US2174490A - Telephoto system - Google Patents

Description

Sept. 26, 1939. F. .1. SOMERS TBLEPHOTO SYSTEM Filed larch 27, 1935 4 Sheets-Sheet 1 RF. R./--. R. E ggizg BUFFER AMP 'AMP. AMP.

VISUAL MON! TOR 2 STAGE I2 0. c. AMP. AMP- AMP. FOR SYNC.

PULSES;

AB C D E F G H J K INVENTOR Sep t..26, 1939. F. J. SOMERS 2,174,490

TELEPHOTO SYSTEM Filad March 27, 1955 4 Sheets-Sheet 2 fig .3

INVENTOR. 90 FRANK J. SOMERS.

' ATTORNEYS.

Sept. 26 19392 F, SGMERS 2,174,490

TELEPHOTO SYSTEM Filed March 27, 1935 4 Sheets-Sheet 3 RAD/ RECEIVER I PULSE AMP.

Ago, [62 04: 2.1 I I63 r04 3;; 16% fig E2 {29 v Y; II, p y *MIIIIII. WI I Y //8{ I I o I W {a a I AUTOMATIC vla 'z a fgk V. & FIX/N6 L0] I I L F. I 127 I r I V 3 STEP BYSTEP n wmiibfififl, .21 TRANSMITTER FRANK J. SOME RS ATT Patented Sept. 26, 1939 TELEPHOTO SYSTEM Frank J. somers, San Jose, Calif., assignor, by

mesne assignments, to Farnsworth Television & Radio Corporation, Dover, De l., a corporation of Delaware Application March'27, 1935, Serial No. iazss 9 Claims.

I My invention relates to a system for transmission of visual information at a distance and relates more particularly to a system designed to transmit and receive images having several gradations of light value.

Among the objects of my invention are: To provide a telephoto system wherein transmission is satisfactory over a circuit or channel where the signal-to-noise ratio may be as low as 2 or 3-1;

to provide a system adapted for the transmission and reception of photographs, drawings or the like, in so-called half-tone form; to provide a system adapted for the transmission of photographs having various degrees of light and shade; to provide inertia limitations; to provide a telephoto system whereby enlargement or reduction may be made in the size of the reproduced image from that of the original picture field; to provide a system for the transmission of photographs or other half-tone reproductions to a distant point, utilizing the lower grades of commercial channels, either wire or radio; to provide 'a system of telephoto transmission having a minimum interfer- 5 ence factor; to provide a telephoto system capable of operating at high speed; to provide a telephoto system utilizing certain desirable characteristics of a grid-controlled arc-rectifier; to provide a telephoto system wherein amplitude changes during transmission have a minimum effect upon the received image; to provide a telephoto-receiving system giving a record in permanent form and a visual image simultaneously; to provide a telephoto-receiving system wherein photographs or other half-tones can be made available at least in part immediately upon reception and be preserved in recorded total form thereafter; to provide a telephoto system utilizing desirable characteristics of cathode ray tubes; to provide a simple and eflicient means and method of transmitting telephoto images over wire or radio channels; to provide a" telephoto system wherein the transmitted impulses are all of equal amplitude irrespective of the degree of light and shade they represent; to provide a telephoto system which can be operated over channels hitherto adapted only for facsimile transmission; to provide a means and method for selecting impulses of uniform amplitude from a heterogeneous train of impulses having varying magnitudes; to provide a means and method of transmitting half-tone picture fields, which includes direct scansion of three dimensional subjects and reproducing said images and/or subjects in the form of a multitone photographic record and as a visual picture a telephoto system having minimum therein.

simultaneously; and to provide a preferred telephoto system utilizing at least in part certain desirable characteristics of any or all of the inventions disclosed and claimed in the following patents and applications:

Patent N o.

Rutherford Issued Philo T. Famsworth 1,773,980 Aug. 26,1930 Philo T. Farnsworth 1, 970, 036 Aug. 14,1934

Serial No. Filed Farnsworth 270, 673 Apr. 17, 1928 Fernsworth 321,805 Nov. 26,1928 Farrisworth and Lubcke. 449, 985 May 5, 1930 Farnsworth 449, 98 May 5, 1930 461, 111 June 14, 1930 Dec. 4, 1930 550,653 July 14,1931 614, 500 May 31, 1932 Farnsworth 664, Apr. 3, 1933 696, 994 Nov. 1 7, 1933 and others.

Certain features herein disclosed are more fully described and claimed in my co-pending application, Serial No. 13,252, filed March 27, 1935, for

a facsimile system, the preferred embodiment of the present invention utilizing some features in common with the preferred embodiment shown My invention possesses numerous other objects and features of advantage, some of which, gather-with the foregoing, will be set forth in the following description of specific apparatus embodying and utilizing my novel method.

Itis therefore to be understood that my method is applicable to other apparatus,

and that I do not limit myself, in any way, to the apparatus of the present application, as I may adopt various other apparatus embodiments, utilizing the method, within the scope of the appended claims.

