US2248556A - Interlaced line method - Google Patents

Description

y 1941- K. SCHLESINGER 8 556 INTERLACED LINE METHOD Filed June 7, 195a- 3 Sheets-Sheet 1 l/Qa' $1M.

y 4 v K. SCHLESINGER r 2,248,556

INTERLACED LINE METHOD Filed June 7, 195a s Sh eet s-Sheet 2 19 20 3 r H920 l I!" HgZb z Fig.2: v" v v \J p \J u L Fig. 2d 1 v H July 8, 1941. K. SCHLESIN GER INTERLACEDLINE METHOD 5 Sheets-Sheet 3 Filed June "I, 1958 Jnveniop:

Patented i July 8, 1941 WTERLACED LINE METHOD Kurt Schlesinger, Berlin, Germany, assignor, by

mesne assignments, to Loewe Radio, Inc., a corporation of New York Application June 7, 1938, Serial No. 212,318 In Germany June 21, 1937 7 Claims.

As well known, the main difficulty in television with interlaced line screens consists in the fact that the two part-screens do not fit exactly one Within the other, and that owing to a slight displacement of the two screens in relation to one another the picture appears to consist of merely one-half the number of lines. The applicant terms this effect a blocking of the lines. Various methods have already been proposed for eliminating this error, which results in a deterioration in the effective number of image points in the ratio of 1:2. It was recognized quite early that in the interlaced line method with double scanning, such as is being adopted quite generally throughout the world, traces of the line impulses at the moment of the image change may very readily lead to the blocking error, since as well known the image change is received synchronously with the line impulse only in the case of the one scanning, whilst in the second scanning it may be disposed exactly between two line impulses. It was accordingly recognized at an early date that the image change impulse must be filtered out from the reception by a frequency filter, which permits of the passage only of this impulse itself, i. e., of a slow impulse, but which on the other hand absorbs as completely as possible the rapid impulses of the line synchronisation. A filter element of this kind is formed in the most simple case by the charging of a condenser by way of a resistance (integration of the image change). A reliable remedy, however, is not obtained by this integration method alone. It is also not to be expected by this method, as owing to the integration the head of the image change impulse is greatly flattened, and it is then not to be expected that the point of initiation of the two image changes occurs exactly within a few image points at the commencement or at the centre of the last line of the image. The flatter the head of the impulse may be the greater must be the inaccuracy of initiation of the image change, and accordingly also the unreliable nature of the two image screens as a whole, the relative position of which screens is governed by the precision of the two image changes and in this way alone for the entire subsequent scanning.

It is also already known that oscillations of twice the frequency of the line frequency play an important part in ensuring reliability of the interlaced line method. Proposals have also already been made to transmit this frequency from the transmitter. A method of this kind, however, is confronted by the difiiculty that a rapid oscillation of this kind is unable to pass through at all in direct fashion by way of the synchronisation channel of the slow relaxation portion when usin the indispensable integration circuits. The signal, therefore, would require to be taken over from the circuits of the line synchronisation in aroundabout fashion.

The synchronisation method of the applicant in accordance with the invention pursues a dif ferent course. Certainly it also operates with a tone circuit, which oscillates in the octave of the line frequency. This circuit, however, is not excited by the remote transmitted, but in direct fashion within the receiver by the line relaxation apparatus. If now at the exact moment of the image change the line relaxation apparatus is at exactly the correct line frequency, and if the line octave derived by the resonance circuit from the line relaxation apparatus is additively impressed in the synchronisation circuit of the slow relaxation apparatus, the latter, when the image change signal is received, will be controlled not only by this signal but also at the same time by the total of image change impulse and line octave. 1f the amplitudes of the two part-oscillationsare correctly tuned in their ratio to one another, the image change will then be able to relax only at two definite points, which are spaced apart by exactly one-half of the length of a line. The interlacing of the lines would accordingly in this case be ensured, and blocking would be avoided.

In this connection, however, it has been assumed that during the image change si al the line relaxation apparatus remains synchronised exactly in the correct line frequency. Normally, i. e., in the case of the known synchronisation connection systems, this is not the case. If in these the image change impulse is transmitted in the form of a single coherent signal of the length of several line periods, the short synchronisation impulses drop out in respect of the line relaxation portion during this time. In. this way the line relaxation apparatus is free of frequency exactly at the time of the image change, and can assume any natural frequency which differs from the proper frequency and is detuned in relation to the line period. In this manner the octave circuit referred to would also be detuned, and blocking again takes place. It is accordingly an essential feature of the present application that care is taken from the transmitter'to ensure that the line relaxation apparatus is maintained exactly in cadence also during the image change. This object is accomplished according to the invention by the fact that the image change impulse is interrupted by a preliminary signal prior to the line change and again commences exactly synchronously with the line change. This initiation of the image change, carried out with sufficient slope of the flank, is then in a position to penetrate into the synchronisation channel of the line relaxation apparatus and thus to maintain this exactly in cadence. In these circumstances the method described in the following then functions without objection:

In Fig. 1 there is first shown in a possible embodiment the coupling of the line relaxation apparatus and the image relaxation apparatus. Within the frame l there is shown the line relaxation apparatus and within the frame 2 the image change apparatus, all inessential details of the connection being omitted. The apparatus are illustrated in their most simple embodiment, consisting each of a large or small condenser 3 /4, a charging resistance 5/5 and a discharge tube in the form of a current gate 6/6, an afteramplifier 1/1 in conjunction with a countercadence transformer 8/3 attending in each case to the deflection in vertical and horizontal direction in the case of the Braun tube 9. The setting up of these two relaxation apparatus I and 2 in accordance with the invention takes place by means of the line octave circuit l9. This circuit is preferably both inductively excited as well as induct vely additionally coupled. The exciting coil is located, for example, in the anode circuit of the line relaxation apparatus I and is shunted in such fashion by means of a parallel resistance I2 that the excitation takes place with a reasonably lower power. The circuit II] is tuned to the frequency 2 fz, i. e., to the octave of the line frequency, by the condenser Ifla. The damping of the octave circuit I is selected to be as small as technically possible, so that the two oscillations during and after the initial excitation by H do not exhibit in relation to one another any appreciable difference in amplitude. The tapping of the line frequency octave also preferably occurs inductively by the coupling coil l3, and the potential 2) is regulated to a value which will be discussed later by the regulating resistance M. The line octave potential thus regulated is now located in the circuit I leading to the synchronizing control grid of the image change current gate 6'.

The receiver it picks up in the manner known per se, in addition to the image signals, also the short synchronisation signals and the long synchronisation signal for line and picture change from the transmitter, separates these by known amplitude filters from the image signals, and by means of the frequency filter, which is shown in classically simple form ll/iii, conducts them dependent on their duration into the two synchronisation channels for the line and image relaxation sections I and 2. I7 is a high pass filter, which permits of the passage only of the short line impulses, and IS an integrating low pass filter for the image change impulses. It is obviously immaterial as regards the invention whether the separation takes place according to length of period in this fashion by resistances and condensers or in other fashion by means of tuned coils and transformers of different natural frequency. In any case the image change impulse arrives behind the low pass filter lfl with flattened head, and it is not to be expected of this rounded synchronisation signal that it results in a definite point of initiation with respect to the image change with a range of fluctuation of less than approximately one-tenth of a line. If, however, in accordance with the invention, the octave of the line frequency, i. e., a comparatively rapid oscillation, is added to this flattened image change impulse following the integration in the train of the lead [5, the current gate 6 receives in respect of the ignition two definite points of initiation, the spacing of whch exactly corresponds to one-half of the line period, the interlacing of the lines then being ensured.

In Fig. 2a-2d there is set forth a graphical representation of the chronological course of the signals.

In Fig. 2a the synchronisation signals in respect of the line are given as I9 and those for the image change as 20.

In Fig. 2b there is set forth the potential behind the low pass filter l8, which contains only the image change, with a greatly flattened wave front.

InFig. 20 there is shown the practically undamped line octave oscillation, such as is obtainable at the regulating resistance (4 behind the tone circuit l0.

Finally in Fig. 2d there is shown the heterodyning of 2b and 2c, in the amplitude suitable for ensuring the synchronisation. The correct amplitude adjustment, such as is preferably performed in practice at M, is such that the power of the auxiliary oscillation 2c alone is insufiicient to cause ignition of the current gate 6. In other words, the line octave oscillation must be weaker than the synchronisation requirement on the part of the current gate. The latter is shown in Fig. 2d by the amplitude s. There is also shown in'Fig. 2b the threshold value 5. It will be seen that the normal image change signal would lead to ignition at the point Z in Fig. 217, but it is also to be recognised at the same time that the section between the head of the signal and the synchronisation threshold is so flat that precision of the initiation of the requisite quality is not to be expected. On the other hand in Fig. 2d there is obtained by the heterodyning of the Hat signal form of 2b with the line octave 20 at the point Z a considerably steeper section between the threshold value and the synchronisation potential. Furthenbefore the ignition moment is reached, the ignition conditions are rendered poorer by the then negative half-wave of the tone .circuit, the polarity of which must accordingly be defined, and improved after the ignition moment Z has been passed, the initiation accordingly being effectively wedged in at Z. In

comparison therewith incorrect polarity of the circuit it] would lead to the tendency to premature ignition. A too strong adjustment of Z would mean self-synchronisation by the octave, and too weak adjustment of Z would cause the effect according to the invention to disappear. As stated, therefore, the correct ratio must be regulated once and for all.

A point which facilitates matters in practice is the fact that by subsequent alterations in the receiver adjustment there is no further variation in the adjustment once made. The amount of the auxiliary potential does not depend on the reception at all, but is supplied in constant amount .by the line relaxation portion, which always oscillates to constant extent. The height of the image change impulse, however, also no longer depends on the reception in the case of modern connection systems, particularly with requires to be done.

the galvanic coupling between synchronisation circuit and image change channel already described by the applicant previously. The interlaced line method is accordingly also invariable within wide limits against alterations in the reception amplification by the person employing the apparatus.

The entire advantage of the coupling between image and line relaxation apparatus by the octave circuit in accordance with the invention would be illusory if the line circuit were not synchronised throughout.

Fig. 3 sets forth a diagram of the manner in which this in accordance with the invention There is shown an image area 2!, which is scanned at the transmitter. As well known, this contains a line margin 22 and an image change margin 23. Normally these two synchronised groups meet together without a break. When, therefore, the image point scans the surface from the left to the right in lines the line relaxation apparatus is unable to take over any special impulses during the scanning of the height h of the image change strip 23. These, however, would again appear immediately if there were an interruption of the image change signal at the area 2d before the edge of the line were reached. Viewed optically an interruption of this kind means the inclusion of a black square 24. The appertaining signal curve upon the scanning is illustrated in Fig. 4 and is distinguished by the inclusion of preliminary line signals at the points 24a, which in a manner of speaking appear as gaps in the course of the image change signal (broken image change signal). These gaps pass at the receiver through the high pass filter and control with their re-ascent the line relaxation apparatus according to frequency. The interruptions do naturally not pass through the low pass filter, so that there is no variation in the function of the image change signal. It is specifically remarked that the gaps are separated by a complete line period. An octave effect is accordingly obtained only in the receiver by the octave circuit, and not at some point between transmitter and receiver.

The practical technical attainment of a signal sequence according to Fig. 4 can take place either optically or in purely electrical fashion. The optical method will always adhere to Fig. 3. It can be realised for example by a rotating Wheel 25, in which slots 26 are provided in the spacing of an entire line period and on which there is projected at the same time a light image 21, which is shorter to the extent of the width of a slot than the spacing between two slots. The image change signal then ceases during the dark period, Viz., the return period of the portion d in Fig. 5. Numerous other optical embodiments are possible on this basis.

A purely electrical method of producing the broken image change signal according to Fig. 4 is illustrated in Fig. 6. This method will always consist in the fact that in the train of a photocell amplifying device, consisting for example of a photo-cell 28 and amplifying tubes 29/30, one of these tubes, for example the tube 39, has a special interrupting grid 35. This interrupting grid, arranged behind a screening grid, is negatively biassed by the line impulse generator 3|, shortly before the actual line signal is generated by 3|. For reduction to practice there can be employed for example a tuned countercadence transformer 32, which under the action of'the anode current impulse performs a single period of the duration of twice the line impulse. The negative half-wave of the upper secondary terminal in Fig. 6 will then cause the interruption of the image change signal in the tube 30. The second positive half of the period will not vary the transmission of the image change signal. This is already taken care of by the limiting resistance 33. On the other hand the negative terminal, in this case the lower one, of the secondary winding of 32 will control the mixing tube 34 and thus transmit a line impulse which corresponds to the black square 24 having the length of the edge h in Fig. 3. numerous other embodiments are conceivable which, however, are all characterised by the taking over of a blocking impulse in the amplifier branch, which requires to pass on the image change signal. This blocking impulse requires to be in advance of the actual line impulse to the extent of a line impulse period and preferably has itself the same duration as the synchronising line impulse. An octave formation at the transmission end is not provided for or necessary in any of these connection systems.

