DE1201394B - Circuit arrangement for transmission of binary information elements by frequency shift keying - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY GERMAN 4WIWt PATENTAMT Int. Cl .:

H041

EDITORIAL

Number:
File number:
Registration date:
Display day:

German class: 21 al -7/01

C 28484 VIII a / 21 al
November 23, 1962
September 23, 1965

The invention relates to a circuit arrangement for the transmission of binary information elements Frequency shift keying. There are already various systems for the transmission of information elements known and in use. Some of them use amplitude modulation, with the transmission takes place according to the bivalent or trivalent system or by single sideband. The frequency modulation systems that work with frequency shift keying are also used Use. Phase modulation systems are also already known.

In all of these previously common transmission systems, the one required for the transmission Passband bandwidth is an increasing function of the keying speed. With the usual telephone circuits this bandwidth is between 300 and 3400 Hz. If such circuits for information element transmission are used, the maximum scanning speed depends on the width of the available passband.

In the systems for the transmission of information elements that work with frequency shift keying, use is made of two frequencies / ₀ and Z ₁ , which correspond to the transmission of the information elements "0" and "1". In the case of the transmission of the run, such a system can be considered as a frequency modulation system in which a frequency slip against a fixed carrier frequency / _{p is} determined by the equation

In such a system, the minimum bandwidth depends on the modulation index. The choice of this modulation index is based on the following considerations: When receiving, it is necessary to discriminate the two transmission frequencies with the greatest possible certainty. The value of the lowest frequency must be equal to or greater than a certain limit dependent on the scanning speed so that the signal representing the information element corresponding to this frequency comprises at least one complete period of the carrier wave. Due to the short duration of the transmitted signal, it is necessary that this signal not be corrupted. A major cause of the mutilation is due to the transition area that can occur when the circuit transitions from one transmission frequency to another. In certain transmission systems, the transition from one transmission frequency to another occurs when the phase of the circuit arrangement for transmission is binary
Information elements through frequency shift keying

Applicant:

Compagnie Francaise Thomson-Houston, Paris

Representative:

Dipl.-Ing. Dipl. Oec. publ. D. Lewinsky,

Patent attorney,

Munich-Pasing, Agnes-Bernauer-Str. 202

Named as inventor:

Hans Cohn,

Les Grandes Terres a Marly le Roy, Seine-et-Oise (France)

Claimed priority:

France of November 24, 1961 (879 982) - -

Assumes a value of 90 or 270 °, the amplitude of the wave then reaching its maximum. Under the The transition from one transmission frequency to the other occurs practically without any transition area instead.

The essential object on which the invention is based is now to avoid the occurrence of such transition areas in transmission systems of this type. Because of this, it is possible to operate a system for the transmission of information elements at a high modulation speed, this transmission, which requires a low bandwidth pass band, can take place via circuits which have only a very limited pass bandwidth. It is also the aim of the invention to provide transmitting and receiving circuits that operate in accordance with the principles set out above.
To solve this problem, the circuit arrangement proposed here for the transmission of binary information elements by frequency shift keying, according to the invention, has a frequency converter which successively transmits the characters output by a mother generator during transmission with a multiplication or division factor dependent on the type of information element to be transmitted, as well as circuit elements which are provided for this purpose.

509 688/314

are seen that the transmission frequency change takes place when the phase is equal to 0 or 180 °, the for Receiving station characters are placed simultaneously on two frequency measuring circuits, which on one bistable circuit are connected, the changes of successive states to the Corresponding to the transmission frequency converter applied modulation characters.

According to a further development of the invention, the frequency converter consists of a numerical divider. The latter can, for example, have bistable trigger circuits connected in a cascade.

To facilitate understanding of the circuit arrangement proposed here, a described system formed from two cascade-connected trigger circuits, of which the former, von a waveform generator receiving square wave signals on the one hand for a given value (1 or 0) of the binary information element to be transmitted as a simple pulse amplifier and on the other hand as Ordinary tilting circle (division by 2) can work when the binary information element is the opposite Has value (0 or 1), in which case this operation continues until the first change of state of the second tilting circle extended, which then the operation of the first tilting circle intended as a pulse amplifier until the next change in state of this second breakover circuit, for which the first tilting circle works again as an ordinary tilting circle, etc., with one such a circuit allows the second breakover circuit with frequencies of the ratio 3: 2 according to the type of to let the binary information to be transmitted work.

