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Can I use a 50 ohm network analyzer to measure 75 ohm devices?

This is generally not recommended since a 50 ohm test set is optimized to measure at 50 ohms. Measuring 75 ohm devices on a 50 ohm test set is not as accurate as measuring on a 75 ohm test set. However, it can be done. Here are the procedures and the caveats.

Method One:

Attach a 50 to 75 ohm pad and calibrate at the 75 ohm plane with a 75 ohm calibration kit with the system impedance set at 75 ohms. The raw directivity is degraded by twice the value of the pad in dB.

Method Two:

Use a 50 to 75 ohm mechanical adapter. Again, calibrate at the 75 ohm plane with a 75 ohm cal kit with the system impedance set at 75 ohms. Mismatch effects will affect the accuracy of the calibration and measurement. The Agilent model 11852B minimum loss pad provides a 50 to 75 ohm impedance matching function from DC to 3GHz. The standard model has a Type-N(f) 50 ohm connector and a Type-N(m) 75 ohm connector. Option 004 provides a Type-N(m) 50 ohm connector, and a Type-N(f) 75 ohm connector.

Revision 2.0 25 January 2000