Browse Prior Art Database

Time Sharing Circuit for Voice and FSK Data

IP.com Disclosure Number: IPCOM000081663D
Original Publication Date: 1974-Jul-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Chrisfield, RP: AUTHOR [+2]

Abstract

This Circuit permits the time sharing of Frequency Shift Keying (FSK) data and voice in telephone lines with no modification to the existing modems. The circuit determines when the phone line is in use for data transmission, hence the data is supreme, and appropriately gates the voice feature on or off.

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Time Sharing Circuit for Voice and FSK Data

This Circuit permits the time sharing of Frequency Shift Keying (FSK) data and voice in telephone lines with no modification to the existing modems. The circuit determines when the phone line is in use for data transmission, hence the data is supreme, and appropriately gates the voice feature on or off.

The circuit is coupled serially to the phone line by transformers 10 and 12. Blocks 1 and 3 of the circuit perform the line sensing function, and are identical, the only difference being the direction of operation. Accordingly only block 1 will be described. The incoming signals pass through current switch gate 1 and are demodulated by high-bandpass filters 14, 15 and amplitude detectors 16, 18. These filters 14, 15 are set to pass the appropriate FSK data frequencies.

The FSK data is detected in amplitude detector 16 which results in a demodulated binary data stream. This output has its levels set such that it drives a VCO (Voltage-Control Oscillator) whose output is the data in FSK form, again ready for retransmission on the phone line.

For FSK line signal inputs, the output of amplitude detector 18 will be an up level signal. This up level signal is used to indicate the presence of data and, through proper logic, gates the audio output (block 2) to the off condition. This allows the reconstructed FSK data to be placed onto the telephone line through the gate current switch 20, for transmission toward the distant end....