Патент USA US2117358код для вставки
May i7, 1938. W. P. PLACE 2,117,358 COMMUNICATION SYSTEM >F'iled Feb. 6, 1934 Toßeopz'vinÜ/:M Appapal‘us T0 Tpanfmz'z‘z‘mg Appapafar SM' _55K-TAT Fülle!" ¿4M f 1 15 ` INVENTOR Willard RPZCZC@` BY @X1/JNM > _ HIS ATTQRNEY 2,117,358 Patented May 17, 1938 UNITED STATES PATENT OFFICE 2,117,358 COMMUNICATION SYSTEM Willard P. Place, Wilkinsburg, Pa., assigner to The Union Switch & Signal Company, Swiss vale, Pa., a corporation of Pennsylvania Application February 6, 1934, Serial No. '709,971 7 Claims. (Cl. Z50-6) My invention relates to communication sys tems, and particularly to ycarrier telephone sys tems using suppressed carrier transmission. ` An object of my invention is the provision, in 5 systems of the type referred to, of an improved circuit arrangement in conjunction With anv elec tron tube modulator-oscillator for suppression of the carrier which is modulated b-y the voice fre quencies. Another object of my invention is`the provision of a similar circuit arrangement in con junction with an electron tube oscillator for sup pression of the reintroduced carrier which is _mixed with the incoming sideband for demodu lation. Other objects and advantages of my _in vention will appear as the speciñcation progresses. In carrier telephone systems using suppressed carrier transmission heretofore proposed, the combination resulting from modulation of the carrier by voice frequencies is applied to a selec' tive network of balanced circuits and the car 20 rier and one sideband are substantially sup pressed and the remaining sideband is passed t0 the communication circuit. The carrier being of irelatively large magnitude, its suppression is `,more difñcult and necessitates a relatively elab orate ñlter arrangement. A balanced modulator oscillator consisting of two Vacuum tubes operat ing in the conventional push-pull manner has also been proposed for carrier telephone systems for balancing out the carrier but such arrange ment requires two Vacuum tubes. In my present invention a bridge type circuit arrangement for an electron tube functioning in conjunction with a tuned circuit for generating a carrier current which is to be modulated by voice frequencies is provided. This bridge circuit substantially eliminates the carrier from the output of the tube by confining the carrier to the bridge circuit, and the associated filter needs only to select between the upper and the lower sideb-and fre ,40 quencies produced from modulation with the re viewof one form of apparatus embodying my in vention, and which apparatus is particularly adapted for telephone communication between two locations on a railway train. The apparatus of Fig. 1 is that for transmitting, and the appa 5 ratus of Fig. 2 is that for receiving. It will be understood that in practicing my invention both locations will be equipped with the transmitting apparatus of Fig. 1 and the receiving apparatus of Fig. 2 so that two-way operation may be ac complished. Fig. 3 is a diagram illustrating the i bridge type circuit arrangement of Figs. 1 and 2. Although the apparatus of Figs. 1 and 2 may be located at any two points: on a railway train, they will be referred to in the following descrip tion as being mounted on the locomotive and in the Caboose of a freight train, respectively. As stated above, in actual practice, both the locomo tive and the Caboose will be equipped with ‘the apparatus of Figs. 1 and 2 in order to provide for two-way communication. The communication circuit from one end of the train to the `other may take different forms, and preferably isthat disclosed in the L. O. Grondahl application for Letters Patent of the United States Serial No. 450,135, ñled May 6, 1930, for Electric train sig naling systems, and wherewith transmission is accomplished between the two ends of a `train throughthe medium of the traffic rails. Although `a specific adaptation of my inven 30 tion is here disclosed, it will be understood that I do not wish to limit myself to telephone systems for railway trains, and my invention is equally useful to other telephone systems of the type here involved. The form here disclosed will serve, 35 however, to illustrate the many applications of my invention. As will appear hereinafter, my invention is not limited to telephone communica tion and may be utilized for the transmission of code messages or for the transmission of control impulses. sult that the iilter network can be of compara Referring to Fig. 1, the reference character ‘ tively simple construction. At the receiving lo MO designates apparatus for generating carrier cation a similar bridge type circuit for the tuned circuit and the electron tube which generate the carrier to be mixed with the