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Sept. 20, 2006

Sept. 20, 2006. NTEN 216 David Williams. Transmission Line Review. impedance: measure of the opposition to a time varying current Transmission line: 2 adjacent conductors with a length > 1/10 th the wavelength of signal through wire. Transmission Line Review. Characteristic Impedance

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Sept. 20, 2006

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  1. Sept. 20, 2006 NTEN 216 David Williams

  2. Transmission Line Review • impedance: measure of the opposition to a time varying current • Transmission line: 2 adjacent conductors with a length > 1/10th the wavelength of signal through wire

  3. Transmission Line Review • Characteristic Impedance • Instantaneous opposition to current for a given voltage on a particular wire/cable/trace • A given type of wire/cable will have characteristic impedance that is the same across all instances of that type (e.g., 50 ohm coax cable)

  4. Signal Reflections • Reflections in transmission lines occur due to change of impedance • Cable-cable • cable-connector • Open ended cable • Shorted cable • Change of geometry

  5. Time Domain Reflectometry • Transmitted pulse hits discontinuity and reflects back • Nature of reflection can tell you characteristic of impedance change • Time to reflection can tell you distance to impedance change • Lab results on long cable

  6. Voltage Standing Wave Ratio • Due to reflections occurring with sine wave signal • VSWR = (Maximum Constructive Interference)/(Maximum destructive interference) =V(incident wave) + V(reflected wave) /V(incident wave) – V(reflected wave)

  7. Time and Frequency Domain • Two points of view to analyze signals • Time = 1/freq. Freq = 1/time

  8. Time Domain • Description of signal with respect to time • Example: oscilloscope

  9. Frequency Domain • Description of frequencies contained in a signal • Example: spectrum analyzer

  10. Fourier Transform • Converting from Time Domain to Frequency Domain and Back Again • Any periodic signal can be broken into an infinite series of sine waves of increasing frequency • Example:

  11. Bandwidth • Defn#1: The amount of data that can be sent through a channel (more accurate term for this is Information Capacity) • Defn#2: The number of frequencies that a signal has or that a system can support (EE definition) • BW = upper frequency – lower frequency

  12. Important Terms • Baseband: Signal or system whose frequency range starts at 0 hertz • Narrowband: signal/system taking up relatively little bandwidth • Broadband: signal/system taking up relatively a lot of bandwidth • Passband: a portion of frequency spectrum between an upper and lower value

  13. Broadband • Can also refer to multiple sub-channels of data on one main channel • TDMA • FDMA • CDMA

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