Elliptical RF Low-pass Filter-Reflectometer

RF Low Pass Filter With DCHere’s a schematic reference for building Elliptical (Cauer) RF Low-pass Filter for FM Amplifier 88-108 MHz. A ninth-order, elliptic, low-pass filter attenuates harmonics generated in the power amplifier. The capacitors for the filter are circuit board pads.

Cauer Elliptic FM Filter

The reflectometer uses printed circuit board traces for micro-strip transmission lines. Transmission line segments (with an impedance of about 82 ohms) on either side of a 50 ohm conductor provide sample voltages representative of the square root of forward and reverse power.

RF Low Pass Output Filter

DC voltages, representative of forward and reflected power to the metering board, where they are processed for power control, metering, and for SWR metering and protection.