Verifying 1 mW 50 MHz Power Reference Output SWR

by Charles Sperrazza

Verification of the Standing Wave Ratio (SWR) of the 50 MHz 1 mW output power reference is a key step in performing a calibration of a RF power meter. Higher than desired SWR can impact the amount of power delivered to the load (power sensor), therefore we must know that the SWR is within limits at our reference point. A thermistor power sensor, coupled with a thermistor power meter such as the TEGAM 1830A, can accurately estimate through calculation the SWR of a 50 MHz reference. By utilizing a unique function that most modern power meters do not offer; the 1830A allows the user to change the value of the thermistor mounts terminating resistance. Utilizing this method for measuring source match works well because it presents the source with two distinctly different values of ΓLoad which allows accurate measurement of the power absorbed under two different conditions. This article will explain how we make this SWR measurement with the 1830A thermistor power meter and a thermistor power sensor.