HP 8721A OPT. 008 75 Ohm Directional Bridge RF Reflectometer BNC

HP 8721A OPT. 008 75 Ohm Directional Bridge RF Reflectometer BNC

The HP 8721A OPT. 008 is a passive 75 ohm directional bridge used to separate incident and reflected RF signals on a transmission line. Option 008 configures the bridge for 75 ohm impedance environments, making it suited for cable television, broadcast, and RF distribution systems that use 75 ohm coaxial infrastructure. The device provides 6 dB coupling on both the incident and reflected ports via BNC connectors.

Specifications & What's Included

• Model: HP 8721A OPT. 008
• Manufacturer: Hewlett-Packard
• Type: Directional Bridge (passive RF reflectometer)
• Impedance: 75 ohm
• Option: OPT. 008 (75 ohm configuration)
• Coupling Factor: 6 dB (incident port); 6 dB (reflected port)
• Labeled ports: SOURCE, LOAD, INCIDENT, REFLECTED
• Connector Type: BNC (all four ports)
• Form Factor: Compact octagonal inline passive device
• Bridge only — no cables, adapters, or accessories included

Applications

Directional bridges like the HP 8721A are used in RF test setups to measure return loss, VSWR (voltage standing wave ratio), and reflection coefficients on 75 ohm transmission lines and components. The 8721A is designed to work with scalar network analyzers and power meters — the SOURCE port connects to the RF signal source, the LOAD port connects to the device under test, and the INCIDENT and REFLECTED ports feed detectors or meters to compare forward and reflected power. This 75 ohm variant (OPT. 008) was commonly used in CATV system testing, broadcast RF plant maintenance, and laboratory characterization of 75 ohm components such as splitters, amplifiers, and cable runs. Hewlett-Packard produced the 8721-series directional bridges as accessories for its scalar measurement systems, particularly the 8757-series scalar network analyzers, during the 1980s and into the 1990s.