System for masking microphonic voice signals in wired telecommunications equipment
View Patent ↗A system to thwart eavesdropping on microphonic audio signals generated by a powered telecommunications device connected to a communications line, comprising a noise generator for applying low level noise to the line, thereby masking microphonic audio signals, and a disconnect circuit for disconnecting the telecommunications device from the line in the absence of power to the telecommunications device.
1. A system of a powered telecommunications device connected to a communications line, comprising:
a transformer and hybrid bidirectionally coupling communications between said telecommunications device and said communications line; and
a noise generator connected to said hybrid applying low level noise to said line, masking microphonic audio signals to thwart eavesdropping on said microphonic audio signals generated by the powered telecommunications device when the device is on-hook and connected to the communications line, without interfering with a normal operation of the powered telecommunications device.
2. The system of claim 1 , further comprising:
a disconnect circuit disconnecting said telecommunications device from said line in the absence of power to said telecommunications device.
3. The system of claim 1 , further comprising:
a control mechanism selectively muting or modifying the spectral content of said noise generator during normal operation of said telecommunications device.
4. The system of claim 2 , wherein said disconnect circuit further comprises
a relay circuitry isolating said telecommunications device from the line during said absence of power, and
a start-up control circuit directing power to said relay circuitry to maintain a relay contact closure when power is present.
5. The system of claim 4 , wherein said disconnect circuit further comprises:
a pushbutton switch connecting the incoming line to said telecommunications device for normal operation when the power is present.
6. The system of claim 1 , wherein said noise generator further comprises
a Schottky diode connected in parallel to a high resistance resistor generating random noise, and an amplifier circuitry amplifying said noise.
7. The system of claim 1 , wherein said noise generator further comprises:
a filter restricting the frequency spectrum of said random noise to audio bandwidth.
8. The system of claim 7 , wherein said noise generator further comprises
high impedance feedback resistors to said amplifier circuitry providing high gain amplification of said noise and introduction of additional random noise.
9. The system of claim 8 , wherein said amplifier circuitry is biased to one half level of said power.
10. The system of claim 9 , wherein said noise generator further comprises:
coupling capacitors between said parallel connected Schottky diode and resistor and said amplifier circuitry to eliminate any DC voltage gain.
11. A method of a powered telecommunications device connected to a communications line, comprising:
generating low level noise; and
applying said low level noise to said line, masking microphonic audio signals to thwart eavesdropping on said microphonic audio signals generated by the powered telecommunications device when the device is on-hook and connected to the communications line, without interfering with a normal operation of the powered telecommunications device.
12. The method of claim 11 , further comprising:
disconnecting said telecommunications device from said line in the absence of power to said telecommunications device.
13. The system of claim 11 , further comprising:
selectively muting or modifying the spectral content of said noise generator during normal operation of said telecommunications device.
14. A method, comprising:
generating and applying low level noise to a communications line connected to a telecommunication device; and
masking microphonic audio signals inadvertently generated on said communication line, to thwart eavesdropping on said microphonic audio signals which pickup audio sounds in a room containing the telecommunication device when the device is on-hook and connected to the communications line, without interfering with a normal operation of the powered telecommunications device.