US2376367A - Field telephone system - Google Patents

Description

y 1945- F. LEIBE 7 2,376,367

FIELD TELEPHONE SYSTEM Filed May 13, 1943 2 Sheets-Sh'eet l PECE/V/NG AMPLIFIER May 22, 1945. F. A. LElBE FIELD TELEPHONE SYSTEM Filed May 13, 1943 2 SheetsSheet 2 INVENTOR. FAHNK a. 45/55 Patented May 22, 1945 mam rcmrnonc srs'rmu Frank A. Leibe, Qua kertown, Pa., assignor to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application May 13, 1943, Serial No. 486,755

6 Claims.

This invention relates to telephone systems of the type in which a receiver and a transmitter at one end of a telephone line are alternately switched into operation, an arrangement especially adapted for use in field telephones. In systems of this type it is desirable that an operator who has finished transmitting and is about to switch his set from transmitting to receiving position shall notify the other operator of that fact so that the latter will know when to switch in his transmitter and commence talking. The invention is particularly intended for systems in which vacuum tube amplifiers are used at each end of the line.

The general object of this invention is to provide a novel switch-over signal that will be automatically transmitted from a set at one end of the line when the set is switched from transmitting'to receiving position. A feature of the inventic-n is the utilization of the vacuum tube amplifier circuits for this purpose.

An important object is the provision of an arrangement that willgenerate a switch-over signal without the use of separate signal-producing devices. This is in general accomplished by creating signal-producing oscillations in the tube circuits for a brief period at the time when the set is switched from sending to receiving position. A feature of the invention is the attainment of this object by the use of simple circuit arrangements automatically producing a brief period of oscillation whenever the set is switched over to receiving position, and which are adapted for incorporation in highly compact field sets without increasing the size of such sets.

Other objects and advantageswill appear from the following description considered in connec tion with the accompanying drawings, in which Fig. 1 is a simplified diagram illustrating one form of the invention, and

Fig. 2 is a similar diagram illustrating another embodiment.

Referring to Fig. 1, a handset I is indicated,

including a receiver ll connected by leads l2,

tem which includes a receiving amplifier tube 20 and a transmitting amplifier tube 2|, together with a suitable arrangement for placing in operation tube 20 when switch I8 is open, and tube 2! when said switch is closed. In theform illustrated in Fig. 1, this is accomplished by alternately energizing the filaments of the tubes, an arrangement that is advantageous for battery operated field sets since it requires the heating of only one tube filament at a time. This switch arrangement is utilized to produce the switch-over signal, and takes advanta e of the fact that if one of the filaments is disconnected when the other filament is simultaneously energized, the former filament will retain its electron-emitting temperature long enough to produce simultaneous operation of the tubes for a brief period lasting until the temperature of the cathode of the de-energized tube drops below the temperature of useful emission. By providing proper coupling between the circuits of the two tubes during this brief period of simultaneous operation, oscillations are produced which are transmitted over the line I! to the other set.

In the form shown, the filament 22 of tube 20 is connected through line 23 and filament battery 24a to line H, and its energizing circuit is completed through line 25 and upper contact 26 of one pole of switch l8 which is connected to line H, said switch being of the double-pole, double-throw type. Operating grid 21 is coupled to transmission line l9 through winding 28 of transformer 29, while the anode 30 is connected to winding 3| of transformer 32 in inductive relation to winding 33 connected across the induction coil l4 and condenser IS in the handset circuits. Tube 20 is preferably provided with a screen grid 34 connected to an appropriate source of positive potential in the usual way. With this arrangement signals coming in on line i9 are impressed through transformer 23 on tube 20, amplified, and transmitted through transformer 32 to the receiver II.

The filament 36 of transmitter tube 2i is connected at one side through line 3'! and 23 to handset line I1, and at the other side through line 38 to filament battery 24!: and the lower contact 39 of the upper pole of switch l8. Operating grid 40 is connected to winding ll of transformer 32, while anode 42 is connected to winding 43 of transformer 2!]. Tube 2| is advantageously provided with a screen grid 44 connected to a suitable source of positive potential. With this arrangement the waves from the circuit of microphone l6 will be impressed through transformer 22 on tube 2|, amplified therein and transmitted through transformer 22 to line It. The opera- .tion of'push switch II will thus serve not only to shift the handset circuits between transmitting a return from transformer winding" being ads iustably connected to resistance 48 to provide variable grid bias from filament battery 24b, functioning as a gain control, with the usual condenser in shunt. The outer end of winding II is connected to a suitable grounded source of positive anode potential. The negative feedback circuit for tube 2| comprises the connection of anode 42 through condenser 5i and. resistance 52 to winding ll of transformer 32, the other end of the winding going to grid 40, the lower end of resistance 52 being connected through parallel resistances 53 and condenser 54 to line 25 and the negative side of battery 24a which provides bias potential for grid 40. The outer end of winding 42 is likewise connected to an appropriate source of positive potential. The negative sides of filament battery 24 and the sources of positive potential'are of course connected in the usual manner, as by grounding to the metal frame.

