This SWR power meter uses a Bruene bridge directional-coupler and a compensated operational amplifier to provide high-accuracy power measurements, even at very low power levels. Matched OA47 Germanium diodes are used in the Forward and Reflected detectors and the feedback-loop of the op-amp, which compensates for the non-linearity of the detector diodes.
A battery-switch circuit turns on automatically when about 1W of RF is sensed and stays on for 5 seconds after a transmission.
Forward-power metering has a 1 second time-constant peak-hang circuit to indicate true PEP. Reflected-power metering has a 10ms time constant which is a help when dipping the reflected power with an ATU. The Power meter has been extensively tested with a wide range of transceivers and linear amplifiers and works very well.