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Publication numberUS2414101 A
Publication typeGrant
Publication dateJan 14, 1947
Filing dateJun 4, 1943
Priority dateJun 4, 1943
Publication numberUS 2414101 A, US 2414101A, US-A-2414101, US2414101 A, US2414101A
InventorsHogan John V L, Ressler Hugh C
Original AssigneeFaximile Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Graphic privacy system
US 2414101 A
Abstract  available in
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

Jan; 14, 1947. J. v, 1 HOGAN ET Al.

GRAPHIC PRIVACY SYSTEM Filed June 4, 1943 5 Sheets-Sheet l Jh VL INVENToRs 0 71, 7i-@Q75 JzgIz/iessler BY Wwf.

ATTORNEY Jan- 14 1947 J. v. L HOGAN ET AL GRPHI PRIVACY SYSTEM s sheets-sheet 2 Filed June 4, 1943 lJan. 14, 1947. J. v. L. HOGAN ET AL GRAPHIC PRIVACY SYSTEM 5 Sheng-sheet 3 Filed June 4, 1945 .NMP4-L 1.52m.



:l W M ATroRNEY 13111.14, 1947. J; v. 1 HOGAN ETAL 2,414,101

GRAPHIC PRIVACY SYSTEM Filed June 4, 1943 5 sheets-sheet 4 IN ouT 2/6 21a 2/7 x Y 2/ 9 22322 f' 220225 ll= 999999999099 :l 22/- :l:- o,o o o o o o o o nlm 222 l l! eeee-aeeeeeee22 4 250 E a a a a e a a e I I I l 3] o o 232 226 o 0 2 5.

O O 0 O C O 5 -`\\`*\\\\`n l I J n). J 1 l l INVENTCRS .aLN/YLJ-[ga/n/ Hzgy/essler %W?MA1TORNEY Jan. 14,1947. J. v. I.. HOGAN I-:TAL 2,414,101

GRAPHIC PRIVACY SYSTEM Filed June 4, 1943 5 Sheets-Sheet 5 SIGNAL RANGE;


ATTORNEY Patented Jan. 14, 1947 Malti GRAHIC PRIVACY SYSTEM .lohn V. L. Hogan, Forest Hills, and Hugh C. ltessler, Bayside, Long Island. N. Y., assignors to Faximile, Inc., New York, N. Y., a corporation of Delaware Application June 4, 1943, Serial No. 489,653

(ci. 17e- 22)v 2 Claims. l

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 sional is obscured by false picture, noise, tone, steady black and/r 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 lbe 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 pluralityl olf 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 subcar iers 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 transmittel'. rIhese 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 i 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. i Any one attempting to intercept the transmission with a' narrow-band receiving system will receive only disconnected lines of desired Z signal filledA in with the undesired signals.4 With a broad-band receiving system the desired signal will be entirely obscured by overlying undesired signals from several interfering channels. In 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 modulation their amplitudes may be made more than twice as great in order to capture the receiving system and electively 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 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 signals 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 subcarrier signals and filter characteristics.

Fig. l shows a block diagram 0f one form of the presentl invention. While not intended to limit the invention in any way, a three element system is shown in which signals from a rst desired picture scanner, a second desired scanner, and an interference generator are scrambled.

This system provides duplex transmission 'and secrecy. The three signals are distributed Vto modulate the three sub-Garder generators thru the circuit changers. The distribution is controlled by the circuit changers which inv turn are operated in a predetermined sequence by the joint operation of the stepping switch andthe transposition switch. The three sub-carriers are modulated by the three signals which iny turn may be sent over a Wire line or used to modulate aradio transmitter. I

Fig. 2 shows a receiving system for decoding and reproducing the two desired picturesignals. The sub-carriers from the wire line or'the output of a suitable radio receiver are fed into three band pass lters each designed to pick out'one of the modulated sub-carriers to the exclusion of the other two modulated sub-carriers. The selected signals are fed to the tworecorders -in the proper ordercorres'ponding to transmitter vcircuit changing sequence by means oi the circuit changers. The circuit clfiangers'` are .operate'd'in 3 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 frequencies A, B and C there are the following 6 orders:

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

I 2 3 4 5 6 I 3 2 4 5 6 I 4 3 2 5 6 I 5 4 3 2 8 I 6 5 4 3 2 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. carrier 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 rotat- 1.

ing drum I3. Scanner I scans the copy and generates and amplifles to any desired degree an electrical signal representing the light and shade of the copy on drum I3. Similarly False picture scanner 2 generates and amplies a signal representing the light and shade of a false picture carried on the surface of drum I4. Drum I4 may be operated at the same speed as drum I3 and in phase or out of iphase 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 4signal 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 E 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 falsepicture or a false signal resembling the picture signal in character has been found to be particularly effective interference in a, secret transmission system.

