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Television Image Scrambler and Unscrambler Using the Audio Subchannel

IP.com Disclosure Number: IPCOM000092861D
Original Publication Date: 1967-Mar-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Fisk, DE: AUTHOR

Abstract

This arrangement provides security in communications, particularly television, by scrambling and unscrambling the video using the audio subchannel.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 67% of the total text.

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Television Image Scrambler and Unscrambler Using the Audio Subchannel

This arrangement provides security in communications, particularly television, by scrambling and unscrambling the video using the audio subchannel.

Sequence generator 10 controls a number of audio tone generators 12, turning each on and off independently. The outputs are mixed in mixer 14 and comprises the signal transmitted by the audio section of a TV transmission system. The mixed output also feeds tone detector 16. This recognizes a particular combination of tones and causes trigger T1 to change state. Trigger T1, alternately allows gate 18 or gate 20 to conduct, feeding either the composite video or its complement, via Inverter 22, to video modulator 24 via mixer 26. The resulting modulated video is combined in mixer 28 with the modulated audio from modulator 30 and transmitted.

At the receiver, separator 36 emits audio and video signals. The audio is fed to tone detector 34 which causes trigger T2 to change state when the correct tone combination is detected. Gate 38 or gate 40 conducts, allowing the received video to pass either inverted, by Inverter 42, or noninverted to the TV monitor via mixer 44.

If tone detectors 16 and 34 are set to respond to the same combination of tones, T1 and T2 both change states sirnultaneously and the video, transmitted to the TV monitor, always has the same polarity. A TV display, then, remains stable and viewable even though the image transmitted is const...