US2284085A - Electric signal transmission system - Google Patents

Electric signal transmission system Download PDF

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Publication number
US2284085A
US2284085A US301324A US30132439A US2284085A US 2284085 A US2284085 A US 2284085A US 301324 A US301324 A US 301324A US 30132439 A US30132439 A US 30132439A US 2284085 A US2284085 A US 2284085A
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United States
Prior art keywords
condenser
impulses
signals
potential
synchronizing
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Expired - Lifetime
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US301324A
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English (en)
Inventor
Collard John
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EMI Ltd
Electrical and Musical Industries Ltd
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EMI Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/44—Receiver circuitry for the reception of television signals according to analogue transmission standards
    • H04N5/52—Automatic gain control
    • 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
    • H04N5/16—Circuitry for reinsertion of DC and slowly varying components of signal; Circuitry for preservation of black or white level
    • H04N5/165—Circuitry for reinsertion of DC and slowly varying components of signal; Circuitry for preservation of black or white level to maintain the black level constant
    • 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
    • H04N5/16—Circuitry for reinsertion of DC and slowly varying components of signal; Circuitry for preservation of black or white level
    • H04N5/18—Circuitry for reinsertion of DC and slowly varying components of signal; Circuitry for preservation of black or white level by means of "clamp" circuit operated by switching circuit
    • H04N5/185—Circuitry for reinsertion of DC and slowly varying components of signal; Circuitry for preservation of black or white level by means of "clamp" circuit operated by switching circuit for the black level

