US2429787A - Duplicate transmission - Google Patents

Description

Oct. 28, 1947. 1 N. H. YOUNG, JR 2,429,737

DUPLICATE TRANSMISSION Filed April 24, 194s 2 sheets-sheet 1 INVENTOR. /voRMA/v' H. You/f6 JR.

N. H. YOUNG, JR

DUPLICATE TRANSMISSION Oct. 28, -1 947.

Filed April 24, 19434 INVENTOR /va/PM/l/v H. rau/v6.13?

Patented Oct. 28, `1947 assigner to Federal Telephone and Radiocorporation, Newark, N. J., acorporation of Dela- Application April 24, 1943 Serial No. 484,793

18 Claims.

This invention relates to improvements 'in methods and means for Vtransmitting intelligence, and more particularly to a facsimile transmission system in which Vthe elfectof interference, as by jamming is minimized.

It is an object of the present invention to provide a novel method of transmitting facsimile intelligence.

Another object of this invention is the provision of a novel facsimile transmitting ,and receiving system Which minimizes the effect of jamming interference.

A further object of this invention is to provide a transmission system inwhich a portion of the 'transmitted signals are sent out in a reverse sense, and in which the receiver transposes the reversed signals and applies them, together With the normal signals, to a signal reproducen A still further and more specic aspect of the present invention is directed toward a system for transmitting facsimile intelligence, wherein each character to be transmitted is sent alternately in a positive and reverse sense as a positive and re- Verse set of pulses, While the receiver includes' timed means for alternately passing the positive set of signals and transposing the reverse set of signals and applying both to a suitable reproducer.

Further objects and advantages of this invention will be apparent from consideration of the specification as illustrated bythe accompanying drawings of possible embodiments of the invention, in which drawings Fig. 1 is a block circuit diagram illustrating the transmitter portion of the system according to the present invention;

Fig. 2 is a'circuit diagram, partially in block form illustrating the receiving portion of the transmission system;

Fig. 3 illustrates a portion of a transmitting drum illustrating the manner in which the characters to be transmitted can be formed in accordance with the present invention;

Fig. 4 is a graphical analysis of the manner in which a typical character can be formed by the drum' portion illustrated in Fig. 3;

Fig. 5 is a block circuit diagram of a modied form of receiving system; and f Fig. 6 is a partial block circuit diagram of a further modified form of receiving system.

In one example of a complete transmission system illustrated in Figs. 1 and 2, Fig. 1 shows a transmitting system generally indicated at l0. This system will consist essentially of a suitable keyboard l2 operating shutters (not shown) 2 which control 'light-controlling slits for use in conjunction with a druin |'4 provided with longitudinally spaced rovv's, each rovv consisting of al' ternate opaque and translucent portions corre- 5- spending to a character to be Vtiansn'iitted and to be more particularly described hereinafter. That row an the drum .|'4 selected by the keyboard l2 operates a suitable control ,circuit I6 'to provide a series of character-corresponding pulses which 10 are used to key a high frequency source i8. En-

orgy from high frequency source 4la is suitably amplified by an amplifier 2u connected to a transymitter i2?. Except for the novel characteristics of' the drum I 4, mentioned above Aand to be described hereinafter, the transmitting system Il) is already known. Such a transmitting system 'has been previously proposed, *for* example, in the copending applications of Edmond M.' Deloraine, S. N. 415,554, filed October 18, 1941, and Edmond M. Deloraine et al., S. N. 469,056, ll-iled .December l5, 1942, and forms no part of the: present invention per se.

The receiving system illustrated in Fig. 2 and gener'ally .indicated at `26 will consist essentially of suitable deniodulating' apparatuszs the output of which is connected to an ampliners. In accordance with 'the present invention, the amplier may .consist of several stages of which the rst'stages 32 maybe ci conventional design while the last stage win include a suitable electrondischarge device 34 from which two output leads 3s and 38 are derived from the anode and cathode respectively. The output of the amplifier' is connected to the grid of a cathode ray tube 4l), a

35 switch 4'2 being adapted to alternately connect the output leads 36 and 38 vvithtnis grid. in accordance with the present Vinvention'the switch 62' may be a single-pole double-throw vibratory switch having a switch ann M and an operating 40 coil '46.

