Digital RF Wattmeter with LC Display

Any radio amateur knows the importance of an accurate RF power meter. A wattmeter can be used to measure gain in amplifiers, bandwidth in filters, field strength from antennas, transmitter power, SWR, return loss and many other things.This RF wattmeter uses an AD8307 to measure the power level. The AD8307 front end circuit is both frequency compensated and optimised for return loss to give optimum input SWR over a wide frequency range. A pre-programmed microcontroller type PIC16F876 with built-in 10-bit analogue to digital converters is used to convert the analogue voltage output from the AD8307 into digital values. Next, a set of lookup tables are used to convert the dBm values into RF voltage and RF power (watts).

Capacitor C2 is missing from the circuit diagram. It should be connected between junction C1/R6/R7 and pin 8 (INP) of IC1. The capacitor at pin 1 of IC1 should be labelled C3, not C2.