incoming sideband for demodulation is provided. This last men current of any convenient frequency say, for ex tioned bridge circuit operates to substantially ceiving apparatus by coniining the carrier to the cuit associated therewith by a bridge type circuit arrangement. The electron tube 5 may take different forms and preferably is a pentode hav bridge circuit. ing a filament 6, a plate l, a screen grid 8 and a ` eliminate the reintroduced carrier from the re ' I will describe one form of apparatus embody ing my invention, and will then point out the novel features thereof in claims. In the accompanying drawing, Figs. 1 and 2, when taken together constitute a diagrammatic ample, '2’000 `cycles per second and which is to be modulated by voice frequencies. The apparatus ‘ MO comprises an electron tube and a tuned cir control grid 9. The ñlament 6 is heated by a battery l0 in the customary manner and is pro vided with a cathode grid ll interposed between the screen grid 8 and the plate 1 to shield the 55 2 2,117,358 screen grid from the secondary electron emission from the plate. A tuned circuit I9 consisting of an inductor I2 and a condenser I5 is associated with the tube 5 by having one terminal, the right hand terminal as shown in Fig. 1, connected with the plate 'I over a wire I6 and its opposite or left hand terminal connected with the screen grid 8 over a wire I 1. A suitable source of current here shown as a battery I3 is connected between a mid terminal I8 of the inductor I2 and the ñla ment 6, the primary winding I4 of a transformer TI being interposed between the mid terminal I8 and the battery I3. The parts are so propor tioned that substantially an equal voltage is ap 15 plied to the plate ‘I and the screen grid 8. The tube 5 is preferably of the pentode type which functions properly with equal voltage applied to the plate and screen grid, such tubes being well known to the art. The parts are further so pro 20 portioned that oscillations take place between the plate l and the screen grid 8 through the tuned circuit I9 which oscillations, as stated above, are of a frequency of '7000 cycles per second. It will be understood, of course, that other frequencies 25 could be generated and that the frequency of '7000 cycles per second is assumed by way of illustra tion only. It is clear that there is current flowing between the plate 'i and the filament 6 and a similar current iiowing between the screen grid 30 8 and the ñlament 8, tube 5 being preferably of such characteristics that the alternating current components of these currents are of approximate ly equal magnitude in response to approximately equal voltages impressed upon the plate and 35 screen grid. It will be understood, however, that pentode tubes having characteristics other 'than that which produces a substantially equal ñow of current as the result of equal voltage on the plate and screen grid may be employed if found 40 desirable, the mid terminal I 8 of the inductor I2 being so adjusted as to produce a balanced condition. These conductances of the tube 5 may be represented by resistors Rp and Rg con~ nected between the filament 6 and plate 1, and 45 between the filament S and grid 8, respectively. To visualize these internal impedances of the tube 5, the ñctitious resistors Rp and Rg are shown on the drawing by dotted lines. However, since the internal impedances of the tube 5 will ordi 50 narily vary somewhat with voltage and different individual tubes, actual resistors Rp and Rg may be connected in the circuits at the locations shown if found desirable to do so in order to obtain greater stability. It is at once apparent that this arrangement between the tube 5 and the tuned circuit Iii forms a bridge circuit, the portions of the inductor I2 »n either side of the mid terminal I8 forming two arms of the bridge, and the plate and grid 60 resistors Rp and Rg forming the other two arms of the bridge. In Fig. 3 this bridge circuit is shown diagrammatically that it may be more clearly understood. When oscillations are gen erated between the plate and the screen grid, the 65 only part of the carrier current flowing in the connection from the mid terminal I8 to the fila ment 6 is a small part that may be caused by an 55 unbalanced condition of the bridge circuit. This carrier frequency current is modulated by 70 voice frequencies in the following manner. The control grid 9 of the tube 5 is provided with a circuit including the secondary winding 20 of a transformer T2 and a battery 2|. The primary winding 22 of the transformer T2 is included in a circuit which also contains a battery 23 and a telephone transmitter or microphone M. Hence, vibrations produced by sound impulses in the microphone M cause