Referring to the drawings:

Figures 1 and 2, when combined, form a diagrammatic circuit reduced to lowest terms of a preferred form of telephoto transmitter employing my invention. In order that the diagram may be conveniently followed in the break between the two figures, circuit connections common to the two figures are lettered on each figure with corresponding characters from A to K,

, inclusive.

Figure 3 is a diagram representing a preferred waveform for rectifier anode supply.

Figure 4 is a circuit diagram reduced to lowest terms of a preferred telephoto receiver.

Figures 5 and 6 are diagrams representing the characteristic curves of the grid-controlled arc rectifiers, showing preferred steady biasing values.

Figure 7 is a diagram showing the preferred varying'bias values ofthe arc-controlled rectifier.

In comparing telephoto transmission with facsimile transmission, it will be found that telephoto is, in a number of respects, more complicated in the equipment required. Defining the terms as herein used, telephoto transmission comprises the transmission of an original picture field and the reproduction of that field preferably and usually at a distant receiving station in all orat least part of its intermediate shades or half-tones. 0n the other hand, facsimile transmission does not attempt to transmit partial values, but merely transmits the extreme contrasts of black and white. Telephoto, therefore, adds to the problem of facsimile the necessity of transmitting relatively fine variations of amplitude due to closely adjacent shades in the original picture field, in addition to the extreme contrasts of black and white. The usual systems of telephoto heretofore disclosed attempt to scan a picture field with an aperture, the number of shades transmitted between complete black and complete white being regulated by controlling the size of the aperture. It has usually been thought desirable to make the aperture as small as possible, thereby securing a large number of value levels between the extremes of light and dark. This procedure leads to a signal train of extremely high frequency, and consequently, if modulatedon a radio carrier, leads to wide side bands, and the necessity for wide channels; and if sent over a wire line requires special phase correction and other corrections well known in the art to prepare Iiihe (lline for the transmis' sion of a wide frequency Furthermore, such prior telephoto transmission is based upon amplitude relations and the channels not only require correction, but also require a signal-to-noise ratio of at least 20-1 for satisfactory transmission. My instant invention, however. provides satisfactory telephoto transmission on a radio circuit or other channels where the signal-to-noise ratio is as low as 2 or 3-1, and also utilizes signals of uniform amplitude. Consequently, a less expensive channel can be used,

as signals for telephoto transmission can be in the form of interrupted and successive uniform amplitude impulses, of amplitude modulation. No substantial phase or frequency corrections are necessary, providing: the radio circuits and equipment are designed with ordinary care according to practices well known in the art. 7

I have found that there are certain desirable characteristics inherent in the Farnsworth system of electronic scanning, as exemplified, descrlfatd and claimed in the foregoing list of patents and applications, for my new purpose will produce a preferred system which is ideal for the transmission of telephoto images. It should be fully understood, however, that 'I do not wish in any way to bev limited to the use of the particular apparatus described by Farnsworth and others listed, and it is also to be understood that the actual apparatus used is subject to design variations according to conditions to be met for any particular installaons.

thus obviating the necessity which, when combined and adapted In order, however, that the broader aspects of my invention may beunderstood, which can, as will be apparent to those in the art, be attained by the use of other apparatus, I shall describe herein a preferred embodiment of apparatus to illustrate my invention comprising a complete system for the transmission of telephoto images.

Broadly described, the circuit shown in Figures 1 and 2 is designed to provide for the transmission of half-tone or variable shade pictures without the necessity of resorting to the usual method of continuously varying the amplitude of the carrier in accordance with the varying lights and shades appearing in the picture.

In my present system, it is only necessary to key the transmitter so that all the impulses except those" used for synchronizing are of the same shape, amplitude and duration. The pulses which are sent out may be square-topped or rounded, it merely being required that they be uniform;

This method of transmission is obtained by scanning the picture in such a way that the final signal impulses are all of the same length and duration but are sent on a time-distribution basis according to (a) the light intensity of the individual elements which go to make up the picture, and (b), their respective positions on the picture. In this respect, it should be understood that the word picture as herein used to describe the picture field to be transmitted, may be either a twodimensional photograph or similar image, or it may be a three-dimensional subject, producing-a two-dimensional optical image on a scanning means.

In practice, the signal train may be obtained by a modification of the ordinary method of scanning a picture a line at a time. In the modification, each line is scanned several times before going to the next, and on each scanning of the same line, the transmitter sends out pulses representing picture elements of one range of light in; tensities only. Thus, if each line isscanned five times, five different shades, ranging from black I way from the spirit of my'invention.

While it is true that the picture is in effect scanned several times for one transmission, when this method is used, the number of picture elements transmitted during the scanning is not reater than that which would be obtained in the ordinary scanning method where variable modulation is used, and the same tone grad tion is used.