It will be clear' to those skilled in this art that in any facsimile system vthe scanning voltages on the cathode ray tube 40 Yhave to be synchronized With the transmitted signals'. Any suitable synchronizing means may be used, and in Fig. 2 I

have illustrated an arrangement which is similar to that disclosed in the aforesaid E. M. rDelorain'e et al'. application. This synchronizing arrangenient4 may consist' of a motor 48, which may be a sychronous 'motor driving a suitable variable speed control device 5 which, in turn, drives a scanning source 52- of any suitable Well-known type. This scanning source 52 is connected to and controls a line and frame scanning lsourceI 5651i which `provides suitable control voltages for' 3 the opposite plates of the cathode ray tube 4G. The scanning source 52 may also supply a synchronous voltage to the coil 46 of the vibrating switch 42. The manner of operation and the function of the aforedescribed receiving system will now be described in more detail. It is contemplated according to the present invention that each row of the control drum I4 represented by alternate opaque and translucent sections for each character be so constructed as to provide alternate groups of pulses for each character, these groups forming pulses in opposite senses. For example, if the transmitting system operates upon a 7line basis as is known to the art, a character such as the letter T can be built up by a series of pulses which will'result by uncovering the corresponding row of the drum |4, this row consisting of sets of translucent sections such as spaced slits a, b, c, d, e, f, g, as shown in Fig. 3. These slits will produce pulses a', b', c', d', e', f', g (Fig. 4(B)) which, on a cathode ray tube will, in turn, produce the sections a, b, c, d, e, f, g (Fig. 4(A)), for building up the character. This arrangement in itself is disclosed in the previously mentioned copending applications and similar arrangements are also known in prior art patents. In accordance with the present invention, however, one set of openings for producing this positive picture of the desired character is followed by a second set of openings or translucent portions of the drum to form a reversed character, as the negative of a lm. In other words, the control pattern forming the reversed letter is so designed as to provide light sections on the cathode ray tube corresponding to the dark sections of the character as rst transmitted and vice Versa. In Fig. 3 these corresponding sections t, u, o, w, zr, y, e, are represented by opaque portions of the drum of the same size and spacing as the respective translucent sections a, to g inclusive. As shown in Fig. 4(C) the opaque portions t to a inclusive on the drum of Fig. 3 will result in absences of pulses t', u', o', w', 1r', y', a', which are the reverse of the positive pulses a' to g inclusive of Fig. 4(B). the letter T and the manner it is built up will be at once apparent from a study of Fig. 4(D).

In the preferred form of the present invention, the drum I4 is so designed that each line representing a character will produce groups of pulses for each character, the groups being alternatelj7 reversed so that at the receiver 26 for any one character there will be received first a group of positive pulses which would produce a positive indication of the character on the oscilloscope 4@ followed by a group of pulses which would produce the reverse image of the character. In accordance with the present invention, however, the receiver includes means whereby the reverse group of pulses for each character is transposed so that only positive pulses will be applied tothe oscilloscope 40. This transposition of the reverse pulses without changing the original positive pulses can be effected in several ways. In the form of invention shown in Fig. 2 it is accomplished by providing two output leads from the last amplifier stage, one lead being derived from the anode in the usual manner which may give, for example, the positive pulses without change, while the other lead 38 is connected to the cathode so that the reverse pulses appearing there will be transposed into positive pulses as those appearing on the lead 36. In order to make the average potential of the outputs the same, the condensers C1 and C2 and the resistors R1, R2 are The resulting picture of so dimensioned that the time constants of C1, R1, and C2, R2 of the output network are sufficiently long. T'he vibratory switch 42 is synchronized by the-apparatus previously described so that its switch arm 44 will contact the output,

lead 36 when the positive pulses are appearing thereon, while it will contact the output lead 38 when the reversed pulses now transposed to positive pulses are appearing thereon. This synchronization may be accomplished by adjustment of variable control device 50 until the visual image on the screen of cathode ray tube 40 becomes brighter indicating the superposition of the two received images. Thus, alternate sets of positive pulses are always applied to the cathode ray tube 4l] despite the fact that the transmitter I sent out and the received 26 received alternate sets of positive and reverse pulses for each character.

