A New RF-dc Substitution Calorimeter with Automatically Controlled Reference Power

A new dual-dry-load calorimeter, incorporating automatically controlled reference dc input power, has been developed at the National Bureau of Standards. The calorimeter will be used as a reference standard at frequencies from dc to 4.0 GHz in the power range of 10 mW to 1 watt. The maxmum measurement uncertainty is 0.26 percent at frequencies below 1 GHz and 0.35 percent at frequencies above 1 GHz. The time required for the measurement system to reach equilibrium is less than two minutes. Construction details and design of the calorimetric and feedback control system are given, along with an error analysis and results of intercomparisons with other standards.