US2026379A - System of pulse transmission - Google Patents

System of pulse transmission Download PDF

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Publication number
US2026379A
US2026379A US500092A US50009230A US2026379A US 2026379 A US2026379 A US 2026379A US 500092 A US500092 A US 500092A US 50009230 A US50009230 A US 50009230A US 2026379 A US2026379 A US 2026379A
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United States
Prior art keywords
picture
current
wave
pulses
pulse
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Expired - Lifetime
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US500092A
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English (en)
Inventor
Philo T Farnsworth
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TELEVISION LAB Inc
TELEVISION LABORATORIES Inc
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TELEVISION LAB Inc
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Priority to US500092A priority Critical patent/US2026379A/en
Priority to FR727571D priority patent/FR727571A/fr
Priority to GB33164/31A priority patent/GB390565A/en
Application granted granted Critical
Publication of US2026379A publication Critical patent/US2026379A/en
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/14—Picture signal circuitry for video frequency region
    • H04N5/20—Circuitry for controlling amplitude response
    • H04N5/205—Circuitry for controlling amplitude response for correcting amplitude versus frequency characteristic
    • H04N5/208—Circuitry for controlling amplitude response for correcting amplitude versus frequency characteristic for compensating for attenuation of high frequency components, e.g. crispening, aperture distortion correction
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/12—Systems in which the television signal is transmitted via one channel or a plurality of parallel channels, the bandwidth of each channel being less than the bandwidth of the television signal
    • H04N7/127—Systems in which different parts of the picture signal frequency band are individually processed, e.g. suppressed, transposed