I claim:

1. Television receiver for receiving transmissions synchronized by line synchronizing impulses and frame synchronizing impulses uninterrupted by the transmitter according to the interlaced line scanning, having a line deflecting oscillator controlled by said line synchronizing impulses, a frame deflecting oscillator, controlled by said frame synchronizing impulses, and an auxiliary oscillator generating auxiliary oscillations being dependent on the line deflecting oscillator, the output of said line deflecting oscillator being coupled to the input of said auxiliary oscillator, the output of said auxiliary oscillator being coupled to the input of said frame deflecting oscillator in such a manner, and the auxiliary oscillator having such a frequency, that always one of the auxiliary oscillations is superposed on each frame synchronizing impulse and that only the heterodyning of the auxiliary oscillation on the frame synchronizing impulses is able to control the frame deflecting oscillator.

2. Television receiver for receiving transmissions synchronized by line synchronizing impulses and frame synchronizing impulses uninterrupted by the transmitter according to the interlaced line scanning, having a line deflecting oscillator controlled by said line synchronizing impulses, a frame deflecting oscillator, controlled by said frame synchronizing impulses, and an auxiliary oscillator generating auxiliary oscillations being dependent on the line deflecting oscillator, the output of said line deflecting oscillator being coupled to the input of said auxiliary oscillator, the output of said auxiliary oscillator being coupled to the input of said frame deflecting oscillator in such a manner, and the auxiliary oscillator having such a frequency, that always one of the auxiliary oscillations is superposed on each frame synchronizing impulse and coincides with the initiation of said frame synchronizing impulse.

3. Television receiver for receiving transmissions synchronized by line synchronizing impulses and frame synchronizing impulses uninterrupted by the transmitter according to the interlaced line scanning, having a line deflecting oscillator controlled by said line synchronizing impulses, a frame deflecting oscillator, controlled by said frame synchronizing impulses, and an auxiliary oscillator generating auxiliary oscillations being dependent on the line deflecting oscillator, the frequency of said auxiliary osicllations being the octave of said line synchronizing frequency, the output of said line deflecting oscillator being coupled to the input of said auxiliary oscillator, the output of said auxiliary oscillator being ocupled to the input of said frame deflecting oscillator in such a manner, that always one of the auxiliary oscillations is superposed on each frame synchronizing impulse and that only the heterodyning of the auxiliary oscillation on the frame synchronizing impulses is able to control the frame deflecting oscillator.

4. Television receiver for receiving transmissions synchronized by line synchronizing impulses and frame synchronizing impulses uninterrupted by the transmitter accorchng to the interlaced line scanning, having a line deflecting oscillator controlled by said line synchronizing impulses, a frame deflecting oscillator, controlled by said frame synchronizing impulses, and an auxiliary oscillator generating auxiliary oscillations being dependent on the line deflecting oscillator, the frequency of said auxiliary oscillations being the double line synchronizing frequency, the out put of said line deflecting oscillator being coupled to the input of said auxiliary oscillator, the out put of said auxiliary oscillator being coupled to the input of said frame deflecting oscillator in such a manner, that always one of the auxiliary oscillations is superposed on each frame synchronizing impulse and that only the heterodyning of the auxiliary oscillation on the frame synchronizing impulses is able to control the frame deflecting oscillator.

5. Television receiver for receiving transmissions synchronized by line synchronizing impulses and frame synchronizing impulses uninterrupted given by the transmitter according to the method of the interlaced line scanning, having a line deflecting oscillator, a frame deflecting oscillator and an auxiliary oscillator comprising a condenser and two inductances being connected in series each to the other and in series to said condenser, said auxiliary oscillator being inductively coupled by said inductances on the one hand to the output of said line deflecting oscillator and on the other hand to the input of said frame deflecting oscillator.

6. Television receiver for receiving transmissions synchronized by line synchronizing impulses and frame synchronizing impulses uninterrupted by the transmitter according to the method of the interlaced line scanning, having a line deflecting oscillator, a frame deflecting oscillator and an auxiliary oscillator comprising a condenser and two inductances being connected in series each to the other and in series to said condenser, means for adjusting the amplitude, the phase and the frequency of the auxiliary oscillation, said auxiliary oscillator being inductively coupled by said inductances on the one hand to the output of said line deflecting oscillator and on the other hand to the input of said frame deflecting oscillator.

'7. Television receiver for receiving transmissions synchronized by line and frame synchroniz ing impulses uninterrupted given by the transmitter according to the method of the interlaced line scanning, having an amplitude filter tube for filtering the synchronizing impulses, a line deflecting oscillator, a frame deflecting oscillator and an auxiliary oscillator being coupled on the one hand to the output of said line deflecting oscillator and on the other hand to said filter tube, so that the level of the filter is dependent on said auxiliary oscillator.

KURT SCHLESINGER.

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