US1684445A - Signaling system - Google Patents

Description

Sept. 18, 1928. 1,684,445

R. K. HONAMAN SIGNALING SYSTEM Filed July 12, 1926 ATTORNEY Patented Sept. 18, 1928. V

PATENT OFFFCBQ RICHARD K. I-IONAMAN, OE BLOOMFIELD, NEW JERSEY, ASSIGNOR TO AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

' SIGNALING SYSTEM.

Application .filed July 12,

This invention relates to signaling systems, and particularly to arrangements in such systems for minimizing noise.

In hi h frequency transmission systems, such as radio broadcasting and carrier systems, in which a carrier frequency modulated by low frequency signals is transmitted, noise currents having frequencies Within the range used for transmission .are introduced into the transmitting medium and give rise to noise at the receiving station of the system. This noise results mainly from the beating of the carrier frequency by the noise currents introduced into the transmitting me dium. Under certain conditions, the components of the noise currents, which are within the limits ofaudibility, are easily heard at the receiving station.

Duringintervals in a broadcasting program of news, music, or the like when no low frequency signals are modulated on the carrier frequency, as, for example, during the quiet intervals in the program, noise of this nature is particularly objectionable because of the fact that the noise stands out during these intervals. On the other hand, during periodsv in the program when the low frequency signals are modulated on the carrier frequency, the noise may be submerged by these low frequency signals.

As stated above, noise becomes audible at the receiving station during the quiet inter-v vals in the program, and results from the interaction of the carrier frequency andthe noise currents introduced into the transmitting medium from extraneous sources. Cer-. tainly, if the carrier frequencycan be cut off during these quiet intervals, the noise will be greatly reduced, rendering these intervals substantially quiet at the receiving station. Furthermore, the carrier frequency serves no useful purpose during these ,quiet intervals.

It is therefore an object of this invention to provide arrangements suitable for transmitting a carrier frequency when there are low frequency signals oriother modulating energy to be modulated thereon, and for substantially suppressing the carrier frequency when there are no such low frequency signals or other modulating energy to be modulated thereon. v

While the nature of the invention will be pointed out with particularityin the ap, pended claims, the invention itself, both as to its further objects and features, will be 19% Serial no. 122,016.

better understood from the detailed description hereinafter following when read inconnection with the accompanying drawing, in which Figure 1 represents one embodiment of the invention, and in which Fig. 2 represents a characteristic curve of a vacuum tube showing the interrelation of plate current an (1. grid voltage.

In F 1, there is shown a transmitter S, or other source of low frequency signals, ar ranged in a series circuit with a battery B, and the primary winding of a transformer T The transformer T connects the circuit of the source of lowfrequency signals S to a duplex modulating" system having. two three-element.thermionic tubes M and M each havinga filament, a grid and a plate, the filaments being heatedto an electron-emitting temperature b r a common battery. The tubes M and M, are preferably similar and equal in their structure and characteristics, and certainly may be replaced by a single duplex tube having a single filament, two grids and two plates; The input circuits of these tubes if, and M are arranged in parallel with respect to the secondary winding of transformer T which winding is in series with a battery B in the common conductor of the input circuits of these tubes. .The secondary of transformer T consists of two windings which may, for example, be wound in the same direction, one in the input circuit of the tube M andthe other in the input circuit of the tube-M,.- The output'circuits of these tubes are also-connected through the primary windings of a transformer T in parallel with respect to a common-plate battery B The secondary winding of transformer T is connected to an output circuit-O.

The primary winding of the. transformer T has a generator G connected thereto, which generates, for example, the carrier frequency to be employed in the system. By virtue of the connection between the generator G and the transformer T the grids of the tubes M and M areboth in phase with respect to the carrier frequency transmitted by generatorG. The oscillations of the carrier;frequencywill therefore be impressed in the same directions on the input circuits of these tubes, and under normal conditions the grids of these tubes will be equally biased negatively by battery Equal currents therefore flow in the output circuits of the tubes M and M but these currents are oppositely directed by the 7 it will have a very high transmitter primary windings of the transformer T Consequentlyythese currents effectively balance and neutralize each other, rent flows in the output circuit 0. r p

In formerarrangements of duplex translating circuits, when low frequency signals were generated at the source S, the grid of one of the tubes M or M became positive while the grid of the other tube became negative, so that the resistance of one tube decreased while the resistance of the other increased. This then caused an'increase in the current fiowing'in the output circuit of the tube in which the grid became positive and a corresponding decrease in the current flowing in the output circuit of the tube in which the grid-becanienegative. The tubes M and M were actuated only when low frequency signals were impressed on the grids of these tubes; i

