US2331456A - Facsimile and picture transmission - Google Patents

Description

i j? fa I 4 1r A f J. W. COX

FACSIMILE AND PICTURE TRANSMISSION Filed NOV. 18, 1941 ,Ma/a

fammi/Tri@ 5 Sheets-Shea?I 1 man INVENTOR.

JOHN W. 60X

BY fww HTTOE/VEY of.1z, `1943. J. w. cox A 2,331,456

FACSIMILE AND PICTURE TRANSMISSION Filed Nov. 18, 13941 3 Sheets-Sheet 2 coppie 7g aen-1 roe 7 mvp INVENTOR. JOHN M COX QYTOENEY Ost.l l2, 1943.

J. w. cox

FACSIMILE AND PICTURE TRANSMISSION Filed Ngv. 18, 1941 s sheets-sheet s n.mwA,

` Patented oct. 12, 1943 FACSIMILE AND PICTURE TRANSMISSION John W, Cox, Berkeley, Calif., assig'nor to Radio Corporation oi' America, a corporation of Dela- Wal'e Application November 18, 1941, Serial No. 419,532

(Cl. TIS-6.6)

9 Claims.

This invention relates to the transmission ofI facsimile and pictures by radio telegraphy.

An object of the invention is to transmit picture signals representing the density or shade of scanned elements of a subject in continuous cycles, the time-position of the signals in each cycle being a measure of the density of the elements.

Another object of the invention is to transmit picture signals representing the density of scanned elements of a subject in continuous cycles, the time-position of the signals in each cycle being a measure of the density of the elements, and to record the signals With densities or shades proportional to their position in the cycle.

Another object of the invention is to generate frequencies proportional to the density of the scanned elements of a subject and to pass the frequencies through filters connected to segments of a distributor and to pick the frequencies olf of the segments by a rotating brush, so that each position of the brush indicates a definite density. l l

Another object of the invention is to produce smoother recordings than can be obtained from on-and-oi keyed signals in picture systems while retaining the transmission advantages of such systems.

Another object is to reduce keying speeds by converting signals of varying amplitude into signals of constant frequency and varying phase and keying the signals on and oil at alternate phases.

Other objects will appear in the following description, reference being had to the drawings, in which:

Fig. l is la diagrammatic illustration of the transmitting apparatus.

Fig. 2 is a diagrammatic illustration of the receiving apparatus.

, Fig. 3 is a series of graphs of the signals at the transmitter.

The invention in this application relates to a picture system in which the amplitude variations of the current from a scanner are converted into frequency variations, as an intermediate step and converting the latter into on-and-off keyed that the amplitude variations of the scannerA output appear in resistance I, across which is tapped the input of amplifier tube 2. The posithrough the primary of transformer 3 and neon tube 4 to the plate of this tube. The cathode of the tube is connected to ground and to the negative terminal of the plate supply. Across the arm containing the primary 0f the .transformer and the neon tube is connected condenser 5. As is well known, this condenser, transformer coil and neon tube constitute an oscillator, the frequency of which depends upon the conductance of the vacuum tube 2, which in turn depends upon the amplitude of the signal voltage or current in resistance I.

The secondary of transformer 3 is connected to band-pass filters 6, l, 8, 9, I0 and Il in parallel, for example, so that the signal output is applied to all six band-pass filters, six filters being chosen by Way of example and not as the requisite number. Each band-pass filter may consist of a capacity and inductance branch I2 in series with shunt capacity and inductance I3, the inductance in this shunt branch being the primary of the trasformer I4, aided if desired by a separate inductance. Other inductance and capacity arrangements may, of course, be employed for selectively passing the frequencies.

The secondary of transformer I4 is connected to a full-wave rectifier I5, which is indicated only diagrammatically. `If desired, a smoothing condenser I6 may be used, though this is not essential in all cases.

