Voice Scrambling US Patents

©Brooke Clarke, N6GCE

Background

Analog

The very early analog voice scramblers used frequency inversion.  These can easily be broken using a frequency inversion converter and just turning the oscillator frequency until clear speech is heard.

 2,083,653 Transmission System June 1937 - two points on a phonograph record are picked up and combined to form the interfering signal that's added to the voice signal rather that just using a standard phonograph with a single pickup.
 

Digital

1,312,572 Secret Signaling System 380/43; 380/260 Aug 12, 1919 - Morse code scrambling using rotating commutation

4,383,322 Combined use of PN sequence for data scrambling and frame synchronization in digital communication systems 375/141; 375/146; 375/147; 375/363; 375/367; 380/46 May 10, 1983 Harris - This is a classical digital method.  It embeds the synchronizing signal into the speech so a header is not needed.
 
 
 

Patent Classes

370 MULTIPLEX COMMUNICATIONS

370/209 GENERALIZED ORTHOGONAL OR SPECIAL MATHEMATICAL TECHNIQUES:  Particular set of orthogonal functions .. Walsh functions

Walsh Functions (aka CDMA)

Now (2002)  Walsh functions are called Code Division Multiple access (CDMA)

 3678204 - 177/15; 370/209 Signal Processing and Transmission by means of Walsh Functions 26 Oct 1970 ITT  by H.F. Harmuth  Number of channels need not be a power of 2.  Aimed at getting 12 telephone channels multiplexed into a single channel.  Multiplies each channel by a different Paley function then adding all 12 channels toghther.  An analog signal must be low pass filtered prior to being applied to the Walsh function.  Uses digital function multiplied times an analog signal.

3,470,324 9/1969 370/209; 165/109.1; 370/533; 375/260; 375/268 System for the Transmission of Information by Carrier Waves over a Single Conductor Sept. 30, 1969 - number of channels is a power of 2

3,522,383 7/1970 375/240; 178/69R Block Precoding for Multiple Speed Data Transmission July 28, 1970 Bell Labs

4,052,565 - October 4, 1977 A digital speech scrambler system allowing for the transmission of scrambled speech over a narrow bandwidth by sequency limiting the analog speech in a low-pass sequency filter and thereafter multiplying the sequency limited speech with periodically cycling sets of Walsh functions at the transmitter. At the receiver, the Walsh scrambled speech is unscrambled by multiplying it with the same Walsh functions previously used to scramble the speech. The unscrambling Walsh functions are synchronized to the received scrambled signal so that, at the receiver multiplier, the unscrambling Walsh signal is the same as and in phase with the Walsh function which multiplied the speech signal at the transmitter multiplier. Synchronization may be accomplished by time division multiplexing sync signals with the Walsh scrambled speech. The addition of the sync signals in this manner further masks the transmitted speech and thus helps to prevent unauthorized deciphering of the transmitted speech. US Class 380/28
Calls:
3204035 - 370/208; 375/362 Orthonormal Pulse Multiplex Transmissions Systems 26 Nov 1962
3678204 - 177/15; 370/209 Signal Processing and Transmission by means of Walsh Functions 26 Oct 1970 ITT (KY-38?)
3742201 - 708/410 Transformer System for Orthogonal Digital Waveforms June 26, 1973
3859515 - 708/410; 324/76.12; 324/76.21; 340/5.81; 382/121 Method and Apparatus for Signal Spectrum Analysis by Hadamard Transform Jan 7 1975 Burroughs
Referenced by many other patents mostly referring to CDMA
4,305,152 Security communication system 380/274; 375/363; 380/38; 380/261; 380/276 December 8, 1981 -embedding a frame and clock signal into the scrambled voice signal to allow synchronization.
4,379,205 Analog signal scrambling system 380/28; 380/276 Bell Labs - A speech scrambling system using discrete prolate spheroidal sequence coefficients (PC). The problem is to provide high fidelity and high security in a scrambling system while limiting the bandwidth of the scrambled signal to the bandwidth of the original speech signal. The disclosed system uses PC to solve this problem. The analog speech signal is digitally sampled (100), converted to PC (203, 204, 205), scrambled (208, 209), and converted to scrambled samples (211, 212, 213). The scrambled samples are transmitted using pulse amplitude modulation (102) in the same bandwidth as the original signal. At the receiving end, the inverse steps are performed to recover the original speech. The scrambling is periodically modified (220, 320) to improve security.