The two main advantages of the system to be described are:

1. The equipment can be made to operate in cases where the signal-to-noise ratio at the receiver is only 3-1 or less compared to a ratio of 20-1 required for variable amplitude transmission;

2.-An ordinary radio transmitter such as is used for code messages can be used as it is only .top of Figure 2.

far as transmission is concerned, a wire channel adapted to carry the keying frequency is perfectly satisfactory, and the full equivalent of a radio channel. I I

In describing a preferred form of transmitter adapted for telephoto transmission over a radio telegraph channel, I shall refer to Figures 1 and 2, the two figures when combined, forming the complete -circuit. The circuit has been divided at the bottom of Figure land continued at the The letters A to K inclusive indicate continuations of the same circuit connection. In explaining my transmitter hereafter, the circuit will be described as if it were joined into one complete diagram without further reference to the lettered breaks.

A picture field I represented in this case as being a photograph or similar field, but which may be any image or scene which is desired to be transmitted, is'focused through a lens 2 on a photoelectric cathode 3 of a dissector tube 4.

This dissector tube may be made in accordance with the teaching of the Farnsworth Patent No. 1,773,980, listed above, or may be the improvement thereon asshown, described and claimed in the Rutherford patent above. It comprises an envelope containing the cathode 3 at one end upon which an optical image may be projected by the lens 2. As the cathode 3 is photosensitive, electrons are emitted from the surface thereof in proportion to the intensity of the light striking the elementary areas thereof. A positive potential is applied from a dissector source' between cathode 3 and a target finger I placed close to the opposite end of the tube.

This target finger I is in the light path, but being of relatively small diameter and out of the focus of the optical system, it does not cause distortion but merely cuts down the total amount of light reaching the cathode by a small amount. Electrons emitted by cathode 3, therefore, are attracted by the positive potential towards the target finger I and are kept in parallel arrangement by the application to the tube of a longitudinal magnetic field created by a focusing coil 8 energized by a focusing source 9 under the control of a variable focusing resistor I0. The target finger 1 is provided with an aperture opening toward the cathode 3 through which electrons emitted from the cathode may pass to be collected by. a target represented by a dotted line inside of the finger 1 and being a continuation of\, the target lead II.

If the electrons in space are not diverted from their paths in the'tube only electrons from a of the cathode 3 will arsmgle elementary, area rive on the inner target, the remainder of the electrons being collected by the outer target finger- I. Thus, there will be a difference in the number of electrons collected by the inner target and the outer finger, which will cause a current to flow through an output resistor I2 from target source 6. If the electron beam is then deflected in two dimensions, the electron beamwill be scanned and will produce a train of picture signals in output leads I3, which will represent electrically the picture field I.

Horizontal scanning is accomplished by the use of a horizontal scanning coil I4 which is energized from a scanning oscillator assembly through a scanning secondary winding I5 applied to a core I6 of a transformer having a grid primary winding I1 and a primary plate winding I8 attached to the respective grid and plate circults of an oscillator tube IS. The constants of the circuits attached to the oscillator tube I9 are so adjusted that tube I9 will self-oscillate, and also to supply a sawtooth current to the secondary coil I5, consequently, to the horizontal scanning coil I4.

In order to completely scan the picture, it will be necessary to scan the picture vertically as well. A vertical scanning coil is'therefore provided energized through leads 2| from a vertical scanning source 22 which is in series with a variable resistor assembly 23 indicated as enclosed by the dotted line 23 in Figure 2. This variable resistor assembly, which may be called a progressive selector, controls the amount of current flowing through the vertical scanning coil 20 in decreasing equal increments.

The action of both the horizontal and vertical scanning is under the control of a synchronizing assembly driven by a synchronous motor 24 which drives a synchronizing rotor shaft 25 through reduction gears 26. The synchronizing shaft 25 carries thereon a four-cycle rotor 21 and a twenty-cycle rotor 28. The twenty-cycle rotor is provided with a twentycycle field 29 which is connected through leads 3!! to a control primary 30"on core I6 so that the scanning oscillator I9 is kept in step with the twenty-cycle frequency generated by the twentycycle rotor 28.

At the same time a four-cycle field 3I generates a pulse which is fed to the input of a low frequency pulse amplifier tube 32, the output of which passes through a low frequency pulse relay coil 33, the magnetic pull'of which acts upon a low frequency pulse armature 34 to place upon a first selector operating magnet 35, current from a selector battery 36. Each impulse applied to the operating magnet 35 causes rotation of first selector shaft 36' by one notch; thus changing the total resistance of combined selector resistors 31, 38 and 39, At each revolution of the first selector shaft 36, contacts are made between first selector arm 40 and associated stationary contact 4| which directs a pulse from second selector battery 42 to second selector magnet 43, thus turning second selector axle 44 one notch. The process is repeated to control the turning of the third selector axle or shaft 45 in a similar manner. Thus, the entire range of resistance in resistors 31-38-39 may be covered in successive steps and the number of steps provided in the assembly will of course correspond to the number of lines desired in scanning the picture from top to bottom.