If the operating period of the second breakover circuit is denoted by T and the first breakover circuit works as a simple pulse amplifier for a given value (1 or 0) of the binary information element to be transmitted, the second breakover circuit takes its first state with every reversal to the second operating mode as a normal breakover circuit over a period of T , then his

T
second state over a period of γ, then

again its first state over a period of T etc. The working period of this tilting circle is thus

T _ 3T

The time spans of two successive half-periods are different and equal to T.

and -γ.

According to a further embodiment of the invention, the numerical divider is applied in cascade another tilting circle, which in the present example is the third tilting circle in the chain. The operation of this third tilting circle is such that each period is made up of two half-periods of the same duration. In the example described above, the third tilting circle also works Frequencies with a ratio of 3: 2 according to the nature of the information to be transmitted. The third tilting circle thus allows square-wave signals to be obtained whose two possible repetition frequencies have a ratio of 3: 2 to one another. A low-pass filter then allows these signals to be converted into sine symbols to convert. As in the example described above, the transmission frequency is changed at the point in time at which the phase is equal to 0 or 180 °.

According to a further development of the invention, the frequency of the square-wave signals is preferably of the generator supplying them, taking into account the duration of the modulation characters, that the one among them to whom the deepest

ίο Transmission frequency is assigned, at least covers a complete period of the wave in question. The receiver circuit thus receives sine waves, whose ratio of the frequencies in the example chosen here is equal to 3: 2.

According to a particularly advantageous embodiment of the invention, the are sent to the recipient arriving sine waves after conversion into square wave signals to two analysis channels at the same time placed, each of two alternating positive and negative of the square-wave signals forming Impulse triggered tripping circuits exist that are influenced by the wave fronts successive pulses after the same triggering times for each channel with half the repetition period the square wave signals of high or low frequency emit marker characters, which respectively can be applied to two coincidence circles that are assigned to an output tilting circle and at the same time from one of the wave crests of each pulse of a square wave signal applied to the analysis channels corresponding pulse are applied, which thus triggers the according to its duration causes one or the other coincidence circle, which in turn may change the state of the output breakdown circuit controls.

The tripping time circuits can be produced mainly by means of monostable circuits, the deliver a pulse at the end of their stroke. These appear according to the channel concerned Pulses in theoretical points in time, in which the wave backs of the pulses of the square wave signals must occur which have triggered the monostable circuits. Due to the transfer conditions namely, it can occur, inter alia, that the duration of each essential pulse of a square-wave signal differs from the theoretical Value differs slightly and it is important that circuits are provided that do, however ensure their display.

According to a further development of the invention, the analysis channels forming each analysis channel are expedient Trip-time circuits produced with the help of a first monostable circuit, its stroke time is slightly smaller than the duration of each pulse of the square-wave signal in question, which is generated by the Analysis channel is to be displayed to which the monostable circuit in question is assigned, which in turn a second monostable common to the two tripping time circuits of the relevant channel Circuit occupied, the stroke time is chosen so that it is in the idle state in an instant which returns somewhat compared to the time of the appearance of the back flank of the impulse later lies who has triggered the tripping time circuits, circuit elements are provided that give a marker of considerable duration to the associated coincidence circle during the stroke duration of the second tilting circle.

Due to these circuits it follows that the time interval between the moment of Applying a pulse to the analysis channels and that of a marker generated by the one or the other of the coincidence circuits assigned to the analysis channels is supplied, elapses, is equal to the duration of the pulse in question. Since the impulses to be identified are unequal Have duration, it follows that the to

shown, of which the declining square wave signals are shown above, which are received either from a sine wave signal receiver or from an unstable multivibrator, in the middle the modulation symbols M and finally below the signal transmitted in series are reproduced. The ones in the top row of FIG. 1 shown square wave signals »Ο« are modulated by the character »M« containing the information,