Although the signal transmitted is analog the process relies on digital circuits.

4,383,322 Combined use of PN sequence for data scrambling and frame synchronization in digital communication systems 375/141; 375/146; 375/147; 375/363; 375/367; 380/46 May 10, 1983 Harris -

4,393,276 Fourier masking analog signal secure communication system July 12, 1983 Bell Labs -

4,434,323 Scrambler key code synchronizer 380/260; 380/44; 380/274  February 28, 1984 Motorola

Calls:
3,610,828  Privavy Communication System 380/260; 380/274; 380/275 Filed May 23, 1967 granted Oct 5. 1971. Sends a 2150 Hz and 67Hz clock and frame signals in the clear that need to be notch filtered out of the audio.
Calls:
3,073,892 Code Signal Generator Jan 15, 1963  380/235; 380/236 TV scrambling but can be used for audio
3,098,936  Signal Translators Utilizing Input Signal Level Which Selectively Saturates Transistor Base-Collector Junction 348/533; 327/309; 327/334; 330/296; 348/529; 348/534; 380/204; 380/225; 380/236 filed 1958, granted 1963 - transistor can be used as phase inverter to scramble speeech in a TV signal
3,069,657 Selective Calling System 340/825.53; 327/1; 340/7.45; 340/825.52; 340/825.58; 367/133; 367/134 filed 1958 granted 1962 Sylvania - PR sequence used for call indicator
3,180,927 Crypto Secure Transmission System 380/235; 375/362; 380/32; 380/211; 380/240; 380/262; 455/46 April 1965 Balanced modulator used for TV scrambling
2,905,747 Secrecy Systems 380/238; 380/252 Sep 1959 TV sound translated up in frequency and masking signal added
2,999,900 Signal Translating Apparatus 380/236; 327/426; 380/275 Sep 1961 TV sound scrambling where transistors improve tube circuits
3,123,672
US 3,618,077:WALSH FUNCTION GENERATOR -
US 3701143:WALSH FUNCTION GENERATOR -
US 3795864:METHODS AND APPARATUS FOR GENERATING WALSH FUNCTIONS -
US 5311176:Method and apparatus for generating Walsh codes -


375 Pulse or Digital Communications

Class 380, Cryptography

380/28  PARTICULAR ALGORITHMIC FUNCTION ENCODING

Search for 380/28 Patents all years - 1790 to 1975 -

1,633,625 Security System 380/28 June 1927 AT&T - Vacuum tube used to distort signal prior to sending over wire or radio.
2,424,998 Electrical Transmission System 380/27; 340/14.2; 380/28, H. Nyquist April 5, 1947 Bell Labs - Permuters on digital lines (maybe for teletype circuits) calls 2,139,676
3,229,037 Coding and Decoding Aparatus 380/43; 178/23R; 380/28; 380/267 Jan 11, 1966 - 5 level teletype where key tape can have any character, but output is MOD 26 and so is printable.
3,536,833 Process for Conceling Communication Signals 380/28; 380/259 Oct 1970 (filed 1965) - uses XOR gate to add singnal then at receiver XOR to remove signal calls: 2,777,897, 3,071,649, 3,077,518, 3,243,507
3,639,690 Digital Privacy System 380/43; 375/247; 380/28; 380/270 Feb 1, 1972 Motorola - Delta modulation XOR key calls 3,202,764, 3,307,648, 3,506,783, 3,507,980
3,657,476 Cryptography 380/28; 331/78; 380/44; 705/55; 713/190 18 Apr 1972 - Digital method to generate a pseudo random number electronically not mechanically.  If the time to repeat for a system operating at 1,000 mega digits a second was 1,000 years then the constants needed would be m=7, N=6 and n=23.
3,959,592380/28 380/275 Method and apparatus for transmitting and receiving electrical speech signals transmitted in ciphered or coded form May 25, 1976 Gretag  - uses an FFT to decompose and then reconstruct speech

380/260 COMMUNICATION SYSTEM USING CRYPTOGRAPHY.. Symmetric key synchronization

380/274  COMMUNICATION SYSTEM USING CRYPTOGRAPHY:Wireless communication: Synchronization:

Voice Scramblers

KYV-2() - Digital
KY-38 - Analog


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