

Unwanted sum and difference of frequencies when two or more signals are amplified by a non-linear device

Intermodulation Distortion

It consist of sudden burst of irregularly shaped pulses characterized by High Amplitude peaks of Short Duration in the total noise spectrum

Impulse Noise

Occurs when information signals from one source produce frequencies that falls outside their allocated bandwidth and interfere with another source

Interference

It is the ratio of the signal power level to the noise power and it is used to determine the degree of intelligibility of a received signal of a certain system

Signal to Noise Power Ratio ``` S/N = Ps/Pn S/N = 10log(Ps/Pn) ```

3 Figure of Merit

* Noise Factor * Noise Figure * Equivalent Noise Temperature

It is a figure of merit used to indicate how much signal to noise ratio deteriorates as signals passes through a circuit of series of circuits

Noise Factor F= S/N(input)/S/N(output)

Noise Factor Expressed in decibel

Noise Figure NF=10log(F)

It indicate the reduction in the sigbal to noise ratio a signal undergoes as it propagates through a receiver

Equivalent Noise Temperature Teq = Ta(F-1) Ta=290Kelvin (17deg Celsius)

Total Gain in Cascaded Systems

Gt=G1xG2xG3......Gn Gt(db) = G1db+G2db+G3db...+Gndb

Equivalent Noise Temperature Referred to the Input

Teqt=Teq1+(Teq2/G1)+(Teq3/G1G2)+.......

Noise Factor at the Output (friss formula)

Ft = F1+(F2-1/G1)+(F3-1/G1G2)+.......

Equivalent Noise Resistance

Req=R1+(R2/G1^2)+(R3/G1^2G2^2)+......