US1811443A - System of selective signaling - Google Patents

Description

June 23, 1931. GA. SOMERSALO SYSTEM OF SELECTIVE SIGNALING Filed Aug. 15, 1927 2 Sheets-Sheet 1 IN V EN TOR.

June 23, 1931. G. A. SOMERSALO SYSTEM OF SELECTIVE SIGNALING Filed 'Aug. 15, 1927 2 Sheets-Sheet 2 Q/N VEN TOR. d. v

" ATTORNEY Patented June 23, 1931 PATENT] OFFICE GEORGE A. SOMERSALO, OF NEW YORK, N. Y.

SYSTEM OI SELECTIVE SIGNALING Application filed August 15, 1927. Serial No. 212,872.

My invention relates to an electric circuit for the selective translation of oscillating currents of a desired frequency or band of frequencies.

In particular, my invention relates to a selective electric circuit in which a number of tuned circuits are connected in cascade by a special form of coupling to reduce to a minimum the reaction of one tuned circuit upon another. i

Heretofore, in systems for the selective transmission of waves, it was common practice to connect several tuned circuits in cascade by one of several types of coupling in which there was always an appreciable amount of reaction between two adjacent circuits. The reaction between the circuits destroys the selective property of the tuned circuits and flattens out the resonance curve,

and, in the limit, may produce a doublepeaked resonance curve. In prior arrangements, the coupling between circuits had to be made very loose in order to prevent the reaction from destroying the selectivity.

But, loose coupling prevents the efficient transfer'of energy from one circuit to another. In one known arrangement, in order to reduce the reaction, and at the same time obtain good energy transfer between circuits, it was proposed to couple adjacent cir'- cuits by vacuum tube relays, thus taking advantage of the supposedly unilateral coupling effect of the tube. But it is nowcommon knowledge thata vacuum tube relay is not unilateral in its coupling effect, due to the inherent capacity'effect between its various electrodes, but will produce undesired reac-. tions between the coupled circuits.

It is, therefore, an object of my invention 40 to devise a selective circuit in which full advantage is obtained of the selective property of all the coupled circuits and, at the same time, elficient energy transfer is obtained without the use of vacuum tube relays. While my invention is capable of use generally where it is desired to select waves of a particular frequency or band of frequencies to the exclusion of others, it is particu larly useful as a selective element in a radio 59 receiving set.

I have illustrated certain features of my invention in the accompanying drawings, in which,

Fig. 1 is a diagram of a wavemeter calibrating' circuit employing the well known unilateral type of connection to the detector, which type of connection is used in a new relation in my invention.

Fig. 2 is a vector diagram showing the relations between the various electric quantities in the circuit of my invention.

Fig. 3 is a diagram of a circuit embodying the principles of my invention.

Fig. 4 is a circuit diagram of a modified forni of my invention.

Fig. 5 is a circuit diagram of still another form of my invention.

Fig. 6 is a circuit diagram showing the preferred form of my invention as embodied in a commercial radio receiving set.

Fig. 6 is a slightly modified form of the preferred circuit.

Referring to Fig. 1, a well known arrangement for calibrating wavemeters is shown, and is reproduced here for the purpose of explaining the principle of operation of my invention. A standard wavemeter circuit including an inductance 1 and a variable condenser 2 is excited in a known manner by a buzzer H, which is provided with a shunting condenser K and an operating battery B. The wavemeter to be calibrated comprises a variable condenser 4 and an inductance coil 3 inductively coupled to coil 1. A telephone 6, shunted by a de- 85 tector 7, is connected by a single wire 5 to one terminal of the wavemeter circuit 3, i. This is known as a unilateral connection. When wavemeter 3, 4; is tuned to the currents generated by the standard wavemeter, 90 the buzzer note will be audible in telephone 6, notwithstanding the fact that there is no return connection of either the phone or the detector to the circuit 3, 4:. This phenomena is known to those skilled in the art, and does 95 not require an explanation, but for the purpose of explaining my present invention I offer the following theory: When circuit 8,

4 is excited, there will be a variable current p ure in lead This urrent ressure be forced partly through the telephone coil operation of Fig.1?) is as follows:

is similar to that in any conductor connected with an electric circuit. As the current pressure in a cable forces the electrons nearer the surface, the electrons here will be forced to the end of the lead 5 and from here to the telephone coil. If the telephone coil were not shunted by a detector 7,-notl1- ing wouldhappen. Now. the electronswill 6, and partly against the detector 7. The reaction of these two against such a pressure is different; The coil will act'like an elastic wall, the actionandthereaction being" equal and opposite. The first transient wave impulse will magnetize the core and the magnetization will set up an opposing electromotive force. This counter electrome- 'tive force will send a current through the c'1rcu1t6,-7.- This refers to the --aud1o fre-' quency wave, since the telephone coil will act as choke towards radio frequency current. The detector 7 will rectify, the current thus making the system operative.

