Acoustical coupler for frequency shift telegraphic systems

Claim 2

For use in a data communication system wherein data signals are transmitted as tone frequency signals over telephone lines to a decoder adapted to respond to mark and space signals in the form of direct current impulses, a coupler for converting first and second tone frequency signals to mark and space signals respectively and being adapted for operative connection with telephone lines and a decoder, said coupler comprising a bandpass amplifier having a bandwidth which has a center frequency adjacent the first and second tone frequency signals, frequency selective means connected with the output of the amplifier and being tuned to one of said tone frequencies to produce a peak amplitude response at said one tone frequency and having a frequency response characteristic such that the amplitude response at the other tone frequency is approximately one-half the peak response, an amplitude discriminator operatively connected with said frequency selective means and having a first conductive state when the output thereof is less than a predetermined amplitude and a second conductive state when the output of the selective means is greater than said predetermined amplitude, said predetermined amplitude corresponding to a value intermediate said peak and said reduced amplitudes for the first and second tone frequency signals, and a decoder driver connected with the amplitude discriminator and operable to produce a mark signal when the discriminator is in its first conductive state and operable to produce a space signal when the discriminator is in its second conductive state and means connected to the output of the frequency selective means and responsive to the absence of a signal for maintaining the decoder driver in a condition which is the same as that produced by one of the first or second conductive states of said discriminator.

Claim 3

The coupler defined in claim 1, wherein said amplitude discriminator is operatively connected with said frequency selective means by a detector connected with the frequency selective means for rectifying and filtering the output thereof to produce a detected signal having an amplitude corresponding to the frequency of the first and second tone frequency signals, the output of said detector being connected with the input of said amplitude discriminator.

Claim 4

The coupler defined in claim 1 wherein the band-pass amplifier includes a negative feedback path, frequency selective means in the feedback path adapted to pass frequencies below the first tone frequency and above the second tone frequency.

Claim 5

For use in a data communication system wherein data signals are transmitted as tone frequency signals over telephone lines to a decoder adapted to respond to mark and space signals in the form of direct current impulses, a coupler for converting first and second tone frequency signals to mark and space signals respectively and being adapted for operative connection with telephone lines and a decoder, a band-pass amplifier having a bandwidth which has a center frequency adjacent the first and second tone frequency signals, frequency selective means connected with the output of the amplifier and producing a peak amplitude response at one tone frequency and a reduced amplitude response at the other tone frequency, an amplitude discriminator operatively connected with said frequency selective means and having a first conductive state when the output thereof is less than a predetermined amplitude and a second conductive state when the output of the selective means is greater than said predetermined amplitude, said predetermined amplitude corresponding to a value intermediate said peak and said reduced amplitudes for the first and second tone frequency signals, and a decoder driver connected with the amplitude discriminator and operaBle to produce a mark signal when the discriminator is in its first conductive state and operable to produce a space signal when the discriminator is in its second conductive state, said band-pass amplifier including an automatic gain control circuit responsive to a voltage above a threshold value for increasing the gain of the amplifier when the amplifier output is above the threshold value and below a predetermined value and for decreasing the gain of the amplifier when the amplifier output is above said predetermined value, said automatic gain control circuit being nonresponsive to an amplifier output below the threshold value whereby the rejection of frequencies outside the bandpass of the amplifier is enhanced by the gain control.

Claim 6

For use in a data communication system wherein data signals are transmitted as tone frequency signals over telephone lines to a decoder adapted to respond to mark and space signals in the form of direct current impulses, a coupler for converting first and second tone frequency signals to mark and space signals respectively and being adapted for operative connection with telephone lines and a decoder, a band-pass amplifier having a bandwidth which has a center frequency adjacent the first and second tone frequency signals, frequency selective means connected with the output of the amplifier and producing a peak amplitude response at one tone frequency and a reduced amplitude response at the other tone frequency, an amplitude discriminator operatively connected with said frequency selective means and having a first conductive state when the output thereof is less than a predetermined amplitude and a second conductive state when the output of the selective means is greater than said predetermined amplitude, said predetermined amplitude corresponding to a value intermediate said peak and said reduced amplitudes for the first and second tone frequency signals, and a decoder driver connected with the amplitude discriminator and operaBle to produce a mark signal when the discriminator is in its first conductive state and operable to produce a space signal when the discriminator is in its second conductive state, said band-pass amplifier including an automatic gain control circuit responsive to a voltage above a threshold value for increasing the gain of the amplifier when the amplifier output is above the threshold value and below a predetermined value and for decreasing the gain of the amplifier when the amplifier output is above said predetermined value, said automatic gain control circuit being nonresponsive to an amplifier output below the threshold value whereby the rejection of frequencies outside the bandpass of the amplifier is enhanced by the gain control.

