Flathagen blogged about his DIY SWR meter project:
The circuit is based on two AD8307 log amplifiers, which are connected to the forward and reflected ports on a directional coupler. The AD8307 amplifiers gives a DC voltage of about 25mV/dB of the input signal, which is amplified using an opamp (LM324). The opamp also provides the reference voltage to the Arduino (AREF) to ensure that the full ranges of the A/D converters are used.
I used the fourth opamp in the quad LM324 to provide input voltage reading. That is why the PCB in the picture has two power jacks. One input and one output. That way I know the drive voltage for the radio. I primary plan to use this device for my Softrock.
Project info at Flathagen DIYycrap blog.
Read more Here