My invention is embodied in the circuit diagrammatically illustrated in Fig. 3. In this figure, an antenna A is connected to ground through the primary 1 of an oscillation transformer.v The secondary 3 of the transformer is shunted by a variable condenser 4 to, form a tunable circuit generally indicated by I. One side of tuned circuit I is grounded, and the other side is connected to one end of a coil or open conductor 6 whichis provided with a shunt condenser 7. Coil 6 is in inductive relation to another coil 8 which, I with variable condenser 9, forms a second tuned circuit 11. One side of circuit This grounded, preferably the side adjacent the end of coil 6 which is conneceted to circuit 1, and the other side of circuit 11 is connected to grid 11 of a vacuum tube 10. V The vacuum tube may serve asa repeater, an ampllfier or a detector, as desired. The plate 12 of the tube 'is connected I to the battery 14 and the filament 13 through the primary winding 15 of a transformer, the secondary 16 being connected to the output circuit. -The transformer may or may not be provided with an iron core as desired. Coil 8 is arranged in non-inductive relation to c0113. I

r The arrangement shown inFig. 3 is some what similar to. that shown in Fig. 1, but the operation of Fig. 3 has to do only with the effectrof the radio frequency currents; The

The incoming signal sets .up a circulating current through the coil?) and the variable condenser 4. The currentpressure will be propagated through the leads to the c'oil 6 and condenser 7, The first transient wave 7 impulse will force the electrons through the denser, but the-reaction; of the coil to suchwindings of the coil and. against the com a wave is different from thatof the condenser. Thecoil will act like an elastic wall,"

and will react upon the current impulse, the action and reaction being equal and opposite. The transient current magnet1zes the core and the flux sets up acounter-eleo' tromotive force. When again the electron current strikes the condenser, these electrons will be first stored, as in a reservoir, then discharged during the vnext half cycle.

Consequently the counter-electromotive force set up in the coil 6 will sendv a current The current in thelead 5 will be small, the

pressure of the current in the circuit 3, 4

being opposed by the pressure of the current in the circuit 6,77. Current flowing in coil 6 induces current in coil 8 and excites tuned circuit II. Potentialvariations acros'stuned circuit II areimpressed upon grid 11' to operate vacuum tube 10. l

' While I have'shown an external condenser '7 connected'in shunt to, coil- 6, it is to be understood that the coil may be so designed that its natural distributed capacity will serve the function of condenser 7, and an additionalicapacity need not be employed.

7 11V do not intend to be limited to any particular quantities'or dimensionsof the variious elements of my invention, but for the. purpose-of illustration only, I find through the condenser 7, this current being 7 in step with the current in the circuit 3,4;

that fora tuning range; from 200 -to 550 meters satisfactory results are obtained when coil 6 is 2 inches in diameter and has approximately 42 turns, while coil 8 it 2% inchesin diameterand has approxi- The series of tuned circuits connected in cascade may be termed a .filter, and in my invention each tuned circuit is connected with the succeeding oneby means of unilateral, aperiodic coils or circuits. It is; ;possible to obtain voltage amplification of the waves within. the filter itselfg- The ratio of thevolta'ge across'coil 8 to the voltage across coil 3 maybe eitherajstep-up or a step-down ratio; depending upon the efliciency of energy transfer through the filter. Of course, this step up .in voltagedoes not mean increased energy, since there is no energy amplification Wltl'llil the filter itself.

* v The mannerof transfer of energy through the filter -may be explainedwith the'aidof the vector diagramshownin Fig.2. J represents thej;current-circulating in circuit I.