Definitions

  • This invention relates to systems for the transmission of electric signals, such as television signals. It provides methods and means whereby low-frequency components difierentially attenuated as compared with higher frequency components in the course of transmission may be re-established, or wherein interference components of low frequency arising in such systems may be substantially removed. It may also be employed for compensating for varying attenuation such as fading in signals possessing two sets of recurrent fixed-level or datum portions such as television signals.
  • a 1 system for the transmission of electric signals having recurrent fixed-level or datum portions in which in the course of transmission undesired changes occur in said signals comprising means for providing a corrective signal which is a substantially continuous function of time and is dependent on the simultaneously observed levels of a plurality of different datum portions and for utilising said signal to correct substantially for said undesired changes in said signals.
  • the invention may be carried into effect according to one aspect which may be referred to as a "delayed or interpolated method, or according to another aspect which may be referred to as an extrapolated method.
  • television signals consist of alternate line and synchronising signals, the line signals varying according to the picture being scanned and lasting for about microseconds, the synchronising pulses lasting for about 10 microseconds and having a definite magnitude and being followed by a black-level period of about 5 microseconds duration. If upon such a waveform a single-frequency induced component is superimposed, it will be impossible during the line signal period to decide how much of the received signal is due to the induced component and how much to the actual line signal.
  • the invention consists basically in eflfecting a delay corresponding to the interval between two synchronising pulses.
  • V Two methods are available for producing this delay.
  • One is to use any of the well known electrical delay networks. If this is adopted it may be necessary to correct for a large amount of distortion and attenuation by means of suitable equalisers and amplifiers, since the requirements demanded of such a network, namely, a delay time of theorder of several hundred microseconds over a frequency range up to about 2 megacycles per second, are exceptional.
  • the delay means may conveniently comprise a suitable length of. television cable and its associated equipmen
  • the other methodof obtaining the delay is to use a device allied to the electron camera in which two beams travel continually over'a circular track. The first beam lays down the signals and the second picks them up again after the required interval as described in the specification of British'Patent No. 471,913. a 1
  • FIG. 1 there is shown a functional circuit for applying the invention in its simplest form.
  • the signals are applied at the terminals III, II. From there they pass through the delay network II which is assumed to be distortionless and free from loss, and so reach the output terminals l3, It by way of the condenser l5.
  • switches I6 and I1 which connect the terminal III to the terminal H through the condenser 13 and the battery l3 as shown in the figure, are closed.
  • the battery I! has an E. M. F. equal to the potential to which the terminal l should be raised, that is, the potential to which the terminal I!
  • condensers l8, 15 are connected together and if it is assumed that the former is large compared with the latter then the former will eventually charge the latter to its own potential. If the connection is effected through the resistance 2
  • the condensers I5 and I3 constitute in eilect observing devices and enable a correcting signal.
  • switches 16 and I5 may be replaced by valve circuits arranged to perform the same operations.
  • Various forms of valve switches have been proposed in connection with so called clamp" D. C. re-establishment, and in particular the six-diode switch described in British Pat ent No. 512,109 may be applied here.
  • Figure 2 shows an alternative arrangement for obtaining a linear restoring. potential.
  • the condenser l5 being connected in the lead from the delay network to the terminal 13.
  • the terminal Ill and the terminal of condenser connected to the output of the delay network are connected respectively through the switches 23, 24 and the condensers 25, 26 to ground, these condensers forming the observing devices in this example of the invention.
  • the plates of these condensers not con nected to earth are taken to the control grids 21, 28 of the valves 29an'd 30 respectively.
  • These valves have a large resistance 3
  • the anode 33 is connected through the condenser 34 and the resistance 35 to the output terminal l3.
  • the condenser 34 being of large capacity compared with that of condenser IS.
  • the output terminal I3 is connected through the switch 33 to the battery 31 and through the battery to ground.
  • the switches 23, 24 and 35 are closed. Condenser thus becomes charged to a value corresponding to 0:, say, and. condenser 26 some other value corresponding to m.
  • the potential change arising at the anode 33 of valve 33 is proportional .to mvi.
  • the charging current flowing from valve 33 through the condenser 34 and the resistance 35 to condenser I5 is also proportional to 122-111.
  • the condenser I! has a potential difference between its terminals equal to '01 due to the charge obtained from the battery 31 through the switch 36.
  • the steady charging current from valve shall increase the potential diflerence across condenser l5 to 02 at the end of the line.
  • condenser l5 supplies the correct restoring potential starting at m and increasing linearly to m.
  • valve 30 In order that the current from valve 30 shall be independent of the potential changes of condenser I5 during the line interval, it is necessary to arrange that the potential changes on the anode of valve 30, which produce the charging current, shall be large compared to the changes occurring in condenser 15.
  • the gainof valves 29 and 30 is therefore made large and the resistance is also made large.
  • the anodes 33 and 33' are, however, also connected through series resistance-capacity circuits 33, 33 and 33', 39' to the grid 40 of the valve whose cathodeis earthed. Between the grid 40 and earth there is connected the condenser 42 and across this condenser is arranged the switch 43 and battery 44 in series. The anode 45 of valve 4
  • valves 30' and 3. are in the correct ratio.
  • the anodes of these valves are also connected to condenser 42 through large condensers and resistances. Hence the total charging current into condenser 42 is The potential diilerence across the condenser 42 is thus equal to ⁇ (112-121) -(va-v'z) ⁇ A. Since the grid of valve 4
  • condenser AIS is therefore supplied with a charging current proportional to ⁇ (v:v1)(v:m) ⁇ A.
