DE1276754B - Method and circuit arrangement for the phase keying of an oscillation of a fixed frequency for the transmission of messages - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

H03c

German class: 21 a4 -16/01

Number: 1276 754

File number: P 12 76 754.3-35 (R 37951)

Filing date: May 23, 1964

Open date: September 5, 1968

The invention relates to a method and a circuit arrangement for phase shifting a Fixed frequency oscillation for message transmission in which a phase shifter bridge a bridge branch with fixed impedances and a further bridge branch with at least one has variable impedance, which with the help of the bias voltage-dependent resistance of diodes a rectifier bridge circuit is changed.

Various arrangements for phase keying are known for the transmission of messages, in which either a phase lead or a phase lag of the carrier oscillation is used. the For this purpose, vibration is generally one of active resistances and capacitive and / or inductive reactance resistances built-up network fed. The phase keying of the on this network Taken vibrations can be achieved either by changes in resistance or by Switching to different resistance values. The resistor network can for example be connected to the Secondary winding of a transformer must be connected with center tap, and fixed phase shifts can be derived by appropriate circuits.

Furthermore, it is already known in frequency modulation circuits to change the frequency of a Oscillator's additional reactances to a resonant circuit on or off contactlessly. this takes place with the help of diodes due to their bias voltage-dependent resistance.

The invention is based on a known circuit in which two identical resistors in series are connected to a voltage source, for example to the secondary winding of a transformer. A series circuit consisting of a capacitor and a variable resistor is connected in parallel to the two resistors. The output voltage is taken between the connection point of the two identical resistors and the connection point between the capacitor and the variable resistor. This arrangement provides an output oscillation which is shifted by a phase angle with respect to the input oscillation, the tangent of which is proportional to the quotient of the capacitive resistance and the variable ohmic resistance. The phase shift is set by the variable resistor. Instead of the capacitor, a coil can also be connected in series with the variable resistor. While the former circuit normally uses a phase method and circuit arrangement
Phase sampling of an oscillation of a fixed frequency for message transmission

Applicant:

Robertshaw Controls Company, Richmond, Va.

(V. St. A.)

Representative:

Dr.-Ing. W. Reichel, patent attorney,

6000 Frankfurt, Parkstr. 13th

Named as inventor:
Perry Hamlin Goodwin Jr.,
Corona Del Mar, Calif. (V. St. A.)

Claimed priority:

V. St. ν. America May 27, 1963 (283 379)

causes the second-mentioned circuit to produce a phase lag, which depends on the value of the variable resistance is adjustable.

The phase and resistance relationships of these known circuits are for example in the Book "Reference Data for Radio Engineers", pp. 120 to 127, 1956, published by the "International Telephone and Telegraph Corporation ", as well as in the book" Applied Electronics "by M. I. T. Staff, Technology Press, pp. 316-319.

In order to increase the capacity of the transmission channels when transmitting messages by means of phase keying To fully exploit it, it is necessary that the phase keying at constant oscillation amplitude and fixed frequency takes place very quickly and in discrete steps, so that the largest possible phase range can be painted over. For example, a Phase shift of 120 ° and a phase shift of during another period of time 140 ° can be made, or phase shift angles are to be generated that are a multiple of a predetermined angle, for example a phase angle sequence of 72, 144, 216

809 599/179

and 288 °. Furthermore, it is necessary, by keying, the circuit arrangement according to the invention ereine To bring about a phase reversal, for example, it also allows a rapid phase keying in dis-72 after + 72 °. Another requirement is to take concrete steps, whereby the phases that with a phase shift of approximately shift over a wide phase change-180 ° the direction of the shift received 5 range from the value of the control voltage remains, so the information whether it is a pre-DC voltage on the rectifier bridge proporeilende or lagging phase shift is traditional. delt. In the drawing are exemplary embodiments of

The known phase sensing circuits in which the invention is shown.

the phase shift by changing an i ° F i g. 1 shows a conventional circuit for phase resistance can be created with a series of cones with regard to a quick and accurate phase capacitor and resistor with the associated

