ICSA341 (Updated 12/2001)1 Electromagnetic Signals Signals –Analog (signal intensity varies smoothly over time) Analog signals can have any value in a range. –Digital (constant level over time, followed by a change to another constant level) Digital signals have a limited number of values.

ICSA341 (Updated 12/2001)2 Analog Signals

ICSA341 (Updated 12/2001)3 Digital Signals

ICSA341 (Updated 12/2001)4 Periodic - consists of continuously repeating pattern and completes the pattern within a measurable time frame. A sine wave is the simplest periodic signal. Aperiodic - a signal with no repetitive pattern & can be decomposed into an infinite number of periodic signals Signals - periodicity

ICSA341 (Updated 12/2001)5 time (sec) amplitude (volts) 1 cycle frequency (hertz) = cycles per second phase difference Periodic Analog Signals represented by sine waves

ICSA341 (Updated 12/2001)6 Units Frequency –Hertz(Hz) = 1 Hz –Kilohertz(KHz) =10 3 –Megahertz(MHz =10 6 –Gigahertz(GHz) =10 9 –Terahertz(THz)=10 12 Period –Second(s) = 1 s –Millisecond(ms)=10-3  s)=10 -6 –Microsecond(  s)=10 -6 –Nanasecond(ns)=10 -9 –Picosecond(ps)=10 -12

ICSA341 (Updated 12/2001)7 Time vs Frequency Plots Time Domain Plot - Changes in Amplitude with respect to time. Frequency Domain Plot shows relationship of Maximum amplitude vs frequency

ICSA341 (Updated 12/2001)8 Time vs Frequency Plots

ICSA341 (Updated 12/2001)9 Electromagnetic Signals Signals are complex Spectrum (range of frequencies) -the spectrum of a signal is the collection of all the component frequencies it contains Bandwidth is the width of the frequency spectrum (highest frequency-lowest frequency)

ICSA341 (Updated 12/2001)10 Complex Signals

ICSA341 (Updated 12/2001)11 Digital Signals represented by square waves or pulses time (sec) amplitude (volts) 1 cycle frequency (hertz) = cycles per second

ICSA341 (Updated 12/2001)12 Electromagnetic Spectrum for Transmission Media