What is the fixed output impedance of digital TDRs?

Digital Time Domain Reflectometers (TDRs) are essential tools used for measuring the impedance and identifying faults in transmission lines, such as coaxial cables and twisted pairs. The fixed output impedance of digital TDRs is typically standardized to 100 Ω. This standardization is important because it allows TDRs to provide accurate measurements and effective reflections from the cable being tested.

When facing a transmission line, if the TDR has an output impedance that matches the characteristic impedance of the line, the reflections will be minimized and the readings will be accurate. In many telecommunications and networking applications, a 100 Ω impedance is commonly found, particularly in balanced cabling systems like twisted pair used in Ethernet and other communication standards. This is why the fixed output impedance of digital TDRs is set at 100 Ω to ensure compatibility and precise measurements in these environments.