Full duplex modems and synchronizing methods and apparatus therefor

Abstract From the Canadian patent

Full duplex modems and synchronizing methods and apparatus therefor which allow the relatively low cost realization of full duplex modems compatible with prior art data sets such as the Bell System 212A Data Set. The modems utilize relatively little bandpass line filtering with post demodulation filters which provide normal filtering of second harmonic products, but further also serving to make up for the lack of the ordinarily heavy line or predemodulation filtering commonly used to reject the other channel. In addition, the automatic gain control is provided after the post demodulation filters rather than on the incoming line itself. Carrier sync and timing error corrections are provided …