Definitions

  • v Tins invention relates primarily to the elec- Figure 5 is a curve representing the sum of protrcal transmission and reproduction of pictures. portional parts of each of the lcurves of. Figure but it is also applicable to other cases where 3, and Figure 6 is a similar curve representing it is desirable to transmit pulses of steep wave the sum of two of .the curve of Figure 3. 5 front through mediawhich tend to suppress the Figures 7 and 8 are diagrams respectively of high frequency components of such pulses, there- .the transmitting and receiving apparatus in a by converting the steep wave fronts into waves radio television system,
  • Figures 9 and 10 are diagrams of modified Among the objects of my invention are: First, forms of dierentiating networks. 10 to provide a method of reducing the band of fre- Asis well known, electrical picture transmis- 10 quencies which it is necessary to' transmit in orsion, whether it bethe transmission o f still picder to produce an electrically transmitted pictures as in telephoto, facsimile transmission or ture having a given amount of detail; second', to.- of television, the picture is scanned by moving an provide a method of transmitting television pic-,- aperture progressively over the entire area of the tures having satisfactory detail over wire lines picture, in order to generate a current which is v15 which are capable of transmitting but a limited at all times proportional to the reected or transband of frequencies; third, to provide a television .mitted illumination 'of the area of the picturebemethod which will permit the transmission of ing scanned.
  • the aperture has anite area television pictures upon radio channels which are Ano details can be transmitted which .are smaller ..20 comparable in width to thosev used for sound than the aperture itself,andthisfactisthe funda- .'broadcasting; fourth, to provide a method of mental limitation of television and other forms picture -transmission which will allow facsimile of electrical picture transmission by all methods telegrams, tele-photography, photo-radio, and now known.
  • Figure 3 is a plurality of curves representing a 'rent frombne fixed value of current to another 50 pulse as modified by a filter and derivatives of fixed value. said pulse.
  • Y .f No electrical circuit which it is practical to Figure 4 is a c e illustrating the currents construct is capable of transmitting a pulse of generated by sc an area of gradually this character, which may be described as a 56 changinglllumination. "square ⁇ front wave. to any great distance; and 66 -pulses is almost impossible.
  • the Fourier method of analysis shows that the square fronted pulse may be considered as made up of an. infinite number of sine waves having all frequencies up to infinity, and that the slimgishness of response of a circuit is equivalent to its failure to transmit the higher of these frequencies; the lower the frequency of cut-oil?, the more sluggish the circuit, and the more gradual the current rise. This results in great loss of detail in the received picture where the high frequencies are not transmitted. Sharp lines are converted into wide, gradually shaded bands, and small details are passed over by the scanning device before the sluggish circuit can respond.
  • the sameterm is applied to a similar eiiect occurring at the receiver.
  • The'incoming picture is traced by an area of illumination which moves across the picture ileld in the same mannerv as the transmitting aperture, and the apparent illumination of any point on the field is the mean illumination of that) area as it passes the point.
  • the frequencies here mentioned are the component frequencies of the pulses, and that the pulses themselves come, in general, at random.
  • the only truly periodic components in the transmission of a picture are the picture frequency itself (say 16 cycles per second) and the scanning frequency, or, as they are sometimes referred to, the lowerv and upper scanning frequencies.
  • the steep wave fronts or instantaneous current rises are converted into sloping wave fronts or gradual current rises. None the less, considered from the receiving end, there is a definite instant of arrival of the wave, which is the instant when the change in current starts to take place. At this instant the rate of change of current, (mathematically its first derivative with respect to time, or di/dt) changes from zero to some finite value. The rate at which I the.current is changing has a discontinuity or instantaneous change of value at 'this point.
  • the broad invention here presented is a method of communicationby electrical pulses which includes the steps of modifying the pulses by removing certain fre-l quency'components therefrom, transmitting the modified pulses, and adding, at the receiver, components substantially equivalent to those -previously removed to restore their original wave form.
  • the broad invention is a method of converting waves or pulses having sloping wave fronts into steep fronted waves by adding thereto components proportional to one o'r more derivatives of the arriving pulse with respect to time, at least one of the added derivative components preferably having a discontinuity at the instant of arrival of the pulse.
  • the derivative components are supplied by a differentiating network.
  • a differentiating network which, in its preferred form, comprises a relatively large impedance for determining the current ilow and establishing the relation oi. current and voltage waves in the network, and a shunt arm of relatively negligible impedance, wherein the voltage drop leads in phase that in the control impedance, and across which is developed a voltage proportional to the derivative of the arriving pulse'.
