DATA TRANSMISSION:
The electronic transfer of data from a transmitter to receiver. It’s of two types.
v Guided Transmission. / Direct Link / Point to Point : the transmission path b/w 2 devices in which signals propagate directly from transmitter to receiver with no intermediate devices (except amplifier & repeater etc to increase the strength ) e,g cable media, twisted pair, optical fiber
v Un Guided transmission / In Direct Link / Multipoint : more than 2 devices share the link. e.g. air, water, vacuum
TRANSMISSION MODES:
v Simplex: signals r transmitted only n one direction. One transmitter & one receiver. e.g tv sys, cable, radio
v Half duplex: Either direction, but only one way at a time. e.g. police radio, chatting, wireless.
v Full duplex: Both directions at the same time. e.g. telephone, RADAR.
SIGNALS:
Electric or electromagnetic representations of data.
v Analog / Continuous Signals: in which the signal intensity varies in a smooth way over time.
v Digital / Discrete Signals: Maintains a constant level for some period of time then changes to another constant level…..
X-axis of signals s always t or theta.
F of dig signal s always 0.
TIME DOMAIN: when the X-axis is t
FREQUENCY DOMAIN: when X-axis is f
PERIODIC SIGNALS:
A signal which repeat itself after equal intervals of time & maintains its periodicity is called a periodic signal. Digital signals, radars signals are periodic but signals on telephone are not periodic.
S ( t + T ) = S ( t )à T=Time period , t=any time, S=signals.
S ( 0 + 2min ) = S ( 0 )
S ( 30 + 2min ) = S ( 30 )
Periodic signal is known as Sinusoidal signal. It has sin & cos both
Rad = ∏/ 180 * angle
PARAMETERS OF SINOSIDAL WAVES:
AMPLITUDE:
Max height which a signal can achieve above the reference axis, denoted by A measured in distance unit (m, cm) .
TIME PERIOD:
Total time taken to complete one full cycle denoted by T measured in time unit (s, min)
FREQUENCY:
Num of cycles per unit time denoted by f =1/T, measured in HZ.
WAVELENGTH:
Distance b/w two consecutive crests or two consecutive trough is cal measured in distance length
PEAK TO PEAK VALUE:
Distance b/w max point (peak) & min point (peak) denoted by p-p measured in distance unit.
CO-AXIAL CABLE: