US2196364A - Television receiving connection system - Google Patents

Description

April 9, 1940- K. scHLEslNGER TELEVISION RECEIVING CONNECTION SYSTEM Filed Nov. 1, .1935

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m WM faten ted Apr. 9, 1940 e; Ala-r4 Application November 1, 1935, Serial No. 47,788

In Germany November 6, 1934 1 scam (o1. 1 78--7.5) I Recently transmission methods have'been devised, particularly by the applicant, in which the synchronisation takes place by means of impulses which raise the aerial current in the transmitter 5 to a maximum. If the transmitter isso moduf lated that white points of the image represent strong currents, and black points small serial currents, the reception-from a transmittersyn chronised in this fashion reveals particularly light stripes along the edges of the image. This is not permissible in practice, as the return lines causedby the white stripes are also brightened, and there is produced in the image a light back- 1!! effect of the image, particularly at dark points of the image. Since the system of white signals possesses certain technical advantages in'lack of interference, adjustment and operation of the transmitter and also in the generation of the signals by optical means, it is important to find circuits which permit of reception from these white-synchronisedtransmitters without the disturbipg return-line efiects. e

The accompanying drawing shows HQ}; valve circuit according to the invention, which incorporates the following technical advantages:

1'. Darkening of the whitereturn lines.

2. Separation of the synchronisation impulses from the contents ofthe image (by amplitude separation).

3. The production of a negative bias dependent on the strength of reception and capable of being used for automatic regulation of the amplifica-v tion. I

v 4; Fundamental preclusion of false actuation of the relaxation apparatus even in the case of excessive intensity in the reception. r

In the single figure, I is the lead proceedin from the anode of thefinal receiving rectifier'Z, the construction of which is not of interest for the present purpose; this lead is connected directly to the first control grid 3 of the cathode ray tube 4. This line supplies positive potential values to the grid if white points should occur in the image. According to the invention, the television tube 4 is furnished with a second control grid5, which has the specific object of blocking the ray during the return lines, but which, however, except in the relaxation moments, should not participatevin the control of the ray. 'The grid 5 may at the same time assume an electronoptical function; For example it may, as a condenser, perform the task of reproducing sharply on theapertureof the diaphragm the'stream 55 ofelectrons proceeding from the cathodetiliIn ground, which interferes considerably with the a singlethe case of present-day television tubes with extreme light intensity, a condenser of this kind is necessary in any case, and the inclusion of the electrode 5- does not, therefore, represent any particular complication. Accordingto the in- 5 according to the invention, which anode is led nected to earth through the medium of the high charge which have leaked off through I9 during out preferably. at the top. This valve is preferably' furnished with. an intercepting grid I3 and screening grid I4, and agrees fully otherwise in construction with the pentodes employed in the present-day radio art with good mutual conductance'(gm v3 mA per volt) andindirectly heated cathode I5. The cathode is con 20 nected 'throughthe medium of a resistance I6 of approximately 500 ohms with a positive potential with respect to earth adjustable at the potentiometer I1, whilst the control grid I8 is conohmic resistance I 9 of approximately 2-3 megohms; The wiping contact of the potentiometer I'I is'e'arthed dynamically through the condenser 20 of 0.01 mf. The control grid iii of 'thefilter valve I2 is connected with theimage current lead I through the medium of the blocking condenser 2i of 0.01 mf.- There then occurs the following: So long as the positive potential peaks occurring at the grid I8 are not equal to,"or greater than, the biasof the cathode I 5 adjusted at I'I no current of any kind is able to flow through the valve I2. If, however, sufficiently strong potential peaks occur, a powerful grid current passes to I3. The grid'current ensures that the'bias of I8 in the limiting case becomes exactly to the same extent negative as the cathode I5 is positive at the highest peak amplitude, so thatlinthe limiting case no more current passes to I8 than is employed for supplementing the portions of the 5 the signal intervals. With the stated dimensions of 2| and I9 only the extreme, potential peaks will, therefore, be able to liberate electrons from the cathode l5. The bias of l8 may be utilised throughthe medium of a filter'chain 22, 23 (0.1

megohm, 1 mf.) for biassing the regulatinggrids,

in accordance withthe invention the intercept ing grid, of the pentodes employed in the receiving amplifier. In this manner thereis obtained an effective regulation of the receiving potential supplied to the television tube.

The extreme potential peaks produce in the cathode resistance 16 of approximately 500 ohms small positive potential impulses. These may be divided in simple fashion by means of a CR or RC filter 24 or 25 into short and long signals, and these may be supplied separately at the terminals 26 to the line relaxation apparatus and to the terminal 21 of the image relaxation apparatus.

A false actuation of the relaxation apparatus in the case of very big signals is rendered impossible by the utilisation, in accordance with the invention, of the grid D. C. potential efiect, which ensures that only the extreme peaks of the signals, i. e., only a definite proportion of the total amplitude, is capable of producing a cathodic current. A state of constancy of the intensity of the synchronisation signals is effectively assisted by the fading compensation effect, according to the invention, via the circuit 2223.

