H - Electricity – 04 – L
Patent
H - Electricity
04
L
363/8
H04L 27/10 (2006.01) H04L 5/06 (2006.01)
Patent
CA 1269186
ABSTRACT OF THE DISCLOSURE A digital data communications system transmits digital data over a telephone line using frequency multi- plexing for the different channels. Each channel in- cludes a receiver and a transmitter coupled to the tele- phone line at spaced points. Each transmitter includes an FSK modulator, a bandpass filter of controllable band- width centered about 5 kHz with tits bandwidth controlled by a bandwidth select signal related to the bandwidth needed to transmit data over that channel. A mixer com- bines the output of the bandpass filter with a local oscillator signal of frequency related to the selected channel to provide a difference frequency signal that is applied to a lowpass filter having a cutoff at 3 kHz that is coupled to the telephone line. Each receiver includes a lowpass filter having a cutoff at 3 kHz that couples the line to a mixer. The mixer combines the input signal with a local oscillator signal of frequency related to that of an associated transmitter to provide a receiver intermediate frequency signal at 5 kHz that is applied to a bandpass filter of controllable bandwidth that receives a bandwidth select signal. The bandwidth select signal controlls the bandwidth in accordance with the frequency of the receiver local oscillator so as to be the same as the bandwidth selected at the transmitter for that par- ticular frequency channel. The output of the bandpass filter is coupled to an FSK demodulator that provides the digital data on its ouput corresponding to that applied at the input of the associated transmitter.
536390
Ogilvy Renault Llp/s.e.n.c.r.l.,s.r.l.
Qei Inc.
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