  • the potential. difference built up across condenser l5 .due to this current is accordingly proportional topotential - ⁇ (vz-v1)(v:.vz) ⁇ A.
  • the total diiference across condenser I5 is thus made to vary in accordance with the full expression given above for v and is thus correct to a secondorder of approximation throughout the line interval.
  • the switch 43 Since the process is required to siart fresh at the .end of each line the switch 43 is provided to .short' circuit condenser and'so prepare it for the 'new charge.
  • the battery 44 is used to avoid short circuiting the gridof valve 4ltoearth.
  • the first stage of'the extrapolated"- method is the same as'the original -clamp" D. C. re-establishment. (see British'latent No. 449,29). It consists ofrneasuring the restoring potential in for the synchronising pulse immediately preceding the. line interval. and then applying a constant potentialofthis magnitude throughout the following lineinterval. This assumes, of course.
  • T is the time interval of one'line' two successive synchronizing ply a restoring potential of:
  • the chief feature of the invention as carried into eiiect according ,to delayed methods is that the restoring potential is determined from observations made on synchronising pulses before and after the line interval for which the restoring potential is to be used.
  • extrapolated methods of re-establishment which will now be illustrated, maybe used. In these a number of successive synchronising pulses are observed and the observations are used to set up the restoring potential'for the line interval following immediately after. the last observed synchronising pulse.
  • variable terms so far considered have all been linear in it, so that the resultant restoring potential varies as a straight line throughout the line interval. It will be obvious that by taking terms proportional plying the second approximation of the extrapolated method, i. e., for producing a restoring potential of form shows diagrammatically how this may be carried out.
  • a rotating system of threeobserving condensers 65, 66, 61 having a clockwise motion and being connected in a star arrangement with the central point earthed.
  • the free plates are periodically brought into contact with the points 62, 63,,
  • the contacts 62 and 63 are connected to the device 66 which comprises a pair of valves arranged in exactly the same manner, for exam-' ple, as the valves 56 and 61 in Figure 4 and performing the same function. From the output of this device connection is made by a large condenser and resistance, 16 and 1
  • the contacts 63 and 64 are connected to the terminal I3 in a precisely similar way, namely, through the device 69, similar-to the device 66, and through the condenser 12 and resistance 13.
  • Figure 5 15 now becomes charged to a potential 122.
  • Condenser 65 also receives a charge depending on 122. Just before the third synchronising pulse reaches condenser I5, the condenser assembly is rotated again through When the third pulse arrives the switch 36 is closed again so that condenser I5 is now charged to a potential vs.
  • Condenser 66 also receives a charge depending onm, and condenser 65 retains a charge depending on or.
  • condenser 61 has a charge depending on m and is connected to contact 64
  • condenser 66 has a charge depending on m and is connected to contact 62
  • condenser 65 has a charge depending on '02 and is connected to contact 63
  • the device 68 is connected to contacts 62 and 63 a charging current is therefore given to condenser 15 proportional to 03-02.
  • the similar device 69 there is also given'a charging current to condenser '15 proportional to 02-01.
  • FIG. 6 A way in which this scheme may be put into practice without the use of moving mechanical parts is shown in Figure 6.
  • This arrangement is identical with that of Figure 5 except that the contacts 62, 63,64 are replaced by leads havin the same reference numbers, the condensers 65, 66 and 61 are now fixed and the brushes are replaced by the array of switches shown.
  • Switches 15, 16, 11 are capable of connecting the condensers as, u, a respectively to the lead "c2.
  • Switches 18, 18, 88 perform asimilar function with respect to the lead 68 as do switches 8
  • Switch 14 connects terminals l8 tolead- 62.
  • the various switches would, of course, consist of suitable valve circuits as already discussed.
  • condenser 61 with a charge depending on v: and' condenser IS with a potential equal to 12:.
  • device 68 is connected to condensers 61 and 66 and therefore gives a charging current to condenser I 5 proportional to try-vs
  • device 88 is connected to condensers 66 and 66 and therefore gives a charging current to condenser l5 proportional to lb-U1.
  • the correct potential difference across condenser I! may be main-' tained throughout the line interval, and-for subsequent synchronising pulses, the series of operations is continued.
  • Swith 85 connects the cathode 8
  • condenser 66 now has a charge depending on m and condenser 65 one depending on in.
  • switch 86 is first closed causing condenser 61 to receive a charge depending on in.
  • switch 86 is then opened and switch 85 is closed, causing condenser 66 to receive a charge depending on Us.
  • Switch 85 is then opened, and switch 84 is closed and opened again, causing condenser 65 to receive a charge depending on us.
  • Figure '3 shows a method of applying delayed D. C. re-establishment in which three successive synchronising pulses are observed. These values are obtained by two delay networks each giving a delay equal to the interval between synchronising pulses. If. v1, or and in are the three restoring potentials observed then m is obtained by means of one delay network and v: by means of two delay networks. The restoring potential derived from these is applied to correct in the line interval between or and D2. It is possible, however, instead of observing the potential v: to observe and store the synchronising pulse prior to that giving the potential or, thereby deriving a correcting potential say.
  • the method of correcting signals representative of the suppressed components derived from the synchronizing signals at a receiving point which includes the steps of receiving the combined signals and impulses, comparing the received synchronizing impulses with each other, deriving energy representative of the difference of the compared impulses, and adding progressively varying energy to the received signals during the time interval between the synchronizing impulses, the variation of the energy being between the limits of zero and a maximum value proportional to the difference between the compared impulses.
  • the method of correcting signals representative of the suppressed components-derived from the synchronizing signals at a receiving point which includes the steps of comparing the received successive synchronizing impulses with each other, deriving energy representative of the difierence of the compared impulses, and adding progressively varying energy to the received signals during the time interval between the synchronizing impulses, the variation' of the energy being between the limits of zero and a maximum value proportional to the diflerence between the compared impulses.