Output trigger circuit applied control signals with un- io that in the middle row of FIG. 1 can be seen. same delays. The frequency of the signal "O" is divided in such a way, it is important that circuits are provided which allow a train of square waves to be received, which ensure that the frequency abruptly changes from this trigger circuit. The two assigned signals are not distorted. The two frequencies "C _t " and "C ₂ ", which are used to perfect this circuit arrangement, are therefore used for the transmission of the information elements from the coincidence circle of the "C t" and "C 2" arrangement. 1 "or" 0 "determined. It is to be noted that the square wave signals of high frequency occupied this frequency change in a characteristic analysis channel supplied to the starting point of the selected transition in the exact breakover circuit via a delay circuit carried out 20 instant in which the phase is switched, its corresponding Delay equal to 0 or 180 ° is reached, the amplitude of the difference between the two durations of the square is zero. The signal sequence thus obtained produces a sinusoidal signal "5" after low and high frequency signals are filtered accordingly. That is Interimpulse. esse of this mode of operation consists in the choice of the further details and the advantages achieved by them and the ratio of the frequency; on frequency and proposed according to the invention type in a phase distortion. This method has the advantage of, for example, the selected embodiment demonstrating the transmission at high speed with a light and its mode of operation explained on the basis of a low modulation index and consequently a gram. to be able to achieve a narrow passband,

Fig. 1 shows a simplified working diagram which can be dimensioned _{to about 1.2 (Z 0 -Z 1),}
the transmitting part of the circuit arrangement; F i g. 2 illustrates the block diagram of the

F i g. Fig. 2 is a block diagram of the transmitting part; Broadcast part. It consists of an unstable tilting fi g. 3 shows a block diagram of the individual circuit B ₀ , which is generated by a sine wave oscillator and switching elements of the transmitter part; replaces a downstream amplitude limiter

F i g. 4 shows the operating curves of the transmitter; can be, a divider with variable divisor

FIG. 5 shows a block diagram of the ratio and a final breakover circuit B ₃ . The divider capture part of the circuit arrangement; ratio changes depending on whether the Modula-Fig. Finally, 6 leaves the Ar- tor signalM “1” or “0” in diagrams. Recognize the two values / performance curves of the receiver. and n 'of the division ratio are such that the

As already mentioned above, the frequency change takes place for the circuit arrangement according to the invention when the phase reaches 0 or 180 °, i.e. i.e. when the amplitude of the current wave passes through its minimum. So that each information element is represented by a signal that comprises at least one complete half cycle of the carrier wave in question, the ratio

between the lower frequency and the modulation element AT and an output transformer L. The speed should be a multiple of 0.5. There are four gates P ₁ , P ₂ , P ₃ and P ₄ in the lower part of the display when the frequency changes. All circuit elements are of the usual direction of change of currents with the frequency Z ₀ type. The inputs of the gate B ₁ are at the output and Z ₁ must be the same, it is important that the output of the breakover circuit B ₂ on the one hand and on the one Upper frequencies and lower 55 output terminal M on the other hand, to which the Modula-Frequeozen an unequal multiple of 0.5, ie tion signals are applied. This TOrP ₁ controls

the gate P ₂ , which is a reverse gate. The inputs of the gate P ₃ are at the output of the gate P ₂ and at the output of the breakover circuit B ₀ . This gate P ₃

Frequency distortion and 60 controls the gate P ₄ , the second input of which is connected to the one circuit, the output of which is connected to the unstable trigger circuit B ₀

is. The gate P ₄ controls the tilting circle B ₁ .

F i g. 4 provides a diagram with the operating characteristics of the transmitter, which shows the mode of operation of the

the middle of a frequency band between 1800 and 65 make circuit arrangement easier to understand. 2000 Hz. A crystal stabilized oscillator provides a sine wave

In order to facilitate the explanation of the mode of operation of the transmission symbol O with the frequency F, which is sent to the input, waveforms of the transmission circuit to an amplitude limiter B _{0 are shown in FIG}

Frequencies of the breakover circle B ₃ correspond to the previously defined conditions. In the example chosen, these values η and n 'are 3 and 2, respectively.

F i g. 3 shows the transmission part in detail in a block diagram. In the upper transmission chain there is an amplitude limiter or unstable trigger circuit B ₀ , bistable trigger circuits B ₁ , B ₂ and B ₃ , a low-pass filter PB, an adjustable damping

IV2, 2 ^J / 2 and so on. The choice of the upper frequency, however, is determined by the cutoff frequency of the circuit used and in particular by its data, namely
Phase distortion. at
Cutoff frequency is around 3400 Hz, the phase distortion increases as one moves away from the center frequency, which is, for example, in

is placed, which can also be an unstable tilting circle. This signal is converted into a crenellated voltage O ₁ by limiting the amplitude. A modulation signal M, for example in the sequence “0” - “1” - “0”, is applied to an input of TOrSP ₁ . For all operating declarations, the judgment is made in negative logic, with the logical “1” being defined by a negative voltage, the logical “0” by a voltage of zero.

