Abstract: A 4800 bit-per-second full duplex modem is described which utilizes the full bandwidth of ordinarily available dial-up telephone circuits for transmission of data in both directions in different pass-band portions thereof. The two pass-bands overlap in about the middle of the telephone band in order to fully utilize that bandwidth for high speed data transmission. The overlap is less than that which will cause a greater error rate than desired from remote echos of transmitted data. Local echos, which are much stronger, resulting from the overlap bandwidth portion are cancelled by an echo cancelling technique. Local echo cancelling is accomplished at the baud rate, generated in each modem, for substraction from a received signal; a cancellation signal is generated from a time varying system that depends upon the modulating and demodulating carrier signals.

Abstract: A technique for reducing the nonlinear frequency characteristics of a carbon granule microphone of the type generally used in telephone handsets wherein a tone outside the voice range is applied to the microphone simultaneously with the audio signal desired to be transmitted. This technique has particular advantages with telephone modems, especially those where the sending and receiving frequencies are hamonically related.

Abstract: For the type of modem that transmits information by way of quadrature amplitude modulation (QAM) over a telephone line, an electronic circuit for compensating for amplitude distortion created by use of an acoustic coupler with an ordinary telephone handset.The circuit is positioned in the acoustic coupler between the modem and the coupler's microphone and receiver. This circuit compensates for amplitude distortion introduced by the acoustic coupling within the data transmission frequency bands of the modem.

Abstract: A telephone handset acoustic coupling cup adapted for use as part of an acoustic data coupler wherein the cup has a flexible, gripping lip surrounding an opening for receiving a telephone handset transmitter or receiver case. Each of two acoustic coupling cups may additionally be eccentrically rotatably mounted on a case in a manner that their openings may be varied in distance from one another by rotating the cups with respect to the case. The cups may also be flexible in a manner to be bendable with respect to said case, all with the view of providing an acoustic data coupler that can accept a wide variety of different sizes and shapes of telephone handsets.

Abstract: A telephone handset acoustic coupling cup adapted for use as part of an acoustic data coupler wherein the cup has a flexible, gripping lip surrounding an opening for receiving a telephone handset transmitter or receiver case. Each of two acoustic coupling cups may additionally be eccentrically rotatably mounted on a case in a manner that their openings may be varied in distance from one another by rotating the cups with respect to the case. The cups may also be flexible in a manner to be bendable with respect to said case, all with the view of providing an acoustic data coupler that can accept a wide variety of different sizes and shapes of telephone handsets.