corresponding variations in the current flowing in the primary winding 22 which variations induce an electromotive force of a corresponding frequency in the secondary winding 20 and this electromotive force, in turn, is impressed between the control grid 9 and the filament 6 of the tube 5. With. the instantaneous potential of the control grid B with respect to the filament E varied at the relatively low voice fre 10 quencies produced by sound impulses in the mi crophone M, the amplitude in the oscillations tak ing place in the tuned circuit I9 is varied accord ingly. It follows, therefore, that the carrier fre 15 quency is modulated in accordance with the voice frequencies and, consequently, upper and lower sideband frequencies are produced. Since most of the carrier is confined to the bridge circuit, and since the voice frequencies are 20 not aiïected by the bridge circuit, the current flowing through the primary winding I 4 of the transformer TI chiefly consists of voice frequen cies and the upper and the lower sideband fre quencies. It follows that the electromotive force induced in the secondary winding 24 of the trans former TI chiefly consists of the sideband fre quencies and Voice frequencies, only the small unbalanced portion of the carrier being carried over. This electromotive force induced in the 30 secondary winding 24 is conveyed to a band-pass filter BPF so proportioned and adjusted as to pass one sideband with very little attenuation and to substantially suppress all other frequen cies, the upper sideband being preferably passed. 35 The filter BPF may take different forms sev eral of which are well-known to the art and as its specific structure forms no part of my inven tion, it is shown conventionally only in order to simplify the drawing. It is clear from the 40 foregoing description, however, that the magni tude of the current applied to the band-pass filter BPF will be relatively small, the major por tion of the carrier being eliminated by the bridge circuit, and hence this filter may be relatively 45 simple in construction. The upper sideband frequency passed by the filter BPF is supplied to the communication cir cuit, in this instance being ñrst ampliñed to a relatively high energy level. As here shown, the 50 sideband passed by the ñlter BPF is impressed be tween the grid 25 and the filament 26 of an elec tron tube amplifier 2l with the result that the upper sideband frequencies are reproduced in the plate circuit of the tube 21 greatly increased in 55 amplitude. The plate circuit for the tube 2l in cludes the input side of an amplifier transmitter AT shown conventionally only and preferably con sisting of two electron tubes connected to operate in the well-known push-pull manner, and, hence 60 the upper sideband frequencies are further am pliñed to a relatively high energy level. The out put side of the amplifier transmitter AT includes the primary winding 28 of an output transformer T3, the secondary winding 29 of which is adapted 65 to be coupled with the communication circuit through the medium of a pair of inductor coils 3U and 3|. The inductor coils 3U and 3l are mounted on the locomotive in inductive relation with the traf ñc rails I and Ia, respectively. Normally these 70 inductoi‘ coils will be connected with the receiv ing apparatus on the locomotive to be described later over normally closed contacts 5I and 52 of acircuit controlling selector SW. Reversing this 75 3 2,117,358 Ul circuit controlling selector SW to the position in dicated by the dotted lines in Fig. 1, transfers the coils 30 and 3| from the receiving apparatus to the secondary winding 29 of the output trans former T3, the circuit being completed over the contacts 56 and 5l. In the form here shown the circuit controlling selector SW is manually oper ated. It will be understood, however, that the selector SW may be automatically operated by suitable coding apparatus and the coils 30 and 3! alternately connected with the receiving and transmitting apparatus should it seem desirable to do so. Referring to Fig.`2, 33 and 34 are inductor coils mounted on the caboose in inductive relation with the traffic rails l and la, respectively. These coils 30 and 3i are connected with an input filter Fl over normally closed contacts 35 and 36 of a manually operated circuit controlling switch SWI . 