The positive output terminal of each rectier is connected to individual segments a, b, c, d, e, f, in a distributor I'I and a rotating brush I8 engages these segments in regular timed succession. This brush is rotated at a constant speed by any of the Well-known speed-control systems employed, for example, in multiplex telegraphy. The rotating brush I8 is connected through load resistance I9 to ground. A slider on this resistance is connected to the grid of vacuum tube amplifier 20, the cathode of which is grounded.

` The anode or plate of this tube is connected through the primaries of transformers 2|, 22 to the positive terminal of the source of supply.

One terminal of the secondary of transformer 2| is connected to the anode of tube 23 and the cathode of this tube is connected to ground through normally blocking bias 24. The other terminal of the secondary is connected to ground through resistance 25. One terminal of the secondary of transformer 22 is connected to the anode of tube 26 and the cathode of this tube is connected to ground through normally blocking` bias 24. The other terminal of the secondary tive terminal of the plate supply is connected of transformer 22 is connected through resistance 28 to ground. The transformers 2| and 22 are connectedin similar polarity to the tubes 23 and 26, but only one tube at a time can pass current dueto the potential applied from the locking circuit later described. Since the current in the primaries of these transformers is direct current, a short pulse will be generated when the brush engages a segment passing current, vand a short pulse of opposite polarity when it leaves the segment, but the connections are such that one pulse only can pass through a tube, say the beginning pulse, though it could alternatively be the ending pulse or both pulses if desired.

A locking crcuit, generally indicated at 29, has two tubes 30, 3|. The grid of tube 30 is connected to the ungrounded end of resistance 25, While the grid of tube 3| is connected to the ungrounded end of resistance 28. The cathodes of the two tubes are connected together and to the negative terminal of the plate supply, which is grounded. The anodes of tubes 30 and 3| are connected together through resistances 32, 33 and 34 and the positive terminal of the source of supply is adjustably connected to an intermediate portion of resistance 33.

The anode of tube 30 is connected through resistance 35 to the grid of tube 3| and it is also connected through resistance 36 to the negative terminal of the source of supply. The anode of tube 3| is connected through resistance 3l to the grid of tube 30. As thus described, the locking circuit 29 is a well-known locking circuit used in multiplex telegraphy and in other circuits and the general theory of this circuit is given in the U. S. patent to J. L. Finch, No. 1,844,950, patented February 16, 1932. One terminal 4| of resistance 33 is connected to the grid of tube 23 and the other terminal 42 is connected to the grid of tube 26. When tube 30 is conducting and tube 3| is blocked, the drop in the left-hand end of resistance 33 fails to'overcome the blocking bias 24 of tube 26, but the line potential applied to the input of tube 23 unblocks that tube. When tube 3| conducts and tube 30 is blocked, the drop in the right-hand end of this resistance similarly fails to unblock tube 23 and the line potential unblocks tube 26. Hence tubes 23 and 26 conduct respectively when tubes 3| and 30 conduct.

The signal output resistance 35 in this locking circuit is connected in the common cathode lead of a push-pull keyer by connecting a slider on the resistance to the middle portion of the secondary of transformer 43. .The endsv of this secondary are connected to the grids of tubes 44, 45 of the keyer and the cathodes are connected together and to ground. The connecting lead from resistance 36 to the middle of the secondary of transformer 43 contains a negative bias source 45. This negative bias has such value that when tube 30 of the locking circuit conducts, the keying tubes are blocked, but when tube 3| conducts the increased potential in resistance 36 overcomes this bias and the keying tubes then conduct.

A source of tone frequency 4T is connected to the primary of transformer 43, though, of course, if desired the direct current signals couldhesent directly to the transmitter. 'I'he anodes of the keying tubes 45 are connected together` through the primary of transformer 48 in push-pull fashion and the positive terminal of the plate supply is Connected to the intermediate portion of this primary. The negative terminal is, as usual, connected to ground. The secondary of the translil) former is connected through lines 49I which may be of any length, to the distant transmitting station.

