US 1789496 A
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Jan 29, 1931. G, W1 PIERCE 1,789,496
' ELECTRI GAL SYSTEM Original Filed Feb 25, 1924 Patented Jan. 20, 1931,
UNITED STATES PATENT OFFICE GEORGE W. PIERCE, F CAMBRIDGE, MASSACHUSETTS ELECTRICAL SYSTEM Original application med February 25, 1924', Serial No. 695,094.- Divided and this application plea J anuary 18, 1928.
The present invention relates to the transmission and reception of intelligence.
In radio telegraphy, it is customary to transmit signals by means of electric waves with a frequency that is desired to be constant. In the reception of suchsignals,'a receiving systemis often employed comprising an electric circuit traversed. by an oscillatory current of frequency such as to give audible beatswith the received signal frequency. For this purpose, particularly when high-frequency waves areemployed, it
is important to keep constant the frequency of the receiving circuit. In the reception of radio-telephone signals, too,'it is useful to maintain aconstant-frequency oscillation at the receiving station to-beat superaudibly with the incoming signals .for superheterodyne reception. In radio telephony and radio telegraphy, and in carrier-current systems where transmitting or receiving is effectedb means of a carrier wave, also, the carrier requency qnay be suppressed at the sending station, the side bands only being transmitted, and these must be supplied again with great accuracy at the receiving station.
The present invention has for its chief ob-- jeots to provide an improved method of and systems and apparatus for transmitting and receiving electrical signals and to reduce interfere'nce to a minimum also, to provide for an accurate control of the receiving-station frequency, and for a cooperation of freqnency control at the transmitting station with control at the receiving station.
Other and further objects of the invention will be explained hereinafter and will be pointed out in the appended claims, it being understood that it is intended to cover in the appended claims all the novelty that the invention may possess. t
In the accompanying drawings, Fig. 1' is a diagram of circuits and apparatus illustrating the present invention in its preferred form; Fig. 2 is a similar diagram of a modified radio-telephonic transmitting system and apparatus, using power amplification; Fig. 3 is a similar diagram of a modified receiving system; and Fig. 4 is a similar dia- Serial No. 247,469.
gram, of a ra-dio telegraphic transmitting system and apparatus.
A complete transmitting-and-receiving system is diagrammatically shown in Fig. 1. y In order to simplify the drawings, and to render the description more easily understood, the complete transmitting-.and-receiving system is omitted from the other figures, which, therefore, show separate transmitting systems and receiving systems. The system of Fig. 1 is more particularly designed for radio-telephone work, but corresponding connections for transmitting or receiving by radio telegraph or by telegraph or telephone over line Wir'es will be obvious to those skilled in the art; 4
The constant'freq'uency of the transmitting and receiving circuits, according tosa preferred embodiment of the'present invention, is attained by the interaction upon the system of electromechanical vibrators, like piezo electric crystals. Such vibrators have the property of executing mechanical vibrations under vibratory electrical stimulus an-d,conversel'y, of developing electrical potentials as a result of their mecnanical vibrations, as is now Well known, and as is explained in a copending application, Serial No. 695,094, filed February 25, 1924:, of which the present application is a division. For convenience, the action of the electric forces to cause mechanical deformation will be termed stimulation and the development of electromotive force by the displacement will be termed response.
The electromechanical vibrator, shown as a piezo-electric body 2, is differently disposed in the 'difierent diagrams, so as to-illustrate a. few of, the many diiferentways in which the vibrator may be employed. Itjis to be understood, however, that the vibrator disposition, in a particular diagram, is not specific to that diagram, but that the vibrator may be similarly disposed in the other diagrams. The oppositely disposed surfaces of the vibrator 2 are provided withopposed electrodes 8 and 12. One of the electric axes of the crystal 2 is assumed, for concreteness, to be in the direction of the thickness of the crystal plate.
A vacuum tube 24 is diagrammatically with three sensitive elements or electrodes,
. namely, a filament 26, a grid 28 and an anode Y pedance element 66 is or late 30. The filament 26 is connected wit a filament-heating battery 31. A plate battery 32 is connected with the filament26 'by a conductor 33, and with the plate 30 by a conductor 35. A load 40, shown in the form of an inductance .coil having a distributed capacity resistance, is connected between the battery 32 and the plate 30. A tuning condenser 48 may be connectedin parallel with the load, or the power of the system may, for some purposes, be increased by electrically tuning some other element.