Changing in discrete steps is not sufficient, since the phase diagram;

Resistance change is too slow. Furthermore, F i g. 2 shows a modified circuit with a

generally the amount of phase shift, 15 series arrangement of capacitor, resistor and

without any change in the amplitude of the output inductance with the associated phase diagram; voltage can be achieved, too low. If the phase F i g. 3 shows a typical current-voltage characteristic

keying by connecting or disconnecting a diode's resistance line;

then arise during the switching process of a- Fig. 4 shows a circuit for phase shifting

on the one hand disruptive switching pulses and on the other hand 20 exercise according to the invention;

the sense of direction of the phase shift is lost, F i g. FIG. 5 shows a modification of the circuit of FIG

since switching does not take place continuously. F i g. 4;

Furthermore, it is not possible to remove the phase keying. 6 shows in a diagram the linearity of the

corresponding to the values of a control voltage by phase shifting the circuit according to FIG. 4

respectively. In the known circuit arrangements 25 or 5 using a diode bridge with

a fast and accurate phase keying characteristic curves according to FIG. 3;

at the expense of linearity and phase range F i g. 7 shows a key signal which is generated during switching or at the expense of a deformation of the oscillation according to FIG. 4 and 5 is used and the change is achieved at the time of phase keying. tion of the transformed impedance for typical keying These disadvantages are in the invention voltages, the phase shifts up to 180 ° according to the method for phase keying of an oscillation without ambiguity with regard to the direction of the supply of fixed frequency, at which the changeable Im- cause phase shift, Pedance of a phase shifter bridge with the help of the This and other properties and advantages of the bias voltage-dependent resistor of diodes invention are changed using a bridge of a rectifier bridge circuit, 35 circuit with semiconductor diodes is achieved, one being eliminated by the fact that the voltage-dependent external sensing voltage inductively into the secondary circuit of a rectifier bridge resistor Transformer is fed, the primary circuit phase shifter bridge arm is coupled in that the variable resistance in the circuit according to a selectable bias voltage to change F i g. 1 replaced. Such a diode bridge circuit of the variable impedance to the rectifier 40 is constructed like a full-wave rectifier to which a bridge is placed and that the rate of change alternating voltage at two diagonal points leads to a delay of the impedance and a direct voltage to the opposite rise and fall of the inductive Coupling set diagonal points is taken. Is controlled. half a DC voltage of suitable polarity is supplied. A circuit arrangement for carrying out these terminals, in order to make the diodes conductive. This method is characterized in that the. If a key is pressed in order to apply a variable impedance to the primary winding of a small external voltage to the bridge, then it contains a transformer whose secondary winding is connected to the two alternating current terminals of the rectifier bridge branches which are connected to the excitation terminals and have a low re-connection , and that there was close to 50. When the full conductivity is applied by applying voltage terminals of the rectifier bridge circuit to a sufficiently high direct voltage corresponding to the sampled direct voltage, which is achieved in FIG. The effective resistance of the primary winding is reduced to a value which, in comparison, takes place with the aid of a transformer, with the resistance of the capacitor C the value that not only approaches the resistance in its secondary zero. While the circular, a more or less large inductance 60 Φ = arc tan applies to the phase angle in the phase shifter bridge arm transformative relationship mized but also a function of the tactile% _c voltage -. provides in its primary circuit, for example, ^x is a serving for phase-shifting capacitor reactance to neutralize and thus an environmental The rectifier bridge circuit of FIG. 4 returning the phase angle to allow. Furthermore, if there is no bias voltage, one of the tasks of the transformer inductance falls or 5 has the task of delaying the high resistance so that no current is delayed in the second impedance change, so that a phase winding of the transformer flows and the detector determines the direction of a phase change Resistance of the primary winding can also indicate if possible. gets high. The circuit of Fig. 5 operates in

general in the same way. When the button is pressed, a phase shift occurs in one Direction generated. When the button is released, the phase shift is reversed. The extent the phase shift depends on the voltage that is applied when the bridge diagonal is touched will. The circuit according to FIG. 5 produces a phase shift that obeys a different formula than with the circuit according to FIG. 4, but follows the same general scheme, so that the Behavior of the circuit as a function of the touch voltage on the bridge in both cases is quite similar, with the latter being preferred for some purposes.

The mode of operation of the circuit is illustrated in FIG. 1 explained. A sinusoidal AC input voltage Ef is fed at point 10 with a phase position E Φ _{ο to} a phase shifter bridge circuit made up of two series branches connected in parallel. One branch in series consists of a capacitor C and a resistor R _x and the other consists of two resistors A ₁ and R ₂ . The output voltage, which can be changed in its phase, is taken from the phase shifter bridge diagonal, i.e. at the connection point between R _x and C and at the connection point between R ₁ and R ₂ . The phase shift of the output voltage E ₀ is denoted _{by ΕΦ ί} . The resistance R _x is variable, so that phase shifts of limited magnitude can be generated in this way. Fig. Ib shows the associated phase diagram. In the diagram, E _{1 is represented} by a vector which is directed from point A via B to point C , while the output voltage is taken off between the center point of the resistor arrangement R ₁ , R ₂ and the center point of the series branch C, R _x , is represented by the vector from point β to point P. Since AC is the hypotenuse of a right triangle, P lies on a semicircle above the vector AC when R _{x is} changed. In a similar way, one can keep R _x constant and change C in order to obtain a location for the points P, which also lie on a semicircle, since the vector I ₂ R _{x is} always at right angles to the vector C , which starts from the point P. The angle Φ is therefore the outer angle of the triangle ABP and is twice as large as the angle PAB. If the reactance of the capacitor C is X _c and the variable resistor is R _x , then the angle is

Φ - 2 arc tan ——.
Rx

In theory, this enables a phase shift of the vector E ₀ between 0 and 180 °, but in practice these values cannot be achieved.

Theoretically, it is also possible to achieve an output voltage whose amplitude does not change with the phase change. This results from the vector diagram of FIG. Ib, since the vector BP (or E ₀ ) is always equal to half the value of the vector AC . It extends the practical limits of the amount of phase shift that can be obtained without distorting the oscillation and without sacrificing the relationship between E ₁ and E ₀ , so that, if necessary, a phase shift of practically 180 ° can be achieved when the bridge circuit is keyed. The point P 'represents a further arbitrarily selected vector E ₀ , the phase angle of which is Φ' , the current in the capacitor C being equal to I ₂ .

The circuit of FIG. 2 differs from that of FIG. 1 in that an inductance X _{L is arranged} in series with the capacitor C and a resistor R , so that an impedance Z ₁ which is in series with the capacitor C results. The phase diagram of FIG. 2b looks similar to that of FIG. Ib with the difference that the inductance X _{1 changes} the theoretical mode of operation somewhat, but without practically changing the end result. The phase angles Φ ' and Φ " correspond to the lagging currents I ₂ and I ₂ ". In Fig. 4 and 5 is the inductance X _L of FIG. 2 replaced by the primary winding T _{p of} the transformer T ₁ . The series resistor R can be omitted as a resistor body, but it is shown because it cannot be completely eliminated.

In addition, a characteristic property of a semiconductor diode, preferably a silicon diode, is used, the current-voltage characteristic curve 9 of which is shown in FIG. 3 is shown. This characteristic curve can be used in the phase shifter circuit to generate a phase shift, the size of which changes linearly with the bias voltage on the diode circuit. In Fig. 4 a practical application in connection with a phase keying circuit for message purposes is given. The oscillation usually has the form of a sine wave and is generated in a stable oscillation generator with the output phase Φ equal to zero. In the present system, it is more a question of the phase change with respect to a reference oscillation than the phase change with respect to a specific time value.

The voltage E Φ _ο thus occurs as an oscillation on the generator 10 and is fed to the terminals 11 and 12, which are connected to the terminals 13 and 14 of the phase shifter circuit. The resistors R ₁ and R ₂ are in series between these terminals, the connection point serving as an output terminal for the phase-shifted oscillation ΕΦ _1. The second output terminal is connected to point 16, which lies between the capacitor C and the primary winding T _{p of} the transformer T ₁ . For theoretical reasons, the resistor R is shown connected at point 17 to the primary winding of the transformer on the side opposite to point 16, while its other side is connected to point 14.