It will be seen, however, that as the horizontal scanning is twenty cycles; and the vertical scanning is on a four-cycle basis, that each line will be scanned five times before moving on to the next line. This process repeats itself automatically so that at the end of each group of five sawtooth waves generated by the horizontal scanning oscillator I9, the selectors operate to move the electron beam to present the next line to be scanned to the target aperture of the dissector tube.

The picture currents produced by this scanning process are passed through output resistor through a similar volume control 52.

amplifiers 41 and 48 have a different number of Thyratron, herein called rectifiers for convenience. A rectifier 49 is connected to the output of the one-stage amplifier 4'! through a volume control 50, and the output of the twostage amplifier 48 is connected to rectifier 5| stages, it will be seen that the outputs of the two amplifiers are out of phase, the output of the one-stage amplifier 41 being applied to the grid 54 of the rectifier 49 in one direction and that of the two-stage amplifier 49 applied to the grid 55 of the second rectifier II in the opposite direction.

Rectifier 49, which receives the impulses from the amplifier having an odd number of stages is supplied with a positive steady bias by bias assembly 56, and rectifier 5| which receives its impulses from the amplifier having an even number of stages is supplied with a'negative steady bias by negative bias assembly 51.

Theplates of the two rectifiers are energized by a two thousand-cycle rotor 59 attached directly to the shaft of the synchronous motor 24, this rotor creating two thousand cycle pulses in the main rectifier anode line 59, which passes through a common anode resistor 60 and then divides at a connection 64 and is applied through a rectifier resistor 62 to connect to anode 64 of the first rectifier 4.9, and through a similar rectifier resistor 65 and connecting wire 66 to anode 61 of the second rectifier 5|. A connection 68 is made from the point where the anode supply.

divides to a keying resistor III. This keying resistor Ill is in series with the bias of an overbiased R. F. amplifier tube (not shown) contained in a radio transmitter assembly II comprising as an example, a master oscillator. b fer, and three stages of R. F. amplification, radiating from the usual antenna system. Means for dverbiasing such an amplifier tube are well known in the art.

The keyingresistor I0 is placed in the circuit of the R. F. amplifier stage so that when current is passed through the resistor between connection 68 and ground 12, the voltage generated by this current will oppose the bias of the amplifier tube, thus reducing the bias and allowing the radio transmitter to operate. When no current is flowing through resistor III, the bias 'on the radio frequency amplifier blocks the transmitter and no signals will be radiated. The complete operation of this circuit will be explained separately.

In addition to applying certain signal variations to a radio transmitter through the circuits just described; I also prefer to transmit a synchronizing pulse. I, therefore, take energy from the twenty-cycle alternator combination 28-28 which is present in leads 30, and apply it to an amplifier input circuit ll to amplify the synchronizing pulses. The amplified pulses are passed through a synchronizing pulse connection "to the resistor" opposite the grounded end. The output of this amplifier passes through resistor 10, and these pulses change the bias on the R. F. amplifier to cause the transmission of the horizontal synchronizing pulse.

Furthermore, in addition to the steady bias on the rectifier tubes 49 and 9| provided by biasing assemblies 56 and 51, I prefer to provide an additional varying bias, more particularly, a bias that will vary'each time an individual line is scanned. This varying bias is provided by placing on the end of the rotor shaft 25 a cylinder '9 having five equal circumferential portions of Asthedifferent light transmission values so that a slit 8| positioned outside of the transparent cylinder will'receive five different light values from axially positioned exciter lamp 92. The light passing through the slit' is directed on a photoelectric cell 83, the output of which'is applied to a pair of grids 94 and 85, connected in parallel, of a pair of amplifying tubes 86 and 81. The outputs oftubes 86 and 91, which appear as voltage drops across their respective plate resistors 88 and 89, are applied to the grids of the rectifiers 49 and SI in opposite polarity. x

The photoelectric cell 83 is energized by a cell source 90 connected across a cell resistor 9|, one end of which is connected to grid 84 of amplifier tube 86, the other end being connectedto the cathode 92 of amplifier tube 81. Thus, the varying bias of the two ' rectifiers 49 and 5| will depend upon the value of the transparency presented to the photoelectric cell, the general action being discussed later.

