Keysight 478A – Coaxial Thermistor Mount

• Designed to measure microwave power from 1μw to 10 MW
• The design of the mount minimizes effects from environmental temperature changes during measurement
• Can be used over a 10 MHz to 10 GHz frequency range
• Throughout the range, coaxial input terminates in a 50Ω impedance, with an SWR of not more than 1.75 without external tuning
• Please see below for information regarding options and specific ranges

The Keysight model 478A coaxial thermistor mount is designed for use with Keysight N432A or 432A power meters to measure microwave power from 1μw to 10 MW. The design of the mount minimizes adverse effects from environmental temperature changes during measurement. For increased measurement accuracy, Effective Efficiency and Calibration Factor are measured for each mount, and at selected frequencies across the operating range; the results are marked on the label of the instrument. Model 478A can be used over the 10-HMZ to 10-GHz frequency range. Throughout the range, the mount terminates the coaxial input in a 50Ω impedance and has an SWR of not more than 1.75 without external tuning.

Each mount contains two series pairs of thermistors, which are matched to cancel the effects of drift with ambient temperature change. Thermal stability is accomplished by mounting the leads of all four thermistors on a common thermal conductor to ensure a common thermal environment. This conductor is thermally insulated from the main body of the mount so the thermal noise or shocks applied externally to the mount, such as those handling the mount manually, cannot significantly penetrate to disturb the thermistor. This thermal immunity enables the thermistors to be used in the measurement of microwave power down to the microwatt region.

Keysight offers several options for the 478A. Each of the part numbers listed below is clickable and will open documentation for that option in a new window. These options can also be ordered from the accessories section above.

• 478A-H55 – 1MHz to 1GHz, max SWR 1.3
• 478A-H63 – 100kHz to 1GHz, max SWR 1.8 to 300kHz, 1.3 to 1GHz
• 478A-H72 – 1MHz to 1GHz, max SWR 1.2
• 478A-H73 – 1MHz to 100MHz, max SWR 1.1 except 1.05 at 50MHz
• 478A-H75 – 1MHz to 1GHz, max SWR 1.3 except 1.05 at 50MHz
• 478A-H76 – 1MHz to 1GHz, max SWR 1.3 except 1.05 at 50MHz. Std lab cal at 50MHz
• 478A-H83 – 1MHz to 1GHz, SWR 1.05 at 50MHz. Std lab cal 1, 3, 10, 30, 50, 100, 300, 1000 MHz
• 478A-H93 – 1MHz to 1GHz, max SWR 1.3 except 1.05 at 50MHz. Std lab cal at 50MHz and 100MHz
• 478A-H13 – 100KHz to 1GHz, max SWR 1.8 to 300KHz, 1.3 to 1GHz, std lab cal at 13 frequencies