The incoming tone signal.. from this line are applied to rectifying and modulating apparatus 50, which operates in conjunction with the radio transmitting apparatus 5|. This transmitting apparatus applies the radio signals to antenna 52 for radiation to the distant receiver. The modulating apparatus may be, for example, like that shown in my application led June 6, 1939, Serial No'. 277,607, or it may be of any other type, as my invention does not depend upon any particular type of modulator. The radio transmitter may also be of any type. For these reasons, the modulator and the radio transmitting apparatus 5| have been shown in block diagram.

Referring to the receiving system of Fig. 2, antenna 53 may be of any type. This antenna is connected to receiving apparatus 54, which may consist of all the devices usually found in efficient radio receiving stations such as tuned radio frequency amplifiers, heterodyne circuits, intermediate frequency amplifiers, first detectors, etc. These are well known in the art and therefore have been indicated by block diagram.

The output of the receiving apparatus is fed into detector-tone keyer 55, though if the signal is not to be transmitted to a distant olce the tone keyer need not be used. If a heterodyne and intermediate frequency is used, as previously indicated, this detector would be the second or audio detector. The tone keyer is shown as feeding into long lines 56 to the distant office, at which point the lines are connected to a sufficient number of amplifying stages 51 and then to rectifier 58. The output of the rectifier feeds into tube 59, having its cathode connected to ground, which is the negative terminal of the plate supply. The grid of tube 59 may have a suitable negative bias 60. The positive terminal of the plate supply is connected to the plate of tube 59 through the primary of transformer 6|. The secondary of this transformer has its opposite ends connected to the anodes of full-wave rectifier 62. The center is connected through the coil of relay 63 to the cathodes of the rectifier. This relay has an armature switch blade 64 biased away from its contact 65, which Contact it is adapted to engage when its coil is energized. Contact 65 is con nected to a rotating brush 66 of a distributor 61. having contacts a, b, c, d, e, and f. Brush 66 is maintained in synchronism and in phase with the rotating brush I8 at the transmitter by any of the various systems that are well known in the multiplex and facsimile art. Contacts a, b, c, d, e, and ,f of the distributor 61 are adjustably connected to a plurality of voltage points e1, e2, es, e4, es and es on a bleeder or potentiometer resistance 68 fed by a source of voltage 69, having its positiveterrninal connected to switch blade 64 through condenser 10. These voltages el to es, in the arrangement indicated, may increase by steps in any desired ratio, but by way of example .the voltages could be 2, 4, 6, 8, I0 and |2, re-

spectively.

The input of amplifier is connected across condenser lll. Current from the plate supply of the tube passes through the primary of transformer 12 and neon tube 73 to the plate or anode of the tube. Condenser 'I4 is connected in shunt to the branch containing the primary coil and the neon tube. The neon tube and condenser constitute an oscillator whose frequency is controlled by the plate impedance of tube 1|, as

in the oscillator at the transmitter. As indicated in the drawings, the negative terminal of the plate supply of tube 'II is connected to ground and to the cathode of tube 1I. The secondary of transformer 'l2 is connected to amplitude limiter Ida and the output of the limiter is connected to a high-pass lter 15, which may consist of series condensers and shunt inductances, but a low-pass filter or other converter may be used by suitable changes, as is well known in the art. 'I'he output of the filter isconnected to transformer 'I6 and the opposite ends of the secondary of this transformer are connected to fullwave rectier TI. The middle portion of the secondary is grounded. The cathodes of the rectifier are connected together and to one end of load resistance 18, the other end being grounded. This resistance may be shunted by filter condenser I9 when desired. Recorder 80 of any type is adjustably tapped across load resistance 18.

The operation of the invention is as follows:

For purposes of explanation, let it be assumed that the scanner output has an increasing amplitude as 'indicated in graph A of Fig. 3. The voltageimpressed on the grid circuit of vacuum tube 2 at the beginning of the graph is a relatively low voltage and therefore the internal plate-cathode conductance of the tube is correspondingly low. The length of time for charging condenser 5 through this impedance is therefore relatively long. When the condenser becomes charged up t0 a certain point, its voltage is suucient to strike through the neon tube 4 and the primary of transformer 3. When this happens, the condenser recharges and 4will charge up and again strike through the neon tube. Thus frequencies will be generated that vary with the amplitude of graph A. It would be impractical to illustrate all the frequencies of the band in the drawings, so the output of the scanner has been indicated as a series of steps, each step being of uniform amplitude and the frequency generated have been indicated as F1 to F6, inclusive, the frequency increasing from Fi to Fs.

