Chapter - 1 Principles Of Communications Flashcards
It is the sending , processing and receiving information by Electrical or Electronic means
COMMUNICATION SYSTEM
Basic Communication System
Transmitter
Transmission Channel
Receiver
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
Basic Transmitter Components
Modulator
Amplifier
Oscillator
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
Basic Receiver Components
Demodulator
Amplifier
Output devices
(Speaker,Monitor,Printer)
It is the path or mediun that the information Travels from the transmitter to the Receiver
ATTENUATION occurs at this point
Transmission Channel
Medium
Classification of Transmission Media
Guided Media -provide conduit
(Transline , Optical Fiber , Waveguide)
Unguided Media -through Air
(Free space , Earth’s Atmosphere)
It is electronic circuit which is capable of increasing the signal magnitude or amplitude without altering the signal waveform characteristics
Amplifier
Q Point of Class A amplifier , Efficiency , Conduction Angle
Active (Linear)
25% or 50%
360deg
Q Point of Class B amplifier , Efficiency , Conduction Angle
Cutoff
78.5%
180deg
Q Point of Class AB amplifier
A little above cut-off
Between A and B
180-359 deg
Q Point of Class C amplifier
Below Cut-off
More than 90%
Less than 180 deg
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
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
It is a Frequency Selective Circuit design to pass some frequency and reject others
Filter
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
Effect has maximum Flatness response in pass band
Butterworth filter
Have extremely good selectivity
Chebyshev Filter
Produce even greater attenuation than chebyshev filter
Cauer Filter
Provide desired frequency response but have a constant time delay in the pass band
Bessel (thompson) Filter
The number of times a particular phenomenon occurs in a given period of time
Frequency
It is the time required for one complete cycle of a repetitive waveform
Reciprocal of Frequency
Period or Time
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
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