The resent inventioncomprises arrangements or substantially suppressing the carrier frequency of the generatorG when'no low frequenc signals are transmitted bythe S and-for transmitting the carrier frequency of'thegenerator G modulated by the low frequency signalstransmitted by theltransmitter S'whensuch signals are generated. :A neon tube N, orother discharge device, is accordingly connected in the input circuit-of one of the tubes, M This neon tube has abreakalown potential which is abovethe potential of the battery B lVhen the potential across the terminals of the neon tube is less than its break-down potential, impedance, and when thenpotential'across'the terminals of the neon tube is'equal to, or less than, its breakdownpotential, it will have a moderate impedance. -Because of this 'factvthe neontube will be ineffective in the system until 'the potentialacross itstermin'als is greater than its break-down potential. And until thi-s'break-down potentialis applied to the terminalsof the neon'tube N, t ierewill be practically no effective current flowingin the primary windings of the transformer T and consequently no current will be transmitted'tothe output circuitO.

The neon tube N 's so arranged in the systerm that when low frequency signals are transmittedby'the source S, a potential will be generated across'the terminals of theupper windingofthetransformer T so that the cumulative potential of the batter B and that generated across the termina s of the'upper secondary winding of-the transformer T will be greater than the breakdown potential of-the neon 'tubeN. When this occurs currentwill flow'from the battery B through theneon tube N in a localcircuit whichincludes the battery B the upper secondary Winding of the transformer T a resistanceR and the neon'tube N. The

neontube N willthereforeshunt the grid and no cur-' and filamentof the tube M so thatthe grid of the tube M will not be biased negatively as much as the grid of the tube M Consethe primary windings of the transformer T,,'

are oppositely directed there will be a re- 'sultant carrier current transmitted to the secondary winding of the transformer T,, which will be proportional to the difference between the'currents flowing in the output circuits of the tubes M and M respectively. The output circuit 0 will therefore receive current of the carrier frequency modulated by the low frequency signals.

The'neon tube N operates very'rapidl so that a change from the condition in W iich carrier current is to be transmitted to the condition in which carrier current is to be suppressed takes. place practically instantly. Furthermoreyno change occurs in the structure of the neontube Nsuch aswill'interfere with its operating characteristics.

Fig. 2 showsa curve characteristic of the tubes M andfM in which grid voltage .is plotted as abscissas against. plate current as ordinates. The point a on this characteristic curve has an ordinatewhich corresponds to the average plate current in both. tubesli/I and M when no low frequency signals are being transmittedto the grids of-these tubes In a perfectly balanced system the current in'the plate circuit of one of the tubes'will be equal to the current in the plate circuit of the other of the tubes. I

\Vhen the'low frequency signals are being transmitted'to the grids ofthese respective tubes. it has beenshown hereinabove that'the neon tube N associated with the tube M shuntsthe grid and-filament of thetube M 50 that the potential of the grid with respect to the'filament of the tube'M will no longer be equal to the potential of the rid with re-v spectto thefilamentof the-tu e M The grid of the'tubeM will be less negatively biased with respect to "its filament than it previously-was. The point b of the characteristic curve represents the point 'at which i the tube M then operates. This point b is less negative than thepoint'a, andthereforethe plate current in the tube M is greater than the plate current in the tubeM Thelines drawn from the points aand b te the axis of abscissas correspond, respectively, to the plate currents in the tubes M and M l Consequently, the current in the secondary windingo'f the transformer T receives 7 a carrier current having an amplitude proportional to" the dif ference between these two lines.

It will be understood that by changingflthe magnitude of the potential of the battery B the magnitude of the resistance R or the break-down potential of the neon tube N, the amplitudeof the carrier current flowing lun 7 high frequency wave by in the output circuit 0 may be suitably controlled. v

It will be understood also that while a neon tube has been shown and described herein for the purpose of illustration, any other device which has a high impedance when the potential applied thereto is below a predetermined value and a moderate impedance when the potential applied thereto equals, or is greater than, the predetermined value, may be employed instead thereof within the scope of the appended claims. While the arrangements of this invention have been shown and described in one particular embodiment merely for the purpose of illustration, it is to be understood that the invention is capable of embodiment in other and widely variedorganizations without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. The method-of signaling which consists in generating a high frequency wave, generating low frequency signals, modulating the high frequency wave by the low frequency signals, and substantially suppressing the high frequency wave when the magnitude of the low frequency signals drops below a predetermined value and freely transmitting the high frequency wave modulated by the low frequency signals when the magnitude of the low frequency signals rises beyond the predetermined value.