With this arrangement the simultaneous operation of tubes 20 and 2| during a brief period after switch I! is-shifted will produce oscillations, due to the coupling between the circuits of .the two tubes through the coils of transformers 29 b and 32, which will be transmitted over line It! and heard in the receiver of the handset at the rate at which the. charge leaks oil of the condenser. With this arrangement, since both tubes will be functioning simultaneously during said period, the coupling between the tube circuits will generate audible oscillations that will be transmitted over the line It to the receiver at the 0pposite end of the line, informing the operator at that end that the other set has been switched from transmitting to receiving position.

while two embodiments of the invention have been described, it will be understood that other embodiments may be employed without departing from the invention as set forth in the claims.

In particular, the tubes may be placed in and out of operation by various known changes in their circuits and inparticular by changing the potentialsapplied to various electrodes, such as '-additional control grids.

What is claimed is:

1. A telephone transmitting and receiving unit comprising a transmitting system including an amplifying vacuum tube, a receiving system including an amplifying vacuum tube, switch means for placing said systems alternately in operation and means for automatically generating a switchover signal comprising means for maintaining the transmitter system tube in operation during a signal period following actuation of the switch means to place the receiving system in operation. and coupling means connecting said systems for generating signal oscillations in the transmitter system during said period.

2. A transmitting and receiving unit as set forth in claim 1, in which the coupling means includes a line transformer coupled to the transmitting system tube output and to the receiving system tube input and a second transformer coupled to the receiving system tube output and to the transmitting system input, and in which said unit includes a microphone circuit in the transmitting system and a receiver circuit in the receiving system, both of 'said circuits being opposite end of the line. This arrangement has the advantage of battery economy since only the filament of the tube that is in use is heated.

Another embodiment is illustrated in Fig. 2, and employs a similar arrangement ,of transmitterand receiver circuits, input and output transformers and double-pole switch, which are indicated by the same numerals as similar parts in Fig. 1. In this arrangement, however, the filaments. 22,- 36 are continuously heated by batteries 24 grounded at the negative pole in the usual way. Controlgrids 21 and ll! are maintained at a negative voltage sufficient to block grounded battery 66. Said potential has a value appropriate to overcome the blocking bias on the control grid and to place each tube in operation when its screen grid is connected to battery 88 by switch it. v A condenser 81 is connected between line 65 and ground, and is of appropriate capacity to maintain on screen grid ll of the transmitter tube 2| a potential sufficient to keep said tube in operation for a brief signal periodafter tube 20 has been placed in operation by throwing switch it from transmitting to receiving position, the duration of the signal period being determined by the coupled to the second thansformer.

3. A telephone transmitting and receiving unit comprising a transmitting system including an amplifying vacuum tube, a receiving system including an amplifying vacuum tube, and means for placing said systems alternately in operation and automatically generating a switch-over signal, comprising switch means for alternately energizing the' fllaments of said tubes, and coupling means connecting'said systems for generating signal oscillations in the transmitter system throughout the period of simultaneous operation of said tubes and systems during the per. sistence of useful emission in the deenergized tube.

4. A telephone transmitting and receiving unit comprising a transmitting system including an including means for alternately applying blocking and unblocking potentialsto' electrodes of said tubes, and means for automatically generating a switch-over signal comprising means for maintaining said unblocking potential on the transmitting tube electrode during a signal period following the application of said unblocking potential to the receiving tube electrode, thereby maintaining both tubes in operation during said signal period, and coupling means connecting said systems for generating signal oscillations in the transmitting system during said period.

5. A transmitting and receiving unit as set forth in claim 4, in which said tubes are each provided with a screen grid and a control grid, both control grids being maintained at blocking potentials, and in which the screen arids are a1: ternatelyconnected to asource of unblocking potential by said switch means. 7

1 6. A transmitting and receiving unit as set v forth in claim 4, in which the means for main-- taining unblocking potential on the transmitting tube during a signal period includes capacitance

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