DE1090276B - Bi-directional amplifier used as a modulator - Google Patents

Description

GERMAN

There are known networks in which by applying a voltage to a pair of auxiliary terminals Transmission properties between the two main terminal pairs can be changed. So z. B. at a modulator as a function of an alternating carrier voltage applied to a pair of terminals The transmission path between the other pairs of terminals is alternately switched permeable and blocked. In the case of ring modulators with passive, non-linear switching elements, the forward direction is of the transmission path reversed periodically.

In known, with active switching elements, ζ. Β. Transistors, populated modulators, is an inversion the direction of transmission is generally not possible. It's already a modulator with transistors has been proposed in which the transmission direction depends on the applied Carrier wave is reversed periodically. In this circuit, all three pairs of terminals are connected to transformers connected, and the transistors used must be symmetrical in order to achieve a gain to be achieved alternately in both directions. One possible application of a network with active Switching elements and two main terminal pairs and one auxiliary terminal pair exist in the bidirectional reinforcement on a two-wire line. It has already been suggested entrance and exit an amplifier element, e.g. a tube or a transistor, with the aid of a pair of terminals applied alternating voltage periodically to connect alternately with the other two pairs of terminals. For this polarity reversal, however, non-linear switching elements, ζ. B. Diodes, required the additional can cause non-linear distortion of the amplified signals.

For the task of increased transmission in both directions of traffic using a two-wire system allow bidirectional amplifiers are also known in which two amplifiers are opposite Forward direction are connected in parallel and in which the two individual amplifiers are powered by an alternating control voltage be locked or opened alternately.

The invention resides in the use of such a bi-directional amplifier, known per se, as an active one Modulator for both traffic directions of a carrier frequency two-wire equalization system, by applying the desired carrier frequency as the alternating control voltage.

The carrier frequency is thus applied to a pair of auxiliary terminals, while the transmission takes place from one pair of main terminals to the other and vice versa. The communication voltage to be modulated is applied to one of the two main terminal pairs, and the one used as a modulator
Two-way amplifier

Applicant:

Standard electrical system Lorenz

Corporation,

Stuttgart t-Zuff enhaus en,

Hellmuth-Hirth-Str. 42

Herbert Aulhorn, Stuttgart-Weil in the village,

and Otto Marschall, Constance (Bödensee},

have been named as inventors

The modulation products and the low-frequency communication voltage then appear to these terminal pairs. While with a modulator with passive switching elements there is always a loss of power in the Transmission direction occurs, the operating points of the active switching elements in the inventive Arrangement can be set so that the gain in the transmission direction at least One is. Since one of the two amplifiers is always blocked when the other is permeable, neither can mutual influence of the modulator termination networks arise. Output and input resistance of unidirectional amplifiers are known to be decoupled from one another. Compared to known modulators the network according to the invention therefore has the particular advantage of being easy to adapt the terminating resistors.

This is of particular importance when one or more filters are connected to the output of the modulator should be, as is customary to suppress unwanted sidebands;

The invention will now be explained in more detail with reference to the exemplary embodiments shown in the drawing will. They are shown in

1 shows a network with two amplifiers,

2 shows a network with two amplifiers in a symmetrical circuit.

The network shown in FIG. 1 has three pairs of terminals 1, 2, 3, 4 and 5, 6. The message band to be transmitted or modulated is placed on terminals 1, 2 and 3, 4. The transistors Ts 1 and Ts2 receive bias voltages from a 24 V

009 610/274

Battery B 1. The transistors are of the pnp type and receive via the resistors Rl and J? 4 negative collector voltage. The series resistors R2 and R5 are located in the base leads. The bias voltage for the emitter and thus the respective operating point of the transistors changes as a function of the alternating voltage applied to terminals 5, 6. With a positive half-wave of the alternating voltage z. B. the transistor TsI a positive or Tj2, Ts 4 in a symmetrical circuit. Additional series resistors i ^ 1 'to R & and additional coupling capacitors Cl' and CTI are therefore required. The inputs 1, 2 and 3, 4 are balanced to ground, so that this circuit is particularly suitable for balanced lines or other symmetry requirements. Similar to the ring modulator, the carrier frequency at terminals 1, 2 and 3, 4 is not attenuated or is strongly attenuated in this circuit