20 The filter FI is preferably a band-pass filter, the parts of which are so proportioned and adjusted as to pass a band of frequencies. having a width substantially equal to the voice frequency range and to attenuate all other frequencies. In this 25 instance the filter Fl is so proportioned as to pass the upper sideband of the carrier of the appara tus of Fig. 1 modulated by the voice frequencies. That is, the filter Fl passes a band extending from 7500 to 9500 cycles, the carrier having been as 30 sumed to be I7000 cycles per second and the voice frequencies being taken as extending from 500 to 2500 cycles. This upper sideband passed by the ñlter Fl is applied to the input of an ampli fier AM and is made to appear in the output cir 35 cuit of that amplifier greatly increased in am plitude. The iilter Fl and amplifier AM may each be any one of several well-known types for such devices and as the specific type of each forms no part of my present invention, they are shown 40 conventionally only for the sake of simplicity. The output of the amplifier AM includes the pri mary winding 3l of a coupling transformer T4 and hence an electromotive force having a fre quency corresponding to the sideband picked up 45 from the traiiic rails is induced in the secondary winding 38 of that transformer. . The receiving apparatus. of Fig. 2 is provide with a demodulator D which includes a pentode 45 and an associated tuned circuit 49 both pref 50 erably similar to corresponding devices of the modulator oscillator MO of Fig. l. The bridge circuit arrangement by which the tuned circuit 49 of Fig. 2 is connected with the plate 41 and screen grid 48 of the pentode 45 is identical to 5.5 that described for the tuned circuit I9 and pen tode 5 of Fig. l and it is thought not necessary to repeat the description. Suffice it to say that the parts are so proportioned and adjusted that oscil lations of the carrier frequency of '7000 cycles per 60 second are generated and ñow in the bridge cir cuit, the small unbalanced portion of the car rier only flowing in the primary winding 44 of a transformer T5 interposed between the mid ter minal 50 of the inductor 42 and the battery 43. It is clear that this carrier will be mixed with the sideband frequencies induced in the secondary Winding 33 of the coupling transformer T4 and applied to the control grid 49, and that there will be produced corresponding upper and lower sidebands. The lower sideband will consist of the received upper sideband less r1000 cycles, name 1y, a band ranging from 500 to 2500 cycles, it being recalled that the upper sideband consists of '7500 to 9500 cycles. In other words, this lower 75 sideband will correspond to voice frequencies. The upper sideband resulting from the mixing of the local carrier with the received upper side band frequencies will consist of the received sideband plus 7000 cycles. The combination pro duced by the mixing of the local carrier with the received sideband will appear in the primary winding 44 of the transformer T5 and will induce an electromotive force of corresponding fre quencies in the secondary winding 53 of that transformer. The secondary winding 53 is con 10 nected with the input side of a band-pass ñlter F3 having parts so proportioned and adjusted as to pass the voice frequencies and to substantially suppress the remaining products of demodulation. The voice frequencies passed by the filter F3 are 15 then applied to a telephone receiver here shown as a loud-speaker LS, after having been first am pliñed whose ing 54 ing 55 by an ampliñer AMI of the usual type and output circuit includes the primary wind of a transformer T6, the secondary wind 20 of which is connected with the operating winding of the loud-speaker LS. To describe the operation of my system as a whole I shall assume that the circuit controlling switches SW and SW! occupy the position illus 25 trated on the drawing with the result that the receiving apparatus on the locomotive and the caboose are both coupled with the communication circuit. As stated hereinbefore, both locations will be provided with the transmitting apparatus 30 and the receiving apparatus of Figs. 1 and 2, re spectively. To telephone from the locomotive to the caboose the operator on the locomotive will reverse the circuit controlling switch SW and speak into the microphone M. The upper side 35 band is then supplied to the traiiic rails through the medium of the inductor coils 30 and 3l hav ing ñrst been amplified, however, to a relatively high energy level. The transmitted upper side band frequencies will be picked up from the traffic 40 rails at the caboose by the inductor coils 33 and 34 and impressed upon the filter FI since the» switch SW is now in the position for connecting the coils 33 and 34 to they receiving apparatus. After amplification the received sideband fre 4.5 quencies are demodulated and the resulting voice frequencies are supplied to the caboose loud speaker. To permit conversation from the caboose to the locomotive the caboose operator will shift the circuit controlling switch SWI to 50 the position for connecting the inductor coils 