Digital data communicating
US4694471A · kind A · utility
Inventor
Key dates
| Filing date | May 5, 1986 |
| Grant date | Sep 15, 1987 |
| Priority date | — |
| Expiry date | May 5, 2006 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L27/10
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
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 wit…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.