The operation of the dissector 4 in general, as far as the scanning is concerned, is unusual only in that each line is scanned five times. The picture currents produced by the scanning process are represented by the voltage dropv across the output resistor 12 and these voltages after being amplified, are applied to the inputs of amplifiers 41 and 48, one of which is a single-stage, and the other a two stage amplifier. The outputs of these amplifiers are fed to the grids of the two rectifier tubes 49 and SL Rectifier 49 has a steady positive bias on its grid and rectifier 5| has a steady negative bias on its grid. With this arrangement, the signal applied to the rectifier grids comprises a series of picture impulses whose heights are proportional to the light intensity of the picture elements being scanned, but due to the fact that the signals applied to rectifier 5| pass through an even number of stages, the pulses applied to it are of opposite polarity to those applied to rectifier 49 which receives its signal, through an odd number of stages. Therefore, a signal which decreases the instantaneous negative bias on the grid 55 for rectifier 5|, tending to make its breakdown voltage lower, willincrease the instantaneous nega-- tive bias on grid '54 on rectifier tube 49 which has a steady positive bias, which tends to prevent it from breaking down. It'is believed that cycle generator, their breakdown is controlled by ,the grid voltage which is effective at the beginning of each positive half-cycle of the two thousand-cycle supply. By adjusting the resistors in the respective biasing assemblies 56 and 51, the rectifiers can be givena steady bias such that neither tube will fire when the signals due to a picture being scanned are within a given range for values corresponding to a given range of light intensity on elementary areas in the picture. When neither tube fires, the voltage drop across the keying resistor III is, such that on the positive halves of the two thousand-cycle supply the voltage is sufiicient to unblock the grid of the radio frequency amplifier in the transmitter and cause signals to be transmitted by the antenna attached thereto.

If. either rectifier tube 49 or ii fires or if both rectifiers fire together. the voltage drop fore not available in resistor to create-a volt- If, however, either one of the tubes is passing current, current which flows through resistor I0 is used in one or both of the tubes and is thereage sufficient to unblock the amplifier grid. It is, therefore, seen that the two rectifier tubes together can be controlledto operate the radio transmitter only when they receive signals corresponding to a given level or range of light intensities. I

The manner in which these two rectifier tubes operate to control the radio transmitter and release energy therefrom only for picture elements which lie within a given range of light intensity can best be explained by reference to a specific numerical example, and reference will also be had to Figures 5 and 6, which show the grid voltage-firing voltage curves of the two rectifiers, plotted one above the other and to the same scale, Figure 5 representing tube 49 and Figure 6, tube 5|.

Let us assume that the alternator voltage is two hundred volts peak at two thousand cycles. Since I prefer to design the alternator to supply a current having a waveform substantially fiattopped and substantially perpendicular sides as shown in Figure 3,-there will be no operation of the rectifiers except under the condition of full two hundred volts applied anode voltage. For a full platevoltage of two hundred volts, the negative grid bias must be more than twentyone volts to prevent the tube from firing. Continuing with the numerical example, let the steady battery bias on rectifier 49 supplied by bias assembly 56 and the drop across resistor 89 be +10 volts and the steady bias applied to rectifier tube 5| by means of the bias assembly 51 and the drop across resistor 88 be 53 volts.

' It will thus be seen that'when no picture signal is supplied, rectifier 49,

whose grid has a bias thirty-one volts more positive than the critical value of 21 volts required to stop the. discharge, will fire on every positive pulse supplied On the other hand, rectifier tube 5| has a bias which is thirty-twovolts more negative than that required to prevent discharge and, therefore, it remains inoperative as long as there is no picture signal.

As already explained, the picture signal is fed to the rectifier tubesthrough twoseparate amplifiers, one having an odd and the other an even number of stages. Therefore, a picture element which tends to increase the effective negative bias on tube 49 will decrease the effective negative bias on tube 5|. 1

Let us assume that we are scanning a line of the picture, and we wish to send out signal pulses only for picture elements which will produce signal voltages between thirty-one and thirty-two ,volts." Referring to Figures 5 and 6, rectifier tube 49 has a steady bias on it of +10 volts and rectifier tube 5| has a steady bias of 53 volts. During any: one scanning line the drops across resistors 89 and 88 remain constant.

"Applying diiferent'values of signal voltages, we find the following: (a) A signal of 31.1 volts makes the effective .bias on rectifier 1 1 b? -2 WM, 59 t at this tube cannot fire. The same signal at the same time reduces the effective bias on rectifier "tube 5| to 21.9 volts so that tube 5| is also inoperative. Under these conditions, the voltage drop across the keying resistor 18 is sufficient to unblock the R. F. amplifier and cause the radio transmitter to send out signal impulses. (b) It can be shown similarly that tubes 49 and 5| will also be inoperative for signals lying between 31.1 and 31.9 volts and the radio transmitter will therefore operate in this range.

(0) If the picture signal drops below 31 volts,

say to 30.9, the effective bias on tube 49 will be 20.9 volts and tube 49 will therefore fire and consequently, the radio transmitter will remain inoperative. At the same time, the bias on tube 5| will be -22.1 volts and it will not fire; but this is immaterial because radio transmission is prevented due to tube 49 firing.

(d) If the picture signal increases above 32 volts, say to 32.1 volts, the radio transmitter will be inoperative again because while rectifier tube 49 will then have a bias. of 21.1 volts which will prevent its firing, tube 5| will fire due to its bias having been reduced to -20.9 volts which is less than the critical value. It is, therefore,

seen that for given values of steady bias the rectifiers can be made to operate in such a way that the radio transmitter is energized only for picture elements having light intensities which 'of the rotating film cylinder 88.