The secondary winding T _{s of} the transformer T ₁ is connected at point 18 to a resistor R _s which is connected to a full-wave rectifier at point 19, the diodes of which have the characteristics according to FIG. 3 have. The opposite terminal 21 of the bridge circuit is connected to the other side of the secondary winding T _s . The diodes 22, 23, 24 and 25 are connected as shown, so that each branch between the terminal 19 and the terminal 21 has two oppositely directed diodes 22 and 24 or 23 and 25 with the connection points 26,27. A rectified output voltage would be positive at terminal 26 if the bridge circuit were supplied with an alternating current.

A bridge circuit constructed and connected in this way on the secondary winding T _s is non-conductive, regardless of the voltage value at the terminals 19 and 21, as long as this is below the breakdown voltage of the diodes when the terminal 26 is positive with respect to the terminal 27. From curve 9 of FIG. 3 it can be seen that a small voltage across the diode makes it conductive when applied in the forward direction. A pushbutton circuit supplies a small voltage which makes the diodes of the bridge circuit conductive. Since the voltage drop across the diode is small when biased in the forward direction, even a small positive voltage between the terminals 27 and 26 makes the diodes 22 to 25 conductive. In the conductive state, the two branches opposite the terminals 19 and 21 have a low resistance, while, if there is no external positive voltage at the terminals 26 and 27, the resistance between the terminals 19 and 21 is so great that it is for the purposes of Invention can be viewed as infinitely large.

The F i g. 3 it can be seen that the resistance of a silicon diode changes practically linearly over a large voltage range. This can be illustrated by a straight line which represents the resistance as a function of the voltage, since the relationship between / and E is approximately quadratic or parabolic. The result of the relationship is shown in FIG. 6 shown. The diode bridge is connected to the secondary winding of the transformer T ₁ . By changing the bias voltage E _K , an output _{phase angle Φ 1 is} generated which changes practically linearly with the applied voltage, namely practically linearly in a range from 0.1 to 0.6 V. The curve contains a section 42 which is linear , a section 43 which has an upper limit in the saturation range of the diodes, and a section 41 which contains a lower non-linear kink. A scanning voltage applied to the bridge can therefore be related to the phase angle Φ _χ , resulting in a family of curves for various parameters of the phase circuit.

Different sized capacitors result in phase shifts of different sizes. A capacitor C _{1 is} specified in which a key voltage of 0.6 V results in a phase shift of 120 °, while in the case of a second capacitor C ₂ of greater value the phase shift is 144 °. Phase shifts of smaller magnitude, which are exactly linear with the applied voltage, can be generated up to values of 30 °. In communication systems, phase shifts of less than 60 ° are usually out of the question for practical reasons, while phase shifts of up to 180 ° can be desirable. By modifying the circuit, a phase shift of about 180 ° can be obtained, which is linear up to 160 ° or more. _

In order to generate a suitable key voltage for biasing the diodes, two connection terminals 28 and 29 are provided which are connected to the connection points 26 and 27 of the bridge circuit. A button 31 connects a resistor 32 and a battery 33 when the button is closed. The resistor 32 can have taps 34, 35, 36 and at regular intervals, which can be switched on by a tap 39, so that the terminals 28 and 29 can be supplied with different voltage values. The voltage of the battery 33 is such that when the key is closed, the resistance between terminals 19 and 21 is zero, while when the key is open, the resistance is very high. If a smaller phase change is desired, the tap 39 can be connected to one of the points 35, 36 or 37. The various tapping points can be selected so that phase shifts result which appear on the curve piece 42 in FIG. 6 and are integer multiples of each other. This is of particular importance in communication systems in which phase shifts of various sizes are required. For example, the touch voltage at point 35 can cause a phase shift of 120 ° and the voltage at point 36 can cause a phase shift of 60 °. It is also possible to use a different voltage or a different capacitor in series with the primary winding of the transformer, so that a phase shift of 144 ° results when a different tap is used to generate the probe voltage. The circuit can also be used when negative phase shifts are required. To do this, X _{c is} replaced by X _L. The phase shift is either + or −180 ° if there is no resistor in series with the capacitance of FIG. 2 is switched. The choice between positive and negative values of the phase shift is generally arbitrary and can be determined by changing the parameters of the phase circuit.