In the transmitting'system shown in the left-hand portion of the diagram of Fig. 1, and in Figs. 2, 3 and 4, the electrode 12 of the electromechanical vibrator is shown-con nected by a conductor 36 with. the grid. The other electrode 8 is connected in Figs. 1 and 3 by a conductor 38 with the filament 26, and in igs. 2 and4, to some point in the circuit of the plate 30. The vibrator is thus connected, in the transmitting-system portion of the diagram of Fig. 1 and in Fig. 3, between the filament and the grid of the vacuum tube and in Figs. 2 and 4, between the grid and the plate. Other connections,'too, may be used. Thus, in the right-hand or receivingsystem portion of the diagram of Fig. 1, the vibrator is shown connected between the filament and the plate, in the plate circuit of the vacuum tube.
An impedance element 66 (Fi s. 1 and 2), 80' (Fig; or 46 (Fig. 4) may be connected in the grid circuit. In Figs. 1 and 3, the imdisposed in parallel with the vibrator. If desired, a biasing battery 64 may be employed to bias the grid 28 to a predetermined potential, so tential of the biased value.
The system will oscillate with a frequency determined by the frequency of some normal mode of mechanical vibration of the vibrator and independent of the electrical parameters of the circuits.
With this setting, the invention of the present application will now-be explained, though it will be understood that the invengrid may fluctuate about the tion is not, in its broader aspects, limited to any particular arrangement. of circuits and .yibrator connections.
1 the usual manner,
' connections serve admirably for radio-telephone transmission. If the transmission is to be applied to. a telephone line, the antenna and ground connection may be replaced by the well known connections to line, wires.
that the'poas to tune the s stem for the maximum cur-' rent, as observa le in the ammeter 54. The impedance element 66 may take the form of the secondary winding of a modulation transformen'as in F igs. 1 and 2-. The primary winding 68 of the transformer may-be connected to a microphone 7 O, in circuit with a source of energy, shown as a battery 72. The variations produced by the microphone will modulate the carrier oscillations of the a system. The operation will be understood by persons skilled in the art without further description. The winding 66 of the modulation transformer may be replaced by a resistor of high resistance, with a new disposition *0f the microphone. Corresponding connections for transmitting by telegraph, or (as will presently appear) for receiving, will be obvious to those skilled in the art, as illustrated in Fig. 4. The freqeuncy of a transmitting station so designed I is very nearly constant and stable.
In the receiving system, too, as shown in v Fig. 3, the vibrator 2 may be connected in the input circuit, between the filament 126' and the grid 128 of-the receiving tube 124, the same as in the transmitting systemv of Fig. 1. In order to illustrate some of the many different ways in which the vibrator may be connected into circuit, however, it is illustrated in the receiving system at the rightbf Fig. 1 as connected in the output circuit, between the filament 126 and the plate 130, shunted by a bypass 74 for direct current. The bypass74 may be a radio choke, an inductance winding, a resistor, or a combination of these. The bypass 74 is prefer ably so chosen that the circuits shall have parameterssuch as to make the system stably non-oscillatory when the crystal is removed series with a receiving antenna 86 and-a. condenser 87, and is grounded or connected with a counterpoise. The antenna 86 will re reive the radio signals transmitted from theantenna 56. A telephone receiver 42, with or without a bypass condenser 44, may be disposed in the p ate circuit of the receiving tube 124. Where the telephone is not needed, it may be replaced by an inductance, the primary winding of a transformer, or the'input terminals of an amplifier, or it may be wholly short-circuited. The locally generated oscillations of the circuits of the tube 124 will beat with the oscillations received by the antenna 86, according to wellknown principles, rendering the received signal audible in the telephone 42, or giving them any required superaudible' frequency for superheterodyne reception. These locally generated oscillations may also be employed to supply a suppressed carrier frequency if desired.
" A system of this character is adapted to receive high-frequency radiations, to which the electrical tuning elements are adjusted, and to superimpose upon them the frequency of mechanical vibration of the vibrator. The two frequencies are thus coexistent at the same time, permitting beats to be produced.