The various signal and sub- 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 Vpredetermined 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 rst mean frequency may be 600 cycles per second wi-th 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 1; the second by the Second sub-carrier generator 8; the third by the Third sub-carrier generator il; the fourth by the Fourth sub-carrier generator I0; the fifth by the Fifth sub-carrier generator II; and the sixth by the Sixth sub-carrier generator" I2.

Any one of the sub-carrier generators 'I through I2 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 |53, |54, |55, |56, |51 and |58. The modulated sub-carrier signalsfrom generators 'I through I2 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 I5I. Modulated signals from generators 'I through I2 are conducted to radio transmitter |43 by means of the corresponding primaries |44, |45, |46, |41, |48 and |49 cou-pled to the common secondary |50.

The signals from generators I through 6 are connected individually to generators 'I through I2 in predetermined sequence by means of relays 55, 66, I'I, E8, 69 and 10, including contacts II through 82, 83 through 94, 95 through |06, |01 through IIB, IIB through |30 and I 3| through |42 respectively. For instance, operation of relay 65 feeds desired picture signal from scanner I to first sub-carrier generator 'I, false picture signal from scanner 2 to second sub-carrier generator 8 and so on. Operation of relay 65 feeds desired picture signal from scanner I to sixth sub-carrier generator I2, false picture signal from scanner 2 to first sub-carrier generator I and so on. Each of the remaining relays 6T, 68, 69 and I0 connect generators I through 6 to generators 'I through I2 in a different sequence.

Relays 65 through 'I0 are operated by means of a suitable source of current, such as battery 34 acting through switch arm 25, one of contacts 26, 23, 29, 30, 32 and 33 and two interconnected contacts on drum 40, such as 46 and 47. Contacts 26 through 33 are selected by rotating arm 25 by means of ratchet wheel 22 pulled by pawl 20.

Pawl vis pulled down by electromagnetic coil i9 energized by battery i8 and a circuit completed through contact i5 riding on drum I3 and Contact i5 on drum I3 closing the circuit to contact I1 once at each revolution of drum I3, 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 2t'. As switch arm 25 is rotated a step at a time, relays 85 through 10 are closed in a sequence which depends; on the way in which contacts 4| through t8 are connected to contacts t1 through 52. Drum dit carries a number of sets of contacts interconnected in dierent ways, so that as it is rotated a step at a time by ratchet wheel 31 actuated by pawl "it, the sequence of closing relays {it} through 10 is changed. One set of contacts on drum is shown in detail, that is contacts 53 through 64. Here contact 58 is connected to contact 60, contact 51 to contact 59, to 62, 55 to 8|, 5ft to 64 and 53 to 53.

Drum B0 is moved one step each time coil 35 is energized by battery 3d acting through arm 2E and one of its associated contacts, a pair of contacts on drum at, switch arm 21 and one of contacts 3|, 2H, 2|2, 213 and 2M. For each position of arm 21, drum iid is moved in a different order, changing the sequence of the closing of relays through 10. The position of arm 21 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 diiferent sequences may be obtained in this way. A large number of drums it 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 |62 connected to antenna |00 and ground ISI receives the radio carrier modulated With the six sub-carriers transmitted by the transmitter of Fig. 3. This radio carrier is sclected, amplified and. demodulated, producing the six modulated sub-carriers which are applied to the inputs of ilters let, |84, |65, |56, |61 and |68 over wires 208 and 2 it.

Filters It through |68 are band-pass filters passing bands corresponding to the transmitter sub-carrier modulation ranges. Fig. '1 shows one possible arrangement of transmission bands. Thus. corresponding to the transmitter of Fig. 3 the First filter 68 passes the frequency band of 500 to 700 cycles; the Second filter |84 passes 800 to 1120 cycles; the Third lter |85 passes i300 to 1820 cycles; the Fourth filter Iii passes 2000 to 2800 cycles; the Fifth lter |51 passes 3000 to 4200 cycles; and the Sixth filter |68 passes 5000 to 7000 cycles.

