DE1202315B - Circuit arrangement for reproducing video signals stored on magnetic tape - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY GERMAN 4057 ¥ W PATENT OFFICE

EDITORIAL

Int. α .:

H041

H04n

German class: 21 al-32/11

Number:
File number:
Registration date:
Display day:

T19263 VIII a / 21 al
November 11, 1960
October 7, 1965 '

The invention relates to a circuit arrangement for reproducing files stored on magnetic tape Video signals in which parts have failed in a section corresponding to a line of the picture are replaced by corresponding parts of a section corresponding to an adjacent row be, with a circuit that the signal depending on its position directly or indirectly via a intermediate stage supplies the playback device.

A circuit for reproducing facsimile signals received by radio is already known. Such facsimile signals are used to od a pen. The like. On a rotating drum with a To press on or to lift off the recording medium, so that a facsimile image is recorded in the manner becomes that a line running helically around the drum in the rhythm of the facsimile signals is described. The spiral-shaped, single line becomes when the recording medium is removed and laid flat cut open so that there is a large number of adjacent lines, similar like the TV picture.

In the case of facsimile transmission, there is generally enough time available so that the used Signal frequencies are quite low. With radio transmission it now regularly happens that the Incident signals with too low a field strength, od by fading effects. The like. So that in a part of the spiral line, d. H. one line of the cut and spread image, none Information is included. It is therefore already a circuit arrangement for reproducing facsimile signals became known in which the failed parts of a line are replaced by corresponding parts of a an adjacent line corresponding section of the signal can be replaced. This known circuit arrangement is equipped with a circuit that sends the signal immediately or depending on its position supplies the playback device via an intermediate stage. The intermediate stage acts In the known circuit arrangement, the received facsimile signal is buffered on magnetic tape that is played and its output in the event of failure directly to the playback device running signal is fed to the playback device.

It would be conceivable to use this principle to eliminate the signal dropout known in technology under the English designation "drop out", which can be traced back to small faults in the magnetic tape, in particular holes or voids
Video signals stored on magnetic tape

Applicant:

Tokyo Shibaura Electric Co., Ltd., Kawasaki-shi

(Japan)

Representative:

Dipl.-Ing. H. Leinweber, patent attorney,

Munich 2, Rosental 7

Named as inventor:

Norikazu Sawazaki, Yokohama (Japan)

Claimed priority:

Japan November 20, 1959 (36 019)

ren is. However, this would require extraordinary effort.

The invention is based on the object of compensating for the signal failure in a particularly simple manner.

The circuit arrangement according to the invention is essentially characterized in that the from Magnetic tape picked up signal via a direct line and additionally via a delay circuit is fed to the circuit, and that a detector which, if the signal fails as a result of a Error in the tape responds, the circuit is operated so that the previously open signal path via the direct line is blocked and instead the route via the delay circuit that has been blocked up to now is opened or vice versa, the signal path that has been open so far is blocked and via the delay circuit instead, the path via the direct line is opened.

To avoid any level jumps when switching from direct signal flow to delayed signal flow - or vice versa - to counteract this is expediently applied to the terminal of the electronic circuit has a limiter stage in which the signal is amplified to a constant value is connected in series with a discriminator.

509 690/317

Video signals are usually frequency modulated, but it is also possible to use phase modulated To use video signals. In both cases it is useful for the detector to respond to a change in amplitude the signals and therefore only responds to a »drop out«.

The invention will be explained in more detail with reference to the drawing; it shows

F i g. 1 a schematic representation of a television picture from a magnetic tape with "drop out",

2 shows a circuit diagram of an exemplary circuit arrangement according to the invention and

F i g. 3 different vibrations to explain the mode of operation of those shown in FIG Circuit arrangement.

According to FIG. 1, the television picture 1 consists, as usual, of a multiplicity of lines 2 which correspond to video signals reproduced by a conventional magnetic tape player. The parts of the picture marked 3, 4 etc. have failed because corresponding signal sections are missing due to voids or other faults on the reproduced magnetic tape. Since the English term “drop-out” is used for this failure in technology, this expression is preferred in the present description. Because of these drop-out effects, it is impossible to obtain signals which are completely identical to the missing ones, but it can be assumed with certainty that the signals in the η-th row are those of the (n + 1) -th or (n- l) -th line are very similar, so that a failed part of the «-th line is replaced by corresponding parts of the (n + l) -th or (n- l) -th line or even a drop-out line η during playback can be replaced by the entire adjacent line n + 1 or n-1 . Such methods make the display essentially complete and free from drop-out phenomena.