A. tunable transmitting system and a tunable receiving system such, for example, as are illustrated together in Fig. 1, each supplied with a suitable vibrator, may, the one transmit, and the other receive, constant oscillations of very high frequency; This has been done by me over considerable distances. Variations in frequency arise from many sources, for all the circuit constants or parameters are continuouslyvarying. For example, the mere running down of the battery, thus changing its voltage, the variation of inductance, the aging of a condenser, deterioration of the vacuum tubes, or a mere V change in temperature-these and many othfrequencies.
er factors each introduces changes in the circuit constants and produces a different frequency from the frequency intended. No. such difiiculties. are encountered in accord-' ance with the present invention. The frequency is maintained constant irrespectlve of the parameter variations. The constancy of the beat note and the consequent certainty-of being; always inadjustment to receive the given signals is found to be of great value, rendering possible the use of very high The beats render audibleunmodulated telegraph signals. :Superaudible beats may also be produced, in the case of telephone and telegraph reception, and these may be used for amplifying purposes, as in superheterodyne apparatus. The superposed frequencies may also be used to supply a carrier wave in a radio telephone system where the system operates by suppressed carriers. These reful where constant-frequency sources are sults may be efiected both in space-communication systems and in w1re-commun1cat1on systems. The 1nvent1on is particularly useused at the transmitting station and also at the receiving station. i
The function performedby the piezo-electric crystal may be performed also by other vibrators similarly operating by internal stresses, such as the tuned magnetostrictionvibrator of application Serial No. 158,452,
filed January 3, 1927, andall such vibrators will be included in the claims under the gen-' eric term .electromechanical vibrator or its equivalent.
The invention is readily adapted to powere amplifying systems, as by a plurality of vacuum tubes; and one such system, adapted for transmission, is illustrated in Fig. 2. The connections are very much as in the trans-- mitting system of Fig. 1, except that the winding 40', instead of being directly coupled to the winding 52 of the antenna circuit, is
coupled to a winding 88 that is shunted by a I condenser 90. The elements 88 and 90'may be tuned so as to pick off one of the many harmonies from the plate circuit of the master oscillating tube 24. The winding 88 is conuected in the grid circuit of\an osclllatlng vacuum tube 92, and that isbiafsed by a battery 94. A winding 96 is connected in the,
plate circuit of the vacuum tube 92, and is.
coupled to the winding 52. The vibrator 2 determines the frequency of oscillatlon of the master oscillating circuit comprising the vacuum tube 24. The master oscillator, which may be of, say, 5 watts, controls, through power amplification of the fundamental or a harmonic, the tube-92 that is adapted to yield an output of much higher power, say 50 watts, and so forth. The frequency of the master oscillator 24 may be caused to beat with the fundamental or' the tric wave of fifteen meters wave length. This 7 range may undoubtedly be extended in both directions. Any desired number of such amplifying units may be' interposed 1n cascade, without in any way departing from the present invention.
A telegraphic transmitting apparatus accordin tofthe present invention 1s illustrated In Fig. 4. The coil 40 is coupled to the coil 52. in the usual manner, as before described. The coil 52 is connected, as before,
througha hot-wire ammeter 54, to an antenna 56, and through a variable condenser 58,
.to a sending key 60. The key 60 is adaptedto make and break contact with a grounded 'contact member 62. The method of telegraphing will be obvious to persons skilled I in the art, and need not be further described.
The grid is connected with the filament by a conductor 34 having the impedance element 46, which may be used to give the grid a su1table potential about which its fluctuations oc cur about a zero value. If desired, however,
the biasing battery 64 may be employed, as
before described, in which event the fluctuations will taken place about the-biased value. Both in telegraphy and in telephony, the oscillations of the system will be kept at practically constant frequency by the vibrators,
making it possible, for example t; use a very high frequency, with all the advantages flowing therefrom. For example, consider a frequency of 50,000,000 cycles, correspondin to 5 G-meter wave length. A control of the requenc to within one tenth of one percent woul obviously involve a difference in variation of 50,000 cycles. With a variation in frequency as great as 50,000 cycles, the signal is-continually running off the setting of the receiving system, with the result that the op'-.