In Fig. 5, the resistance A ₅ forms one branch of the bridge circuit, and a capacitor C is connected in parallel with the primary winding of the transformer T _1, whereby the relationship between the Tastspannung and the resulting phase shift is slightly changed. In such a circuit, the capacitance and the inductance as well as the resistance R ₅ behave in a known manner and similarly to the arrangement according to FIG. 1, in which the capacitor C is in series with the resistor R _x . In this case, X _{L is changed} by the resistance transformed by the secondary winding of transformer T _{1 in} order to more or less neutralize the reactance of C "as required. In such a circuit, the transformed inductance .X ^ in the primary circuit of transformer T _{1 is} normally kept smaller than the reactance X _L of C "so that the direction of the phase shift is not ambiguous. For this purpose, a resistor R _{4 can be connected} in series with the secondary winding, which, however, is preferably parallel to it according to FIG. 5 is arranged. When the resistance is i? ₄ bridges the secondary winding, the transformed impedance cannot be greater than a value given by i? _{4 is} determined because this resistance is shunted to the resistance of the diode bridge. In a practical implementation, i? ₄ the size of 30 kilo ohms and C a capacity of 0.022 microfarads, while R _{5 has} a value of 10 kilo ohms. These values result for a phase connection with a frequency of 1025 Hz.

A pushbutton circuit 49 is connected to terminals 28 and 29 and can be used for the circuit according to

9 ίο

F i g. 4 or 5 can be used. The separate signal does not immediately affect the primary winding of the gate K ₁ , K ₂ , K _z are each in series with a battery transformer. This property of the different voltages, to schematically represent the finding, is to indicate the amount of the delay measure of the phase shift, which is caused by the rise in the curve 47 at point 51 and a different bias voltage of the diodes 5 in the fall of the curve when opening of the switch

is achieved. the point 52 can be set. When a

F i g. 7 shows the result of a keying. The tactile new phase position of the output oscillation E Φ ₁ or signal 45 has a voltage E _K , which is set as long as pull ΕΦ ₂ , also results in a gradual one

leads to how the button is pressed. The rest of the transition corresponds to section 51 of the curve

Periods of time, the transformer transforms the io 57. If you look at the output oscillation ΕΦ ₀

high resistance value of the secondary circuit, which returns when the circuit is opened

Resistance R _x of FIG. 1 and as large as the section 52 of the transformed impe-

is made that he danzkurve the non-sampled phase so close that the phase does not immediately go to the original

as possible at the value £ i » ₀ . The key signal 46 returns to its original value. According to the invention

in dashed lines corresponds to a keying voltage 15 tion, the delay is a predetermined one

2E _K and generates a phase fraction that is twice as large as the normal key signal, so that a phase

shift when the switch is operated. Size detector or demodulator for the sense of direction

Larger bias voltages can be used to respond even when the phase change occurs

even larger phase changes within the limit is approximately 180 °. This way, between

cause the diode currents. 20 leading and lagging phases can be distinguished.

The phase can also deviate from E Φ _ο if the button is not pressed, and it can open and close the circuit by generating a phase shift opposite to that of the diode bridge If possible, an inversion circuit can be used for the phase shift circuit so that the various phase shifts, 25 are sufficient, but this measure can be taken into account when deciding on the selection of the sampling voltages in the circuit. The trans in both directions can get. Such a formator T ₁ can be used both in the primary winding as an arrangement, for. B. can be used if four have a high impedance phase shifts of + and -72 ° and + and in the secondary winding, so that at least a leakage flux between the -144 ° is required. Optionally, 30 windings can also be avoided and the transformer approximates two or more different phase shifts to an ideal transformer. In the case of an open caused by the different key secondary winding of the transformer, the transvoltages with respect to any other phased impedance for R _{x of} the primary winding is very low angle compared to an input voltage and approaches the value infinite. When short-dialed, which speaks of the phase shift of zero, the secondary winding of the transformer is closed. the transformed impedance is almost zero. if

