DE1762549C3 - Circuit arrangement for avoiding brief failures of a carrier-frequency television signal taken from a magnetic memory. Eliminated from: 1289091 - Google Patents

Description

In known arrangements for storing television signals, the television signal is usually recorded in the form of a carrier frequency frequency-modulated oscillation on a magnetic tape. The signal taken from the memory is usually limited to a constant value and then demodulated to recover the television signal. The limiter causes level fluctuations compensated for the carrier frequency television signal taken from the memory. at complete signal failure caused by defects in the magnetizable layer of the magnetic tape, the demodulator delivers an output signal which is an extreme value of the television signal, usually whose white value corresponds to. In one of the television signal reproduced television picture therefore cause signal failures by setting maximum brightness, which extend over a more or less large part of a line, extremely disturbing noticeable.

It is already known that when playing video signals stored on magnetic tape, in which in parts have failed in a section corresponding to a line of the image, these are replaced by corresponding To replace parts of a section corresponding to an adjacent line. This is done at a known arrangement, the signal picked up from the magnetic tape directly and on the other hand A changeover switch is fed via a delay device, which is triggered by a Error signal is actuated and the instantaneous or the delayed signal on the output line the arrangement switches. In this way, the interference in the TV picture that spreads over you Extending part of the line period is essentially eliminated.

In the known arrangement described above, however, the dimensions are optimal more than one half cycle of the carrier frequency is required to detect a signal failure. Signal failures of shorter duration are therefore not recorded and therefore continue to cause disturbances

ίο of the television picture in the form of bright points (so-called Starry sky),

In a circuit arrangement to avoid brief signal failures in one of one magnetic memory decreased carrier frequency

th television signal in which the failed parts of a period through the correlated parts of a temporally adjacent line period can be replaced by the input taken from the memory the signal applied to the arrangement by one line

period delayed and the delayed or the undelayed Signa! is transmitted to the output of the arrangement by means of a changeover switch, which through one by means of an error detector in the event of a signal failure witnessed error signal is actuated, is invention,

according to the carrier-frequency television signal by superimposing an auxiliary frequency into a multiple implemented higher frequency position and fed the umgeset / L signal to the error detector.

Ok according to the circuit arrangement white;

the advantage. due to imperfections in the magnetism r signal failure, including such a very short duration. avoid those of the known arrangement nich; can be eliminated.

Diet.rfindung is now to be with the help of the embodiments Illustrative figures are explained in more detail. Us shows

Fic. 1 an embodiment of the erfindungsge measured circuit arrangement as a block diagram.

Fig. 2 shows the circuit in practice Circuit groups of the block diagram according to FIG. 1.

Fig. I shows an embodiment of the invention Circuit arrangement as a block diagram.

The arrangement is via the input circuit 11 the amplified, daily, frequency-modulated signal taken from the magnetic memory fed. This arrives in a mixing stage 12, in which it by mixing with an auxiliary frequency generated by the auxiliary oscillator 13 in a higher frequency position is implemented, which is several times higher than the frequency position of the carrier frequency signal. Is this z. B. at an average of 7 MHz. so the frequency of the converted signal can be of the order of magnitude of 50 MHz. A filter 14 separates the modulation products formed in the mixer 11 the sum or difference frequencies and also suppresses the auxiliary frequency.

The carrier frequency converted into a higher frequency range The frequency-modulated signal is then passed into a limiter, if necessary after being limited 15. via line 21 to the device for obtaining the error signal. This contains one Signal shaper with threshold device 50. which supplies an error signal for actuating switch 30, when the signal amplitude falls below a predetermined threshold value. A simple one is sufficient for this Rectifier 80. Furthermore, a delay

and therefore Born reaches 5 Polantat ^α menaction of the resistors 31, 33 and the transistors 32 and 34 is short-circuited in two mutes and therefore not the output of the device geeines signal failure is changed, so that now the resistors 31, arrives and is unencumbered.

tvi 21 the in

35

hesitated Signa g

The £ '^ ⁿ "

under a

an ^d « ^Β ^ ^5α " »5 stör 56 f

forms. * ° ^la "f 5
Transistor 51Jioher ^

Basis of the TranMteπs
one

frequency-modulated signal is transposed to a higher frequency position before demodulation, let _S! ch * o use the devices provided for the transposition at the same time to derive the error signal; this can be obtained from the carrier-frequency signal converted into a higher frequency position.

The delay device 20 and the switchover 30 can in this case either by way of the carrier-frequency signal in the original frequency position as in Fig. 1. by way of in a higher Frequency position converted carrier-frequency signal or preferably by way of the domodulated video signal be arranged.