33 and 30.! with the transmitting apparatus on the caboose and the locomotive operator will restore the circuit controller SW to the position illus trated for connecting the receiving apparatus on 55 the locomotive with the inductor coils 30 and 3|. From this point on the operation will be similar to that already described in telephoning from the locomotive to the caboose. While a telephone system has been described, it is clear that by replacing the microphone M with a generator adapted io supply a predetermined frequency within the voice frequency range, say for example, a frequency of 1000 cycles per sec ond, and then coding this current according to a prearranged code, the loud-speaker at the other location will sound a note corresponding to the prearranged code and code messages can be com municated between the two locations. Further inore, by replacing the loud-speaker LS with tuned circuit networks selectively responsive to different low frequencies within the voice fre quency range, an automatic control can be estab lished between the two locations Although I have herein shown and `described 75 4 2,117,358 only one form of apparatus embodying my in vention, it is understood that various changes and modiñcations may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention. Having thus described my invention, what I claim is: l. In combination; an electron tube provided with a cathode, a plate and two grids; a tuned 10 circuit having opposite terminals connected one directly to said plate and the other directly to one terminal and cathode, means to connect the out put side of said first ñlter between the other grid and cathode of the tube, a transformer having one winding interposed in the connection between said mid-terminal and the cathode anda second winding connected across the input terminals of said second filter, and means for at times con necting the input terminals of the ñrst ñlter with a communication circuit. 4. In combination, a communication circuit, a l0 ñlter adapted to pass a given side band of a carrier of said grids and said circuit including an in ductor, circuit means for connecting a mid-ter minal of said inductor with said cathode, a cur 15 rent source disposed in said circuit means to of predetermined frequency modulated with a signaling frequency, means to connect at times the input terminals of said ñlter with said cir supply substantially equal voltages to said plate plate and two grids; a tuned circuit including an and said one grid for causing oscillations of a inductor and a condenser and tuned to resonance predetermined carrier frequency to be generated by the tuned circuit and balanced out of said 20 circuit means, means for varying the potential of the other grid of the tube with respect to the cathode at a given frequency for modulating said oscillations whei‘eby side bands corresponding to said cai‘ricr modulated at said given frequency 25 flow in said circuit means with the carrier fre~ quency substantially eliminated, and means cou pled with said circuit means for receiving said side bands. 2. In combination; an electron tube provided 30 with two grids as well as a plate and a cathode, a tuned circuit having opposite terminals con nected one directly to said plate and the other directly to one of said grids and said circuit in cluding an inductor, a circuit connection for l35 connecting a mid-terminal of said inductor with the cathode to form a bridge circuit consisting >of the two portions of said inductor and the tube impedances existing between the plate and the cathode and between said one grid and the cath 40 ode, a source of current interposed in said circuit connection to supply'voltages to the plate and said one grid for causing oscillations of a pre determined carrier frequency between the plate and said one grid through the tuned circuit and 45 which are balanced out by said bridge circuit, means for impressing between the other grid and the cathode a side band telephone current whereby side band frequencies resulting from demodula tion ñow in said circuit connection with the car 50 rier frequency substantially eliminated, receiving apparatus including a loud~speaker and a filter adapted to pass voice `frequencies, and a trans former having one winding interposed in said circuit connection and a second winding con 55 nected with the input terminals of the filter of the receiving apparatus. 