US 4,375,691 AGranted

Method and device for frequency translation

AssigneeMinnesota Mining and Manufacturing Company

InventorBrian K. Hackett

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Abstract

A digital communications system includes a plurality of master stations communicating with a plurality of terminals over a single communication line which carries a plurality of duplex communication channels, each corresponding to a particular master station. A frequency translator coupling each terminal with the communication line permits the remote station to selectively communicate over any of the channels by translating the frequency of a selected channel to that of the terminal's receiver and by translating the frequency of the terminal's transmitter to that of the selected channel. Upon selection of a particular channel, the terminal's transmitter is disabled for a duration sufficient to allow its receiver to pick up a resynchronization signal periodically sent out by the master station whose channel has been selected. The receiver then enables the transmitter in synchronism with any other terminals using the same channel. The translator employs a pair of multiple frequency oscillators controlled by a counter whose output corresponds to a selected channel. The counter is advanced by a manually operable switch, or alternatively, by a remotely generated digital word.

Claims18

Dependent claims

In a digital communications system including a plurality of master stations communicating with a plurality of terminals over a communications line carrying a plurality of communications channels each associated with one of said master stations, each of said terminals including a receiver and a transmitter operating on predetermined frequencies, a modem and means responsive to a request from any of the master stations for transmitting data information to that master station, each of said master stations including means for synchronously polling the terminals and for periodically delivering a resynchronizing signal to each of the terminals to synchronize the latter, a frequency translator for use with each of said terminals comprising:

first frequency translator means for translating the frequency of a selected one of said plurality of channels to the frequency of the terminal's receiver, including:
(1) multiple frequency oscillator means for producing a plurality of translation frequencies each associated with one of said channels, and
(2) means for mixing each of said translator frequencies with the frequency of the corresponding channel;
second translator circuit means for translating the frequency of the terminal's transmitter to the frequency of the selected channel, including:
(1) multiple frequency oscillator means for producing a plurality of translator frequencies each associated with one of said channels, and
(2) means for mixing each of said last named translation frequencies with the frequency of the corresponding channel,
said first and second frequency translator circuit means being coupled between the modem of the associated terminal and said communications line;
and
selectively operable channel select means operably coupled with said first and second translator circuit means for selecting one of said channels to place the terminal in communication with the master station corresponding to said one channel.

6 more elements

In a digital communications system of the type including a plurality of master stations interrogating a plurality of synchronously responsive terminals over a single communications line carrying a plurality of duplex communications channels each associated with one of the master stations, each of the terminals having a receiver, a transmitter, and a modem and wherein each of the master stations periodically sends out a signal on its associated channel to resynchronize the terminals, a method of communicatively interfacing at least one of the terminals with all of said communications channels, comprising the steps of:

(A) selecting one of said channels;
(B) disabling the receiver and transmitter of said one terminal for a prescribed time interval following step (A);
(C) translating the frequency of the channel selected in step (A) to the frequency of the receiver of said one terminal;
(D) translating the frequency of said one terminal transmitter to the frequency of the channel selected in step (A);
(E) enabling said one terminal's receiver after completing step (B);
(F) enabling said one terminal's transmitter after completing step (E);
(G) demodulating a communications signal received by said one terminal on said communications line after performing step (C);
and
(H) modulating a communications signal generated by the transmitter of said one terminal after performing step (D).

6 more elements

A communications system comprising:

a plurality of master stations for transmitting and receiving information on frequencies unique to each of said master stations;
a plurality of terminals for communicating with said master stations and each including a transmitter and receiver having fixed transmitting and receiving frequencies different from any of said unique frequencies of certain of said master stations, each of said terminals including a modem for modulating and demodulating communications signals at said fixed frequencies;
a multichannel communications line communicatively connecting said master stations with said terminals;
and
means at each of said terminals coupled between said communications line and the corresponding modem for translating the transmitting frequency of any of said master stations to the fixed receiving frequency of the associated terminal, and for translating the fixed transmitting frequency of said associated terminal to the receiving frequency of any of said master stations, whereby any of said master stations may communicate with any of said terminals.

2 more elements

Dependencies are inferred from the claim text.