2. The method of signaling which consists in generating a high frequency wave, generating low frequency signals, modulating the the low frequency signals, transmitting the modulated high he quency wave when the magnitude of the low frequency signals is above a predetermined level, and substantially suppressing the high frequency wave so that it remains untransmitted when the magnitude of the low freiluerlicy signals is below said predetermined eve 3. The method of signaling which consists in generating an alternating current wave of one frequency, generating low frequency signals, superimposing said low frequency signals on said alternating current wave, and substantially suppressing the alternating current wave when low frequencysignals are being generated below a predetermined level and freely transmitting the alternating current wave modulated by the low frequency signals when the low frequency signals are being generated above said predetermined leve 4:. The method of signaling which consists in generating a wave of one frequency, generating a wave of a second frequency, superimposing the wave of the second frequency on the wave of the first frequency, and substantially suppressing the wave of the first frequency when the wave of the second fresignals, when quency is being generated at a level below a predetermined value andfreely transmit ting the wave of the first frequency modulated by the wave of the second frequency when the wave of the second frequency is' erator of a high frequency wave, a source of low frequency signals, means for modulatng the high frequency wave by the low frequency signals, means for transmitting the high frequency wave modulated by the low frequency signals when the energy level of the low frequency signals is abovea predetermined value, and means for substantially suppressing the high frequency wave so that it remains unmodulatcd and untransmitted when the energy level of the low frequency signals is below the predetermined value.

7. A signaling system comprising a generator of an alternating current'wave, a generator of low frequency signals, means for superimposing the low frequency signals on the alternating current wave, and means for substantially suppressing the energy of the alternating current wave when the energy of the low frequency signals drops below a predetermined level and for freely transmitting the energy of the alternating current wave with the superimposed low frequency signals when the energy of the low frequency signals rises abovethe predetermined level.

8. A signaling system comprising a generator of current of one frequency, a generator of current of a second frequency, means :for superimposing the wave of the second frequency on the Wave of the first frequency, and means for substantially suppressing the wave of the first frequency when the wave of the second frequency is being generated at a level below a-predetermined value and for freely transmitting the wave of the first frequency modulated by the wave of the second frequency when the wave ofthe second frequency is being generated at a level above the predetermined value.

9. In a translating system, a pair of translating devices having input and output circuits, a circuit for the reception of signal waves, another circuit containing a source of energy of a carrier wave, one of said circuits being symmetrically associated with said input circuits and the other being oppositely associated with said input circuits, at receivpreventing the flow mg circuit diflt'erentially associated with said outputcircuits, and means for substantially of energy of the carrier Wave tothe receivingcircuit when the level of theenergy of the signal waves is below a-predetermined value and for freelypermitting the flow of energy of the carrier vvave modulated by energy of the signal waves to the receiving circuit when the level of theenergy of the signal Waves is above the predetermined value. c

10. In a translating system, apair of translating devices having'input and output circuits, a circuit for the reception of signal '11 A modulating system comprising a pair of translating devices, a source of high frequenc energy symmetrically connected with said evices, a source of modulating energy oppositely connected with said devices, 'an output circuit diflerentially connected with said devices, and means consisting of a discharge device connected to one of the translating devices for substantiall unbalancing the translating devices when'te modulating imi-44c energy is normal, whereupon the output circuit will receive high frequency energysuperimposed by modulating energy.

a '12. A modulating system comprising a pair of translating devices, a source ofhigh flquenc energy symmetrically connected-with said evices, a source of modulating energy oppositely connected with said devices, :an out oing circuit differentially connected wit said devices,andrmeans consisting-eta discharge device connected to one of the translating devices for substantially vincreasing the flow of current a in a one ofsaid translating devices beyond'thatoccurring in the other of said translating dev ces, whereupouthe outgoing circuit will; receive hi h frequency energy superimposed by modu ating energy.

13. A modulating system comprising a pair ottranslating devices a source of'high -frequency energy symmetrically connected with said translating devices, a source ofi modulating energy oppositely connected with said translating devices, a an outgoin circuit differentially connected with sa-i translating devices, and a discharge device connected to one of said translating devices which vvillbe inefiective until theinodnlatingenergy rises beyond a predetermined value, whereupon the flow of current in the translatingdevice to which the discharge device is connected will substantially exceed the flow of current in the other translating (device. a i

"In testimony whereof, I-have "signed my name to. this specification this .lOth .day; of

July 1926. V V

RICHARD :K. ,HONAMAN.

Images