Claim 7

The coupler as defined in claim 4 further including carrier responsive means having its input operatively connected with said frequency selective means, enabling means connected with said amplitude discriminator for rendering it effective to control the decoder driver when the enabling means is in a first state and ineffective to control the decoder driver when the enabling means is in a second state, said carrier responsive means having its output connected with said enabling means and adapted to switch it to the first state when a carrier is received.

Claim 8

In a data set coupler for converting first and second tone frequency signals to mark and space signals, amplifying means for said tone frequency signals, frequency selective means exhibiting resonance at one of said tone frequencies, means connected with said amplifying means for energizing the frequency selectivity means with constant amplitude current impulses of a frequency corresponding to either the first or second tone frequency whereby the voltage thereacross has an amplitude dependent upon the frequency of said impulses, and amplitude responsive means connected with the frequency selective means for producing output signals in accordance with the amplitude of the voltage applied thereto, said amplitude responsive means comprising first and second diodes with conductive paths having separate and common portions and bias means there for whereby the first diode conducts and the second diode is cut off when an input voltage on the first diode is less than a predetermined value and whereby the second diode conducts and the first diode is cut off when an input voltage on the first diode is greater than the predetermined value said predetermined value being intermediate the values of voltage output from the frequency selective means which correspond to mark and space signals, and means developing an output signal indicative of the conductive stage of one of said diodes.

Claim 9

In a data set coupler for converting first and second tone frequency signals to mark and space signals, amplifying means for said tone frequency signals, frequency selective means exhibiting resonance at one of said tone frequencies, means connected with said amplifying means for energizing the frequency selectivity means with constant amplitude current impulses of a frequency corresponding to either the first or second tone frequency whereby the voltage thereacross has an amplitude dependent upon the frequency of said impulses, and amplitude responsive means connected with the frequency selective means for producing output signals in accordance with the amplitude of the voltage applied thereto, said amplitude responsive means comprising first and second diodes with conductive paths having separate and common portions and bias means there for whereby the first diode conducts and the second diode is cut off when an input voltage on the first diode is less than a predetermined value and whereby the second diode conducts and the first diode is cut off when an input voltage on the first diode is greater than the predetermined value said predetermined value being intermediate the values of voltage output from the frequency selective means which correspond to mark and space signals, and means developing an output signal indicative of the conductive stage of one of said diodes.

Claim 10

The combination defined in claim 6 additionally including switching means connected with the output of the amplitude responsive means, said switching means comprising first and second transistors, the first transistor having its input effectively connected with said second diode and its output connected to the input of the second transistor, the second transistor having its output adapted for connection to utilization means with the output representing a mark signal in a first conductive state and representing a space signal in a second conductive state, said transistors being maintained in opposite conductive states, said first transistor being maintained in the second conductive state when the output of the amplitude responsive means is indicative of either a mark signal or the absence of a carrier, whereby the second transistor is in the first conductive state for either a mark signal or the absence of a carrier.

Claim 11

The combination defined in claim 7 further including a mark signal detecting circuit with enabling means connected with the second transistor for changing the bias thereon between first and second bias levels when a carrier is received whereby the output of the first transistor in its first conductive state is effective to switch the second transistor to its second conductive state to Indicate the receipt of a space signal.

Claim 12

The combination defined in claim 8 wherein the amplitude responsive means is operatively connected with the frequency selective means by a detector for rectifying and filtering the output thereof to produce a detected signal, the output of the detector being applied to the first diode in the amplitude responsive means.

Claim 13

In a data set coupler for converting first and second tone frequency signals to mark and space signals, a band-pass amplifier having a bandwidth which has a center frequency intermediate the first and second tone frequency signals, a negative feedback path including frequency selective means adapted to reject the first and second tone frequencies and to pass frequencies below the first tone frequency and above the second tone frequency whereby the pass band of the amplifier includes the first and second tone frequencies, an automatic gain control circuit connected to the amplifier output and responsive to a voltage above a threshold value for controlling the gain of the amplifier, frequency selective means connected with the output of the amplifier and producing an output having an amplitude corresponding to the frequency of the amplifier output, and amplitude responsive means connected with the frequency selective means for producing output signals corresponding to the amplitude of the voltage applied thereto wherein the amplitude responsive means comprises first and second diodes with conductive paths having separate and common portions and bias means therefor whereby the first diode conducts and the second diode is cut off when an input voltage on the first diode is less than a predetermined value and whereby the second diode conducts and the first diode is cut off when an input voltage on the first diode is greater than the predetermined value, said predetermined value being intermediate the values of voltage output from the frequency selective means which correspond to mark and space signals, and means developing an output signal indicative of the conductive state of one of said diodes.

