Arrangement for electric intercommunication
United States Patent 2144936

442,986. Wireless signalling. LORENZ AKT.-GES., C., 1, Lorenzweg, Tempelhof, Berlin. April 17, 1935, No. 11870. Convention date, April 25, 1934. [Class 40 (v)] In a combined transmitter-receiver, the speech currents from the microphone M, in addition to feeding the modulation transformer TM, are used to disable the receiver and remove a disabling voltage from the master oscillator. For this purpose two rectifier-filter systems GS comprising dry rectifiers connected as a Graetz bridge produce D.C. control voltages in the resistances R1, R2, which control the bias of the master oscillator and some of the receiver valves respectively.

Hans, Rochow
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The invention is concerned with a circuit ar- a rangement for electric intercommunication be- v tween two stations. It is well known to provide I for such purposes a switching device which is i operated manually and in such a manner that at t each station the receiver is rendered inactive t when the transmitter is cut in. If the direction c of intercommunication is changed, then at both stations the switching must be effected manually.

It has also been suggested to so improve these arrangements that the switching is made with the aid of relays which are controlled by speech, i. e. the arrangement of relays is such that the receiver of the station just speaking is switched Sby a relay energized by the speaking currents Sover an amplifier. Arrangements of this kind have the disadvantage however that the relays must be very sensitive and accurately adjusted in order to ensure a good intercommunication.

In addition the relays must be slow releasing in order not to become deenergized during the short pauses intervening between the individual words.

This on the other hand however entails the disadvantage that at the beginning of the speech certain parts thereof are cut off by the relays, unless very complicated arrangements are employed, i. e. arrangements, which are not adapted for use with apparatus required to be as light as possible.

The invention solves the problem by deriving from the speech currents a continuous current which by displacing the grid potential acts to start the transmitter and to stop the receiver.

The invention will be understood from the following description and be particularly pointed out in the appended claim, reference being had to the accompanying drawing which is a diagrammatic representation of an embodiment of the invention.

The microphone M is included in the input circuit of a low frequency amplifier N. The output circuit of the low frequency amplifier is connected with two transformers TS and TE. In the secondary circuits of these transformers bridge connections of the Graetz type are disposed which contain dry rectifiers of a well known kind. The rectified currents are passed over filter circuits S in order to control the transmitter and receiver. The connection is such that the continuous currents shall produce in the transmitter and receiver actions which are the reverse of each other. The transmitter when voice-actuted is so biased that the controlling transmitter ihich is quartz controlled, does not oscillate. y the influence of speech a continuous voltage s applied over resistance RI to the controlling ransmitter, this voltage being such that this ransmitter will be caused to oscillate and to ontrol the final stage working in push-pull manier. An action exactly the reverse of this is nroduced in the receiver. The continuous voltage renders the bias of the receiver negative so ;hat the receiver will be insensitive. This is attained by leading the continuous voltage to the resistance R2. Resistance R2 is included in the grid circuit of all the stages. The high frequency stage and the two low frequency stages are however additionally biased by a battery Z, i. e. biased negatively, whilst the grid of the audion is connected directly to the resistance. When the arrangement is subjected to speech, the whole level of the receiver gets displaced. The output circuit of the low frequency amplifier N is connected not only with the transformers TS and TE but also with a transformer TM, i. e. the modulation transformer of the transmitter. Here the final stage is modulated in a well known manner with the aid of the method of modulating 25 grid potentials.

The additional current consumption for the controlling arrangement according to the invention is very small. The arrangement may for example be such that the resistances Ri, R2 each 3 require a current of 5 ma.

What is claimed is: A two-way radio telephone station comprising a radio transmitter including a three-element vacuum tube having grid biasing means for nor- 35 mally preventing operation of said transmitter, a radio receiver including a three-element vacuum tube having grid biasing means normally rendering said receiver operative, a connection between said vacuum tubes for maintaining the cathode 40 elements of said tubes at the same potential, a source of low frequency currents for modulating said transmitter, and means including separate rectifier elements having their output circuits directly connected respectively to said vacuum tubes 45 for supplying direct current from said low frequency current source to vary the biasing voltages of said vacuum tubes to render said transmitter operative and to render said receiver inoperative. HANS ROC0W.