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The HP 8721A Directional Bridge is used for making transmission and reflection measurements from 100kHz to 110MHz. It is intended for use with the HP 8601A Generator Sweeper and the HP 8407A Network Analyser.

The original cost was $200 in 1980 and was part of the 11652A Reflection Transmission Kit which cost $475 in 1980. A HP Manual was downloaded from the web.

On one side, connections for Reflection measurements.

Functionally similar to a directional coupler.

On the other side, connections for Power Monitoring.

Functionally similar to a power splitter.

Frequency Response: 100kHz to 110MHz ±0.5dB
Impedance: 50Ω
Load Port VSWR: <1.063 (30dB Return Loss)
Directivity: >40dB 1MHz to 110MHz, >30dB 100kHz to 1MHz
Coupling: 6dB ±0.6dB
Transmission: 6dB ±0.2dB Insertion Loss
Maximum Input Power: +20dBm
Connectors: BNC female

April 2008

Bought the unit (no S/N) on eBay FR. Initial tests are ok. Measurement techniques are described in the HP 8721A Manual and the HP Application Note 121-1 "RF Network Analysis with the HP 8407A".

August 2019 
All the 8407A & 8410C based Network Analyser System, including the 8721A, has now been Sold.