  • a vacuum tube be connected with its control circuit across this shunt arm, its output current is proportional to the voltage in this arm, and this current may be circulated through a similar network to generate a higher derivative.
  • these reconstructed pulses are used to control the illumination ofthe area whichl scans the field of the received picture, giving detail whichis even better than that produced by a receiver connected directly to the trails-l mitter, since the aperture distortion of the transmitter is completely corrected. .By adding a still higher derivative component theA aperture distortion at the receiver is largely compensated, since the powerful pulse corresponding to the infinite discontinuity at the instant of arrival gives a sharp outlineabout the pictured masses, pro-l ducing an illusion of relief.
  • the essential feature of this transmitter is a special type of photo cell comprising an en-v velope 2,.. preferably cylindrical in form, and
  • a lens system' 3 focuses an image this of the object 5, upon a4 photo-sensitive cathode whose picture is tdbe transmitted, plate t.. Parallel to and closely adjacent to the cathode is a screen anode 1, which is maintained. at a vpotential posil tive to the cathode by means of a battery or other source 8.
  • ode are vfocused ata corresponding point in the inventionto a television trans- Serial NOS. 270,673, 449,984,
  • a target or collector I3 which is preferably maintained slightly positive with respect to the shield by means of the source 8, and which collects those electrons which fall upon the aperture. Since electrons are liberated simultanously from the entire area of the image. there is thus formed a complete electron image of the object to be pictured, and if a fluorescent screen were placed in the tube in the plane of the aperture, the picture would appear upon it.
  • the electron stream which forms the electron" image is deflected magnetically by means of coils I6, and serves to deflect the' image across the' aperture at the low scanning frequency.
  • saw-tooth oscillations are'used for the vertical movement of theimage; which is moved uniformly downward over-the aperture in about 115th second, and then returned to its original position practically instantaneously.
  • the other oscillator deilects the image from side to side at substantially constant speed, equivalent to from 2,000 to 4,000 cycles per second. so that electrons enter the aperture consecutively from each unit area of the picture field as projected on the cathode, and
  • the electron current collected by the target I3 passes through a resistor I1, causing a potential drop across this resistor which actuat'es an amplifier I8.
  • the part of the apparatus thus fiar described may be identical in construction and operation with that' disclosed in my U. S. Patent No. 1,773,980- and applications above mentioned.
  • the amplifier I8 is shown as feeding into a low pass lter which removes all of the frequenii above a predetermined cut-olf value.
  • the lllter ' is shown as feeding into a line 2l. The reasons for using the filter will be discussed ⁇ in detail below.
  • the resistor 22 may be omitted.
  • the 26 is connected across vacuum tube 28, preferablyv of the screen grid type, so thatits output impedance is high.
  • the 26 is connected through another network comprising an -inductor 21 and a variable resistor 28.
  • the-closing impedance is a' I for s wave which' 'had through' 'a maar designed for substantially complete cut-o2 above 7 k.
  • the resistor 22 had a value of 1/4 megohm
  • variable resistors 25 and 23 a value of about 3ll millihenries each. Setting the variable resistors 25 and 23 at about 2,000 ohms gave the best ap ⁇ pearance to the picture. The impedance of the line was negligible as compared to that of the control resistor 22.
  • Coupled to the plate circuit of the tube 2l through a condenser is a cathode-ray receiving tube or oscillight 3
  • the oscillight has a hot filament 33 which releases electrons to be accelerated by the anode 35 and focused in a spot upon a fluorescent screen 30 in the large end of the oscillight.
  • the intensity of this spot is controlled by the grid 32, and it is deflected, preferably magneticallmby the coil 3l supplied by an oscillator 3l, in a manner to' correspond with the deflection of the electron stream by the transmitting scanning oscillator. This causes the transmitted picture to appear upon the iluorescent screen, traced by the focal spot.
  • the amplifier I8 be connected directly to the grid 32, and if it capable of amplifying a broad band of frequencies, ⁇ say ofthe order of 300 to 1,000 kilocycles, an excellent reproduction of the object 6 will appear upon the fluorescent screen 30 of the oscillight.
  • the sharply ⁇ defined edges are spread out into wide, shaded bands', and the picture assumes the general appearance of a dow cast upon a distant screen by a. large light so ce; i. e., the dark portions of the image are surrounded by a large penumbra..
  • the signals are picked-up by the antenna 42', and passed through the amplifier-detector 43, and after detection are impressed upon the grid of the highy impedance tube 44.
  • the plate circuit of this tube comprises an inductor 23' and resistor 25', which have the same function as the similarly designated elements in Figure 1, the resistor 22 being unnecessary in this case since its function is filled by the plate impedance of the tube. From this point forward, the circuit is identical with that shown in Figure 1, with the exception of the gridbiasing resister 45 and grid condenser 45', which are used in accordance with usual amplifier practice, and which are unnecessary in the line terminal apparatus where the tube 44 is omitted.
