US2237640A - Television system - Google Patents

Description

rniusvisrou' lltudolii Uriel, Germany,

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This invention relates to television systems and more particularly to the method and means for providing interlaced television pictures, and is a divisional of my copending application Serial No. 275,427, filed May 24, 1939 and entitled Television systems.

In the transmission of television pictures in accordance with the line skip method, it is known to use an odd number oi lines per picture, so that the two line sequences are always made up of .a broken number of lines (for instance 122 lines). With this apportioning, oi the number of lines, the lines transmitted during the second line sequence rail in the receiving image into the interspaces oi the first line sequence. Then the frequency or the relatively-slow image for frame frequency (canbe doubled in. the receiving image without requiring a wider transmission frequency band than when transmitting by non-interlacing method, and without the necessity of carrying out ,adif ferent vertical deviation for the two line sequences. :l-litherto the opinion has been that this end could beachieved only when utiliz ing an odd, number oi lines i'oreach complete picture, i. e a fractional number of linesper line sequence.

In accordance with the invention a method is proposed by which this result can also be obtaihed with an'even number of lines per image,

1. e. at a whole number of lines per line sequence (at two line'sequences per picture). To this end, in the second line sequence, the line impulses are so. placed that they have a distance from the impulses oi the first line sequence which is equal to a number of total line periods plus one half line period.

Before enumerating the advantages hereby obtainable, the difference between the new method and the known method will be described with reference to the drawing in which Fig. l is a graphical sketch of the time occurrence of line impulses according to the invention and Fig. 3 shows in block diagram form apparatus embodying the invention in which two controlled multivibrators of different frequencies are used to alternately key separate channels to provide line synchronizing impulses.

Fig. 1 relates to the known method, and more specifically to the case of only 11 lines per picture chosen for the sake of simplification. The first line sequence covering the time of ,6, second, contains five line periods, and the second line sequence likewise extending over second likewise contains five line cycles.

The return for therelatively slow picture or (iii. llmiii thl quency. Thus a frame deflection therefore must begin in the center of a line cycle, it the preceding and following return coincide with the beginning of a line cycle, Any line impulse of the second line sequence always has a distance or time interval irom'the impulse of the first line sequence that is a whole number measured in line cycles.

Fig. 2 shows the method according to the invention for the simple case of only 10 lines attwo line sequences per picture. Each of the two line sequences extends over 1 second and covers five total line cycles in the manner indicated by the lines ct toe. The impulse a, has a distance from the last impulse of the first line sequence which is'e'qual to one halt line cycle, the impulse t has a distance of 1 line cycles, c has 2 /2 line cycles etc. The line impulses of the second line sequence, therefore, have a phase displacement equal to one half of a line cycle relative to the line impulses of the first line sequence. This can also be visualized in such manner that the impulses ci the first line sequence are considered continued within the second line sequence. These impulses would then have the position a to d" shown in dotted line inliigure 2. The impulses a to c are situated in the center between the impulses a to d".

At the position a to e of the impulses during the. second line sequence, interlacing is possible in the same way as in the case of an odd. line number represented in Figure 1, since in. fact, the impulses a to e fall into the center of the line when the frame impulse is combined with the double picture freline ship transmission can in fact ice-achieved with the method according to Figure 2.

As compared with known methods, the new one has the advantage that a television transmitter can be adapted to'interlaced transmission in a simpler manner when said transmitter was hitherto operated with the ordinary picture analyzing. at ordinary picture analyzing the number of lines per picture is always an even number (for instance 180), Thus, in case of 10 lines per picture, the impulses in the first half of the picture would have the same position as in Figure 2 during the first line sequence and during the second half of the picture the impulses would have the position ato (1. There-' fore, it the ordinary picture analyzing method is to be converted into an interlaced analyzing method, it is only necessary to delay the impulses a to d by one half line cycle whereby they assume that position b to c. (it does not matter that the first line impulse a will not occur at this displacement, since the. synchronizing impulse for the framing deflection does cover a few cycles).

The said displacement of the impulses can in fact be carried out in a much simpler manner in a television transmitter which was operated only necessary that during the second half of v picture, a delay device be inserted into the line across which the impulses are passed to the highfrequency transmitter. It is obvious that in practice this can be done at less cost than in the case of the replacement of a perforated disk by one having another division.

If the line impulses are produced by means of a purely electric impulse generator, a delay arrangement may likewise be inserted in the impulse lin during the second half of the picture. This is likewise a simpler measure than the providing of a new impulse generator and the'insertion of new frequency divider stages throughout, through which the deflection frequency for the frame is derived from the line impulse frequency.

For the insertion of the delay arrangement for the line impulses of the second picture half, the synchronizing impulses for the frame deflection can be directly used.

As delay means, a multivibrator whose discharge paths have equal operating periods may be used, and furthermore, also a saw tooth generator for instance which releases a new impulse when the half of its amplitude is reached.

In Fig. 3 I have shown in block diagram one arrangement which may be used to provide synchronizing impulses of such order as to produce interlaced pictures with an even number of integral lines 5| is shown as a source of fundamental frequency control which may, for example, generate the frequency equal to the line frequency. Two multivibrators 53 and 55 are provided and are fed with the control frequency, the multivibrator 53 being a frequency divider so as to provide an output having a frequency equal to the frame frequency, while the multivibrator 55 is used as a frequency multiplier and has its constants so chosen as to provide a frequency equal to twice the frequency of the line impulses. Alternatively, 5| may actually feed impulses having a frequency equal to the frame frequency to the multivibrator 53 as well as feeding impulses equal to twice the line frequency to themultivibrator 55. The use of the multivibrators is to provide a substantially rectangular wave form, and as is well known, by taking output energy, for example, from the two plate circuits of the multivibrator there will be derived energy which has identical wave shape, except that one wave will be 180 degrees out of phase with the other, as is well known and as is shown, for example, on page 273, Fig. 131, of the textbook Radio Engineering" by Terman, McGraw Hill Book Co., New York, 1932. The same procedure is used with respect to the multivibrator 55- and accordingly, there will be derived from the multivibrator 53 the frame frequency impulses 54 and 54', while from the multivibrator 55 there will be obtained the wave forms 55 and 56' equal to twice the line frequency. The use of multivibrators for frequency multiplication and dividing, is, of course, well known and is shown for example, in U. S. Patent No. 2,132,655 to J. P. Smith, entitled System for producing electrical impulses" which issued October 11, 1938.

The outputs from th multivibrators 53 are fed respectively to the two keying stages 5'! and 59, while the two outputs from 55 are fed respectively to the same keying stages. Thus each of the keying stages 51 and 59 are controlled by the combined impulses of 54 and 58 and 54 and 56' so that alternatively, one or'the other of the two stages is keyed and thus can provide an output. The outputs of the two keying stages are then fed to their respective wave shaping circuits BI and 63 and the outputs combined and fed, for example, to the radio transmitter of the television system. The wave shaping may be done, as shown in the above identified Smith Patent No. 2,132,655, or may be accomplished by the us of impedance correcting networks, such as shown in Smith Patent No. 2,045,315, issued June 23, 1936, for "Television system or Stocker Patent No. 2,045,316, issued June 23., 1936, for Impedance coupled amplifier. The keying of the impulses may likewise be accomplished after the fashion shown in the first mentioned Smith patent. Under these conditions, the two keying stages will provide the line frequency for the two line sequences wherein the phase shift for the second of the two sequences is provided with a delay equal to one half the time period necessary to scan one line. The wave shaping circuits are merely provided to either elongate or shorten the pulses before being mixed with the picture signals for transmission by the radio transmitter.

a line cycle.

Having described my invention, what I claim is:

1. A synchronizing system for an even line interlaced television system comprising means for supplying frame synchronizing and double line synchronizing frequency impulses, a multivibrator fed by the frame synchronizing impulses, a multivibrator fed by double line frequency impulses, means to derive output energies having out-of-phase components from each of the multivibrators, two keying stages each fed with energy derived from each of the two multivibrators, means to shape the output of each of the keying stages, and means for combining the outputs of the keying stages.

2. A synchronizing system for an even line interlaced television system comprising a first multivibrator, a secondmultivibrator, common means for controlling both of said multivibrators, means to derive output energies having out-ofphase components from each of the two multivibrators, means to combine a portion of the derived energies of each of the multivibrators, means to combine other portions of the derived energies of the two multivibrators, means to shape each of the combined energies, and means to combine both of the shaped energies.

E. A synchronizing system for an even line interlaced television system comprising a source of control frequency, two separate relaxation I oscillators, means to control each of the relaxation oscillators by different energy from the source of control frequency, means to derive from each of the relaxation oscillators energy having ing the shaped energies the same wave shape but displaced in phase from each other, means to combine the energies from the two relaxation oscillators which hav minimum phase angle, means to combine the energies from the relaxation oscillators having maximum phase angle, independent means to shape each of the combined energies, and means for combin-

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