Graphic privacy system

Jan. 14, 1947.

J. V. L. HOGAN ET AL

GRAPHIC PRIVACY SYSTEM

Filed June 4, 1943

2,414,101

Sheets-Sheet 1

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INVENTORS V.L.

Jlessler

ATTORNEY

Jan. 14, 1947. j _{v L} hogan etal 2,414,101

GRAPHIC PRIVACY SYSTEM

Filed June 4, 1943 5 Sheets-Sheet 2

<img file="US2414101A_D0002.tif" />

Jan. 14, 1947.

2,414,101

J. V. L. HOGAN ET AL

GRAPHIC PRIVACY SYSTEM

Filed June 4, 1943 5 Sheets-Sheet 3

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<img file="US2414101A_D0004.tif" />

INVENTORS John, V. JAToon-rE JLu^h, G.RessL&amp;r-

<img file="US2414101A_D0005.tif" />

Jan. 14, 1947.

J. V. L. HOGAN ETAL.

2,414,101

GRAPHIC PRIVACY SYSTEM

Filed June 4, 1943

Sheets-Sheet 4

<img file="US2414101A_D0006.tif" />

<td colspan="2"></td><td> Π</td><td> A</td><td> A</td><td> A</td><td> n</td><td> A</td><td> A</td><td> A</td><td colspan="3"> n ri nr</td>

<td></td><td> Θ</td><td> Θ</td><td> ©</td><td> θ</td><td> θ</td><td> e</td><td> θ</td><td> θ</td><td> Θ</td><td> a</td><td> a</td><td> 9</td>

<td></td><td> Θ</td><td> 9</td><td> 9</td><td> 9</td><td> 9</td><td> 9</td><td> 9</td><td> 9</td><td> 9</td><td> Q</td><td> 9</td><td> 9</td>

<td></td><td> O</td><td> O</td><td> O</td><td> O</td><td> O</td><td> O</td><td> O</td><td> O</td><td> O</td><td> o</td><td> o</td><td> O</td>

<td></td><td> 9</td><td> Θ</td><td> 9</td><td> 9</td><td> 9</td><td> Θ</td><td> a</td><td> Θ</td><td> a</td><td> a</td><td> a</td><td> a</td>

<td></td><td></td><td> &lt;a</td><td> a</td><td> Θ</td><td> Θ</td><td> Θ</td><td> s.</td><td> Θ</td><td> θ</td><td> Θ</td><td> θ</td><td> a</td>

<td colspan="2"> ~22&amp;*</td><td> □</td><td> LI</td><td> LI</td><td> □</td><td> U</td><td> u</td><td> u</td><td> LI</td><td> U</td><td> LI</td><td> LI</td>

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INVENTORS

John/ V. LJ-Cq$ra/ns Huph C.Ressler u ATTORNEY

Jan. 14, 1947.

J. V. L. HOGAN ET AL

GRAPHIC PRIVACY SYSTEM

Filed June 4, 1943

2,414,101

Sheets-Sheet 5

<img file="US2414101A_D0009.tif" />

<td> SIGNAL DESIGNATION</td><td> CL</td><td> b</td><td> c</td><td> d</td><td> e</td><td> f</td>

<td> signal frequency range</td><td> 500-700 CYCLES</td><td> 800*1120 CYCLES</td><td> 1300* 1820 CYCLES</td><td> 2000-2800 CYCLES</td><td> 3000-4200 ' CYCLES</td><td> 5000-7000 CYCLES</td>

<td> CORRESPONDING FILTER</td><td> s</td><td> It</td><td> i</td><td> J</td><td> k</td><td> I</td>

<td> FILTER PASS BAND</td><td> 500*700 CYCLES</td><td> 800*1120 CYCLES</td><td> 1300-1820 CYCLES</td><td> 2000-2800 CYCLES</td><td> 3000-4200 CYCLES</td><td> 5000-7000 CYCLES</td>

INVENTORS

C.TieR^Zer·

ATTORNEY

Patented Jan. 14, 1947

2,414,101

UNITED STATES PATENT OFFICE

2,414,101

GRAPHIC PRIVACY SYSTEM

John V. L. Hogan, Forest Hills, and Hugh C.

