Making 75Ω Measurements

Use the following procedure to measure 75Ω components with the FieldFox in CAT or NA mode.

1. Use adapters to go from 50Ω to 75Ω. If you are using both ports, you need two adapters. The simplest method is to use a 50Ω to 75Ω adapter such as the Keysight N9910X-846.

2. When using Smith Chart format in NA mode, set the system impedance to 75Ω. To do this: press Meas Setup, Settings, edit the System Z0 to 75.
   Note: System Z0 is changed back to 50 when the FieldFox is Preset.

3. Perform either a QuickCal with 75Ω load or OSL Cal at the desired 75Ω reference plane.  A CalReady (Preset Cal) is NOT accurate for 75Ω measurements.

1. • OSL / Mechanical Cal (highest accuracy)

   • • To adapt from 50Ω to 75Ω, use a 50Ω to 75Ω adapter such as the N9910X-846. The 11852B minimum loss pad can be used but usually results in a less accurate cal. Calibrate in the 75Ω environment.

     • A 75Ω Cal Kit must be used to perform a Cal. On the FieldFox, the following 75Ω Cal Kit choices are presented when a 75Ω connector is selected:

     1. 1. Keysight 85036B / 85036E are Type-N 75Ω Cal Kits

        2. Keysight 85039B is a 3 GHz, Type-F, 75Ω Cal Kit. See Keysight.com webpage. This Cal Kit contains Open and Short standards and the following which can be purchased separately:

           • Two 75Ω Type-N to 75Ω Type-F adapters:

           • • 85039-60013: Type-F (f) to Type-N (m)

             • 85039-60011: Type-F (m) to Type-N (f)

           • Two 75Ω Type-F Loads:

           • • 85039-60004: Type-F (f)

             • 85039-60007: Type-F (m)

1. • QuickCal with 75Ω load

   • • Adapt to 75Ω using an adapter such as the N9910X-846. Do NOT use a minimum loss pad such as the 11852B. QuickCal assumes a coaxial transmission line propagation constant model, as with the N9910X-846 50Ω to 75Ω adapter.  Propagation constants of devices such as minimum loss pads (11852B) or attenuators do not follow the same mathematical function, and therefore cannot be used accurately with QuickCal.

     • You must use a load during a QuickCal, and that load must be 75Ω. Do NOT use a 50Ω load and then adapt to 75Ω. When prompted to Measure Load, connect a 75Ω load. It is NOT optional. There is no cal kit selection. QuickCal math does not require the load specifications. When the load is connected, it assumes no reflections.

     • Once your calibration is complete, you can view the return loss, DTF, or S11 data.

75Ω Cables

• The 11857B cable set consists of two 75Ω cables. Matched cables are NOT necessary and unmatched cables are less expensive than matched cables. Order with option B24 for unmatched cables (male-male, and male-female)

• Individual 75Ω Type-N cables are available as part numbers:

• • 11857-60005 - N(m) - N(m) 75Ω - 24 inches

  • 8120-2409 - N(m) - N(f) 75Ω - 24 inches

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