The blocking of the ray results from utilisation of the anode circuit ll. This circuit is obviously traversed by amplified impulses which have become negative. According to the invention, the connection between the anode II and the electrode 5 is made so poor in capacity that the tube [2 has a good h gh frequency amplification. The amplification, in accordance with the invention, is made at least of such extent as prescribed by the reciprocal of the control sensitivity of the blocking electrode 5 compared with that of the main control grid 3 in the tube 4. This degree of amplification cannot be accomplished solely by making the lead 363 and the resistance 9 low in capacity, but also involves the selection of the valve [2 with particularly great mutual conductance and possibly resonance chokes 29. Whereas the quenching of the long image change s'gnals causes no difiiculties at all in practice, this is not quite so simple in the case of the short line impulses. The circuit 38 requires to possess an amplification only in respect to these two periods. It s, therefore, also possible to employ two series-connected resonant step-up transformers, the secondary sides of which are connected to the electrode 5 (maintained in accordance with the invention without current), and the natural frequencies of which coincide w'th the two basic periods of line impulse and image change impulse. For this purpose transformers are suitable having small iron cores, which the applicant has already described and used previously in synchronisation connections.

Accord ng to the invention, the strength of the impulse reaching the blocking electrode 5 is adjusted by the screening grid I6 independently of the adjustments of the gird circuit l5, l8. It is, therefore, possible to adjust the responding potential for the filter independently at the potentiometer I1, and to determine at the screening grid [4 without interference to the occurrences at the grid-cathode circuit what amounts of current are to be allowed to reach the blocking electrode. These advantages would not be obtainable when using triodes l2, and could also not be utilised fully when employing tetrodes in which the intercepting grid 13 is missing.

According to the invention, the coupling of the grid I8 with the image current circuit I does not take place in ptu'ely capacitative fashion through the medium of a condenser 2!, but additionally in galvanic fashion by way of the resistance 28. The latter is made highly ohmic,

and is in such relation to the grid resistance I9 that the direct potential possesses in the line 22 the value required by the regulating grids of the receiving amplifying tubes for full sensitivity. The applicant has found that in the case of transmitters and receivers which transmit also the D. C. value of the light intensity, such as possible in the case of superhet receivers and certain transmission amplifiers, for example intermediate frequency amplifiers, a separation of the synchronisation signals from the contents of the image in the case of all possible image contents is only possible without interference if the transmission of the direct potential is performed not only to the grid of the television tube but also to the grid of the filter tube. If, for example, the transmitter oyperates with black impulses, and if it transmits a uniformly black area, the differences in amplitude between the impulse and the mean value of the image is merely small. If a pure condenser coupling were provided between grid !8 and line I, the bias of the grid I 8 would be much too high to permit of a regulation of the tube [2 with these small differences in amplitude. By reason of the galvanic coupling, however, the bias of the grid is decreased to such extent in the desired direction that the small differences in amplitude are sufficient for removing the blocking effect on the tube 12.

I claim:

1. In a television receiver an amplifier for amplifying the mixture of the image signals and of the synchronizing signals, a cathode ray tube having at least a cathode, a main control electrode and an auxiliary control electrode, a grid controlled tube for filtering the synchronizing signals from said mixture, and at least one deflecting voltage generator, the output of said amplifier being connected on the one hand to said main control electrode and on the other hand to the grid of said filter tube, the anode of said filtering tube being connected to said auxiliary control electrode, the cathode of said filter tube being connected on the one hand via a resistance to a fixed potential and on the other hand to said deflecting voltage generators.

2. In a television receiver an amplifier for amplifying the mixture of the image signals and of the synchronizing signals, a cathode ray tube having at least a cathode, a main control electrode, and an auxiliary control electrode, a grid controlled tube for filtering the synchronizing signals from said mixture, and at least one defiecting voltage generator, the output of said amplifier being connected on the one hand to said main control electrode and on the other hand to the grid of said filter tube, the anode of said filtering tube being connected to said auxiliary control electrode, the cathode of said filter tube being connected on the one hand via a resistance to a fixed potential and on the other hand to said deflecting voltage generator, said filtering tube being a pentode, the screen grid of which being biased independently on the cathode potential.

3. In a television receiver an amplifier for amplifying the received modulated high frequency, an amplifier amplifying the mixture of demodulated image and synchronizing signals, a cathode ray tube having at least a main control electrode and an auxiliary control electrode, a grid controlled tube for filtering the synchronizing signals from said mixture and at least one de' fleeting voltage generator, the output of said second mentioned amplifier being connected on the one hand to said maincontrol electrode and. on the other hand via a condenser to the grid of said filtering tube, the anode of said filtering tube being connected to said auxiliary control electrode, the cathode of said filtering tube being connected on the one hand to a fixed potential and on the other hand to the input of said deflecting generators, the grid of said filtering tube beingconnected on the one hand to earth and on the other hand to the input of the first mentioned amplifier for fading regulation.

KURT SCHLESINGER.

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