Frequency F1, when it is produced, is presented to al1 of the filters from 6 to Il, inclusive, but it can pass only band-pass filter 6. However, the current from rectifier I5 cannot flow except when the rotating brush |8.is on contact a, connected to this rectifier. At this time current will pass through the resistance I9 to ground. Brush I8 may rotate at any speed, but for purposes of illustration the speed is assumed to be that indicated in Fig. 3.

Under the assumption made, pulses will pass into resistance |9-only when the brush I8 engages contact a and these pulses will ow from this contact for four revolutions of the brush. Immediately yafter the start of the fourth revolution, when the brush engages contact b, it is assumed that the amplitude modulation of the scanner increases and frequency F2 is produced.

A pulse will then be produced through contact;

viormers 2| and 22.

tacte, frequency F5 will be produced and a pulse will be produced upon engagement of the brush with the contact e and also when the brush engages the contact upon the succeeding revolution. When the brush leaves contact e and passes on to contact f, frequency Fe is generated and a pulse is sent through the resistance I9 and since this frequency is still being generated when brush I8 next engages contact f, a second pulse is sent. All these pulses are indicated in graph C of Fig. 3. Each of the pulses indicated in graph C is amplified and passed through trans- This generates short pulses in these transformers, but only one, namely that in transformer 2|, can pass through tube 23 and the positive potential applied from the high potential end of resistance 33 overcomes blocking bias on the tube. The pulse in transformer 22 cannot pass tube 26 because it is blocked.

The pulse from transformer 2| passes from the upper end of transformer 2| through tube 23 into ground and up through resistance 25 and back to the lower end of the secondary of this trans-` former. The drop in resistance 25, which is negatively applied to the input of tube 30, blocks tube 30 and due to the well-known unbalance of this type of Finch locking circuit, this immediately unblocks tube 3|. When tube 3|) was blocked, the potential of the slider on 'resistance 36 was raised. Also, the blocking of tube 30 and unblocking of tube 3| blocks tube 23 and unblocks tube 26. When the brush leaves segment'a, a pulse of inverse polarity is produced in transformers 2| and 22, but it cannot pass either tube as it has the wrong polarity. When the brush engages the other five segments b, c, d, e and ,f on the distributor, no current flows as frequency Fi is still being generated. Therefore when the brush makes the second revolution and again engages contact a, a pulse is again passed through resistance I9 by rectifier I5, but the pulse generated in the secondary of transformer 2| cannot pass tube 23 because it is blocked, whereas the pulse generated in the secondary of transformer 22'can pass tube 26, which is now unblocked. Passage of the pulse through tube 26 sends current through resistance 28 and this blocks tube 3| of the locking circuit, which immediately unblocks tube 30. h

When tube 3| was conducting during the yfirst described revolution of brush I8, a potential was produced in resistance 36 indicated at 88, but when tube 3| was blocked, as just described, the potential in resistance 36 decreased to minimum r value, as indicated at 89,.

When the brush I8 starts on the third revolution, frequency F1 is still being generated and a pulse again blocks tube 30 and unblocks tube 3|, thus producing a potential drop in resistance 36 as indicated at 90. When the brush starts the fourth revolutiton and again engages contact a, frequency F1 is still being generated, but the pulse produced in transformer 2| cannot pass its tube 23 while the one in transformer 22 does pass its tube 28, which blocks tube 3| and unblocks tube indieeted et s2 and this is terminated upon the in graph E of Fig. 3. It will now be apparent how this graph is produced and further explanation is unnecessary.