The sub-carrier bearing the desired picture modulation is separated from the undesired subcarriers by 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 |16 which applies recording signals to marking electrode |88. Marking electrode records the desired picture on a suitable medium carried-on or passing over the surface of recorder drum |11. Drum |11 is turned by synchronous motor |18 through shaft |19 in synchronism with the transmitter drum I3. Suitable power for operating motor |18 is generated by Synchronous q, h, 1,9', lc and l.

motor power supply |15 and is fed to motor |18 over wires 201 and 208.

Connection of the correct iilter 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 31 operating a corresponding selector switch and interconnecting drum in which the same numbers refer to corresponding parts. Ratchet coil I9 is energzed once for each revolution of drum |11 by means of contactors I82-|33-|84.

The relay system of the receiver of Fig. 4 includescoils |31, |88, |89, |90, |9| and |92 corresponding to coils 65, 63, 81, E8, 58 and 18 respectively of the transmitter of Fig. 3. When coil |81 is energized, contacts igt-|34 are closed, connecting filter |68 in the circuit, when coil |88 is energized, filter |51 is connected in the circuit between receiver |62 and scanner driver |16, and so on. Contact 21 at the receiver is turned to correspond to the coded position of contact 21 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 |68, |10, |1l, |12, |13 and |14 are connected to filters ItS, |85, |55, |65, |51 and 863 respectively. These controls are particularly useful in the case of transmission over a long wire line.

Fig. 7 shows diagrams and a table vsetting forth the signal range and nlter pass characteristics of the system shown in Figs. 3 and 4. The ranges of modulation frequency swings of thevarious sub-carriers are shown at a, b, c, d, e and f. The characteristics of the corresponding band-pass iilters for separating these signals are shown at Evidently either frequency or amplitude modulation may be used, although frequency modulation is preferred.

While the` detailed description of the various gures 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 '1, 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 intel. cepting 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 diierent desired signals on more than one sub-carrier and utilizing -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 subcar riers are used forsuccessive 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 f a given direction by a single step at a time, it may be rnc-ved 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 ll of Figs. 3 and 4. The drum 220 of Fig, 5 includes twelve rows of contact points 21T-2l 9 without intent to limit the invention to any particular number. Six of the contacts in each row contact the input wires ZIB 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 228 one row of contacts at a time in one direction while relay 225 operating pawl 222 and rachet 22| 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 221 steps the drum one row of contacts at a time in the opposite direction. Likewise relay 23| operating pawl 23D and rachet 229 turns drum 22D 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 Vare started also varies the sequence.

Fig. 6 shows a further modication in which a drum 2&3 having commutator segments 24U-24|, etc., replaces the step operated contactor drums BD of Figs. 3 and 4 and 22u of Fig. 5 and commutator switch 23S-23'! 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 236-231 at the same speed as drum 233 or at a speed change obtained by means of gear b-ox 244 and commutator drum 243 at a four to one speed reduction obtained by means of gear box 2152 corresponding to the number of segments in commutators Nil-21H. Thus the outgoing circuit of switch 236-231 is changed at each revolution of drum 233 until six changes have taken place. The input wires 238 are connected in one order to outgoing wires 239 during these six changes by interconnection of the commutator bars 24g-24|, etc. At the end of the six changes, drum 2l3 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 23S- 237, a series of twenty-four changes takes place before the sequence is repeated. It wil1 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.

What is claimed is:

1. In a system for privacy transmission of a line by line facsimile, the combination of, a source of desired facsimile signals, a source of undesired signals, at least two sources of sub-carrier signals of slightly dierent frequency, means for frequency modulating one of said sub-carriers with said desired signals, means for frequency modulating at least one other of said sub-carriers with said undesired signals at predetermined intervals integral multiples of the line frequency of said facsimile, and means for combining said modulated signals to provide privacy in the transmission of said desired signals.

2. In a privacy facsimile transmission system, the combination of, means for generating a lineby-line desired picture signal including margin intervals, means for generating an undesired signal, means for generating two carrier signals, means for modulating one of said carriers with said picture signal, means for modulating the other said carrier with said undesired signal, and means for interchanging said modulations at predetermined intervals during said margin intervals to provide privacy in the transmission of said desired picture signal.