For example, to cause the transmitter to operate .for picture elements delivering 10 to 11 volts to the rectifier grids, the transparentfilm for the scanning line in question is set to cause the photoelectric cell 83 to operate to pass 'sufflcient current to make the sum of the drops across resistor 89 and the bias value placed on the grid 54 of the tube 49 by the biasing assembly 56, to be --11 volts. At the same time, the drop across resistor 88, together with themes supplied by bias assembly 51 to tube 5| will become -32 volts; thus the range of light intensities which can cause the radio transmitter to operate is automatically set for each repeated scansion of the same scanning line by the drum'carrying the transparent film, and its associated photoelectric cell, which, operating through amplifier tubes 84 and 85 fix the varying bias of the rectifiers.

It should be noted that the grid bias voltages controlled by the photoelectric cell 83 are applied to the rectifiers through separate amplifier tubes 86 and 81. The outputs of thesetubes, which appear as voltage drops across their plate resistors 89 and 88, are applied to the grids of the rectifiers in opposite polarity. It should also be noted that the characteristic curves of straight lines. While this linearity is a fortunate circumstance in that it makes for an easy ad the rectifiers are the rotating drum are arranged in orderly manner so that the bias provided to the rectifiers 49 and starts in at a low value for the first scanning of a line and ends at a high value at cell 83, when plotted on a time basis is shown in Figure 7.

By proper selection of transparencies for the I rotating drum 80 and by adjusting the steady bias assembly 56 and 51, it is possible to obtain any desired range of light values for each scansion' and. it is quite obvious that certain shades may be accentuated if desired. In other words, the selection of the five different values need not necessarily differ byequal values and any arrangement may be made which will suit the subject matter best. However, for the five scannings of 'the same line, we may adjust these values so that the radio transmitter is operating for example, as follows: i

In scanning a given line:

First scanning Transmit signals for picture elements producing 0 tom g volts Second scanning 10 to 20 volts Third scanning 20 to 30 volts Fourth scanning to volts Fifth scanning 50 to volts It is obvious that the grouping of voltages referred to above is that which might be given when an object was scanned five times, but it should be pointed out that my system as described is not limited to any particular number of scannings of a single line and that if a greater number of scannings is made, the range of voltage for the picture elements on a single scanning will be less and for a lesser number of scannings the range will preferably be greater. It is possible, however, because of the extreme sensitivity-of the arc-controlled rectifiertube to reduce the range to a fraction of a volt where a single line is being scanned at large number of times in order to obtain extreme detail.

As explained above, a pulse amplifier is provided which is connected to the scanning oscillator l9 and to the;keying resistor 10 to send out a synchronizing pulse at the end of each traversal of a line. f'rne polarity of the syn hronizing pulse and the intensity are such as t; completely unblock the radio frequency amplifier in the same manner as the pulses produced by the two thousand-cycle generator, and to cause the radio transmitter to send out a synchronizing signal at the end of each traversal of the field by the scanning aperture. This signal is adjus ed preferably to be of-a length corresponding to ten per cent of the,

period of scansion of one line, which for thep'resent example would be ten per cent of .05 second, or .005'second. The synchronizing pulse is, therefore, ten times as long as any one of the two thousand-cycle picture pulses sent out by the transmitter and can therefore be readily separated from these picture pulses at the receiving end by a simple resistance-capacity filter, as will be later described. It is also an advantage to make the corners of the synchronizing pulses rounded to facilitate separation from the signal at the receiver and this may be done by control of the amplifier waveform as is well lmown in the art.

The descriptionabove given completes the 011.-

cuits and operation thereof in the complete telephoto transmitter. I prefer, however, in order to check the operation of the transmitter to utilize a visual monitor assembly 95 for picking up the radio space current in a miniaturereceiver so that proper adjustment'may be maintained on the transmitting device. This is in accordance with all modern practice andthe general operation of the visual monitor will be similar to that oi the receiver about to be described, with the exception that it may be possible, if desired, to utilize synchronizing pulses taken directly from the main transmitter.

At the receiving end, a preferred example of which is indicated by the diagram comprising Figure 4, the output of a radio receiver lllil of ordinary design is in the form oi pulses grouped in accordance with the picture signals. This form of output has been described fully in my copending application referred to above and is obtained by the use of an arc-controlled rectifier tube similar to that used in the transmitter, but preferably having an anode excitation of around five thousand cycles, the grid being controlled by the amplified and rectified radio signal. This particular type of receiver output is used in order that the signal-to-noise ratio may" be low and that the signals be separated from the noise which would ordinarily accompany it, due to the sharp selection of amplitude inherent in the operation of a grid-controlled rectifier. In other words, the output is composed of a series of uniform amplitude, five thousand-cycle waves, the grouping of the series corresponding to the value of the picture impulses being transmitted.

This grouped signal is passed through an output resistor IM and fed. through a grid connecnon-I02 to the control grid I02 of a visual monitor cathode ray tube I03 which preferably has a fluorescent'screen having a considerable time lag light therefrom is focused on a moving film I06 or' sensitized paper which after being exposed is passed into an automatic developing and fixing bath l 01 to emerge as the finished'product.

