The Keysight 478A Coaxial Thermistor Mount is a precision RF and microwave power measurement instrument engineered for use with Keysight power meters including the 431, 432, N432A, and 436A. It delivers accurate power readings across a 1 µW to 10 mW range with thermal stability optimized to minimize environmental temperature effects. Each unit is individually calibrated with NIST-traceable calibration factors and effective efficiency data at selected frequencies.
Technical Specifications
Frequency Range & Impedance
• Standard 478A: 10 MHz to 10 GHz
• Option H72/H75/H76: 1 MHz to 1 GHz
• Option H13: 100 kHz to 1 GHz
• 50 Ω impedance; 200 Ω ± 1% operating resistance
Return Loss Performance
Standard 478A VSWR specifications: 10–25 MHz ≤ 1.75 (11.3 dB); 25 MHz–7 GHz ≤ 1.30 (17.7 dB); 7–10 GHz ≤ 1.50 (14 dB). Option H76 (1 MHz–1 GHz) achieves ≤ 1.05 (32.3 dB return loss) at 50 MHz, with ≤ 1.3 performance across other bands.
Power Handling Specifications
• Maximum peak power: 200 W
• Maximum average power: 30 mW
• Maximum energy per pulse: 10 W·µs (≥ 1 kHz PRF); 5 W·µs (< 1 kHz PRF)
– Key Features
• Dual series thermistor pairs (four total) matched to cancel ambient temperature drift
• Thermistor leads mounted on common thermal conductor, isolated from main body to reject external thermal shock
• Field-replaceable thermistor assembly for restoration of zero-set capability post-overload
• Individual calibration with frequency-selective calibration factors traceable to NIST standards
– Typical Applications
RF and microwave power measurement from microwatt to milliwatt levels; precision power characterization across VHF through microwave bands; thermal power detection in standards-referenced measurement systems.
– Compatibility & Integration
Direct interface with Keysight 431, 432, N432A, and 436A power meters. Multiple frequency options enable deployment across extended bands from 100 kHz to 10 GHz.