Non-Patent Citations
1 *None
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2510046 *Apr 18, 1947May 30, 1950Zenith Radio CorpRadio-wire signaling system
US2547598 *Sep 13, 1947Apr 3, 1951Zenith Radio CorpSubscription image transmission system and apparatus
US2551068 *Oct 5, 1948May 1, 1951Zenith Radio CorpCoded-sound, television receiver
US2601505 *Mar 23, 1949Jun 24, 1952Zenith Radio CorpSubscription type television transmitter
US2612552 *Jun 10, 1949Sep 30, 1952Zenith Radio CorpSubscription type signaling system
US2636936 *Sep 10, 1946Apr 28, 1953Rca CorpTelevision secrecy system
US2649498 *Mar 3, 1949Aug 18, 1953Zenith Radio CorpBlanking arrangement for subscription television receivers
US2656408 *May 21, 1949Oct 20, 1953Zenith Radio CorpSubscriber signaling system
US2656411 *Sep 5, 1951Oct 20, 1953Zenith Radio CorpTelevision subscriber signaling system
US2677719 *May 29, 1948May 4, 1954Zenith Radio CorpSubscriber television system
US2678347 *May 19, 1949May 11, 1954Clothier Stewart LTelevision control system
US2707208 *Mar 31, 1945Apr 26, 1955Rca CorpSecrecy facsimile system
US2710343 *Aug 9, 1950Jun 7, 1955Dale BelfordSecrecy system for transmitting television signals
US2823252 *Dec 15, 1952Feb 11, 1958Zenith Radio CorpSubscription television system
US2843654 *Dec 1, 1951Jul 15, 1958Internat Telemeter CorpSubscription television system using land line
US2843655 *Dec 3, 1951Jul 15, 1958Internat Telemeter CorpSubscription television with scrambled transmission and marquee and barker
US2847500 *Aug 9, 1951Aug 12, 1958Zenith Radio CorpSubscription television system
US2862049 *Feb 4, 1955Nov 25, 1958Zenith Radio CorpSubscription television
US2866961 *Feb 1, 1954Dec 30, 1958Zenith Radio CorpSubscription television encoding apparatus
US2875268 *Oct 18, 1952Feb 24, 1959Zenith Radio CorpSubscription television system
US2912486 *Jan 12, 1955Nov 10, 1959Skiatron Elect & TeleSubscription television system
US2952735 *Apr 18, 1955Sep 13, 1960Paramount Pictures CorpSecrecy system
US2954423 *Dec 5, 1957Sep 27, 1960Zenith Radio CorpSubscription television
US2956110 *Aug 25, 1954Oct 11, 1960Skiatron Elect & TeleScrambled television
US2961482 *Nov 26, 1956Nov 22, 1960Paramount Pictures CorpCryptography system
US2974188 *Dec 19, 1956Mar 7, 1961Citizens Bank Of MarylandBilateral video transmission system
US2983781 *Jan 12, 1955May 9, 1961Skiatron Elect & TeleTelevision
US3011015 *Jan 4, 1955Nov 28, 1961Skiatron Elect & TeleTelevision
US3069492 *Oct 10, 1957Dec 18, 1962Blonder Tongue ElectScrambled television apparatus and method
US3106604 *Jan 12, 1955Oct 8, 1963Skiatron Elect & TeleMultiple code subscription television system
US3107274 *Dec 31, 1954Oct 15, 1963Zenith Radio CorpSubscription television
US3231818 *Nov 9, 1961Jan 25, 1966Paramount Pictures CorpAudio secrecy system for subscription television
US3274333 *Oct 23, 1952Sep 20, 1966Skiatron Elect & TeleScrambled television system
US4177486 *Dec 2, 1944Dec 4, 1979Prehn Lawrence DFacsimile device
US4343970 *Feb 19, 1953Aug 10, 1982Bell Telephone Laboratories, IncorporatedSignaling system
US4392021 *Jul 28, 1980Jul 5, 1983Technical Communications CorporationSecure facsimile transmission system using time-delay modulation
U.S. Classification380/243, 358/425, 380/26, 358/408
International ClassificationH04N1/44
Cooperative ClassificationH04N1/448
European ClassificationH04N1/44S