A digital AM radio with CQUAM stereo

An all-digital compatible quadrature amplitude modulation (CQUAM) radio is discussed. The incoming signal is digitally demodulated and the in-phase (I) and quadrature (Q) channels are separated. The I and Q signals are then low-pass filtered and decimated to produce lower-sample-rate baseband signals. The resulting baseband signals are manipulated to recover the left and right channels if a stereo signal was transmitted. A phase error is estimated and supplied to a numerically controlled oscillator which calculates the next sample demodulation terms. The theoretical algorithms for these functions are presented, and the performance of the radio is discussed