Ressler, Bayside,. Long Island. N. Y., assignors to Faximiie, Inc., New York, N. Y., a corporation of Delaware

Application June 4,1943, Serial No. 489,653

Claims.

The present invention concerns radio and wire facsimile systems and, in particular, a system for multiplex and/or secret transmission.

One object of the present invention is to provide an improved multiplex and/or secret system of facsimile transmission.

Another object is to provide a secret system of facsimile transmission in which the desired signal is obscured by fal'e picture, noise, tone, steady black and/or steady white signals.

Still another object is to provide a secret system of facsimile transmission in which a large number of signal sequences and combinations may be readily selected.

A further object is to provide a system of facsimile transmission which may be readily operated as a standard non-secret system, as a multiplex system, as a secret system or as a combined multiplex and secret system.

These and other objects will be apparent from the detailed description of the various figures of the drawings.

Briefly, the invention consists in sending over a wire line or a radio channel a plurality, of amplitude or frequency modulated sub-carrier signals. Each of the modulated sub-carriers represents frequency or amplitude variations around or at corresponding spaced mean frequencies. One or more of the modulated subcarriers contains the desired intelligence signal. Some or all of the remaining modulated subcarriers represent undesired signals. The undesired signals may include, for instance, one or more false pictures, random signals having the characteristics of the desired signal, random noise, an all black signal, an all white signal, and one or more steady or varying tone signals. The desired signal modulation is automatically interchanged with the various undesired signals in a predetermined sequence. The sequence is complicated but automatic and may be changed at will;

At the receiver a number of band-pass filters are provided, corresponding to the number of mean sub-carrier frequencies used at the transmitter. These filters are designed to separate the desired signal from all the undesired signals. The output of the correct filter, corresponding to the sub-carrier containing the desired signal, is selected automatically by means of a selecting system similar to that at the transmitter. One or more desired signals may be transmitted in multiplex with interfering signals on the remaining sub-carriers.

In order to eliminate transients in the received copy all switching is preferably done at the end of a scanning line, during the margin interval.

Any one attempting to intercept the transmission with a narrow-band receiving system will receive only disconnected lines of desired (Cl. 178—22) signal filled, in with the undesired signals.. With a broad-band receiving system, the desired signal will be entirely obscured by overlying undesired signals from several interfering channels. In 5 order to increase the effect of the undesired signals in some cases, the swing or amplitude of the undesired signals may be made considerably greater than that of the desired signal, increasing the effective modulation; with frequency i0 modulation their amplitudes may be made more than twice as great in order to “capture” the receiving system and effectively exclude the desired signal.

In the drawings:

Fig. 1 shows in block diagram a facsimile transmitter embodying the present invention.

Fig. 2 shows in block diagram a facsimile receiver embodying the present invention.

Fig. 3 shows a circuit diagram of a facsimile 20 radio transmitter embodying the present invention.

Fig. 4 shows a circuit diagram of a facsimile radio receiver embodying the same form of the invention and suitable for reproducing the sig25 nals from the transmitter of Fig. 3.

Fig. 5 shows a modified transposition drum construction.

Fig. 6 shows a further modified switch and drum construction.

Fig. 7 shows one possible frequency distribution of sub-carrier signals and filter characteristics.

Fig. 1 shows a block diagram of one form of the present invention. While not intended to 35 limit the invention in any way, a three element system is shown in which signals from a first desired picture scanner, a second desired scanner, and an interference generator are scrambled. This system provides duplex transmission and 40 secrecy. The three signals are distributed to modulate the three sub-carrier generators thru the circuit changers. The distribution is controlled by the circuit changers which in turn are operated in a predetermined sequence by the ¹⁵ joint operation of the stepping switch and' the transposition switch. The three sub-carriers are modulated by the three signals which in turn may be sent over a wire line or used to modulate a radio transmitter.

pig. 2 shows a receiving system for decoding and reproducing the two desired picture, signals. The sub-carriers from the wire line or the output of a suitable radio receiver are fed into three band pass filters each designed to' pick out' one 55 of the modulated sub-carriers to the exclusion of the other two modulated sub-carriers. The selected signals are fed to the two- recorders in the proper order corresponding to transmitter circuit changing sequence by means of the circuit 60 changers. The circuit changers are operated in

2,414,101 a sequence corresponding to the transmitter sequence by means of a similar stepping switch and transposition switch. While not intended to limit the invention, a preferred method of changing the sequence code is to change the circuits of the transposition switch.