The advantages of the foregoing system in avoiding jamming interference will be at once apparent to those skilled in this art. Unless the jamming station knows full details of the system described herein, it will send out normal positive jamming signals to jam the positivev pulses which are being sent out from the transmitter I0. While some of this jamming interference would then interfere with the reproduction of the character produced in the usual manner by the pulses a to g inclusive, they would not interfere with the reproduction of the character resulting from the absence of pulses t to e inclusive. In other words, the proposed system involves the transmission of two opposite types of pulses so that if one type is successfully jammed the other will come through and identication of the intelligence to be transmitted is assured.

Other arrangements may be used to alternately switch the positive and transposed pulses synchronously to the cathode ray reproducer. In Fig. 5, for example, the receiving stations |26 may consist of a receiver 28 and a multi-stage ampliiier |30 which may be similar to the amplifiei` 30 of Fig. 2 without the condenser-resistor output network. The two output leads from the amplifier |30 are fed to an electronic switch of any suitable well-known construction, the operation of which may be synchronized by a synchronizing voltage source such as provided by the arrangement shown in Fig. 2. The output from the electronic switch can be fed through a suitable levelling amplifier 60 of the type now known in television systems to equalize the two sets of pulses, and thence to the cathode ray tube or other facsimile reproducer 40.

In the switch arrangement illustrated in Fig. 6, the receiving system 22B will be identical with that illustrated in Fig. 2 except that in this case a rotary mechanically driven reverse switch may be used in place of a vibratory switch. This rotary switch'62 may include, for example, two rotating conducting sections 64 and 66 fed from the amplier 39 through suitable slip rings and alternately contacting a stationary brush 68 connected to the facsimile reproducer 40.

While the principles of the foregoing system have been described for purposes of Yillustration in connection with certain apparatus, it will be apparent to those skilled in this art, that broadly speaking, the principles of this invention are applicable to other types of facsimile and builtup character systems. For example, instead of forming the positive and reverse pulses by a rotating drum, the same could be formed by opaque and translucent portions in a rotating disc and employed in a system such as disclosed in my copending application, S. N. 456,651, led August 29, 1942. Additionally, while the reproducer has been illustrated as in the form of a cathode ray tube, it is clear that the principles of the present invention are equally applicable, for example, to photographic reproducers.

While I have illustrated a straight multi-stage amplifier in which the positive and transposed signals are derived `from the anode and cathode of the last stage, for the purpose of transposing one set of pulses, a similar result could be obtained by using two parallel amplifiers, one of which could contain an even number of stages and the other an odd number of stages, although unless compensated for this would have the disadvantage oi making one signal stronger than the other. Furthermore, while I have illustrated several forms of switch arrangements for applying the alternate sets of pulses to the reproducer, it will be clear to those skilled in this art that any switching system which can provide synchronous commutation may be employed. Accordingly, while I have described above the principles of my invention in connection with specific apparatus and certain modications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of my invention as set forth in the objects and the accompanying claims.

I claim:

1. The methodof transmitting intelligence, which includes the steps of sequentially producing positive and reverse sets of pulses repetitive of the same character to be transmitted, transmitting said positive and reverse sets of pulses, receiving said positive and reverse sets of pulses, transposing said reversed pulses into positive pulses at the receiver, and alternately applying the received positive pulses and the transposed reverse pulses to a character reproducing device.

2. An intelligence transmission system comprising, in combination, means for sequentially producing positive and reverse sets of pulses corresponding to a character to be transmitted, a transmitter controlled by said means, a receiver, means connected to said receiver for transposing said reverse pulses into positive pulses, a character reproducer, and switching means alternately connecting the received positive pulses and the transposed reverse pulses to said character reproducer.

3. The combination according to claim 2, in which said character reproducer includes a cathode ray tube, a line and frame scanning source for said cathode ray tube and variably timed means controlling said scanning source, in combination with means for controlling said switching means from said variably timed means.