Hold pre-tensioned and reinforced on terminals 3, 4 OK. If a signal is present at the output of the network, which is switched via the capacitor CI between the filter, which is coupled into a coil on the input side in the base and emitter. Contains equal-shunt branch, this coil can be designed as a transformer at the time the emitter bias of the transistor is formed, the primary windings of which are negative instead of TsI, so that it is blocked. of resistors R 4, i? 4 'are inserted into the circuit

During the negative half-wave the tran- 15 will be. The output is then free of direct current and sistor Ts2 is open and a signal at terminals 1, 2 can be well matched to the input resistance of the subsequent filter by selecting the transmission ratio of the transformer accordingly. The coupling capacitors C 4, C 4 'can of course be dispensed with in this ao case.

amplify the signal that is coupled in via the capacitor C1 between the base and the emitter. The capacitors C 3 and C 4 are used to decouple the signals without direct current.

In order to shift the transistor operating points into a region of the characteristic curve which is particularly favorable for blocking and unblocking the two transmission paths, it is expedient to superimpose a DC voltage on the AC control voltage. This can e.g. B. by the dashed lines in the drawing indicated direct current source B 2.

The alternating voltage applied to terminals 5, 6 therefore effects between terminals 1, 2 and 3, 4 a periodic interruption of the communication voltage corresponding to their frequency in both directions, which in turn can be amplified in both amplifiers. At terminals 1, 2 and 3, 4 arises hence a modulated AC voltage. The created, unconverted message tape is also present on both pairs of terminals. Depending on the purpose, there may be unwanted Frequency ranges at the output can be suppressed by filters or hybrid circuits. In the inventive The unconverted message band as a result of reflections can be used as a modulator lead to self-excitation of the arrangement, since the communication voltage is higher than that of the modulation products. To avoid this disadvantage, one of the two coupling capacitors can be screened in the form of filters or hybrid circuits be replaced. In this case the network is only one-way for the (low) communication voltage, however, permeable to the modulation products in both directions. The input level can be significant higher than with the ring modulator without causing additional non-linear distortion. There no transformers are required at terminals 1, 2 and 3, 4, the expense of the invention Circuit less than known modulators or bidirectional amplifiers.

The function of the circuit according to FIG. 2 corresponds in principle to the arrangement according to FIG. 1. The two amplifiers each contain two transistors TsI, Ts3

Claims (5)

Patent claims: 1. Use of a bidirectional amplifier known per se, in which two amplifiers are opposed Forward direction are connected in parallel and in which the two individual amplifiers alternately blocked and opened in a manner known per se by an alternating control voltage as an active modulator for both traffic directions of a carrier frequency two-wire equalization system, by applying the desired carrier frequency as the alternating control voltage will. 2. bidirectional amplifier according to claim 1 as an active modulator for both directions of traffic a carrier frequency two-wire equalization system is used, characterized in that that its two individual amplifiers to suppress the carrier frequency push-pull amplifier are. 3. six-pole network according to claim 1 and 2, characterized in that the symmetrical stages are equipped with transistors of the same conductivity type. 4. six-pole network according to claim 1 and 2, characterized in that the symmetrical stages are equipped with transistors of opposite conductivity type. 5. Six-pole network according to claim 1 and one or more of the other claims, characterized in that that by a DC voltage superimposed on the expensive alternating voltage, the transistor operating points are also postponed. Considered publications: German Patent Specifications Nos. 351 958, 915 828, 692; Austrian Patent No. 151 815; SEG-Nachrichten, issue 2/1957, pp. 93 to 100. 1 sheet of drawings © 009 610/274 9.60