The three channel system shown is capable of providing 720 sequences. Calling the sub-carrier

<td colspan="5"> frequencies A, B and C there are the following 6</td>

<td> orders:</td><td></td><td></td><td></td><td></td>

<td> A A</td><td> B</td><td> B</td><td> C</td><td> C</td>

<td> B C</td><td> C</td><td> A</td><td> A</td><td> B</td>

<td> C B</td><td> A</td><td> C</td><td> B</td><td> A</td>

<td> 1 2</td><td> 3</td><td> 4</td><td> 5</td><td> 6</td>

Numbering these orders 1 to 6 as shown above there are 720 possible sequences as follows:

<td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 5</td><td> 6</td>

<td> 1</td><td> 3</td><td> 2</td><td> 4</td><td> 5</td><td> 6</td>

<td> 1</td><td> 4</td><td> 3</td><td> 2</td><td> 5</td><td> 6</td>

<td> 1</td><td> 5</td><td> 4</td><td> 3</td><td> 2</td><td> 6</td>

<td> 1</td><td> 6</td><td> 5</td><td> 4</td><td> 3</td><td> 2</td>

and so on thru the full 720 sequences before repeating.

Fig. 3 shows one form of the present invention in which one desired signal is scrambled with five interfering signals by utilizing six different subcarrier channels. The various signal and subcarrier generators are shown in block since they may be conventional and are well known in the art. The “Desired picture scanner” I scans facsimile copy in any conventional manner as, for instance, copy attached to constant speed rotating drum 13. Scanner I scans the copy and generates and amplifies to any desired degree an electrical signal representing the light and shade of the copy on drum 13. Similarly “False picture scanner” 2 generates and amplifies a signal representing the light and shade of a false picture carried on the surface of drum 14. Drum 14 may be operated at the same speed as drum 13 and in phase or out of phase with it or it may be operated at a different constant speed or at a variable speed. The object of the false picture is to provide a confusing pattern or copy, which might be recorded at an intercepting receiver tuned broadly enough to include the false picture channel. The preferred false picture is similar to the desired picture so that in case both pictures are recorded there is no way of distinguishing between the two. “Noise generator” 3 generates a random noise signal as, for instance, by “shot effect” in a thermionic vacuum tube followed by a high gain amplifier, a controlled noise signal by amplifying power frequency hum or other noise signals, or a random signal generator generating random signals of the character of the desired signal. “Tone generator” 4 generates an interfering tone as, for instance, a complex wave made up of a number of sine wave alternating current signals mixed together and distorted to produce a wave form having maximum disturbing qualities. “Black-signal generator” 5 generates a steady signal representing full black in the system. “White-signal generator” 6 generates a steady signal representing full white in the system. Both black and white signals are generated so that no matter what phase of signal is used in a broadly tuned intercepting recorder one of them will produce a full black masking record. The interference caused by a “false picture” or a false signal resembling the picture signal in character has been found to be particularly effective interference in a secret transmission system.

In order to transmit the signals from generators i through 6 they are utilized to modulate six separate sub-carriers. Each of these sub-carrier generators operates at or around a predetermined mean frequency and may be either amplitude modulated or frequency modulated over a predetermined range above and below this mean frequency. While not intended to limit the number or values of frequencies usable under the invention, one possible arrangement of sub-carrier frequencies and normal frequency modulation ranges is given in the following, it being understood that the same sub-carrier frequencies might be amplitude modulated and, in that case, they might be more closely spaced: the first mean frequency may be 600 cycles per second with a normal modulation range of 500 to 700 cycles; the second mean frequency 960 cycles with a normal modulation range of 800 to 1120 cycles; the third mean frequency 1560 cycles with a normal modulation range of 1300 to 1820 cycles; the fourth mean frequency 2400 cycles with a normal modulation range of 2000 to 2800 cycles; the fifth mean frequency 3600 cycles with a normal modulation range of 3000 to 4200 cycles; and the sixth mean frequency 6000 cycles with a normal modulation range of 5000 to 7000 cycles. The first modulatable sub-carrier is generated by the “First sub-carrier generator” 7; the second by the “Second sub-carriei· generator” 8; the third by the “Third sub-carrier generator” 9; the fourth by the “Fourth sub-carrier generator” 19; the fifth by the “Fifth sub-carrier generator” ί ί; and the sixth by the “Sixth sub-carrier generator” 12.

