US2297612A - Television and like system - Google Patents
Television and like system Download PDFInfo
- Publication number
- US2297612A US2297612A US275787A US27578739A US2297612A US 2297612 A US2297612 A US 2297612A US 275787 A US275787 A US 275787A US 27578739 A US27578739 A US 27578739A US 2297612 A US2297612 A US 2297612A
- Authority
- US
- United States
- Prior art keywords
- valve
- signals
- synchronising
- diode
- anode
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/04—Synchronising
- H04N5/08—Separation of synchronising signals from picture signals
Definitions
- the present invention relates to television and like systems.
- the picture signals are transmitted with the brighest picture points corresponding to the peak signal amplitude and the darkest points corresponding to approximately 30% of the peak amplitude.
- the synchronizing signals are interspersed with the picture signals and comprise pulses which reduce the amplitude of the transmitted signal from the 30% level to zero level.
- the scanning generators it is necessary to control the scanning generators by means of the synchronising pulses which must be free from the picture signals in order to prevent the latter from upsetting the synchronisation. and advantage has been taken of these differences in amplitude to effect such separation.
- separators have been suggested for the purpose of separating the picture signals from the synchronising pulses.
- a suitably biassed diode valve in series between the anode of a thermionic valve amplifying television signals and the scanning generators so that the diode valve only conducts during synchronising pulse periods.
- This method suffers from a number of disadvantages; for instance, the separating diode has a considerable capacity between its electrodes which tends to transfer the picture signals of higher frequency to the scanning generators, thus interfering with correct synchronisation and in addition is detrimental to the vision signals due to the by-passing effect at the higher frequencies.
- a method for the amplitude separation of synchronising signals from picture signals which comprises biassing a uni-directional conducting device connected in shunt with a portion of an impedance network to which the mixed signals are applied in such a manner that the state of conduction of said uni-directional device is changed during synchronising pulse periods.
- the invention comprises applying to a thermionic valve the combined picture signals and synchronising pulses, said valve being associated with an impedance shunted by a diode valve, the arrangement being such that the diode is rendered non-conducting during the synchronising pulses, whereby the amplitude of the synchronising pulses is increased compared with the amplitude of the picture signals.
- a circuit comprising a thermionic valve to which the combined picture signals and synchronising pulses are applied and an impedance shunted by a diode valve associated with said thermionic valve, which diode valve is biassed such that it is rendered non-conducting during synchronising pulse periods for separating the synchronising signals from the picture signals.
- the change in the state of conduction of the diode valve may be utilised to increase or decrease the gain of said thermionic valve to which the combined picture signals and synchronising pulses are applied.
- FIG 1 shows one form of the present invention
- Figure 2 shows a modifying form
- valve 2 may be either an anode bend detector or a vision frequency amplifier to which the picture and synchronising signals are applied.
- the vision frequency amplifier it is assumed that the D. C. component is present in the signals as applied to the grid of the valve.
- the picture signals for application to the picture reproducer as for example, a cathode ray tube, are taken from the terminal 5 which is connected to a source of positive potential, as is also the screening grid of the valve 2.
- the synchronising signals are taken from the junction of resistance 3 and 4 and are applied through the coupling condenser 6 to the grid of a valve I which is used for amplifying and shaping the synchronising pulses.
- the valve I is provided with a suitable grid resistance 8.
- a resistance potentiometer comprising resistances 9 and I0, the resistance 9, which is preferably variable, being shunted by a condenser II.
- a diode valve I2 is connected between the junction of resistances 3 and 4 and the junction of resistances 9 and If the anode of the diode I2 being taken to this latter junction.
- valve l In the anode circuit of valve l is connected a resistance I3 which is taken to a suitable positive potential.
- a condenser M is connected between the anode of valve i and the source of negative supply and the frame synchronising pulses are derived across this condenser.
- a transformer winding I5 In the screen grid circuit of the valve I is connected a transformer winding I5 which is used for the purpose of supplying line synchronising pulses to the line scanning generator. Should the line scanning generator be a blocking oscillator with a reaction transformer, the winding I5 can be an extra winding on the blocking oscillation transformer. Any other suitable method of coupling, as for example, by the use of a resistance and condenser, may be employed for coupling valve I to the line scanning generator.
- the television signal has a waveform of the Marconi-EMI type, which is illustrated in the Wireless World for October 4th, 1935, page 373
- the signal is applied 7 picture signals are obtained across the resistance 7 3 in the anode circuit of valve 2 and are applied to the picture reproducer.
- the synchronising signals are applied to the valve 2 and cause the current of this valve to decrease below a certain value the potential drop across the resistance 4 decreases to such an extent that the oathode potential of diode I2 rises to a value more positive than the anode potential of the diode I2.
