Signals and Frequencies

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Signals and Frequencies

• Zhangxi Lin
• January 2001

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Frequencies

• DC - Direct Current
• AC - Alternating Current
• 60 Hz (cycles)
• sine wave (analog)
• Sound (20 hz through 20,000 hz)
• 1,000 hz 1 khz

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Signals Time-Domain Concepts

• Signal travels with a velocity v (18,600
  miles/sec or 300,000 km/sec).
• Periodic signal
• peak amplitude (A)
• frequency (f)
• period (T 1/ f)
• phase (?)
• wave length (? vT)

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Signals Frequency-Domain Concepts

• S(t) sin(2?ft) 1/3 sin (2 ?(3f)t)
• Fundamental frequency f
• Second frequency 3f
• Spectrum (f-3f)
• Bandwidth (3f - f 2f)

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Analog Signals

• Audio signals
• 20 Hz-20 kHz
• Telephone channel bandwidth 4000 Hz with 300-3400
  Hz for voice bandwidth.
• Video signals
• TV receiver 483 lines and 30 scans per second.
  In the US 525 lines are used with 42 are lost
  during vertical retrace.
• Frequency is 525 X 30 15,750 lines/sec
• A bandwidth of 4 MHz is needed. The standard
  bandwidth is 6 MHz including guardband.

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Transmission Impairments

• Guided media, such as twisted pair cable, coaxial
  cable, and optical fiber
• Attenuation signals get weaker
• Delay distortion (different velocities of
  frequencies)
• Noise
• Wireless transmission
• Free-space loss (distance effect)
• Atmospheric absorption (
• Multipath (signals from direct and reflected
  path)
• Refraction (waves are bent and change the
  distance)
• Thermal noise

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Electro-magnetic Spectrum

• 30-300 Hz 10-1Mm .....ELF (extremely low
  frequency)
• 300-3000 Hz ....................1Mm-100 km
• 3-30 kHz 100-10 km ...........VLF
• 30-300 kHz 10-1 km .............LF
• 300-3000 kHz 1 km-100 m ....MF

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Electro-magnetic spectrum

• 3-30 MHz 100-10 m ...................HF
• 30-300 MHz 10-1 m .................VHF
• 300-3000 MHz 1 m-10 cm .......UHF
• 3-30 GHz 10-1 cm ...................SHF (super
  high frequency)
• 30-300 GHz 1 cm-1 mm .......... EHF (extremely
  high frequency)

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Radar bands

• 1-2 GHz ............30-15 cm ....L Band
• 2-4 GHz ...........15-7.5 cm.....S Band
• 4-8 GHz ........7.5-3.75 cm.....C Band
• 8-12 GHz ......3.75-2.50 cm... X Band
• 12-18 GHz ......2.5-1.67 cm...Ku Band
• 8-27 GHz .....1.67-1.11 cm....K Band

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Radar Bands - cont.

• 27-40 GHz 1.11 cm-7.5 mm .Ka Band
• 40-75 GHz...............................V Band
• 75-110 GHz............................W Band
• 110-300 GHz ......................mm Band
• 300-3000 GHz...................u mm Band
  .

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Satellite TV bands

• S-Band 1700-3000 MHz
• C-Band 3700-4200 MHz
• Ku1-Band 10.9-11.75 GHz
• Ku2-Band 11.75-12.5 GHz (DBS)
• Ku3-Band 12.5-12.75 GHz
• Ka-Band 18.0-20.0 GHz

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Bandwidth for TV signals
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US Frequency Allocation Chart
http//www.fair-rite.com/pr09.htm