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 > 1/10 th 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:

14. 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

15. 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

16. Broadband Can also refer to multiple sub-channels of data on one main channel TDMAFDMACDMA