If a signal "0" is transmitted, gate P ₁ (FIG. 3) is blocked. The output is in the "0" state. The output of gate P ₂ is then in the "1" state, and gate P ₃ is permeable. This is all done as if the output O of the tilting circle B ₀ directly to the. Input O of the tilting circuit B ₁ would be switched, which is therefore a simple repeater of the tilting circuit B ₀ . It follows that the bistable trigger circuit B ₂ signals

supplies whose repetition frequency F is equal to - = -. Accordingly, the repetition frequency occurring at the output of the trigger circuit B ₃ is equal to -τ-. These

Crenellated signals are converted into sinusoidal signals by means of the low-pass filter PB. These then appear on the controllable attenuator AT, then on the output transformer L and finally on the transmission line. The transmission of the information element "0" is characterized by the sending of a sine signal on the line, the frequency of which is equal to a quarter of that of the signal "0" emitted by the oscillator.

The description of the transfer process of an information element "1" now follows. At the end of the transmission of the previous signal "0", the trigger circuit B _{2 is returned} to the state "1", as is the curve B _{2 in} FIG. 4 has. The gate P ₁ is designed in such a way that it opens when a modulation signal "1" is applied to one of its inputs when the trigger circuit B ₂ is in the "1" state. This gate is then blocked in all other cases. In other words, while a moment “1” is being transmitted, the signal emitted by the breakover circuit B _{2 is present at the output of gate P 1.} In this case, the gate P ₂ supplies the complementary signal of the breakover circuit B ₂ , which is applied to the gate P ₃ (diagram P ₂ ). The gate P ₃ is blocked, except when the tilting circle P ₂ is in the "0" state. The connection previously established between the output O of the breakdown circuit B ₀ and the input O of the breakdown circuit B ₁ is interrupted with the exception of the time span in which the breakdown circuit B ₂ is in the "0" state. This is all due to the fact that the trigger circuit B ₁ supplies signals whose repetition frequency is equal to -γ when the trigger circuit B _{2 is} in the "1" state. During the period in which the breakdown circuit B _{2 is} in the "0" state, the breakdown circuit B _{1 works} as a pulse amplifier.

From the above description it can be seen that in the course of the transmission of a moment "1" the frequency of the signal emitted _{by the breakdown circuit B 1}

gnale alternately equal ^ -, then F, then - ^ - and

finally F is. In other words, during this period of time the breakdown circuit B ₂ causes two operating periods instead of three operating periods in the event of a moment "0" being transmitted. Because of this, the frequency of the oscillations of the signals transmitted on the line is reduced in the ratio of 1: 1.5. With the method just described, it is therefore possible, starting from an oscillation with a fixed given frequency, to transmit characters on the line that have two different frequencies that correspond to the type of information elements to be transmitted and that are mutually in a selected simple ratio, in in the example under consideration in the ratio of 1: 1.5.
On the basis of FIG. 5 and 6, the operation of the receiver will now be described. The signals S delivered from the transmitter pass through the transmission line to the terminals of the input transformer TE of F ig, 5. These signals are modulated with sinusoidal frequency S, mutilation of the signals are neglected, where it during the transmission by damping, Phase distortion, noise and the like are subjected. After the conversion, the signals pass through a band filter FPB, which eliminates the unnecessary frequencies and reduces the interference spectrum. The signals then pass through an amplifier A ₁ with independent gain control, which equalizes the input level. The signals are then clipped in an amplitude limit ZCtB ₀ ' and differentiated in the differential element D. The two wave fronts of the crenellated signals obtained then hit a bistable tilting circle B ₁ ', at the output of which under ideal conditions (curves B ₁ ' in FIG. 6) these

Signals are identical to the signals at the output of the trigger circuit B _{3 of} the transmitter part (curve B ₃ in FIG. 4). It is now sufficient to reject the points of interest of these clipped signals in order to restore the original modulation signal.

