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Signals and Frequencies

Signals and Frequencies. Zhangxi Lin January 2001. 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. Signals: Time-Domain Concepts.

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Signals and Frequencies

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  1. Signals and Frequencies Zhangxi Lin January 2001

  2. 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

  3. 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)

  4. 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)

  5. 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.

  6. 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

  7. 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

  8. 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)

  9. 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

  10. 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 .

  11. 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

  12. Bandwidth for TV signals

  13. US Frequency Allocation Chart http://www.fair-rite.com/pr09.htm

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