Impedance Mismatches & Return Loss
The Echoes that Destroy Data
The Reflection Coefficient
When a signal traveling along a 100-ohm cable hits a 110-ohm connector, some energy is reflected. The Reflection Coefficient () describes how much energy 'bounces'.
VSWR: Voltage Standing Wave Ratio
In RF engineering, the 'echo' interferes with the outgoing signal, creating stationary high and low voltage points on the cable. This is called a Standing Wave. A high VSWR (e.g., 3:1) can physically damage the transmitter's power amplifier by dumping its own energy back into itself as heat.
TDR: Time Domain Reflectometry
We find these mismatches using a TDR. By sending a pulse and measuring the time it takes for the 'echo' to return, we can pinpoint the exact distance (in meters) to the damaged part of the cable or the bad connector.
TDR Simulator
Time-Domain Reflectometer Analysis
return_loss: 11.1 dB
A TDR sends a fast electrical pulse. When it hits a change in impedance (like a break or a short), some energy bounces back. If the cable is Open, the reflection is in-phase (up). If it's a Short, it's out-of-phase (down). By measuring the time delay, we know exactly where to dig or which connector to replace.
Conclusion
Impedance is about continuity. Any break in the physical symmetry of the cable is a potential point of failure for high-speed data.