4. The combination according to claim 2, in which said character reproducer includes a cathode ray tube and line and frame scanning means therefor, in combination with means synchronizing said scanning means and said switching means with the received signal.

5. The combination according to claim 2, in

which said switching means is an electronicl switch, in combination with means synchronizing the operation of said switch with the incoming signals.

6. The combination according to claim 2, in which said switching means is a single-pole, double-throw vibratory switch, in combination with means synchronizing the operation of said character reproduced and said vibratory switch with the kincoming signals.

which said character reproducer includes a cathode ray tube, and a line and frame scanning source for said cathode ray tube, and in which said switching means comprises a rotary sing-lepole, double-throw contactor, in combination with motor-driven means controlling said scanning source and operating said rotary contactor.

8. The combination according to claim 2, in which the means for transposing said pulses comprises an ampliier including an electron discharge device having an anode, a cathode and a grid, an output lead for one set of pulses connected to said anode, and an output lead for the opposite 'set of pulses connected to said cathode, in combination with means for equalizing the level of the two sets of pulses appearing Lon the output .leads- Y 9. In an intelligence transmission system kof the type in which a keyboard controls the transmission of light to a light-sensitive source through a rotatable drum perforated with a plurality of sets of perforations corresponding to characters to be transmitted, the combination of means forming and transmitting pulses in accordance with the sets of perforations chosen by the keyboard, the sets of perforations on the drum corresponding to a character to be transmitted including alternate groups to provide positive and reverse sets of pulses for each character, a receiver, means at said receiver for transposing said reverse set of pulses into positive pulses, a character reproducer, and switching means alternately connecting the received positive pulses and the transposed reverse pulses to said character reproducer.

10. The combination according to claim 9, in which said character reproducer includes a cathode ray tube, a line and frame scanning source for said cathode ray tube and variably timed means controlling said scanning source, in combination with means for controlling said switching means from said variably timed means.

11. The combination according to claim 9, in which said character reproducer includes a cathode ray tube and line and frame scanning means therefor, in combination with means synchronizing said scanning means and said switching means with the received signal.

12. The combination according to claim 9, in which said switching means is an electronic switch, in combination with means synchronizing the operation of said switch with the incoming signals.

13. The combination according to claim 9, in which said switching means is a single-pole, double-throw vibratory switch, in combination with means synchronizing the operation of said character reproduced and vibratory switch with the incoming signals.

14. The combination according to claim 9, in which said character reproducer includes a cathode ray tube, and a line and frame scanning source for said cathode ray tube, and in which said switching means comprises a rotary singlepole double-throw contactor, in combination with motor-driven means controlling said scanning source and operating said rotary contactor.

15. The combination according to claim 9, in which the means for transposing said pulses comprises an amplifier including an electron discharge device having an anode, a cathode and a grid, an output lead for one set of pulses '1. The combination according to claim 2, in

connected to said anode, and an output lead for the opposite set of pulses connected to said cathode, in combination with means for equalizing the level of the two sets of pulses appearing on the output leads.

16. A control drum for the generation of character-signifying signals, having a plurality of longitudinally spaced sets of indicia, each set being in the form of alternate opaque and translucent sections of varying size related to the signal to be generated, each set having at least one group of alternate opaque and translucent sections to generate a positive character-identifying signal followed by a group of alternate opaque and translucentsections generating a reversed character identifying signal.

17. An intelligence transmitting system comprising, in combination, means for sequentially producing positive and reverse sets of character signals repetitive of the same character to be transmitted, and transmitting means operated by said signal producing means.'

18. A receiver of intelligence in the form of alternately sensed repetitions of character signals comprising, in combination, receiving means, a signal reproducer, and timed means for alternately reversing the sense of the received character signals and applying the same to said reproducer.

' NORMAN I-I. YOUNG, Ja.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,199,634 Koch May 7, 1940 1,474,426 Affel Nov. 20, 1923 1,563,326 Bown Dec. 1, 1925 1,935,776 Hammond, Jr. Nov. 21, 1933 1,312,574 Pierce Aug. 12, 1919

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