3. In combination with telephone receiving ap paratus including a ñrst filter adapted to pass a given side band of a predetermined carrier fre 60 quency modulated with voice frequencies, a sec ond filter adapted to pass voice frequencies and a loud-speaker connected with the output side of said second filter; an electron tube having two grids as well as a plate and a cathode, a tuned 65 circuit including an inductor and a condenser and tuned to resonance at said predetermined carrier frequency, means to connect one terminal of said tuned circuit directly to the plate and a second terminal of said circuit directly to one of 70 the grids of said tube, means including a source of current for connecting a mid-terminal of said inductor with the cathode of said tube for causing the tuned circuit to produce oscillations of said carrier frequency and for suppressing said carrier 75 frequency in the connection between said mid cuit; an electron tube provided with a cathode, a 15 at said predetermined carrier frequency, means to connect one terminal of said tuned circuit directly to said plate and a second terminal directly to one 20 of said grids, other means including asource of cur rent for connecting a mid-terminal of said induc tor with said cathode for causing said tunedcircuit to produce oscillations of said carrier frequency and for suppressing said carrier frequency in the 25 connection between said mid-terminal and cath ode, a transformer having one winding interposed in the connection between said mid-terminal and cathode, receiving means including a signaling device responsive to said signaling frequency and 30 a filter adapted to pass such frequency and conà nected to a second winding of said transformer, and means to connect the output terminals of the ñrst mentioned filter with the other grid and cathode of said tube. 35 5. In combination; an electron tube provided with a cathode, a plate and two grids; a tuned circuit having one terminal connected directly to said plate and a second terminal connected di rectly to one of said grids and including an in ductor, circuit means for connecting a mid-ter minal of said inductor with said cathode to form a bridge circuit consisting of the two portions of said inductor and the tube impedances existingbe tween said plate and the cathode and between said one grid and the cathode, a source of current 45 interposed in said circuit means to supply sub stantially equal direct current voltages to said plate and said one grid for causing oscillations to take place between the plate and said one ' grid through the tuned circuit, and means for 50 impressing upon the other grid of the tube the frequencies of a signaling current to vary the am plitude of said oscillations as a function of the instantaneous value of the signaling current to cause current of the resultant side band frequen 55 cies with the carrier suppressed to flow between said mid-terminal and said cathode. 6. In combination; an electron tube provided with a cathode, a plate and two grids; a tuned circuit having its opposite terminals connected 60 one directly to the plate and the other directly to one of said grids and including an inductor, cir cuit means for connecting a mid-terminal of said inductor with said cathode, a current source dis~ posed in said circuit means to supply voltage to 65 said plate and said one grid for causing the tuned circuit to generate a predetermined carrier fre quency current, means for varying the potential of the other grid of the tube with respect to the cathode at the frequency of a signaling current 70 to vary the amplitude of the carrier current as a function of the instantaneous value of the signaling current to produce in said circuit means the resultant side band frequencies with the car 75 2,117,358 rier frequency eliminated, and means coupled With said circuit means for receiving said side bands. '7. In combination; an electron tube provided With a cathode, a plate and two grids; a tuned circuit having its opposite terminals connected one directly to said plate and the other directly to one of said grids and including an inductor, circuit means for connecting a mid-terminal of said inductor with the cathode to form a bridge circuit consisting of the two portions of said in ductor and the tube impedances existing between the plate and the cathode and between said one grid and the cathode, a source of current inter posed in said circuit means to supply voltage to 5 the plate and said one grid for causing oscilla tions of a predetermined carrier frequency be tween the plate and said one grid through the tuned circuit, means for varying the potential of the other grid of the tube with respect to the cathode at a given frequency to vary the ampli tude of said oscillations as a function of the in stantaneous value of said given frequency to pro duce in said circuit means the resultant side band frequencies with the carrier frequency substan 10 tially eliminated, and means coupled with said circuit means for receiving said side bands. WILLARD P. PLACE.