MAc wrote:

I was thinkink about it, but i want to do it "as much analogue as
possible" ;-)

You'll get some good ideas from "The Tandem Match - An Accurate
Directional Wattmeter" by John Grebenkemper, KA3BLO, in Jan. 1987 QST.
See also corrections to the article in Jan. 1988 Technical Correspondence.

Roy Lewallen, W7EL