  • the method of correcting signals representative of the suppressed components derived from the syn-1 chronizing signals at a receiving point which includes the steps 01 comparing the received successive groups of synchronizing impulses with each other, deriving energy representative of the difference of the compared impulses, and adding progressively varying energy to the received signals during the time interval between the synchronizing impulses, the variation of the energy being between the limits oi! zero and a maximum value proportional to the difference between the compared impulses.
  • th method of correcting signals representative of the suppressed components derived from the synchronizing signals at a receiving point which includes the steps of receiving the combined signals and impulses, delaying the combined signals and impulses, comparing delayed synchronizing impulses with undelayed synchronizing impulses, deriving energy representative of the difierence of the compared impulses, and adding progressively varying energy to the received signals during the time interval between the synchronizing impulses, the variation of the energy being between the limits of zero and a maximum value proportional to the diiierence between the compared impulses.
  • the method of correcting signals representative of the suppressed components derived from the synchronizing signals at a receiving point which includes the steps of receiving the combined signals and impulses, comparing the received synchronizing impulses with eachother, deriving potential mcreasing linearly with respect to time between the limits of zero and a maximum value in proportion to the difl'erence of the compared impulses, and adding said derived potential to said received combined signal and impulses.
  • a television system having video signals combined with interspersed .synchronizing impulses and in which direct current and low frequency components of the video signals are sup-- ing signals at a receiving point which includes the steps of receiving the combined signals and impulses, comparing the received synchronizing impulses, deriving potential increasing parabolically with respect to time between the limits of zero and a maximum value inproportion to the diil'erence of the compared impulses, and adding said derived potential to said received combined signal and impulses.
  • a direct current insertion television system comprising means to receive video signals combined with interspersed synchronizing impulses in which direct current and low frequency components of the video signal are suppressed which combined signals and impulses are subjected to distortion in transmission, means for comparing the received synchronizing impulses with each other, means for deriving energy representative of the diiference of the compared impulses, and means for adding progressively varying energy to the received signals during the time interval between the synchronizing impulses, the variation of the energy being between the limits ofzero and a maximum value proportional to the diflerence between the compared impulses.
  • a direct current insertion television system comprising means to receive video signals compared impulses, and means for adding progressively varying energy to the received 1811 18 during the time interval between the synchronizing impulses, the variation of the energy being between the limits of zero and a maximum value proportional to the difference between the compared impulses.
  • a direct current insertion television system comprising means toreceive video signals combined with interspersed synchronizing impulses in which direct current and low frequency components of the video signals are suppressed which combined signals and impulses are subjected to distortion in transmission, means for comparing the received synchronizing-impulses with each other, means for deriving potential increasing linearly with respect to time in proportion to the difference of the compared impulses, and means for adding said derived potential to said received combined signal and impulses.
  • a direct current insertion television system comprising means to receive video signals combined with interspersed synchronizing impulses in which direct current and low frequency components of the video signals are suppressed which combined signals and impulses are subjected to distortion in transmission, means for comparing the received synchronizing impulses with each other, means for deriving potential increasing parabolically with respect to time in proportion to the diflerence of the compared impulses and means for adding said derived potential to said received combined signal and impulses.
  • a direct current insertion television system comprisingmeans to receive video signals combined with interspersed synchronizing impulses in which direct current and low frequency components of, the video signals are suppressed which combined signals and impulses are subjected to distortion, intransmission, means for delaying the combined signals and impulses, means for comparing delayed groups of synchronizing impulses with undelayed groups of synchronizing impulses, means for deriving energy representative of the difference of the compared impulses, and means for adding progressively varying energy to the received signals during the time interval between the synchronizing impulses, the variation of the energybeing between the limits of zero and a maximum value proportional to the difference between the comtion of the energy being between the limits of ,45 pared impulses.
  • a direct current insertion television system comprising means to receive video signals combined with interspersed synchronizing impulses in which-direct current and low frequency components of the video signals are suppressed which combined signals and impulses are subjected to distortion in transmission, means for delaying the combined signals and impulses, means for comparing delayed synchronizing impulses with undelayed synchronizing impulses, means for deriving energy representative of the difference of the compared impulses, and means for adding progressively varying energy to the received signals during the time interval between the synchronizing impulses, the variation of theenergy being between the limits of zero and a maximum value .proportional to the difference between the compared impulses.
  • a direct current insertion television system comprising means to receive video signals combined with interspersed synchronizing impulses in which direct current and low frequency components of the video signals are suppressed which combined signals and impulses are subjected to distortion in transmission, a delay network fed by said received signals, said delay network having an output circuit, thermionic means connected across said output circuit, means common to both named thermionic means for deriving a potential proportional to the difference between the received energyand'the ene y Of the output