If the current were free to flow through the lead 5', coil 6 and some way back again without reducing the amount of current cirdenoted by F (Fig. 2) will have the same phase. Following the'common way of drawingvecto-r diagrams the electromotive force E 'set up in the secondary winding 8 will lag 90 degrees behind the flux. The condenser 9 being tuned to resonance, the secondary load current J flowing through it will lead the voltage by nearly 90 degrees. It'will be opposed by the load component J of: the current in the primary winding 6,v and consequently this load component will be nearly 180 degrees out of phase with the flux, and nearly opposed to magnetizing currentJ The vector sum ,of both-the actual current J 7 through the condenser 7-will thus be small compared with both of them, the magnetizing current and the load current. A comparatively small current in the aperiodic coil 6 (Fig. 3) will cause alarg'e circulating current in the circuit II. The terminal voltage V across coil 8 will be greater, equal to or smaller than the terminal voltage across coil 3, depending upon the nature of the coil 6 and condenser 7 This coil and condenser should be. preferably so designed that astep-up voltage ratio exists. 7

Thecomparative efficiency of this energy transfer can be seen from the vector diagram. The energy transferred from e011 6 to the circuit 8,9 will be proportional to the current vector J the energy lost in coil 6 will again be proportional to the vector J Thus only a small portion ofenergy is lost.

Another way to explain this filter circuit would be 'to consider the unilateral coil as a diminutive transmitting aerial with a very small natural capacity, but a great se lf-inductance. 'This diminutiveaerial is inductively coupled to the next filter stage acting as receiver.v Notwithstanding the small size of the unilateral coil, compared with an aerial, the former may be very efiicient. The natural capacity may be smaller, but it has afar greater self-inductance. In an aerial the' energy will be stored mainly in the conductor itself and in the electrical field surrounding it, in the unilateral coil direct inductive or capacitative coupling. Take for example, theordinary transformer type of coupling in which two tuned circuits are inductively coupled. Considering each circuit alone, the voltage and current are at a miximum when the circuit is tuned to resonance, but when the two are coupled together the resonance curve generally shows two peaks, which broaden the curve and destroy selectivity. In order to eliminate the double-hump in the curve the coupling must be reduced. This so-called optimum coupling, however, is very loose, and does not permit efficient transfer of energy. I

In my systemthere is'no such harmful reaction between the tuned circuits. The amplification curve for each circuit shows a single peak, the resonance peak of the second circuit being sharper than that of the first. If a number of filter stages are contive than the preceding one. If all circuits are tuned simultaneously, the last circuit will have the greatest effect upon the selectivity, and with the number of stages the selectivity will rise notin geometric progression, but in a progression steeper than the geometric. The energy transfer will be greatest for the frequencies near the resonance, whereas for frequencies farther away this transfer is very small. It may be said that a part of the peak energy has been transferred to the next circuit. There is no tendency to build up a double peak.

The arrangement shown in Fi 4 is an extension of the circuit shown in 1* ig. 3, and like elements are represented by the same reference numerals. In this arrangement there are five tuned circuits I-V in the entire 1 filter, but an amplifying tube 10 is inserted between circuit II and circuit III for the purpose pling instead of the inductive coupling shown. In order to reduce the effect of natural capacity between coil 6 and coil 8, it will be advantageous to place coil 6 at the grounded end of coil 8. This applies also to coils 15,118 and 21. If there be considerable capacity between coils 6 and 8, this capacity will provide a return path to circuit ofy Elli

V J to Fig. 4.

v i In the is impressed upon a second amplifying tube It is to be noted that the functionfof the tubes'is to supply additional energy to the waves to compensate for the loss:in the filter and to amplify the voltage. The tubes are not relied upon to prevent reaction between the circuits, and thenumber of tubes inserted in the filter-is kept as small as possible consistent with the amplification required, I

' In'Fig. 5 I provide additional amplifica tion by connecting an amplifying tube in cascadewith tube 10 through'an untuned transformer 28-29. This transformer may or may not be provided with an iron core, as

desired-. Fig. 5 .is similar in 'otherrespects preferred form of :my invention, shown in Fig. 6, I first amplifythe incoming signal before entering the filter by amplifying tube 40, the. grid ofw'hichis connected directly to the antenna," and to ground through a choke coil 31. The choke coil is preferably so designed as to render the an tenna circuit aperiodic. The filter in this arrangement consists of an unbroken cascade of resonant circuits I to 'IV', or as many" as desired. After passing through the filter the waves are impressed upon an untuned 1 The last amplifier tube is coupled by transformer 61, 62 to a detector tubex70, which voltage amplifier consisting of vacuum tubes and 60, coupled by a transformer 51,52.

detectsrthe' high frequency wave and derives therefrom the low frequency signal. If'desired,'the low frequency signal current'may be. amplified by an audio'freque'ncy amplifier indicated at T. V The advantage of the arrangement shown inIFig 6 is that by first amplifying the in; coming signal Wave before it reaches the filter a longer and more selective filter maybe used before the voltage: amplification stage.