The voltage drop in resistance .36 produced by the marks 88. 90, etc. is impressed upon thef grids of keying tubes 44 and 45 as a positive voltageand unblocks these tubes, so the tone current from generator I'I can pass to lines 49 leading to the modulator 50. During the spaces between the pulses as at 88 and 9| the voltage drop in resistance 38 cannot unblock the tubes and the tone current cannot pass. However, by` well-known changes, the spaces can cause tone current to be sent and the marks can interrupt it. The modulation of graph E is impressed upon thetransmitter 5| and radiated from antenna 52. It will be assumed that the modulatorv is so connected that the radio waves will be transmitted during the passage of the marks 88, 90, 92, etc. and blocked during the spaces 89, 9|, etc., though by well-known reversal circuits the inverse transmission could be obtained.

The radio frequency waves modulated and radiated at the transmitter are received by antenna 58 and the receiving apparatus 54 and 55 in Fig. 2 extracts the audio component of graph E and transmits it as tone current over the long lines 56 to amplifier 51. The output of this amplifier is rectified at 58 and amplified at 59. It will be assumed that the circuits are such that the plate current in the amplifierof tube 59'assumes the shape of graph E of Fig. 3 instead of the inverse, which could be produced in well-known ways if desired.

The square wavesvof graph E of Fig. 3, of course, cannot pass throughtransformer 6| in this form. A pulse will pass through at the beginning of the mark and at the end of the mark only, and these will be rectified by full-wave rectifier 62 and passed through the coil of relay 63 in the form indicated by graph F. These pulses are identical in phase with the pulses at the transmitter. Relay 63 will be energized at the passage of each of the pulses of graph F. Since brush 66 is rotating in synchronism and in phase with brush I8 at the transmitter, pulses 93, 94, 95 and 91 will be produced when distributor brush 66 successively engages contact a and at this time condenser 10 will be charged with a relatively low voltage E1 and produce a given low conductance in tube 1|. This will cause the oscillator to produce the low frequency Fi having the same value as F1 at the transmitter. After pulse 91 is formed and brush 66 next engages contact b, frequency Fi has been supplanted by frequency F2 at the' transmitter and pulse 98 is formed while brush 66 is on contact b. Pulses will likewise be passed by this contact during the next two revolutions, as at 99 and |00. 'Ihis places a higher charge on condenser 'II and reproduces the higher frequency F2. As soon as brush 66 leaves contact b and next engages contact c, frequency F: is being generated at the transmitter and therefore a pulse will be formed at IOI at this time. This will produce a still higher voltage E: on'condenser 'I0 and give tube Il a still higher conductance, which reproduces frequency F3. Of course, on passage of the brush to a contact of lower voltage, condenser I0 wil discharge down to that voltage. n

In .this way oscillator I3-14 will reproduce the assine to produce the amplitude variation shown by' 1 graph G, which is of the same form as the amplitude variation in the output of the scanner, as

indicated by graph A.

Instead of feeding a scanner output of varying amplitude into input resistance I of Fig. l, I may feed into this resistance the output of a constant frequency variable dot output, such as de scribed in the U. S. patent to Henry Shore and J. N. Whitaker 2,083,245, June 8, 1937, which is a well-known form of facsimile and picture transmission. In that case, a condenser |02 would be shunted across the input of vacuum tube 2 by closing the switch |03. Also, resistance would be adjusted to the right value to give the input to the tube the correct time-constant to vary the internal plate impedance of that tube inversely with the length of the dot signals. Thus the frequency of the condenser-neon tube oscillator 5-4 would vary with the length of the dot.

It will be apparent that the oscillator need not be of the condenser-neon tube type. This has been given by way of example only. The oscillator may be of the beat type such as is well known in the art and is disclosed, for example, in the Patent 2,257,282 of J. Ernest Smith, J. N. Whitaker and G. R. Clark, Serial No. 270,332, filed April 27, 1939.

Various other modifications may be made without departing from the spirit of the invention.

Having described my invention, what I claim -ing said voltage of varying frequency into voltage pulses of constant frequency having phases that vary with the frequency of the first-mentioned voltage, means for producing on-and-oif signals starting at each alternate one of said pulses and ending. at the next succeeding pulse and means for transmitting said on-and-off signals.

