A presentation on Bandwidth 8/17/1996 D.Geneus

Topics The Electromagnetic Spectrum Signals Signal Bandwidth Channel Bandwidth References

The Electromagnetic Spectrum James maxwell showed that the electric field due to electron motion is accompanied by a magnetic field. The combination of these two fields produce an electromagnetic field that travel through space at the speed of light. Electromagnetic waves can exist from low frequencies to extremely high frequencies. AUDIORADIORADARVISIBLE LIGHTINFRAREDUV-RAYSX-RAYS Frequency in Hz

Signals A time varying event. Signals can be periodic and nonperiodic. A signal can be decomposed into combination of pure tones, called sine waves, at different frequencies. The different sine waves that compose a signal can be plotted as a function of frequency to produce a graph called the frequency spectrum of a signal. Most signals occupy a range of frequencies. This range of frequency is called the bandwidth of the signal. signal graphical representation periodic Square wave Triangular wave Sawtooth wave nonperiodic time amplitude frequency amplitude continuous spectrum

Signal bandwidth Frequencies in the audio spectrum can be heard by the human ear. The ear “hears” by detecting very small changes in air pressure. The frequencies ranging from about 20 Hz to 20,000 Hz are in the audio, or sound spectrum. Telephone speech cover the frequency range from about 300 Hz to 3000 Hz. The bandwidth is about 3,000 Hz. 20 Hz 20,000Hz frequency bandwidth

Bandwidth is defined as the frequency band around the carrier frequency containing 99 percent of the signal power. Amplitude Modulation(AM) is the variation of the amplitude of a radio wave as to carry information. The bandwidth for an individual AM station is about 10,000 Hz. Frequency Modulation (FM) is the variation of the frequency of a radio wave as to carry information. The bandwidth for an individual FM station is about 200,000 Hz. The signal broadcast over the air by a television station has a bandwidth of about 6 MHz. Signal bandwidth frequency bandwidth fc =carrier frequency fc+fm=upper sidebandfc+fm=lower sideband

All Amplitude Modulation(AM) are transmitted within a band of frequencies from 550 KHz to 1,600 KHz. Telephone carriers multiplex 12 telephone channels on a single cable. Each channel requires about 4,000Hz bandwidth. The band of frequencies for telephone carriers is from 60 to 108 KHz. The standard frequency assignments for television stations is as follows: channels 2 through 13 are in the very high frequency(VHF) bands and channels 14 through 83 occupy the ultra high frequency(UHF) bands VHF bands range from 54 MHz to 216 MHz and UHF bands range from 470 MHz to 890 MHz. total bandwidth utilized by total number of channels bandwidth of an individual channel frequency Channel bandwidth 550 KHz1,600 KHz 88 MHz108 MHz AM FM

Introduction to Telecommunication Electronics, second edition, A.Micheal Noll Modern Electronic, Jefferson C. Boyce Eletronic Communications, third edition, Dennis Roddy and John Coolen References