Abstract: A device for testing printed circuit boards and/or flat modules for electrical circuits is indicated, wherein at least one support plate (3) equipped with contact pins (4, 4') of different lengths is located in a housing (1). A cover plate (7) is positioned above the support plate (3) and contains at least one receptacle (10) for a test sample in the form of a printed circuit board or flat module. In addition, a unit (16) is provided for producing a partial vacuum to pull the test sample against the contact pins (4, 4'). To perform the in-circuit and the function tests, the underside of the cover plate (7) containing the receptacle (10) for the test sample has a slide (12) with spacers (15) protruding at right angles from one of its sides, which is able to move between two end positions, crosswise to the movement of the test sample.

Abstract: A circuit arrangement is indicated to generate a clock frequency for a data transmission system by using a voltage-controlled fundamental wave quartz oscillator (VCXO), whose frequency can be changed within narrow limits as a function of the control voltage. To double the frequency of the fundamental wave quartz oscillator (VCXO), its output (A) is connected to the input of a rectifier bridge circuit (1) having an ohmic resistance (2) placed at its output. The ohmic resistance (2) is connected to both inputs of a comparator (3), and the clock frequency (f) is present at the output of the comparator.

Abstract: A system for line-conducted digital telecommunication between a switching exchange of a telecommunication network and a subscriber connected to this network is provided. The digital transmission path passes to a transfer point accessible for the subscriber, to which the subscriber may connect his devices by free choice up to the full use of the maximum available transfer rate. The activation of the particular transfer rates are controllable by the switching exchange.

Abstract: A system is disclosed, which operates with active units for the line-conducted, digital transmission of communications between the exchange of a telecommunication network and subscribers connected thereto. At least one cross connector, operating with active electrical components, is connected to the exchange by a line containing at least one optical and/or electric transmission element. At least two distribution terminals, operating with active electrical components, are connected to the cross connector by a line containing at least one optical and/or electric transmission element. At least one subscriber is connected by an electrical line to the distribution terminals, which are always installed near a subscriber.

Abstract: A switching device is presented for the transmission of telecommunication signals between a telephone network exchange and at least one subscriber connected thereto, where the exchange is able to transmit metering pulses, in addition to the voice signal. The signals are transmitted as digital signals between the exchange and the subscriber via a two-wire line, Which is connected with the exchange through a hybrid switching unit. To prevent the metering pulses from interfering with the voice signals, a parallel resonant circuit consisting of an inductance and a capacitor is connected to the two-wire system of the hybrid switching unit, and the receiving branch of the hybrid switching unit has an active and a passive filter connected in series. The passive filter is adjusted for the metering pulse frequency, and a filter that is tuned to the passive filter is used as the active filter, which compensates for a decrease in the NF (low frequency) level caused by the passive filter, with a corresponding increase.

Abstract: A process is indicated for the bidirectional transmission of digital data through a glass fiber, whereby the bits from data to be transmitted are compressed by a factor >2 into bursts, in packages of equal quantities, without changing the transmission rate. The bursts in one direction of the transmission are sent by an emitter station through a glass fiber to the other station, during the pauses between the bursts in the other transmission direction. Independent external pulse generators are used at both ends of a glass fiber to determine the transmission rates of the stations. If the frequencies of the two pulse generators deviate from each other, the bursts of the data flowing at the lower transmission rate are displaced with respect to the bursts of the other flow of data, by the width of one bit of the pertinent continuous flow of data.

Abstract: A controllable amplifier, which has two symmetrical outputs, at which two output signals mirror-symmetrical with respect to each other are present, is used for amplification of a burst signal. To achieve the largest possible eye opening of the signals to be fed to a comparator, a predetermined d.c. voltage difference for the formation of matched signals is adjusted for both output signals. After this, the arithmetic mean values of the two matched signals are formed and are fed to a second comparator. The output value of the second comparator is fed to an integrator, to which a reference voltage is also fed. In case of a deviation of the mean values of the two matched signals from each other, the amplifier is adjusted in a compensating direction by the integrator.

Abstract: For controlling the level of electrical signals a circuit arrangement is formed with two series connected amplifiers. A first amplifier containing a first variable resistor, operates at maximum amplification when a low input signal level is received. A second amplifier comprises a series connection of a second variable resistor and a current-controlled voltage source with two complementary outputs. The outputs of the voltage source are connected to a comparator and a controller with two separate outputs. One of the controller outputs transmits a control signal while the other output simultaneously transmits a blocking signal. A first output of the controller is connected with the first variable resistor, while a second output of the controller is connected to the second variable resistor.

Abstract: Apparatus for bidirectional transmission of optical signals between two stations connected by a light transmission path of optical fibers, each station including a laser module comprised of a laser diode and an adjacent monitor diode, the latter performing the dual functions of detecting light emitted by such laser diode in its transmission mode, and for detecting light transmitted from the other station when such adjacent laser diode is not in its transmission mode.