Both cathode ray tubes are thus simultaneously energized. 'At the same time part of the output of the radio receiver is conducted through connection I08 to a synchronizing amplifier tube I09. The picture pulses are prevented from operating or influencing this synchronizing amplifier by means of a low pass resistance-capacity wave filter comprising a condenser H0, and resistor III, a series capacity H2 and a grid resistor III, which descriminates against rapid steep sided picture pulses and passes the rounded synchronizing pulses. The synchronizing pulse then appears alone in the anode circuit H5 of the synchronizing amplifier and controls, as in the transmitter, the output of a receiving lateral scanning oscillator 6, the output of which is passed through transformer H1, through leads .8 to thedateral scanning coil H8 of receiver cathode ray tube I05, and also to monitor tube .45 This cathode ray' tube preferably has an instantaneous screen and the .winding i22 has I22. This relay will, therefore, operate once for every five cycles produced by the twenty-cycle scanning generator H6. The relay operated by movable arms, one of which, selector arm I24, is connected in series with a three-step-by-step selector I operating exactly the same as that shown enclosed in the dotted line 23 of the transmitter drawing in Figure 2. The output of this step-by-step selector is applied to the vertical scanning coil I26 of the receiver cathode ray tube through a supply line I21 and also to monitor tube I03 as indicated by a broken circuit X-X. The other arm I21" normally closed, controls the current from a relay assembly source I29, which is the main supply for a series of locking relays which operate to change the effective resistance of'a main cathode ray tube by a resistor I30. The drop across this resistor is applied to a beam bias grid I30 of the visual monitor I03 through lead I3I and to the beam bias grid I3I' of the receiver cathode ray tube by lead I32.

In order to reproduce'in the receiver tubes the various shades appearing in the transmitted picture, it is desirable to change the bias on the cathode ray receiving tubes to a different steady value for each repeated traversal of the same scanning line, and todo this in synchronism with the rotation of the transparencies which operate the rectifier bias supplies at the transmitter. This is readily done by relay arms I40, I, I63 and I44 connected to short portions of the bias control resistor I30. The relays carrying the so that the bias of the the relay gaps are open. At the end of the first scansion of a given line at the transmitter a-p0rtion of the output of the lateral scanning oscillator H6 is picked up by a pulse winding I45 on transformer I I1 and passed through a pulse amplifier I46. The amplified pulse is applied to the operating winding I41 of the first relay thus operating the relay, shorting out a portion of the resister I30, and at the same time drawing down a locking arm I48. The bias is thus adjusted for the second scansion of the same line.

The actuation of the locking arm I48 closes a connection with a locking winding I49 of the I first relay, the current passing also through an operating winding I50 of a first delay relay. Thus, the first bias relay is locked. In series parallel with winding I50 of the first delay relay is a condenser I5I which must charge before the first delay relay can close, and its value is made such that this relay does not close until after the pulse from the pulse amplifier has operated the first bias relay and then dropped to zero. After the pulse passes, and condenser I5I charges, winding I50 of the first delay relay becomes energized, closes a connection I50, hifting the out put of the pulse amplifier I46 to winding I52 of the second bias relay. The pulse-thenoperates bias arm I4I shorting another portion of resistor I30 and also operating locking arm I53, which latter arm closes the circuit to a delay winding I54 of a second delay relay.

The winding I54 is also shunted by a capacity I55, which delays the operation oi this relay until the pulse has passed, whereupon the current ,passing through the winding I54 will operate transferlarm I55 and locking arm I56 which again transfers the output of the pulse amplifier to operating winding I51 of the third bias relay which in turn operates the bias arm I43 to short out still another portion of resistor I30, and operates locking arm I50 which closes the circuit and transfers current to the energizing winding I60 of the last bias relay winding I64 which in turn operates the bias arm I44 to short out the remainder of the resistor, and lock the bias relay. All or the delay relays have locking windings and remain closed during the progressive shorting of resistor At the end of five scannings of the same line at the transmitter, the receiver multivibrator actuate's tube I2I and relay I22. This relay opens all the lock-up windings, releasing .all of the relays andalso operates the step-by-step selectors so that the spots of the cathode ray tubes are moved down ready for the next scanning line. The cycle isthen repeated.

The four bias relays should be capable of closing in about .005 second. The three transfer re- I lays, by having the condensers shunt them; are arranged to be time delayed by about .03 second after the operating voltage is applied. Relays for these speeds do not present any new problems as high speed relays operating much faster than this are available. However, I do not desire to limit myself to this particular method as many other means for effecting the desired bias changes for the cathode ray tubes will occur to. those skilled in the art.

For example, a synchronous motor carrying a set of transparencies and a photoelectric cell such as that used at the transmitter might be substituted for the relays at the receiver or a series of arc-controlled rectifiers might be used. The apparatus describedfor this bias change is in itself no part of the instant invention and is simply used as an example of a means.

