US2223084A - High frequency system - Google Patents

Description

NOV; 26, v A w gs s Q HIGH FREQUENCY SYSTEM Filed May 13, 1938 In vemars J/freoll'enner lVa/fgqrry Hagen Patented Nov. 26, 1940 HIGH FREQUENCY SYSTEl/I Alfred Wiessner and Wolfgang Hagen, Berlin,

Germany, assignors to C. Lorenz Aktiengeselischaft, Berlin-Tempelhof, Lorenzweg, Germany,

a company ApplicationMay 13, 1938, Serial No. 207,758 In Germany May 20, 1937 2 Claims.

The present invention relates to high frequency systems, and more particularly to an arrangement for receiving messages transmitted by means of high frequency carrier waves over cables.

The intelligence transmission over line networks by means of high frequency carrier currents, the so-calledwire-radio is well known. These carrier frequencies are impressed upon a telephone network, in -an exchange, office, for

instance, and are again derived from the network in the receiving positions by the aid of electric separating filter devices. Generally, a plurality of different frequencies is simultaneously impressed upon a line network so that the receiving positions must be provided with filtering means for again separating the various carrier frequencies. It has been found that the circuits employed in broadcasting'receivers of standard type are not sufiiciently selective for effecting 20, the necessary separation. I It has therefore been suggested to furnish receiving devices for wire-radio systems with band filters which are adapted to selectively be rendered effective and ineffective so as-to pass merely "one single of a plurality of frequency bands, but this expedient becomes disadvantageous in cases that the wavelengths of a transmitter are subjected to variations, since matching to a changed wavelength involves considerable difiiculties so 30 that reliable passing ranges will be obtained in such units only by the provision of complicated expenditures. Moreover, it has been proposed to provide the receiving positions with an oscillatory circuit the inductance of which having tapping points so as to obtain adjustability to dififerent frequencies. However, this arrangement introduces the disadvantage that frequency adjustments cannot be made independently of one another and, moreover, that a distinctive separa- 40 tion free of cross talks cannot-be obtained between the frequencies transmitted over cables.

These disadvantages are avoided according to the present invention which proposes the use of adjustable oscillatory circuits in the receiving ranged that one thereof acts as selective circuit equipments, said oscillatory circuits being so arexplanatory representation with respect to certain frequency conditions, Fig. 4 diagrammatically shows a coupling circuit according to the invention, while Fig. 5 diagrammatically shows still a further modification.

The Fig. 1 illustrates a correspondingarrangementwhich comprises three resonance circuits I, 2 and 3 of the parallel type'and connected in series. The high frequency supplied over the line is conveyed to these circuits over the transformer 4. Each of the three resonance circuits I, 2 and 3 is tuned to one of the frequencies transmitted over the line and is connected to the succeeding portion of the receiving equipment in any suitable manner. The received wave is derived across the resonance circuit tuned thereto. Since the other two resonance circuits are tuned to the incoming frequencies which are to be separated, these circuits will act as rejector, circuits so that a high quality selective effect willbe obtained.

The Fig. 2 illustrates afparticularly suitable embodiment according to the invention. Three resonance circuits 5, 6 and 'I of the series type are used and connected in parallel with each other. The high frequency incoming over the line network is applied to these circuits over the transformer 4. The high frequency, is derived from the above mentioned resonance means between the grounded point E and the notgrounded end of the inductance of the oscillatory circuits. A switch 9 may, for instance, serve for connecting these circuits to the input side of the broadcasting receiver in. Also in this case the resonance circuit connected to the receiver acts as selective circuit while the two other circuits in parallel thereto act as by-pass circuits. characteristic impedance of the line is matched to the resonance circuits by means of the repeater 4.

The arrangement shown in the drawing may be used as an additional member to a standard broadcasting receiver, for instance, by providing the arrangement in a suitable box. It is also possible to utilize this arrangement as an input circuit for a specific wire-radio receiver in which the tuning circuits are directly connected to the first amplifying tube.

In cases that the arrangement would not present the required selectivity it is also within the scope of the invention to arrange the filter The the resonance circuits may be correspondingly tuned to the new frequency by means of an adjustment of the condenser forming part of the circuit.

The Fig. 3 illustrates the resonance curves of the filtering circuits shown in Figs. 1 and 2. Investigations have proven that, e. g., on using three frequencies of 150, 180 and 220 kilocycles differences prevail with respect to the sharpness of the resonance curves since the width increases at the higher frequencies. equal curves forthese three frequencies, a requirement which is necessary for matching the low-frequency portion, it is possible to insert additional ohmic resistances in one or more of the resonance circuits as shown by resistances 2i and 22 in Fig. 5 which is later described in detail} or to correspondingly dimension the inductance to capacity ratio.

The higher frequency range of the low-frequency band transmitted by the agency of the carrier frequencies are generally attenuated due to the shape of the resonance curve as shown in Fig. 3. In order tocompensate the attenuation of the higher frequencies and in accordance with a further feature of the invention a coupling device is provided in one of the low-frequency stages as illustrated in Fig; 4. This figure shows a typical low frequency amplifier tube I 2. By low frequency is meant a frequency which is of a different and lower order from the frequency of the'wave received over the line. Thus, for example, the tube I2 may represent a conventional audio frequency amplifier tube which follows the frequency.

Still another embodiment according to the invention is shown in Fig. 5 according to which a selective action corresponding to that shown in Fig. 2 is accomplished in the three parallel tuning circuits H in front of the first tube I6, while a further selective action iseffected in the three In order to obtain serially arranged resonance circuits [9 in front of the second tube I8 which may be a tube of a detector stage. The output of tube I8 is coupled by means of condenser 23 and resistance 24 to a low frequency portion of the type shown in Fig. 4. The inductance coils of the resonance members of the three serially connected selective circuits l9 are simultaneously employed as primary windings of repeaters 20 which serve as coupling to the succeeding amplifying stage. Cores of high frequency iron may be used in these repeaters in case of need. Also in the arrangement shown in Fig. 5, the individual circuits may be conjointly adjusted, e. g., by means of a knob common thereto.

The resonance circuits of the various stages may furthermore be somewhat de-tuned relative to one another so as to obtain a band filtering effect for each of the three frequency ranges.

What is claimed is:

1. In a high frequency system, a receiving device for messages transmitted over cables by means of high frequency carrier waves, said de-. vice comprising an incoming line, a number of oscillatory circuits arranged in stages and having inductances and capacities one of said stages including oscillatory circuits connected in series and a further one of said-stages including oscillatory circuits connected in parallel to one another, a low-frequency portion having coupling means and being coupled to said stages, means for selectively rendering oneof said oscillatory circuits of each stage efiective as a selective circuit and simultaneously rendering the remainder of saidseri'es oscillatory circuits effective as rejector cir-- cuits and the remainder of said paralleloscilla tory circuits effective as by-pa ss circuits, andresistances included in' the individual oscillatory circuits and adapted to provide equal resonance characteristics for all oscillatory circuits. said coupling means of said low-frequency portion being dimensioned so as to compensate distortionsset up in the rejector and by-pass circuits.

2. In a high frequency system, a receiving de-;

vice as defined in claim 1, in which the resonance circuits in the different stages are somewhatde-

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