Digitalizing an SWR-Meter

One of the common problems of Power/SWR meters is the totally false measurement in SSB mode. Even in setting "peak" these instruments are far away from the real values, they show a value which is much lower (about 1/4 to 1/2 of the real value) which is useless. Real values are only displayed in FM or CW mode.

To solve this problem I have built an digital instrument for measuring of the peak values. The real effective power value is then calculated by software and display on a blue LC-display.

My implementation is based on a Vectronics PM-30 which has a reasoably good directional coupler.

The original mechanical instrument has been repalced with the home-brew digital display:


This is the PCB with the micro controller and other components:


Very important is the separation of input wires and the digital electronic with inductors and capacitors.

This circuit works perfectly. When I talk to the microphone in SSB mode this instrument shows immediately the maximum output power and SWR.

This is the complete circiut:

swr_sch.gif (32983 Byte)