  • the action of the terminal network in restoring the picture can best be understood from a mathematical analysis of the picture pulses and the distortions which they undergo between the transmitter and receiver.
  • the changes in illumination in a picture are sudden; i. e., the aperture, traversing a' portion of the picture having a constant illumination 1c, suddenly arrives at another portion having a' different illumination h.
  • the result is a current in thc resistor Il which has, up to time 0, a value proportional to k, and after time 0 a suddenly increased value proportional to h.
  • N is merely the value of o atthe cut-oi! frequency and that the curve holds true whatever the value of cut-oli. Dividing all of the abscissas by N wouldy convert the X axis into a true time axis for the one particular value of cut-oil chosen.
  • the eireet of the terminal network described above is to add components proportional to the first and second derivatives to the incoming current wave. so that curve 5I represents the resulting wave as applied to the grid I2 of the cathodeg ray receiver.”
  • Such changes vcomprise avery large majorityv of the4 impulses occurring in plomo-transmission,- but ina few cases there isa gradual change of illumination of light to dark -or the reverse.
  • curve 52 indicates a currentwhicn gradually "Y10
  • issteadyuptotimet1. rises t1 and tz, and then resumes a steadystate ata new value.
  • the form in which thiscm're'nt would be restored by the network'here shown, is indi- -cated'l'ouhly by curve ll.-
  • the change in causes a steep fronted pulse, which raisesA the level of the lentire current at t1.
  • Thefundamenpicture current level to follow the level of the tially undistorted.
  • the effect is curve 53. In this curve, thelevel is as much below the true level as it was above in the opposite sweep, and the average effect is substanmuch exaggerated in the figure.
  • the compensating network differs from the ordinary amplifier, in that the impedance whose voltage drop in applied to the input circuit of the tube does not control its own current flow,
  • the current wave would differ from the voltage wave, being proportional to its integral.
  • the voltage across the inductance would still be proportional to the derivative of the current wave, but it would be identical in form with the voltage wave. This is the condition in ordinary impedance coupled amplifiers.
  • the restoring circuit as a whole, even including the tube 26, usually attenuates rather than ampliiies the received signal, and an additional tube or tubes must be provided where amplication of the received signals is necessary.
  • the additional amplifier where required,-may best be inserted ahead of .the network, as in the radio adaptation of the invention, and it may be of any approved type which'is adequate to amplify the received signal band.
  • Its nal tube is preferably, like the tube 44, of the screen grid type, having a plate resistance which may be considered as infinite, this resistance controlling the current ow and acting as the element 22.
  • the value of the second derivative component in the 'wave lies largely in compensating for aperture effect in the receiver.
  • the lter used should i pass uniformly the frequencies up to fc, attenuate the frequencies from fc to some other value f at an increasing rate, all frequencies above f' being substantially eliminated.
  • the conditions of Athe particular problem will determine the width of the band of increasing attenuation between je and f'. the compromise being between band width and fringes on the transmitted images due to the oscillations. Even with the sharpest cut-offs obtainable, however, these fringes have not proved in practice to be a serious detriment.
  • the resistive element in the network be the adjustable one, vor even that Separate elements be used, since a resistor and a variometer in series, or a variometer wound with resistance Wire, would give the effect required.
  • FIG. 9 there is shown a circuit which will differentiate a voltage wave, although its* general applicability is not as great as that of the circuit already described.
  • the high control impedance is provided by a small condenser B5, the shunt arm being formed by a relatively negligible resistance 66 in series with a large capacity 61. The latter is bridged by a high resistance leak 68 through which the grid of the tube 10 is biased by a battery 1
  • Figure 10 illustrates a circuit giving components of both first and second derivatives, as well as the fundamental.
  • control impedance is again supplied by a condeiser 15, while the condenser 16 gives a fundamental voltage drop, the
  • resistor Il a first derivative
  • inductor 18 a second derivative'com nent.
  • the condition of sharp and reestablishing the sharp fronted pulse If the attenuation is proportional to frequency above some specied value, the first derivativealone is complete compensation of the original pulse.
  • Second derivatives may be added in this case, as before, to compensate for'the distortion of the receiving aperture. It should be mentioned here, that the second derivative also helps to compensate for any distortion caused between the terminal network and the receiving oscillight itself by the capacity of the leads and apparatus.
  • This capacity integrates the pulses fed it, converting a portion of the second derivative back to first derivative, and rst derivative to fundamental.
  • the method of picture transmission which comprises the steps ,of scanning a picture field to produce picture current corresponding to a predetermineddegree of detail, filtering said current to remove the high frequency components thereof, transmitting said currents, .initiating at the receiving end components substantially equiva ⁇ lent to the components removed in ltering, and