According to FIG. 2 are of a known, omitted in the drawing playback head of a Signals removed from the magnetic tape are sent to input terminals 5. The usually frequency or Phase-modulated input signals are amplified by the video amplifier 6. The amplified video signals are fed to the electronic switch 9 via two parallel lines, directly on the way via the line 17 and on the way via a delay circuit 7, which with a Amplifier 8 is connected in series. A detector 10, which is fed by the amplifier 6 with video signals and responds to a signal failure, an electronic switch 9 operates so that it selectively the releases the first direct or the second indirect signal path to a limiter stage 11 in which the Signal is limited to a constant value.

During normal operation, the electronic switch 9 connects the direct line 17 to the limiter stage 11. However, if a drop-out point located on the magnetic tape comes in front of the playback head and accordingly there are no video signals, the detector 10 comes into action and causes the switch 9, to disconnect the direct line 17 to the limiter stage 11 and to connect the second line to the stage 11 via the delay circuit 7 and the amplifier. If all or part of the line η is to be replaced by corresponding parts of the line n + 1 or n-1 , then the delay time to be selected for the delay circuit 7 corresponds to the time required for one line;

in the case of the television standard used in Japan, these are 63.5 m / sec.

The signals passed through the switch 9 pass the limiter stage 11, which is a discriminator 12 supplies a constant and amplified output video signal. The video signals at the discriminator output are practically free from drop-out phenomena and are connected to output terminals 13 fed.

The electronic switch 9 can cause amplitude changes in the video signals; but because the video signals are frequency or phase modulated, the amplitude changes have no disadvantageous Influence.

In Fig. 3 shows a video output signal a of the amplifier 6 with a drop-out space 14. The detector 10 causes the electronic switch 9 to switch the switching connection via the direct line 17 to the delay line 7, 8.

ao lay. The latter supplies the limiter stage 11 with a delayed video output signal b of the immediately preceding sampling period, the position of which corresponds to the blank 14. Only during this period does the switch 9 connect the delay lines

s5 device 7.8 with the stage 11. The detector 10 generates an output signal of a substantially rectangular one only during the duration of the blank 14 Pulse shape. The pulse 15 can be precisely rectangular by suitable means built into the detector 10 Form 16 can be brought to a practically instantaneous response of the electronic switch 9 to achieve.

It goes without saying that the signals from the amplifier can, under normal operating conditions, be reversed 6 sent through the delay circuit 7, 8 and when the detector responds through the switch 9 complete video signals of the immediately following sampling period of the limiter stage 11 via the direct line 17 are fed.

Claims (3)

Patent claims: 1. Circuit arrangement for reproducing video signals stored on magnetic tape, at which parts have failed in a section corresponding to a line of the picture, the be replaced by corresponding parts of a section corresponding to an adjacent line, with a circuit that directly or indirectly transmits the signal depending on its position an intermediate stage feeds the playback device, characterized in that that the signal picked up from the magnetic tape via a direct line (17) and in addition is fed to the circuit (9) via a delay circuit (7), and that a detector (10), which responds if the signal fails due to an error in the tape, the circuit (9) so actuated that the previously open signal path blocked via the direct line (17) and instead the path via the delay circuit (7), which has been blocked so far, is opened or vice versa The open signal path is blocked by the delay circuit (7) and instead the path is blocked the direct line (17) is opened. 2. Circuit arrangement according to claim 1, characterized in that the connecting terminal of the circuit (9) a limiter stage (11), in which the signal is amplified to a constant value, with a discriminator in series (12) is switched. 3. Circuit arrangement according to one of claims 1 or 2 for phase or frequency modulated Video signals, characterized in that the detector (10) responds to a change in amplitude which responds to signals. Considered publications: German Patent Specifications No. 1022 635, 1014153; U.S. Patent No. 2353,631. 1 sheet of drawings 509 690/317 9.65 © Bundesdruckerei Berlin