A particularly useful property of the invention is a transformed impedance value is in Fig. 7 shown. She may wish to obtain these extreme values when looking at it, Order to be used in which the phase change then it is necessary to change the ratio of the impedances is about 180 °. The normal procedures to phase shift the secondary circuit accordingly of vibrations for readjustment. This is within the ability of those skilled in the art directional transmission does not reveal any way that knows that the transformed impedance is about with a detector changes between a phase shift by the square of the turns ratio. on 0 and 180 ° differ, except when a reference- this way can change a limited range is present at the receiver, with which the 45 susceptible impedance values when palpating the secondary genes Vibration is compared. This is because the circle with the help of different biases that according to the usual theory, two oscillation changes in impedance of a completely different range Sections of a wave with 180 ° phase shift in the primary circuit are transformed, like the are identical, so that it is not possible to specify the specific case required.

determine whether a shift occurs on a lead 50. Both in the case of the series connection according to FIG. 4 as or lagging based. According to the invention, even with the parallel connection of capacitance and a phase shift of 180 °, inductance according to FIG. 5, the effect of the inductive and the directional sense of this phase shift is opposed to the effect of the capacitance. without ambiguity, as can be seen from FIG. 7 results if in FIG. 1 the capacitor can be determined by an inductor. The curve 47 represents the response 55 activity is replaced, the resulting phases of the primary winding of the transformer T ₁ would be opposite to a shift. By varying the impedance change of the diode bridge as a result of a keying voltage at the diode bridge, a keying signal 45 can be represented, while curve 48 is a keying very high impedance which corresponds to phase shifter signal 46. circuit as a variable reactance element

The curve has a kink 51 and results from 60 occurs, changed to a very small reactance value

the reactance in the secondary circuit, which will still be one that is in series with the resistance elements

Series or parallel resistance is located between the trans or the capacitive element. The diminishing

formator and the diode bridge may contain. tion of the inductance serves to reduce the influence of the in

Even in the absence of resistance, the series allows the capacitance to be increased and thereby

the highly inductive secondary winding of the transfer 65 to increase the phase shift. If the

mators T ₁ no sudden increase in the current, so value X ₁ in the series circuit is the value of X _c

that when opening or closing the bias voltage exceeds, then the direction of the phase shift

circuit of the diode bridge reversed a change in the Impe shift. Using the formulas for

considering the reactance when C and L are connected in parallel, one finds the same relationship between X _c and X _L. Preferably, X _{c is} greater than the maximum value of X _L in order to avoid an unintentional phase reversal. In Fig. 5 prevents the resistance i? ₄ that the transformed inductance exceeds a value at which this phase reversal can occur. In Fig. 4, the resistor R _{3 is} in series with the diode bridge in order to prevent the minimum value of the impedance of the secondary circuit from being too low. The resistor therefore serves as an aid to achieve the maximum phase shift when opening or closing the key. In the circuits according to FIG. 4 and 5, either resistors R ₃ or U ₄ or both can be used.

The values of X _L and X _c can be interchanged in order to intentionally obtain a phase reversal in a keying. Furthermore, the transformation ratios can be chosen so that different values of the sampling voltage change the impedance in the secondary circuit of the transformer, so that X _L in the phase shifter circuit can be changed from a value which is greater than X _c to a smaller value, and vice versa. Various settings and modifications can be made as required, so that the invention is not bound to the examples shown. If certain frequency values are also given for the sensed oscillation, these are only intended to serve as an example. The circuit can also be carried out for other frequencies.