In order to identify the type of signals of the telegraphy modulation transmitted by the transmitter, it is therefore sufficient to determine the repetition frequency of the square-wave signals emitted _{by the trigger circuit B 1 '}

to eat. For this purpose, these signals are applied to two analysis channels, each of which has a trigger time circuit, the trigger times of these circuits being slightly less than the minimum duration of a short pulse B ₁ 'for one and slightly less than the minimum duration of a long pulse B ₁ 'are for the other. These circuits, which are put into operation when each pulse occurs, each send a signal to a coincidence circuit upon expiry of their triggering time, to which the _{signals emitted by the trigger circuit B 1} arrive directly. Due to this circuit, the wave back of each _{signal supplied by the breakdown circuit B 1} 'coincides in time with one of the two signals emitted by the tripping circuit, and consequently one of the two coincidence circles just mentioned becomes permeable and emits a signal that the delivery of a short or long pulse characterized by the tilting circle B ₁ '. The signals emitted by the coincidence circles mentioned are applied to an output trigger circuit, the state of which characterizes the reception of signals with the frequency / ₀ or Z ₁ .

The tripping time circuits consist of two monostable input circuits B ₂ and B ₄ 'for each channel, which are connected to the input of a monostable output circuit B ₆ ' for the first channel, while the monostable input circuits B ₃ ' and B ₅ ' of the other channel are connected to the monostable Output circuit B ₇ 'are switched. The monostable circles B ₄ 'and B _B ^f on the one hand and B ₂ ' and B ₃ ' on the other hand are acted upon by the fronts in front of the signals supplied by the tilting circle B ₁ ' , while the monostable circles B ₂ and B ₃ 'are the wave backs of the same Receive signals. The tripping times obtained by the multivibrators B ₂ , B ₄ 'on the one hand and B ₃ ', B ₅ ' on the other hand are somewhat shorter than the duration of the short and long pulses emitted by the trigger circuit B ₁ '. The corresponding curves B ₂ ... B ₅ of FIG. 6 illustrate this mode of operation. The monostable circles B ₆ ' and B ₇ ' have the same stroke times, which are relatively short compared to the duration of the pulses supplied by the tilting circle B _1. In the course of their stroke, these monostable tilting circles place the gates £ T assigned to the gates P ₅ and P ₆ , markings B ₆ and B ₇ (FIG. 6). These signals are accordingly centered on the back flanks or front flanks of the pulses B ₁ , which have controlled the triggering of the multivibrators B1 and B ₂ ' on the one hand and B ₃ ' and B ₅ ' on the other.

With each change of state of the breakover circuit B ₁ ' two monostable circuits are triggered, so that marking characters B ₆ ' and B ₇ ' are applied to the gates P ₅ and P ₆ with delays which correspond to the duration of a short or long pulse B ₁ ' correspond, the delay is calculated from the relevant change of state. These short or long pulses are also applied directly to the gate P ₄ , which is assigned to the amplifier A ₂ , which emits a short pulse A ₂ with every change in the state of the breakdown circuit B ₁ '. As a result, each of these short pulses forcibly coincides in time with a pulse B ₆ ' and B ₇ ' , which characterizes the fact that the pulse just delivered by the breakover circuit B ₁ 'is a short pulse falling between the pulses A ₂ and B ₆ ' or a long pulse falling between pulses A ₂ and B ₇ '. As a result, one or the other of the gates P ₅ and P _{6 is} permeable for a brief moment and applies a control signal to the relevant input of the output trigger circuit B ₉ ', the successive state changes of which represent the telegraphy modulation signal.

As already briefly mentioned, the stroke times of the monostable tilting circuits B ₂ ', B1 on the one hand and B ₃ ', B ₅ ' on the other hand are somewhat shorter than the duration of the short and long pulses delivered by the tilting circuit B ₁ '. On the other hand, the lifting times of the tilting circles B ₆ ' and B ₇ ' are short compared to the lifting times of the aforementioned tilting circles. Such a circuit allows marking characters B ₆ ' and B ₁ ' _{to be applied to gates P 5} and P ₆ , which are centered with respect to the theoretical moments in which the pulses A ₂ must occur, which correspond to the wave backs of the pulses, the tilting circle B ₁ 'has triggered the monostable trigger circuits B ₂ ' and S ₄ 'or B ₃ ' and B ₅ ' . With a sufficient duration of the marking characters B ₆ ' and B ₇ ', such a circuit allows opening of the gate P ₅ or P ₀ in the event that the pulses emitted by the trigger circuit B ₁ ' differ slightly from the theoretical duration Would have duration.

