The heart of the unit is an RF assembly built around a proprietary bi-directional RF power sensor designed specifically to cover the 6 GHz bands. The sensor consists of series connected couplers; one senses forward signal strength – the other senses reflected signal strength. Twin leveling-loop circuits keep a pair of detection diodes at fixed potentials, maintaining conduction in each diode's square-law region. The design minimizes modulation error while maintaining a fast response time. Readings from both detection circuits are converted by a microcontroller to generate the display readings. Each frequency band has been independently calibrated at the factory over the -10 to 50 degrees C temperature range and the data stored in the microcontroller's integrated EEPROM.