1. Wave Propagation, and Reflections
Transmission Lines
Wave Propagation, and Reflections

2. Electrical Wave Mechanics

3. Notice the reflection at the boundary where mechanical media change!
Mechanical Waves
Notice the reflection at the boundary where mechanical media change!

4. More Mechanical WaveAnalogy
Jelly Babies Wave machine!

5. Old School Demo (still brilliant)
(start at 19 min; 20 min in shows great demo)
The legend Dr. JN Shive from Bell Labs demos wave reflections, inventor of __________ ??

6. Transmission Lines Image credits: Farid Farahmand, UC-Davis;
Wikimedia Commons

7. Transmission Line Model
Distributed inductance
Distributed capacitance

8. Characteristic Impedance
Input voltage V+ causes current I+ to flow in infinitely long line:
Wave propagation speed
zo ~ 50 W
zo ~ 100 W

9. Avoiding Reflections: Impedance Matching
𝜌= 𝑟𝑒𝑓𝑙𝑒𝑐𝑡𝑒𝑑 𝑏𝑎𝑐𝑘𝑤𝑎𝑟𝑑 𝑤𝑎𝑣𝑒 𝑖𝑛𝑐𝑖𝑑𝑒𝑛𝑡 𝑓𝑜𝑟𝑤𝑎𝑟𝑑 𝑤𝑎𝑣𝑒 = 𝑧 𝐿 − 𝑧 𝑜 𝑧 𝐿 + 𝑧 𝑜
Reflection Coefficient
incident zL zs
reflected
Set zL = zo for no reflections

10. Reflections Can Wreak Havoc
Lab/testing action starts at 5 min. First 9 min is brilliant intro to transmission lines