14-11-2012, 04:19 PM
Transmission Fundamentals
Transmission Fundamentals.ppt (Size: 241 KB / Downloads: 26)
Electromagnetic Signal
Function of time
Can also be expressed as a function of frequency
Signal consists of components of different frequencies
Time-Domain Concepts
Analog signal - signal intensity varies in a smooth fashion over time
No breaks or discontinuities in the signal
Digital signal - signal intensity maintains a constant level for some period of time and then changes to another constant level
Periodic signal - analog or digital signal pattern that repeats over time
Period (T ) - amount of time it takes for one repetition of the signal
T = 1/f
Phase () - measure of the relative position in time within a single period of a signal
Wavelength () - distance occupied by a single cycle of the signal
Or, the distance between two points of corresponding phase of two consecutive cycles
Time vs. Distance
When the horizontal axis is time, as in Figure 2.3, graphs display the value of a signal at a given point in space as a function of time
With the horizontal axis in space, graphs display the value of a signal at a given point in time as a function of distance
At a particular instant of time, the intensity of the signal varies as a function of distance from the source
Frequency-Domain Concepts
Fundamental frequency - when all frequency components of a signal are integer multiples of one frequency, it’s referred to as the fundamental frequency
Spectrum - range of frequencies that a signal contains
Absolute bandwidth - width of the spectrum of a signal
Effective bandwidth (or just bandwidth) - narrow band of frequencies that most of the signal’s energy is contained in
Data Communication Terms
Data - entities that convey meaning, or information
Signals - electric or electromagnetic representations of data
Transmission - communication of data by the propagation and processing of signals