2. In a picture transmission system containing a scanner having a variable amplitude output, means for converting the varying amplitude of the scanner into voltage of varying frequency, means for converting predetermined bands of frequencies of said varying 'frequency into voltage pulses of constant frequency having phases that vary with the frequency of the first-mentioned voltage, means for producing on-and-off signals starting at each alternate one of said pulses and ending at the next succeeding pulse and means for transmitting said signals.

3. In a picture transmission system containing a scanner having a variable amplitude output, means for converting the varying amplitude of the scanner into voltage of varying frequency, a commutator, a brush engaging the segments of said commutator at constant speed, a plurality of band-pass filters, each adapted to pass a different band of frequencies of said varying frequency, means for passing voltage pulses from the output of said filters through different ones of said segments when contacted by said brush, means for means for converting the varying amplitude of the scanner into voltage of varying frequency, c

means for converting said varying frequency into voltage pulses of constant frequency having phases that vary with the frquency of the rst- .mentioned voltage, means for producing on-andon' signals starting at each alternate one of said pulses and ending at the next succeeding pulse, means for transmitting said on-and-oi signals, means for receiving the transmitted signals and converting them into signals having frequencies 'varying with the phase of the received on-andp signals, means for converting the signals of varying frequency into signals of varying amplitude and means for recording the signals of varying amplitude as a variation of shade.

5. In a picture transmission system containing a scanner having a variable amplitude output,

means for converting the varying amplitude of the scanner into voltage of varying frequency,

means for converting predetermined bands of frequencies of said varying frequency into volt- Sage pulses of constant frequency having phases Athat vary with the frequency oi' the first-mentioned voltage, means for producing on-and-oi! signals starting at each alternatel one of said pulses and ending at the next succeeding pulse. means for transmitting said signals. means for receiving the transmitted signals and converting them into pulses having said constant frequency 'and said varying phase, means for producing signals having frequencies varying with said phase, means for converting said Signals of varying frequency into signals of varying amplitude and means for recording the signals of "varying amplitude as variations of shade. i l 6. In a picture transmission system containing a scanner having a variable amplitude output, means for converting the varying amplitude of the scanner into voltage of varying frequency, a plurality of band-pass lters, each adapted to pass a different band of frequencies of said varying frequency, a commutator having segments connected to said filters, a brush engaging said segments at constant speed, and permitting a voltage pulse from the output of each filter to pass through said brush from said segments. means for producing on-and-oif 'signals starting at each alternate one of said pulses and ending at the next succeeding pulse, means for transmitting said on-and-off signals, means for receiving the transmitted signals and converting them into pulses having said constant frequency and said varying phase, a second brush connected to the last-mentioned means. a commu- .tator having segments engaged by said brush at said constant speed, means connected to the lastmentioned segments for converting the pulses passing therethrough into signals having frequencies varying with the phase of the pulses, means for converting said signals ofvarying frequency into signals of varying amplitude and means for recording the signals of varying amplitude as variations of shade.

7.\In the reception of Asignals transmitted at constant frequency and varying phase, means for receiving the transmitted signals and converting them into signals having frequencies varying with the phase of the received signals, means for converting the signals of varying frequency into signals of varying amplitude and means for recording the signals of varying amplitude as a variation of shade.

8. In the reception of signals transmitted at constant frequency and varying phase, means for receiving the transmitted signals and converting them into pulses of said constant frequency and said varying phase, means for producing signals having frequencies varying with of varying frequency into signals of varying amplitude and means for recording the signals of varying amplitude as variations of shade.

9. In the reception of signals transmitted at constant frequency and varying phase. means for receiving the transmitted signals and converting them into pulses of said constant frequency and said varying phase, a brush connected to 'the last-mentioned means, a commutator having segments engaged by said brush at said constant speed, means connected to the segments for converting the pulses passing therethrough into signals having frequencies varying with the phase thereof, means for converting said signals oi" varying frequency into signals of varying amplitude and means for recording the signals of varying amplitude asvariations of shade.

JOHN W. COX.

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