It can therefore be seen that the spot of the receiver cathode ray tube travels in synchronism with the scanning at the transmitter, that the transmitter scanning aperture traverses thesame line several times, and that a pair of arc-rectifier tubes causes picture elements of different intensity ranges to be picked out, separated and transmitted during each repeated scansion. v The signals thus produced key the radio transmitter so as to send out signals in the form of dots of uniform length, and shape, and a relatively longer corresponding to intensity of picture elements being transmitted, for each scansion. The receiver is also provided time lag screen and a cathode for automatic photographic recording.

The receiver is enabled to operate under conditions of relatively poor signal-to-noise ratio -2 or 3 to 1--because its output tube is a gridcon'trolled rectifier whose platev supply is fed by a five thousand-cycle a. 0. source. The bias of this grid-controlled rectifier is adjusted so that it operates for the peak voltage of the signal, and

with a visual monitor having a ray tube arranged noise of less intensity than the signal does appear in the picture.

I claim:

1. The combination with an electron image dis-=- sector of ,a telephoto transmitter comprising a picture field within said electron image dissector, means for scanning a portion of said field a plurality of times within said image dissector to produce a picture signal before the remainder is scanned, a signal transmitter, and means for changing the response of said transmitter to said signal in accordance with different levels thereof at each successive scansion of said portion.

2. The combination with an electron image dissector of a telephoto transmitter comprising a picture field within said electron image dissector, means for scanning each line of said field a plurality of times to produce a picture signal before scanning the next line, a signal transmitter, and means for changing the response of said transmitter. to said signal in accordance with different amplitude levels thereof at each successive scansion of said line.

3. The combination with an electron image not dissector of a telephoto transmitter comprising a picture field within said electron image dissector. means for scanning a portion of said field a plurality of times to produce a picture signal before the remainder is scanned, a signal transmitter, means for changing the response of said transmitter to said signal in accordance with different levels thereof at each successive scansion of said portion, means for scanning remainingportions in like manner, and means for transmitting a synchronizing signal between each successive scansion of all the portions.

4. The combination with an electron image dissector of a telephoto transmitter comprising a picture field within said electron image dissector,

means for scanning each line of said field a plurality of times to produce a plurality of substantially identical successive trains of signals representing a single line before scanning the next line; a signal transmitter, means for selecting impulses within a diflerent predetermined amplitude range fromeach of said identical trains, and means for keying the transmitter by the selected signals.

5. The combination with an electron image dissector of a telephoto transmitter comprising a picture field within said electron image dissector, means for scanning each line of said field a plurality of times to produce a plurality of substantially identical successive trains of signals representing a single line before scanning the next line, a signal transmitter, means for selecting impulses within a different predetermined amplitude range from each of said identical trains, means for grading the average levels of said ranges in accordance with the gradations of light and shade of said field it is desired to transmit, and means for keying the transmitter by the selected signals.

' 6. The method of telephoto transmission which comprises scanning each line of a. picturefield a. plurality of times to produce successive substantially identical trains of picture impulses before Y scanning the next line, selecting from each of" beam in accordance with the said trains impulses within a diflerent predetermined amplitude range, transmitting the selected impulses, repeating the steps on succeeding lines,

' receiving said signals, creating a beam of electrons, modulating said beam. by said signals,

' changing the average response of said beam by a different predetermined amount for each successive scansion of the same line, repeating the steps on succeeding lines, creating a visual indication of the strength of said beam, moving said scansion at the transmitter, and photographing said visual indication.

7. The method of telephoto transmission which 1 comprises scanning each line of a picture field a plurality of times to produce successive substantially identical trains of picture impulses before scanning the next line, selecting from each of said trains impulses within a different predetermined amplitude range, transmitting the selected impulses, repeating the steps on succeeding lines, receiving said signals, creating a pair of electron beams, modulating both of said beams by said v signals, changing the average response of said beams by a diiferent predetermined amount for each successive scansion of the same line, repeating the steps on succeeding lines, creating a ,persistent'visual indication. of the strength of one, of said beams creating a transient visual indication of the other of said beams, moving said termined amplitude range, transmitting the se-' lected impulses, repeating the steps on succeeding lines, receiving said signals, creating a beam of electrons, modulating said beam by said signals, changing the average response of said beam by a different predetermined amount for each successive scansion of the same line, said amounts being changed to correspond to the amplitude range selection at the transmitter, repeating the steps on succeeding lines, creating a visual-indication of the strength of said'beam, and moving said beam in accordance with the scansion at the transmitter. v

9. The combination with an electron image dissector of a telephoto transmitter comprising a picture field within said electron image dissector, means for scanning each line of said field a plurality of times to produce a plurality of trains of signals representing a single line before scanning the next line, a signal transmitter, means for selecting impulses within a predetermined amplitude range from each of said trains, means for cyclically varying the response of said signal transmitter to diiferent impulse levels on succes- FRANK J. SONIERS.

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