Claim 14

In a data set coupler for converting first and second tone frequency signals to mark and space signals, a band-pass amplifier having a bandwidth which has a center frequency intermediate the first and second tone frequency signals, a negative feedback path including frequency selective means adapted to reject the first and second tone frequencies and to pass frequencies below the first tone frequency and above the second tone frequency whereby the pass band of the amplifier includes the first and second tone frequencies, an automatic gain control circuit connected to the amplifier output and responsive to a voltage above a threshold value for controlling the gain of the amplifier, frequency selective means connected with the output of the amplifier and producing an output having an amplitude corresponding to the frequency of the amplifier output, and amplitude responsive means connected with the frequency selective means for producing output signals corresponding to the amplitude of the voltage applied thereto wherein the amplitude responsive means comprises first and second diodes with conductive paths having separate and common portions and bias means therefor whereby the first diode conducts and the second diode is cut off when an input voltage on the first diode is less than a predetermined value and whereby the second diode conducts and the first diode is cut off when an input voltage on the first diode is greater than the predetermined value, said predetermined value being intermediate the values of voltage output from the frequency selective means which correspond to mark and space signals, and means developing an output signal indicative of the conductive state of one of said diodes.

Claim 15

The combination defined in claim 10 additionally including switching means connected with the output of the amplitude responsive means, said switching means comprising first and second transistors; the first transistor having its input effectively connected with said second diode and its output connected to the input of the second transistor, the second transistor having its output adapted for connection to utilization means with the output representing a mark signal in the first conductive state and representing a space signal in a second conductive state, said transistors being maintained in opposite conductive states, said first transistor being maintained in the second conductive state when the output of the amplitude responsive means is indicative of either a mark signal or the absence of a carrier, whereby the second transistor is in the first conductive state for either a mark signal or the absence of a carrier.

Claim 16

The combination defined in claim 11 further including a mark signal detecting circuit with enabling means connected with the second transistor for changing the bias thereon between first and second bias levels when a carrier is received whereby the output of the first transistor in its first conductive state is effective to switch the second transistor to its second conductive state to indicate the receipt of a space signal.

Claim 17

For use in data communication system wherein data signals are transmitted as tone frequency signals over telephone lines to a decoder adapted to respond to mark and space signals in the form of direct current impulses, a coupler for converting first and second tone frequency signals to mark and space signals respectively and being adapted for operative connection with telephone lines and a decoder, a band-pass amplifier having a bandwidth which is centered between the first and second tone frequency signals, a frequency selective network connected with the output oF the amplifier and including a parallel resonant circuit tuned to the second tone frequency signal and producing a peak amplitude response at the second tone frequency and a reduced amplitude response at the first tone frequency, a detector connected with the frequency selective network for rectifying and filtering the output thereof to produce a detected signal having an amplitude corresponding to the frequency of the first and second tone frequency signals, an amplitude discriminator connected with the detector and having a first conductive state when the detected signal is less than a predetermined amplitude and a second conductive state when the detected signal is greater than said predetermined amplitude said predetermined amplitude corresponding to value intermediate the detected signal amplitudes for the first and second tone frequency signals, and a decoder driver connected with the amplitude discriminator and operable to produce a mark signal when the discriminator is in its first conductive state and operable to produce a space signal when the discriminator is in its second conductive state and a mark-detecting circuit connected with the output of the frequency selective network and responsive to the absence of a signal for maintaining the decoder driver in a condition which is the same as that produced by the first conductive state of said discriminator.

Claim 18

For use in data communication system wherein data signals are transmitted as tone frequency signals over telephone lines to a decoder adapted to respond to mark and space signals in the form of direct current impulses, a coupler for converting first and second tone frequency signals to mark and space signals respectively and being adapted for operative connection with telephone lines and a decoder, a band-pass amplifier having a bandwidth which is centered between the first and second tone frequency signals, a frequency selective network connected with the output oF the amplifier and including a parallel resonant circuit tuned to the second tone frequency signal and producing a peak amplitude response at the second tone frequency and a reduced amplitude response at the first tone frequency, a detector connected with the frequency selective network for rectifying and filtering the output thereof to produce a detected signal having an amplitude corresponding to the frequency of the first and second tone frequency signals, an amplitude discriminator connected with the detector and having a first conductive state when the detected signal is less than a predetermined amplitude and a second conductive state when the detected signal is greater than said predetermined amplitude said predetermined amplitude corresponding to value intermediate the detected signal amplitudes for the first and second tone frequency signals, and a decoder driver connected with the amplitude discriminator and operable to produce a mark signal when the discriminator is in its first conductive state and operable to produce a space signal when the discriminator is in its second conductive state and a mark-detecting circuit connected with the output of the frequency selective network and responsive to the absence of a signal for maintaining the decoder driver in a condition which is the same as that produced by the first conductive state of said discriminator.