Any one of the sub-carrier generators 7 through 12 may be amplitude or frequency modulated by any one of the scanner and signal generators I through 6. The modulation due to any of the generators i through 6 may be adjusted in its amplitude or swing by suitable means, such as the corresponding output controls 153, 154, 155, (56, (57 and (58. The modulated sub-carrier signals from generators 7 through 12 may be transmitted to a receiving point as, for instance, over a radio channel by utilizing them to modulate a radio transmitter (43 sending out signals from antenna 151. Modulated signals from generators 7 through 12 are conducted to radio transmitter 143 by means of the corresponding primaries 144, 145, 146, 147, (48 and 149 coupled to the common secondary (50.

The signals from generators I through 6 are connected individually to generators 7 through 12 in predetermined sequence by means of relays 65, 66, 67, 68, 69 and 70, including contacts 7f through 82, 83 through S4, 95 through (96, 107 through 1(3, 1(9 through (30 and 131 through 142 respectively. For instance, operation of relay 65 feeds desired picture signal from scanner I to first sub-carrier generator 7, false picture signal from scanner 2 to second sub-carrier generator 8 and so on. Operation of relay 66 feeds desired picture signal from scanner ( to sixth sub-carrier generator f 2, false picture signal from scanner 2 to first sub-carrier generator 7 and so on. Each of the remaining relays 67, 68, 69 and 79 connect generators I through 6 to generators 7 through 12 in a different sequence.

Relays 65 through 70 are operated by means of a suitable source of current, such as battery 34 acting through switch arm 25, one of contacts 26,

28, 29, 30, 32 and 33 and two interconnected contacts on drum 40, such as 46 and 47. Contacts through 33 are selected by rotating arm 25 by means of ratchet wheel 22 pulled by pawl 20.

2,414,101

Pawl 20 is pulled down by electromagnetic coil 19 energized by battery J 8 and a circuit completed through contact 15 riding on drum 13 and contact ί S on drum 13 closing the circuit to contact 17 once at each revolution of drum 13, and preferably phased to make this contact during the margin interval. Pawl 20 is returned to its initial position ready for the next stroke by spring 2i. As switch arm 25 is rotated a step at a. time, relays 95 through 70 are closed in a sequence which depends; on the way in which contacts 41 through ¢6 are connected to contacts 47 through 52. Drum βδ carries a number of sets of contacts interconnected in different ways, so that as it is rotated a step at a time by ratchet wheel 37 actuated by pawl 39, the sequence of closing relays 05 through 79 is changed. One set of contacts on drum 40 is shown in detail, that is contacts 53 through 64. Here contact 58 is connected to contact 60, contact 57 to contact 59, 56 to 62, 55 to S1, 54 to 64 and 53 to 63.

Drum 46 is moved one step each time coil 35 is energized by battery 34 acting through arm 25 and one of its associated contacts, a pair of contacts on drum 40, switch arm 27 and one of contacts 3 i, 2 i!, 212,213 and 214. For each position of arm 27, drum 48 is moved in a different order, changing the sequence of the closing of relays 65 through 70. The position of arm 27 may be set in a predetermined way at the start of transmission and may be shifted at predetermined intervals and in a predetermined order. A very large number of different sequences may be obtained in this way. A large number of drums SO may be provided as “keys” to the transmission sequences, each drum having different contact interconnections.

Fig. 4 shows a receiving system for analyzing the transmission of the transmitter of Fig. 3 and for reproducing the copy of the desired picture scanner correctly and free from interference from the false picture scanner, noise generator, etc. “Radio receiver” 162 connected to antenna 160 and ground 161 receives the radio carrier modulated with the six sub-carriers transmitted by the transmitter of Fig. 3. This radio carrier is selected, amplified and demodulated, producing the six modulated sub-carriers which are applied to the inputs of filters 163, 164, 165, 166, 167 and 168 over wires 289 and 2!9.