Claims (12)

Patent claims: 1. A method for phase keying an oscillation of a fixed frequency for the transmission of messages, in which a phase shifter bridge has a bridge branch with fixed impedances and a further bridge branch with at least one fixed impedance and with at least one variable impedance, which changes with the help of the bias voltage-dependent resistance of diodes of a rectifier bridge circuit is, characterized in that the voltage-dependent rectifier bridge resistance is inductively (T ₁ ) coupled into the phase shifter bridge arm, that a selectable bias voltage (49) for changing the variable impedance is applied to the rectifier bridge (19 to 27) and that the rate of change of the impedance is set by a Delay in the rise and fall of the inductive coupling is controlled. 2. The method according to claim 1, characterized in that a sensed voltage (31; K ₁ , K ₂ , K ₃ ) is supplied as a bias to the rectifier bridge circuit (19 to 27), which is non-conductive in the absence of bias and depending on the gated Voltage becomes conductive to a variable extent, and that a phase shift step is caused by the sudden change in conductivity of the rectifier bridge circuit and impedance change in the phase shifter bridge branch. 3. The method according to claim 2, characterized in that the bias changes be chosen such that the impedance changes have several equal phase shift steps corresponding to the selected bias changes. 4. Circuit arrangement for performing the method according to one or more of the preceding claims, characterized in that the variable impedance contains the primary winding (Tp) of a transformer (T ₁ ) whose secondary winding (T _s ) to the AC terminals (19, 21) of the Rectifier bridge circuit (19 to 27) is connected, and that the gauged DC voltage (49) is applied to the DC voltage terminals (26, 27) of the rectifier bridge circuit (19 to 27), which can suddenly assume several predetermined voltage values. 5. Circuit arrangement according to claim 4, characterized in that the rectifier bridge circuit has four solid-state diodes (22 to 25), the anodes of two diodes (23, 25) during the keying with the positive pole (29) of the DC voltage source (49) and the Cathodes of the other two diodes (22, 24) are connected to the negative pole of the DC voltage source and the secondary winding (r _s ) of the transformer (T ₁ ) on the one hand with the connection point of the first and third diode (22, 23) and on the other hand with the Connection point of the second and fourth diode (24,25) is connected. 6. Circuit arrangement according to claim 4 or 5, characterized in that a capacitor (C) as reactance of the fixed impedance in the bridge branch with the changeable Impedance is provided. 7. Circuit arrangement according to claim 4 or 5, characterized in that the fixed impedance in the bridge branch with the variable impedance mainly has an ohmic resistance (R ₅ ) , while the variable impedance consists of the primary winding of the transformer (T ₁ ) to which a Capacitor (C) is connected in parallel. 8. Circuit arrangement according to claim 7, there-. characterized in that the reactance of the capacitor (C) is greater than the reactance of the primary winding of the transformer (T ₁ ) when a bias value is applied to the rectifier bridge (22-25) and is less than the reactance of the primary winding when another Bias value on the rectifier bridge (22 to 25). 9. Circuit arrangement according to one or more of claims 4 to 8, characterized in that resistors (R ₃ , i? ₄ , 32) limit the change in impedance in the secondary circuit of the transformer (T ₁ ) for the keyed and non-keyed values of the direct voltage (49) . 10. Circuit arrangement for phase keying an oscillation for message purposes by practically 180 ° according to one or more of claims 4 to 9, characterized in that in the secondary circuit of the transformer (T ₁ ) impedances (Ts, R ₃ , R ₄ ) on the response of the secondary circuit delay the keying so that the change in impedance also occurs with a delay in the primary winding of the transformer (T ₁ ) during keying. 11. A circuit according to claim 10, characterized in that the impedance of an ohmic resistor (R ₃ ) in series with the secondary winding (T ₃ ) and the AC voltage circuit (19, 21) of the rectifier bridge. 12. A circuit according to claim 10, characterized in that the impedance is parallel to the secondary winding (T _s ) and to the terminal points (19,21) of the rectifier bridge has a resistor (2? ₄ ). Considered publications: German Auslegeschrift No. 1001346; Swedish Patent No. 125293; "Rohde & Schwarz-Mitteilungen", issue 6, 1955, P. 404. 1 sheet of drawings