Pulse or digital communications – Repeaters – Testing
Patent
1986-05-05
1987-09-15
Griffin, Robert L.
Pulse or digital communications
Repeaters
Testing
375 62, 375 88, H04L 2710
Patent
active
046944710
ABSTRACT:
A digital data communications system transmits digital data over a telephone line using frequency multiplexing for the different channels. Each channel includes a receiver and a transmitter coupled to the telephone line at spaced points. Each transmitter includes an FSK modulator, a bandpass filter of controllable bandwidth centered about 5 kHz with its bandwidth controlled by a bandwidth select signal related to the bandwidth needed to transmit data over that channel. A mixer combines 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 particular frequency channel. The output of the bandpass filter is coupled to an FSK demodulator that provides the digital data on its output corresponding to that applied at the input of the associated transmitter.
REFERENCES:
patent: 4336613 (1982-06-01), Hewes
patent: 4394626 (1983-07-01), Kurihara et al.
patent: 4517519 (1985-05-01), Mukaiyama
patent: 4539524 (1985-09-01), Goode
Griffin Robert L.
Hieken Charles
Huseman M.
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