Filters 163 through 168 are band-pass filters passing bands corresponding to the transmitter sub-carrier modulation ranges. Fig. 7 shows one possible arrangement of transmission bands. Thus, corresponding to the transmitter of Fig. 3 the “First filter” 163 passes the frequency band of 500 to 700 cycles; the “Second filter” 164 passes 800 to 1120 cycles; the “Third filter” 165 passes 1300 to 1820 cycles; the “Fourth filter” 166 passes 2000 to 2800 cycles; the “Fifth filter” 167 passes 3000 to 4200 cycles; and the “Sixth filter” 168 passes 5000 to 7000 cycles.

The sub-carrier bearing the desired picture modulation is separated from the undesired subcarriers ty means of the proper filter, which is automatically switched into the circuit at the proper moment. The selected modulated subcarrier is applied to the input of “Demodulator and driver” 1 76 which applies recording signals to marking electrode 188. Marking electrode 180 records the desired picture on a suitable medium carried on or passing over the surface of recorder drum 177. Drum 177 is turned by synchronous motor 178 through shaft 179 in synchronism with the transmitter drum 13. Suitable power for operating motor 178 is generated by “Synchronous motor power supply” 175 and is fed to motor 178 over wires 207 and 208.

Connection of the correct filter into the circuit is accomplished by means of the same type of mechanism as is used at the transmitter of Fig. 3, including ratchet wheels 22 and 37 operating a corresponding selector switch and interconnecting drum in which the same numbers refer to corresponding parts. Ratchet coil 19 is energ'zed once for each revolution of drum 177 by means of contactors 182—183—184.

The relay system of the receiver of Fig. 4 includes coils 137, 188, 189, ISO, 191 and 192 corresponding to coils 65, 66, 67, 68, 69 and 70 respectively of the transmitter of Fig. 3. When coil 187 is energized, contacts 193-199 are closed, connecting filter 168 in the circuit, when coil 188 is energized, filter 167 is connected in the circuit between receiver 162 and scanner driver 176, and so on. Contact 27 at the receiver is turned to correspond to the coded position of contact 27 at the transmitter, so that the sequence of operation at the receiver corresponds exactly to that at the transmitter. In effect, the pass-band of the receiver follows the desired picture signal over the various sub-carriers automatically.

In order to adjust the system to correct for variations in frequence response or other causes of unequal response for the various bands, adjustable gain controls 169, 179, 171, 172, 173 and 174 are connected to filters 163, (64, 165, 166, 167 and i 68 respectively. These controls are particularly useful in the case of transmission over a long wire line.

Fig. 7 shows diagrams and a table setting forth the signal range and filter pass characteristics of the system shown in Figs. 3 and 4. The ranges of modulation frequency swings of the. various sub-carriers are shown at a, b, c, d, e and f. The characteristics of the corresponding band-pass filters for separating these signals are shown at g, h, i, j, k and Z. Evidently either frequency or amplitude modulation may be used, although frequency modulation is preferred.

While the, detailed description of the various figures of the drawings refer particularly to frequency modulation of the sub-carriers, the invention applies to amplitude modulation equally as well. The frequency modulated sub-carrier generators shown simply become amplitude modulated sub-carrier generators.

While six sub-carriers are shown in Figs. 3, 4 and 7, other numbers may be employed. A minimum of two are required in which one will generally have greater amplitude or a wider modulation swing to “capture” any broad tuned intercepting receiver and thus exclude response to the smaller modulation of the desired signal on the other sub-carrier. Also, there may be used four or indeed any number of pairs of such sub-carriers, in which one sub-carrier carries a desired signal and one the interference in each pair, the desired signal being automatically switched from one pair to another at each revolution of the scanning drum. Many other combinations are possible as, for instance, two desired signals and one interfering signal.

By spacing the various sub-carriers about a channel apart and varying the mean frequency in a predetermined pattern, such as may be determined by a cam control, a still higher· degree of privacy may be obtained.

