Hi Ed, I built a phasing RX for DGPS beacon reception a few years ago and I got some 40 dB rejection of the unwanted sideband using only two "all-pass" filters in the AF phasing section. The bandwidth was only a few hundred Hz, limited by a 3-section active BPF centered at 500 Hz. Achieving accurate 90 degree phase shift over the entire voice spectrum is a completely different story...=20 73 Johan SM6LKM