On the Low Pass Filter PCB there is and the SWR/PWR meter. The SWR/PWR meter uses one transformer (FT50-43) in which you twist two wires (0.4mm) and wind 12t.Cover about 80% of the core. The 1/2T is a piece of RG58 without outer plastic. The R1/R3 and R2/R4 are used to help the Microcontroller regulate the power range.
To calibrate the Swr meter, TX must be set for CW or AM operation, and set the power about 5W, connect 50Ω dummy load and adjust the 40pf trimmer to read Vrefl close to zero.
The SWR-meter is set by 100K trimmer in order to display correctly the FWD-Power and REFL-Power. To compute the value of the SWR we will use the following formula
SWR = (1 + √ (Power Refl/ Power Fwd))/(1- √ (Power Refl/ Power Fwd))