Random multiplex transmission and reception may be obtained by transmitting different desired signals on more than one sub-carrier and utiliz2,414,101 , ing a corresponding number of recorders at the receiver. For instance, half the number of subcarriers utilized may carry desired multiplex signals while the remaining sub-carriers may carry interfering signals. Thus, the frequency spectrum available (as characteristic of the communication channel) may at will be used either to provide for the transmission of more intelligence with a lower degree of privacy, or less intelligence with a higher degree of privacy.

Although one embodiment of the invention has been described in conjunction with a facsimile system in which (a) the sub-carrier used is changed in value for each successive scanning line, in a selected sequence, and (b) the particular sequence in which the available sub-carriers are used for successive lines is changed at the end of each sequence, it should be noted that the sub-carrier change may be made at intervals either longer or shorter than the time required to scan a single line, and that the sequence change may be made at intervals either longer or shorter than the time required to run through a single sequence. It is not necessary that the rotary circuit-transposing drum 40 be rotated in a given direction by a single step at a time, it may be moved either clockwise or counter-clockwise and by any number of steps, thus contributing a further factor tending to increase the degree of privacy. Neither is the invention limited to the provision of privacy for the transmission of graphic material by facsimile, for an appropriate choice of interval between shifts from one sub-carrier to another (usually such an interval as will cause least interference with the transmission of the desired intelligence) and its attainment by the use of two synchronized contactors (one at either end of the system) will serve to provide privacy for other methods of electrical communication such as telegraphy, the teletype, telephony, etc.

Fig. 5 shows a modified form of transposition drum 40 of Figs. 3 and 4. The drum 220 of Fig. 5 includes twelve rows of contact points 217—219 without intent to limit the invention to any particular number. Six of the contacts in each row contact the input wires 216 while the remaining six contact output wires 218. The interconnection of the six input contacts with the six output contacts is varied from row to row of contacts. While there are many possible ways in which the row of contacts placed in the circuit may be varied, four stepping relays are shown. Relay 226 operating pawl 224 and rachet wheel 223 steps drum 220 one row of contacts at a time in one direction while relay 225 operating pawl 222 and rachet 221 steps drum 220 two rows of contacts at a time in the same direction. At the other end of drum 220 relay 232 operating pawl 228 and rachet 227 steps the drum one row of contacts at a time in the opposite direction. Likewise relay 231 operating pawl 230 and rachet 229 turns drum 220 two rows of contacts at a time in this second direction. A very great number of sequences are possible with this system as, for instance, one rotation of drum 220 one row of contacts at a time, one rotation in the opposite direction two steps at a time, five-sixth rotation two rows at a time, etc. Turning drum 220 end for end provides a further series of sequences. A large number of unlike drums may be provided and by replacing the drum a new series of sequences is possible. Changing the point at which the drums are started aiso varies the sequence.

Fig. 6 shows a further modification in which a drum 243 having commutator segments 240—241, etc., replaces the step operated contactor drums 40 of Figs. 3 and 4 and 220 of Fig. 5 and commutator switch 23B—237 replaces the step operated switch 25—26, etc., of Figs. 3 and 4. These commutator switches are driven continuously and preferably directly from the transmitter or receiver drum 233 thru shaft 234 which turns commutator switch 236—237 at the same speed as drum 233 or at a speed change obtained by means of gear box 244 and commutator drum 243 at a four to one speed reduction obtained by means of gear box 242 corresponding to the number of segments in commutators 246—241. Thus the outgoing circuit of switch 236—237 is changed at each revolution of drum 233 until six changes have taken place. The input wires 233 are connected in one order to outgoing wires 239 during these six changes by interconnection of the commutator bars 249—241, etc. At the end of the six changes, drum 243 has rotated to bring a new set of differently connected commutator bars into the circuit interconnecting wires 238 and 239 in a different order. With four changes of interconnections cn drum 243 and six circuits on switch 236—237, a series of twenty-four changes takes place before the sequence is repeated. It will be evident from this description that the invention is not limited to any particular number of changes in either switch or drum and hence that a series of any desired number of terms before repeating may be secured by using a larger or smaller number of circuits, commutator segments, and/or speed ratios.

While only a few embodiments of the present invention and a few modifications have been shown and described, many modifications will be apparent to those skilled in the art within the spirit and scope of the invention, as set forth in the appended claims.