Abstract: A bidirectional communication device for transmitting and receiving communications signals in a system which presents a transmission path for conducting a communications signal from the device, a reception path for conducting a communications signal to the device, and an echo path which conducts echo signals from the transmission path to the reception path, the device having an echo canceler connected between the transmission path and the reception path for minimizing echo signals in the transmission path, the echo canceler comprising an adaptive filter for filtering the communications signals from the device according to a filter characteristic having a plurality of filter coefficients, wherein a first group of the coefficients, constituting less than all of the coefficients, has finite filter coefficient values and the remaining ones of the plurality of coefficients have values of zero.

Abstract: A system for demodulating a FSK digital signal comprising: first and second frequency detectors connected to detect the frequency of the digital signal, the first frequency detector producing an output signal whenever the digital signal is detected to have a first frequency and the second frequency detector producing an output signal whenever the digital signal is detected to have a second frequency; first and second low pass filters each having an input connected to receive the output signal produced by a respective frequency detector and an output for providing a smoothed version of the signal at the respective filter input; and signal combining circuitry connected to the outputs of the first and second filters for providing a demodulated output signal representing the FSK digital signal.