, erator has toshift continuously, trying to catch it here and catch it there. A part of the signal is detected, but a large part is often lost. Accordin to the present invention, on the other han it is possible to main tain the fre uency to within l/ 100,000 of one as much as cycles, could readily be han- 'dled. These oscillations may also be employed,
' with or without amplification, to serve as 36 sources in carrier-wave-systems, 'orto aid in the receiving apparatus of a carrier-wave system At the receiving station, the local oscillator will replace the suppressed carrier wave and this, with the received side band, will give the complete signal.
The vibrations of the electro-mechanical vibrator may also, in accordance with the "present invention, be communicated to air 'or to some other elastic medium, as water, to produce sound for in'tercommunication or any other desired purposes.
' The use of the Pierce oscillator,-as it is termed in the art,in the present invention is particularly advantageous, because the system is always certain to'oscillate at. the frequencydetermined b the crystal, and at no other frequency. ;I?;ing some crystal-controlled oscillators heretofore proposed, for example, a comparatively slight variation of the ,circuit parameters, .such as might be caused b runnin down of the battery voltage, wi cause t easystem to oscillate at a frequenc quency, saving the crystal inert and out of operation altogether. The circuits continue tooscillate, but at a difierentfrequency from .rthe crystal frequency." This happens with- ,out the operator even becoming aware of that fact. The system continues to oscillate withiout the crystal, and the operators work beis involves a variation of only different from the crystal fre-' comes entirely vitiated. The transmitting end, for example, may kee on transmitting without the operator knowing that, at the receivinfg end, it becomes necessary to shift and. hunt .o
r the signals, merely because the system at the transmitting end is oscillating without'control by the crystal. This is imossible with the Pierce oscillator. The
ierce oscillator can not oscillate except with the aid of the crystal, and at any other than the crystal frequency.
disconnected from t system, there are no oscillations. crystal in circuit, any variation in the parameters of the system, no matter how great, is
automatically compensated for by the crystal itself. As the circuit is thus' always under the control of the crystal, the frequency of its oscillations is always constant. Once the system starts oscillating, it is impossible for the frequency of the oscillations to drift out of control by variations in the parameters of the system, or for any other reason.
The Pierce oscillator,-crystal and all, comprises a periodic system,-that is, a closed system in which any energy liberated in the system must swing periodically from the kinetic or motional form to the potential or stored form and back again, until dissipated. The period or frequency of these swings is a constant of the system. called its natural frequency or natural period.
Other uses and applications and other modifications within the scope of the present invention-will also readily occur to persons skilled in the art. It is therefore desired that the above-described embodiments of the invention shall be regarded as illustrative of the invention, and not restrictive, and that the appended claims shall be construed,
broadly, except insofar as it may be necessary to impose limitations in view of the prior art. Y T
What is claimed is: 1-. A transmitting and receiving system having, in combination, means for transmitting signal waves, means for receivingthe.
signal waves, a local oscillating system comprising an amplifying relay having an inherent regenerative coupling, a source of energy, a piezo-electric body,'and means connecting the relay, the source and the body together, the connecting-means being such that the local system can not oscillate through the inherent regenerative coupling when the body is disconnected from the system, whereby the When the crystal is c On the other hand, with the' frequency of thewaves of the local oscillating I s l system is maintained; substant ally constant, and means for combining the rece ved waves with the local waves.
2. A transmitting and. receiving system having, in combination, means for transmitting signal waves, meansfor receiving the 7 signal waves, each of the said means comprising a source of electric energy, a tube 30 receiving system for mamtammg .the frequency, a receiving system for receiving the having a plurality of electrodes, an electro- I of the system being such that the system will I not oscillate in the absence of the vibrator, the terminals being adapted to act conj ointly both for electric stimulation and electric response to effect the oscillation of the system and means for evidencing beats.
3. A transmitting-and-receiving system having, in combination, a transmitting system for transmitting electric waves, an electromechanlcal vlbrator' connected with the system for maintaining the frequency of the transmitting system substantially constant,
. the connections being such as to prevent the operation of the transmitting system at other than the said substantially constant freelectric waves, the receiving system being traversed by local oscillations, and an electro-mechanical vibrator connected with the quency of the local oscillations substantially constant, the connections of the secondnamed electromechanical .vibrator with the I recelvmg system being such as to prevent the local oscillations at other than the secondname'd substantially constant frequency.
In testimony whereof, I have hereunto subscribed my name. a
GEORGE W. PIERCE.