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Picture Signal Circuits (AREA)
  • Control Of Amplification And Gain Control (AREA)
  • Variable-Direction Aerials And Aerial Arrays (AREA)
US301324A 1938-10-19 1939-10-26 Electric signal transmission system Expired - Lifetime US2284085A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB30210/38A GB521744A (en) 1938-10-19 1938-10-19 Improvements in or relating to electric signal transmission systems

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US2284085A true US2284085A (en) 1942-05-26

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US301324A Expired - Lifetime US2284085A (en) 1938-10-19 1939-10-26 Electric signal transmission system

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US (1) US2284085A (enrdf_load_stackoverflow)
DE (1) DE836045C (enrdf_load_stackoverflow)
FR (1) FR862398A (enrdf_load_stackoverflow)
GB (1) GB521744A (enrdf_load_stackoverflow)
NL (1) NL81368C (enrdf_load_stackoverflow)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2547020A (en) * 1944-12-26 1951-04-03 Int Standard Electric Corp Method and means for the transmission of low-frequency calls intelecommunication systems by interrupting the carrier
US2550178A (en) * 1946-11-21 1951-04-24 Rca Corp Direct current reinsertion circuit for television systems
US2564017A (en) * 1949-06-04 1951-08-14 Bell Telephone Labor Inc Clamp circuit
US2829197A (en) * 1951-02-16 1958-04-01 Avco Mfg Corp Noise limiter for television receiver
US2907822A (en) * 1952-04-17 1959-10-06 Marconi Wireless Telegraph Co Interference reduction in television and other communication systems

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2547020A (en) * 1944-12-26 1951-04-03 Int Standard Electric Corp Method and means for the transmission of low-frequency calls intelecommunication systems by interrupting the carrier
US2550178A (en) * 1946-11-21 1951-04-24 Rca Corp Direct current reinsertion circuit for television systems
US2564017A (en) * 1949-06-04 1951-08-14 Bell Telephone Labor Inc Clamp circuit
US2829197A (en) * 1951-02-16 1958-04-01 Avco Mfg Corp Noise limiter for television receiver
US2907822A (en) * 1952-04-17 1959-10-06 Marconi Wireless Telegraph Co Interference reduction in television and other communication systems

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Publication number Publication date
NL81368C (enrdf_load_stackoverflow) 1956-05-15
GB521744A (en) 1940-05-30
FR862398A (fr) 1941-03-12
DE836045C (de) 1952-04-07

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