Leandro.minon@gmail.com-PRINCIPLES OF COMMINICATION (prelims)
Extremely Low Frequencies- AC power distribution signals (30-300hz)
Voice Frequencies-human speech (300hz-3khz)
Very Low Frequencies- upper end of human hearing range, for submarine communications, government
and military systems (3khz-30khz)
Low Frequencies- marine and aeronautical navigation (30-300khz)
Medium Frequencies- commercial AM radio broadcasting (300khz-3Mhz)
High Frequencies- referred as short waves, two-way communication, amateur radio and citizens band
(3Mhz-30Mhz)
Very High Frequencies- mobile radio, marine and aeronautical communications, FM radio broadcasting
(30Mhz-300Mhz)
Ultra High Frequencies- commercial television broadcasting, land mobile communications services,
cellular phones, radar and navigation systems, microwave and satellite radio systems (300Mhz-3Ghz)
*1Ghz and above- microwave frequencies
Superhigh Frequencies- majority used for microwave and satellite radio communications systems (3Ghz30Ghz)
Extremely High Frequencies- seldom used for radio communications, very sophisticated, expensive
(30Ghz-300Ghz)
Infrared- electromagnetic radiation associated with heat, heat-seeking guidance systems, electronic
photography, astronomy (0.3Ghz-300Thz)
Visible Light- electromagnetic frequencies visible, optical fiber systems (0.3Phz-3Phz)
Communication- transfer of information
Information
*Analog- human voice
*Digital- computer data
ADC (Analog to Digital)- better transmission
TV plus- DAC (Digital to Analog)
Means of Transfer:
*Wired- physical, fiber optics (copper cable- electrical signal; fiber optics- light signal)
*wireless- atmosphere (electromagnetic: electric field, magnetic field)
3 components:
*transmitter (encoding, modulation, multiplexing)
*channel or medium (means of transfer, conversion for compatibility)
*receiver (decoding, demodulation, demultiplexing)
HARTLEY’S LAW: I=B x t (Information is DIRECTLY PROPORTIONAL to the product of bandwidth and
time)
*I- information
*B- bandwidth
*t- time
Frequency- number of cycles per unit time seconds
Wavelength- distance occupied by one cycle
*wavelength= c/frequency (c=3x10^8, speed of light; wavelength being inversely
proportional to frequency)
*bandwidth=f(max)-f(min)
Types of Communication:
*Simplex (one-way)- TV broadcast, radio
*Duplex (two-way)
-Half Duplex (alternate)- walkie-talkie
-Full Duplex (simultaneous)- telephone, cellphone
Transceiver- single unit
AM broadcast- 535kHz to 1605kHz
FM broadcast- 88MHz to 108MHz
Decibel (dB)- means of comparing two powers
P (input)- always reference
Case 1- gain
Case 2- loss
Case 3- neither gain or loss (value is always ZERO)
Three types of gain:
*Power gain
*Voltage gain
*Current gain
Noise- undesired signal, random and periodic, tends to interfere the proper and easy reception of the
signal
*Correlated Noise (if there is an information): harmonic distortion, intermodulation
distortion
*Uncorrelated Noise (regardless whether there is a signal or none):
-- external: atmosphere noise, extra-terrestrial noise (solar, cosmic), industrial
noise/ man-made noise
--internal: thermal noise, shot noise, transit-time noise
P=kTB (thermal and shot noise is the product of temperature, Boltzmann’s constant, and bandwidth)
*temperature in Kelvin