From the diagrams of FIG. 6 it can be seen that the time required for the receiver to display a long or short pulse is equal to the duration of the pulse concerned. The display times are therefore significantly variable, as they depend on the duration of the impulses. It follows from this that special circuits must be provided in order to avoid systematic distortions being introduced into the telegraphy signals which occur at the output of the trigger circuit B ₉ ' . For this purpose, the display times are evened out by using an additional monostable circuit B ₈ ' in the display channel of the short signals at the output of gate P ₅ , the stroke time of which is equal to the difference between the time periods of the long and short signals. At the end of its stroke time, this monostable circuit delivers a signal Bl _a , which is applied to the breakover circuit B ₉ ' . Because of this circuit, the time interval that elapses between the beginning of a short pulse B ₁ ' and the occurrence of the signal Bl _a , which characterizes the display of this pulse, is the same as that between the beginning of a long pulse JS ₁ ' and the occurrence of the relevant Signal P ₆ is. Since these display times are the same, any distortion is avoided.

Claims (7)

Patent claims: 1.Circuit arrangement for the transmission of binary information elements by frequency shift keying, characterized by one output from a mother generator Characters when sending successively transmitted frequency converters with one of the type the multiplication or division factor dependent on the information element to be transmitted and by circuit elements which are provided for the transmission frequency change to take place, if the phase is equal to 0 or 180 °, the characters arriving at the receiving point be applied simultaneously to two frequency measuring circuits, which are connected to a bistable circuit are whose changes in successive states are sent to the transmission frequency converter applied modulation characters. 2. Circuit arrangement according to claim 1, characterized in that the frequency converter consists of two tilting circles connected in cascade, of which the first one Generator square wave signals receiving trigger circuit on the one hand for a given value (1 or 0) of the binary information element to be transmitted as a simple pulse amplifier and on the other hand, can work as an ordinary tilting circle (division by 2) if the binary information element has the opposite value (0 or 1), in which case this operation continues until the first change of state of the second tilting circle, which then functions as the first tilting circle as a pulse 509 668/314 amplifier determined, until the next change of state of this second tilting circle, for which the first tilting circle works again as an ordinary tilting circle, etc., with one such Circuit allows the second breakover circuit with frequencies of the ratio 3: 2 according to Art to let the binary information to be transmitted work. 3. Circuit arrangement according to claim 2, characterized in that the second breakover circuit of the frequency converter to a third, its state at each working period of the second The breakover circuit changing the breakover circuit is connected in cascade, this circuit allowing this third tilting circle with frequencies of the ratio 3: 2 according to the nature of the to be transmitted To let information work, and the operation of this tilting circle runs in such a way, that each period is composed of two half-periods of equal duration. 4. Circuit arrangement according to claim 2 or 3, characterized in that the frequency of the Reckteckignale the generator delivering them, taking into account the duration of the Modulation symbol is determined in such a way that the one among them which has the lowest transmission frequency is assigned, comprises at least one complete period of the wave in question. 5. Circuit arrangement according to one of claims 1 to 4, characterized in that the Sine waves arriving at the receiver arrive at the same time after being converted into square-wave signals two analysis channels are laid, each consisting of two alternating from the the square wave signals forming positive and negative impulses are triggered time-trip circuits, which are influenced by the wave fronts of successive impulses after the same Trigger times for each channel with half the repetition period of the square signals emit high or low frequency markers, which each indicate two coincidence circles which are assigned to an output breakover circuit and at the same time from one of the wave crests of each pulse of a square wave signal applied to the analysis channels corresponding pulse are applied, which thus its duration corresponding to the Triggering of one or the other circle of coincidence, which in turn, if necessary controls the change in state of the output breakover circuit. 6. Circuit arrangement according to claim 5, characterized in that each analysis channel forming tripping time circuits with the help of a first monostable circuit are, whose stroke time is slightly smaller than the duration of each pulse of the square-wave signal in question to be indicated by the analysis channel to which the monostable in question Circuit is assigned, which in turn is one of the two tripping time circuits of the relevant Channel's common second monostable circuit occupied, its stroke time in such a way is chosen that it returns to the idle state in a moment opposite to the The time of the appearance of the back flank of the pulse is somewhat later, which is the trigger time circuits has triggered, wherein circuit elements are provided which during the stroke duration of the second tilting circuit to the associated Give a marker of considerable duration to the coincidence circle. 7. Circuit arrangement according to claim 6, characterized in that the of the coincidence circle of the analysis channel used when identifying the high-frequency square-wave signals delivered characters to the output trigger circuit via a delay circuit whose corresponding delay is equal to the difference between the two durations of the is the pulse corresponding to the square wave signals of low and high frequency. For this purpose 2 sheets of drawings 509 688/314 9.65 © Bundesdruckerei Berlin