The first amplifying tube 40 will; of course, also amplify the voltage. In this 'position a special tube giving great energyiamplifiization may be employed.

' In Fig. v6 the amplifying "tube is coupled to the first filter-circuit I by means of a unilateral coil 46. A choke coil 33 has been added to connect the plate with *the'bat tery 42. This Way of coupling shows .a greater selectivity than that of Fig. 6, a unilateral coupling is more selective than the transformer coupling. I

WhileI have offered certain theories of operation in the foregoing description of my invention, it is to be understood that the scope of-my invention is not-to be restricted prising a number of tuning-stages connected in cascade, means for'indu'ctively coupling "these stages with substantial elimination of mutual impedances between adjacent stages, said means including an open coil, and means of amplification associated with these stages. 2." An electric signaling system comprising a number of tuning s'tages connected in cascade, means for couplingsaid stag'es,fineluding a substantially open coil in conduc tive relation to a stage and inductively coupled to the following stage, said coil having a substantial distributed capacity, and means of amplification associated with the stages.

3. An electric wave filter comprising a number 'of tuning stagesconnected in cascade and means for coupling s'aidj stages, these means including a substantially open coil in conductive relation to a 'stagc and inductively coupled to the following stage and having a negligible coupling capacity. 4:."An electric wave filter comprising a number of stages connected in cascade, each stage consisting of a'coil shunted by'a condenser, said coil and condenser forminga circuit resonant; tothe desired frequency,

and means for coupling said stages, these means including a substantially open coil in conductive'relation to a resonant stage and inductively coupled with the coil of the cuit andinductively coupled to thefollowing circuit, said coil having a substantial distributed capacity, the corresponding parts in each'circuit having no common magnetic field. v I

'6. An electric wave filter comprising a number of stages connected in'ca'scade, each stage including a circuit resonant to the desired frequency, and means for coupling two consecutive "circuits including asubstan tially open coil connected with one and inductively coupled with the other circuit, the

corresponding parts of each circuit having 7 substantially no common magnetic or electric field.

7. A system for selecting electric Waves comprising a pair of circuits resonant to the frequency to be selected and an open coil in non-inductive conductive relation With one of the circuits and inductively coupled to the other circuit said coil having a substantial distributed capacity. 8. A system for selecting electric waves comprising a series of independent tuned circuits arranged in cascade, and means for coupling said circuits comprising an open coil external to both circuits and connected to the preceding circuit and inductively coupled to the following circuit, said coil having a shunted capacity.

9. A system for selecting electric Waves comprising a series of independent tuned circuits arranged in cascade, each circuit comprising an inductance coil shunted by a condenser, each coil inductively coupled to an open coil having one end connected to the preceding circuit.

10. An electric signal selecting system comprising tWo resonant circuits connected in'cascade each of the circuits consisting of an inductance shunted by a capacity, the

I inductances being in non-inductive relation to each other, the circuits having one common point, and an open coil having one end free and its other end connected to a point of the preceding circuit differing from the common point, said coil being inductively coupled to the coil in the succeeding circuit.

11. An electric signaling system comprising an aerial, a selector, and an amplifier, said selector forming a continuous unit comprising a number of tuning stages connected in cascade, and means for substantially eliminating resonance distortive reaction of a stage upon the preceding stage, said means including an open coil.

12. An electric Wave receiving system comprising an antenna, a selector consisting of a number of stages in cascade, each stage including a circuit resonant to the desired frequency, and of means including an open coil for coupling said stages With substantial elimination of resonant distortive reaction therebetWeen, and means for preventing variations in the antenna constants from afi'ecting the tuning adjustments of said selector, said last mentioned means comprising an electron discharge device coupling the selector to the antenna.

GEORGE A. SOMERSALO.

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