F i g. 2 shows a practical circuit example of FIG Vector groups of the arrangement according to the invention. That from the magnetic memory abgenorr - .. '. E iemoduherte 35 De video-frequency signal is called lmp- tn t at 11 Danzwandler serving transistor 22 is supplied. From the emitter of this transistor and the emitterw.derstand 32 the signal passes through the resistors 24 and 25 on the one hand without delay and on the other hand the runtime chain 20 is delayed by one line perK.de. to two further impedance converters 26 and 27. At the emitters of the two transistors 26 and 27 and The transmitter resistors 28 and 29 are two equal

like electronic switch of the switching device 30 45 continued after connected. Every electronic switch consists of J «J from the series-connected opposites 31. 33, 35 or 31 '33' and 35 '. Between every two wideist stands are the emitter-collector paths of two transistors 32, 34 or 32 'and 34'. The transistors of each switch can alternate due to the opposing switching voltage supplied to their bases in the senior b / w. locked state brought Sl d bi 11 supplied carrier fre-

device 20 with a running time equal to the duration of a line period of the television signal and a switch 30 is provided, which the carrier-frequency signal either directly or via the delay device 20 to the initial teaching. With the arrangement according to FIG. 1 can still be signal dips prove which the peak values of the

_{original ^^ ^ ^ d} removed from the magnetic tape

Do not record carrier-frequency vibrations. The carrier-frequency Si converted to the £ '^ ^{n "}

The effort for the implementation of the carrier-free io higher frequency age "Jg? _{D enen the two} s

quenten Sinais in the higher frequency position is not fed gnal Zur uieicn _b ^ ^ _condensate _

very considerably, after for this application diodes 82 and BJ, aw ^ ^ ,, - ^ _{85 84} with dressic requirements on the quality of the mixer and sator »" taHw. On _{the Scheitdwert der}

of the filter are not high. ^e ^ ^e * corresponds to a time constant

In the event that for demodulation of the carrier-frequency signal voltage from the carrier
Venetian sovereigns memory carrier-removed sliding ^c ^ P ^{a "n} ™ £.""· _50, the television signal Schaltspannunfrequenzmodulierten a transposer ^ Hv'KKcken the electronic formwork

Dsmodulator is used, in which the fre- quency for ^dl % ^ mrec ^ ^ is _changed . _whom n

The frequency-modulated signal before demodulation in a ters 30 is generated _{and therefore} the

h Fl tsit will let _S! ch * o the ^ίτ ^ ^Λτ ^^ ^ SJ 80 from the setpoint

sinks. The _{18 üaagi} this with the Transibistabile switching stage, "^ _at the base of the

S Fixed voltage at the starting from dK »P _{switching run in}

S ^ _{switching states} . _{If the} signal at the connection ^ dc \ Bads dfcs Transistors ^ gJg DC voltage at the base 51 falls below ük ^ icsig g bistabüe switching stage

^of . ^TransI ^ ° ",,! Κη«. Switching status reversed, .n the other stable switch ^ ^^^ _dn .

r ^ ° «of _{the base of the oil} .

tn t, "t ^d hrough the bpann g ^^ _change

sistor 56 given unc ^ »d _lable against this voltage, eg ^ ^a ^ _{n adjust} . Stand 59 au _n ^ ⁿ JgW ^. Reversal of the KOTdens ^ or TO _occur

J ^ .J ^^ ÄSnnSS somewhat delayed. The target value of the ^ '8na> voltage _{switch 30 on} f

^^^ eJ follows therefore not so-S ^ SS signal failure, but enduing ^ _{ensures that} the

f _d ung ^ interfering, instantaneous signal

, _after ⁸ _the disorder has subsided, ersindi.11 uc

id 57 of the transistor _is the interposition ^ _Wide rstand GJJ _{the antisense} strength

_the switching paths of the elcktrof the phase splitter

ouch

56

SeJ 61 one

in the senior b / w. blocked g

will. As long as the carrier fre-

CTKÄ KÄS ■

Transistor 27 occurring signal through the interconnector;

1 sheet of drawings

Claims (2)

Patent claims: 1. Circuit arrangement to avoid brief signal failures in one of one magnetic memory removed carrier-frequency television signal, in which the failed Divide a line period by the correlated parts of a temporally adjacent line period be replaced by the removed from the memory, fed to the input of the arrangement Signal delayed by one line period and the delayed or undelayed signal is transmitted to the output of the arrangement by means of a changeover switch, which is through a means an error detector is actuated in the event of a signal failure, characterized in that, that the carrier-frequency television signal by superimposing an auxiliary frequency converted to a frequency that is several times higher and the converted signal to the fault; detector is fed. 2. Circuit arrangement according to claim 1, characterized in that the error detector a peak rectifier (70, 80) to which a carrier-frequency signal is supplied, and a Contains signal shaper with threshold value (50), which when falling below a predetermined signal level a yeast error signal that sets in at the beginning of the signal failure and after the end of the Signal failure persists for a while.