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Title: Code operated switching device for communications systems and the like
Claims: The invention is claimed as follows: 1. In a communication system for sending and receiving data, the combination including: a plurality of data transmitting means each being represented bby a predetermined discrete interrogation code, code interrogation means for generating a discrete code signal corresponding to a selected one of the interrogation codes and representing a particular one of said data transmitting means, code operated switch means coupled to each of said data transmitting means, each code operated switch means including, input means for receiving first and second RF frequencies having predetermined difference and sum frequencies, a single filter circuit coupled to said input for passing said first and second RF frequencies and said control signal, at least one of said first and second RF frequencies being modulated with a control signal, detector means coupled to said single filter circuit for receiving said first and second RF frequencies and producing therefrom an intermediate frequency which includes said control signal, normally open circuit means coupled to said detector means and operative in response to said control signal, and data retrieval means coupled to said code operated switch means to receive data signals from the discrete data transmitting means which has been interrogated when said normally open circuit means is closed. 2. The communications system according to claim 1, further including means operable so that the absence of FSK modulation of said first and second RF frequencies represent a first logic state and the presence of said FSK modulation represents a second logic state, said code operated switch being interrogated in response to changes in said first and second logic states, said code operated switch further including logic detector means coupled between said detector means and said normally open circuit means for operating said normally open circuit means in response to a predetermined logic code. 3. The communications system according to claim 2, further including comparitor means coupled between said mixer means and said logic detector means, said comparitor means having an adjustable element to set a given threshold level to allow passage of said control signals which only exceeds said threshold level, thereby eliminating extraneous signals from passing therethrough. 4. The communications system according to claim 1, wherein said normally open circuit means is a relay which is actuated in response to the presence of said control signal to allow data signals to pass from said data transmitting means to said data retrieval means through said code operated switch means in a direction oppostie that of the direction from which said first and second RF frequencies are received. 5. The communications system according to claim 4, further including signal generator means for applying a test signal to said relay to determine at a remote location that said relay is actuated in response to the control signal. 6. In a code operated switching apparatus, the combination including: input means for receiving first and second RF frequencies from a central station and having a predetermined frequency difference, at least one of said first and second RF frequencies being modulated with a predetermined control signal at the central station, detector means coupled to said input means for detecting an intermediate frequency which includes said control signal a single filter circuit coupled to said input means of said detector means for passing said first and second RF frequencies and said control signal, and switch means coupled to said detector means to be operated in response to said control signal. 7. The code operated switching apparatus as set forth in claim 8, wherein the absence of FSK modulation of said first and second RF frequencies represents a first logic state and the presence of FSK modulation represents a second logic state, the apparatus further including logic detector means coupled between said detector means and said switch means for operating said switch means in response to a predetermined logic code. 8. The code operated switching apparatus as set forth in claim 7, further including comparitor means coupled between said detector means and said logic detector means, said comparator means having an adjustable element to set a given threshold level to allow passage of said control signals which only exceed said threshold level, thereby eliminating extraneous signals from passing therethrough. 9. The code operated switching apparatus as set forth in claim 6, wherein said switch means is a relay which is actuated in response to the presence of said control signal to allow passage of data signals through the apparatus in a direction opposite that of the direction from which said first and second RF frequencies are received. 10. The apparatus as set forth in claim 9, further including signal generator means for applying a test signal to said relay to determine at a remote location that said relay is actuated in response to the control signal. 11. The apparatus as set forth in claim 6, further including a first highpass filter means coupled to said input means, first highpass filter means being coupled to an output terminal through a second highpass filter, RF amplifier means coupled to said first highpass filter means for receiving said first and second RF frequencies and amplifying the same said detector means including a transistor and a capacative output, inductive circuit coupled to the output of said detector means tuned to said intermediate frequency for developing said intermediate frequency and the control signals associated therewith, IF amplifier discriminator means to develop audio signal information in response to FSK modulation of said first and second RF frequencies, said IF amplifier discriminator means being coupled to said mixer means, the output of said IF amplifier discriminator being coupled to one input of an operational amplifier which functions as a comparator circuit, an adjustable voltage input coupled to a second input of said operational amplifier whereby a setting of predetermined minimum voltage value is maintained to pass only signal information above said minimum value thereby eliminating the possibility of extraneous signals from passing through said comparator, logic circuit means coupled to the output of said comparator for producing a control signal in response to receiving a proper code modulated into said first and second RF frequencies by FSK modulation, and test signal means coupled to said relay for indicating actuation at a remote location of said relay. 12. The code operated switching apparatus as set forth in claim 6, wherein said switching means is normally open in the absence of said control signal, and closes only in response to predetermined code information of said control signal. 13. The communication system according to claim 1 wherein said code and communication means includes circuit means for FSK modulation of said first and second RF frequencies. 14. The communication system as set forth in claim 1 wherein said code interrogation means includes means for FSK modulation of said first and second frequencies, said modulation means for decreasing the frequency of one of said first and second RF frequency to provide said control signal. 15. The code operated as switching apparatus as set forth in claim 8 wherein the central station includes means for FSK modulation, said first and second RF frequencies simultaneously to produce said control signal. 16. The code operated switching apparatus as set forth in claim 8 wherein said detector means selects the difference of frequency between said first and second RF frequencies to develop an intermediate frequency corresponding to said control signal. Other info: Inventors: McVoy, David S. (Sarasota, FL, US) Application Number: 376386 Filing Date: 1973-07-05 Publication_date: 1976-02-03 Assignee: Coaxial Scientific Corporation (Sarasota, FL) Primary Class(es): 340/7.43 340/7.21, 375/272, 725/97 Other Classes: US Patent Ref:
Other Refs: Other References: IRE Dictionary of Electronics Terms and Symbols, The Institute of Radio Engineers, Inc., 1961. | |