- This has the effect of rendering diode I2 nonconducting and a synchronising pulse is applied via condenser 6 to the grid of valve I.
- the resistance of the diode I2 in the conducting state is very low and effectively short circuits the resistance 4.
- the effective anode impedance of valve 2 during the picture periods is thus the resistance 3.
- the effective anode impedance of valve 2 comprises resistances 3 and 4 in series, and by making resistance 4 about two or more times as great as resistance 3 it is possible to amplify the synchronizing pulses considerably more than the picture signals.
- the separated synchronizing pulses are applied to the valve 1 in the positive sense and by a suitable choice of the coupling condenser B and resistance 8 it is possible to bias valve 1 by means of its grid current so that this valve only conducts during synchronising pulse periods. This has the effect of improving the shape of the synchronising pulses.
- the condenser I4 in conjunction with the anode resistance I3 of valve 1 serves to integrate the line and frame pulses and to produce frame pulses which are larger in amplitude than the line pulses. The amplitudes of the line pulses are so small that substantially only frame pulses affect the frame scanning oscillator.
- the line pulses are taken from the transformer winding I5 to the line scanning generator.
- the anode-cathode impedance of valve '1 is arranged to be large compared with the resistance I 3 so that when a line synchronising pulse is applied to valve I the condenser I4 is only discharged slightly and the condenser is recharged to its maximum value in approximately half a line period. On the application of a frame synchronising pulse to valve 1, however, the condenser I4 is discharged to a greater extent owing to the longer duration of the frame synchronizing pulse compared with the duration of the line synchronising pulse.
- the large amplitude frame pulses across the condenser I 4 can be applied directly to the frame scanning oscillation generator or via an amplitude separator.
- the method of separation of picture signals from synchronising pulses described will also function in systems in which the synchronising pulses have amplitudes which are greater than the amplitudes of the picture signals.
- the signals should be applied to the grid of valve 2 in a reverse sense so that the synchronising pulses are applied in a negative sense similarly to those oi the Marconi-EMI type already discussed.
- the diode valve 12 Since the diode valve 12 is connected in shunt with the resistance 4 and the valve is conducting during the picture periods the capacity of the electrodes of this valve are ineffective to spoil the picture signals and in addition the capacity of the heater windings do not affect the picture signals.
- the bias on the diode valve I2 can be adjusted by means of the variable resistance 9 so that the valve I2 only insulates during the synchronising pulse periods.
- Interference may also be eliminated by grid current in the valve 1 by making the amplitude of the synchronising pulses applied in'this valve sufficiently great. It is preferable in this case to make resistance 8 of a suitably low value, say, five times the value of resistance 4.
- the combined picture and synchronising signals are applied to the control grid of a'pentode valve I so that the valve I acts as 'a self-establishin D. C. amplifier, as described in the'specification of U. S. Application Serial No. 720,205 the synchronising pulses being applied in the positive sense, through a capacity I9 and leak resistance 20.
- the applied signals establish D. C. potentials at the control grid of the valve I with consequent production of potentials at the anode of valve I6 which are 180 degrees but of phase with the applied signals.
- the anode of valve 16 is loaded with a resistive impedance Consisting of the resistances 11, 2
- the anode of the diode I8 is connected to the anode of valve [6 and the cathode of the diode I8 is suitably biassed due to the potential applied between the end terminals of resistance 2! and resistance 23.
- and 22 is connected directly to the screen electrode of valve IS.
- biassing potentials applied to the screen electrode of valve I6 and to the cathode of the diode I8 are chosen so that when the potential of the control grid of valve [6 is above a predetermined value, for example that potential corresponding to the application of the synchronising pulse, the anode current of the valve I6 is sufficient to cause the anode potential of valve 6 to fall to a chosen value, above which chosen value the diode l8 becomes conducting.
- the diode valve is may be biassed so that it is rendered conducting when the potential of its anode falls below 30 volts.
- the diode I8 On the arrival of a synchronising pulse, the diode I8 is thus rendered non-conducting and by arranging that the arrival of a synchronising pulse results in zero anode current in the valve 16 throughout the period of the synchronising pulse a constant potential is applied at the terminal 24 from whence the line and frame deflecting circuits may be actuated by the leads 25 and 28.
- a picture signal renders diode I8 conducting so that no actuating potentials are applied to leads 25 and 26 during the periods of arrival of picture signals.
- the arrangement described thus results in sep aration of the picture and synchronising signals and, to obtain good separation, the resistance ll should be considerably greater than the impedance of the diode IS.
- the picture signals are fed directly from terminal 24 to the junction of resistances 22 and 23 during picture periods, which path has no capacity in shunt therewith.
- valve [6, and direct D. C. coupling may be employed if desired.