  • the method of picture transmission which comprises the steps of scanning a picture field to produce picture current corresponding to a predetermined degree of detail, transmitting pulses corresponding to the low frequency components adding to the received pulses components proportional .to a derivative of said pulses with rev4.
  • the method of picture transmission which comprises the 'steps of scanning a'picture field to produce picture current corresponding to a predetermined degree of detail, transmitting pulses correspondingK to the low frequency components only of said currents, receiving said. pulses, and adding to the received pulses components proportional to a plurality of derivatives of said pulses with respect to time.
  • the method of picture transmission which comprises the steps of scanning a picture field to produce picture current corresponding to a predetermined degree of detail, transmitting pulses corresponding to the low frequency components only of said currents, and utilizing changes of slope in the wave front of the received pulses to create ⁇ steep fronted pulses for forming the rec'eivedl picture.
  • -means for attenuating thehigh frequency com-- pornents ⁇ of said current a communication channel for conveying 'impulses corresponding to the ⁇ modied current to a receiving station, means actuated by the received impulses for regenerat-v v received picture.
  • a picture transmission system means for scanning an object to produce a picture current, means for attenuating the high frequency components of said current, a communication channel for conveying impulses corresponding to the modified current to a receiving station, means actuated by the received impulses for generating an impulse substantially proportional to a derivative of the receivedmodule with respect to time, and means responsive to said derivative impulse for forming the received picture.
  • a picture transmission system means for scanning an object to produce a picture current, means for attenuating the high frequency components of said current, a communication channel for conveying impulses corresponding to the modified current to a receiving station, said channel terminating in a circuit of relatively high'impedance, an element in said circuit wherein the voltage drop leads the drop in said circuit and havingrelatively low impedance with respect thereto, and means responsive to the voltage drop in said element for forming the received picture.
  • means for scanning an object to produce a picture current means for attenuating the high frequency components of said current, a communication cham.
  • nel for conveying impulses corresponding to the modified currentJ to a receiving station, said channel terminating in a circuit of relatively high resistance, an inductor in series with said circuit having a relatively low impedance with respect thereto at the highest transmitted frequency,
  • a picture transmission system means for scanning an object to produce a picture current, means for attenuating the high frequency components of said current, a communication channel forconveying impulses corresponding to the modied current to a receiving station, said channel terminating in a circuit of relatively high impedance, a closing impedance comprising elements wherein the voltage drop has com- "ponents leading and in phase withv the drop in said circuit impedance and of low impedance relative to said circuit at the highest frequency A transmitted. and means responsive to the voltage drop in said elements for forming the received picture.
  • a picture transmission system means for scanning an object to produce a picture current, means for attenuatin'g the high frequency 20 components of said current, a communication channel for conveying impulses corresponding .to the modied current to a receiving station, said Vchannel terminating in a circuit oi relatively high resistance, a closing impedance comprising an inductor and a resistor having substantially equal impedances at the highest frequency transmitted, said impedances being low relative to the impedance of the circuit, and means responsive to the voltage drop in said impedance for forming the received picture.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Television Systems (AREA)
  • Radio Transmission System (AREA)
US500092A 1930-12-04 1930-12-04 System of pulse transmission Expired - Lifetime US2026379A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US500092A US2026379A (en) 1930-12-04 1930-12-04 System of pulse transmission
FR727571D FR727571A (fr) 1930-12-04 1931-11-25 Système pour la transmission des impulsions
GB33164/31A GB390565A (en) 1930-12-04 1931-11-30 System of electrical picture transmission

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3351710A (en) * 1961-10-13 1967-11-07 Denki Onkyo Co Ltd Narrow band facsimile communicating system
US3377425A (en) * 1964-08-31 1968-04-09 Sarkes Tarzian Aperture correction circuit
US3622698A (en) * 1969-03-03 1971-11-23 Magnavox Co Facsimile system with selective contrast control

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE739803C (de) * 1937-01-15 1943-10-05 Josef Briza Ing Verfahren zur elektrischen Bilduebertragung und zum Fernsehen

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3351710A (en) * 1961-10-13 1967-11-07 Denki Onkyo Co Ltd Narrow band facsimile communicating system
US3377425A (en) * 1964-08-31 1968-04-09 Sarkes Tarzian Aperture correction circuit
US3622698A (en) * 1969-03-03 1971-11-23 Magnavox Co Facsimile system with selective contrast control

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FR727571A (fr) 1932-06-20
GB390565A (en) 1933-04-13

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