:? Hi !! The modulation level can't be increased. It is in fact the backscattering signal coming from an RFID system placed 20feet apart. The transmitting and receiving antennas are placed side by side, that's why the input signal can reach a +20dBm level. The big advantage is that I can have access to the carrier frequqncy. I know of a circuit that uses a mixer (marked MCL JSIQ-911D-1, couldn't find any spec. from it) that works in this application.
Big thanx.