- This threshold black level may be r I claim:
- means for separating said signals comprising a thermionic tube having anode, cathode, and at least one control electrode, means for impressing said signals onto said thermionic tube to control the current in the anode-cathode circuit thereof, a potentiometer arrangement connected in the anode-cathode circuit of said thermionic tube, a uni-directional conductor connected substantially in parallel with at least a portion of said potentiometer whereby signals attaining a predetermined amplitude are partially short-circuited by said uni-directional conductor and whereby a definite division may be made between said synchronizing signals and said Video signals, means for impressing said synchronizing signals onto an integrating circuit, and separate output means electrically connected to said integrating circuit whereby said line and frame synchronizing signals may be separately removed from said apparatus.
- said potentiometer unit comprises a pair of resistive members serially connected and whereby one of said resistive members has a value considerably greater than the other of said resistive members.
- a first thermionic tube having anode, cathode and at least one control electrode, means for impressing said signals onto the control electrode-cathode path of said thermionic tube, potentiometer means connected in the output circuit of said thermionic tube, a time constant circuit, uni-directional conducting means connected substantially in series with said time constant circuit, said series circuit being connected substantially in parallel with at least a portion of the resistance in said potentiometer, a second thermionic tube having anode, cathode and at least one control electrode, means for impressing at least a portion of the voltage variations across at least a portion of said potentiometer onto the control electrode-cathode path of said second thermionic tube, an integrating circuit connected in the output circuit of said second thermionic tube, and separate output means connected to said second thermionic tube for separately
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- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Details Of Television Scanning (AREA)
- Video Image Reproduction Devices For Color Tv Systems (AREA)
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB16195/38A GB515427A (en) | 1938-05-31 | 1938-05-31 | Improvements in or relating to television and like systems |
Publications (1)
Publication Number | Publication Date |
---|---|
US2297612A true US2297612A (en) | 1942-09-29 |
Family
ID=10072890
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US275787A Expired - Lifetime US2297612A (en) | 1938-05-31 | 1939-05-26 | Television and like system |
Country Status (3)
Country | Link |
---|---|
US (1) | US2297612A (de) |
DE (1) | DE935612C (de) |
GB (1) | GB515427A (de) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2907821A (en) * | 1956-01-19 | 1959-10-06 | Marconi Wireless Telegraph Co | Television apparatus |
US2935555A (en) * | 1954-10-06 | 1960-05-03 | Rca Corp | Modulator for color television transmitters |
US3248478A (en) * | 1961-10-20 | 1966-04-26 | Philips Corp | Circuit arrangement for separating two signals from a composite signal |
Family Cites Families (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE380247C (de) * | 1920-09-02 | 1923-09-05 | Aeg | Schaltung zur Beseitigung von auf Telegraphenleitungen durch parallelgehende Wechselstromleitungen hervorgerufenen Influenz- und Induktionsstoerungen |
DE459150C (de) * | 1922-07-21 | 1928-05-03 | Radio Electr Soc Fr | Verfahren zum stoerungsfreien Empfang fuer drahtlose UEbertragung |
GB346666A (en) * | 1930-01-08 | 1931-04-08 | Theodore Ainslie Smith | Improvements in or relating to thermionic amplifying systems |
BE407481A (de) * | 1934-01-25 | |||
US2144995A (en) * | 1934-10-08 | 1939-01-24 | Pulvari-Pulvermacher Karl | Means for avoiding disturbances in the reception of electric oscillations |
AT143054B (de) * | 1934-10-08 | 1935-10-10 | Karl Dipl Pulvari-Pulvermacher | Schaltanordnung zum störungsfreien Empfang elektrischer Schwingungen. |
CH198016A (de) * | 1936-04-29 | 1938-05-31 | Rca Corp | Radioempfangsschaltung mit Mitteln zur mindestens teilweisen Unterdrückung von kurzdauernden Störungen. |
GB496246A (en) * | 1936-05-28 | 1938-11-28 | Marconi Wireless Telegraph Co | Improvements in or relating to radio receivers and the like |
-
1938
- 1938-05-31 GB GB16195/38A patent/GB515427A/en not_active Expired
-
1939
- 1939-05-26 US US275787A patent/US2297612A/en not_active Expired - Lifetime
- 1939-06-01 DE DEE2353D patent/DE935612C/de not_active Expired
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2935555A (en) * | 1954-10-06 | 1960-05-03 | Rca Corp | Modulator for color television transmitters |
US2907821A (en) * | 1956-01-19 | 1959-10-06 | Marconi Wireless Telegraph Co | Television apparatus |
US3248478A (en) * | 1961-10-20 | 1966-04-26 | Philips Corp | Circuit arrangement for separating two signals from a composite signal |
Also Published As
Publication number | Publication date |
---|---|
DE935612C (de) | 1955-11-24 |
GB515427A (en) | 1939-12-05 |
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