US2103079A - Wave signaling system - Google Patents

Description

Dec. 21, J, KI-JOHNSON WAVE SIGNALING SYSTEM Filed NOV. 15, 1954 :NVENTOR I John KeHy Johnson Patented Dec.'2l, 1937 John Kelly Johnson, Rye, N. Y., assignorto Haz'elt tine Corporation, JerseyClty, N. J., a. corpo-f ration of Delaware' Application November` 15, 1934, serial No; 153,103

4 claims. (ci. 25o-zo)v lThis invention relates to wave signaling systems wherein modulatedcarrier wave signals are transmitted over cable conductors between portionsof signaling apparatusrsituated s ome disv5 tance apartyas in different portions of a room or building; More especially the invention pertains to remotely controlled tuned radio broadcast receivers in which the input portion is housed in a portable control unit connected by cable conductors tothe' receiver proper.

' An object of the invention is to providean improved form of remote coupling over cable conductors, lwhich is simplified as to construction and manipulation, and which is `highly efficient,

as compared to known couplings for similarpur-l v poses, throughout a relatively wide range of frequencies such as the complete frequency operating range of a multi-Wave band receiver. A feature of thel invention resides in utilization of the capacity inherent between the cable conductors in part to effectthe desired coupling.

The superheterodyne type of receiver-has been adapted to remote control operation by housing the tuned radio frequency amplifier and-.oscil-l later-modulator portions in a small portable unit cable-connected to the main receiver chassis containing the intermediate frequency, detector and audio frequency units. Of necessity the antenna and ground connections are wired directly to terminals on the main chassis due to its more or less permanent location as com-pared to the portable circuit. The `signals picked up ,by the antenna, however, must be first impressed on the input portion of the receiver contained in the portable unit, and, to this end, they are conveyed thereto over the cable conductors.

A problem is thus presented, particularly inmulti-wave band receivers, of providing a coupling from the antenna over the cable conductors to the tuned input, which is simple in construction and manipulation as well as efficient and effective throughout the-wave band or bands for which the receiver is tunable.v Ityhas been proposed by Way of solution of this problem to connect-the antenna and ground terminals at the chassis to respective conductors of a cable pair, and to connect the remote terminals of this cable pair to the tuned input of the remote control unit in an orthodox manner, as for ex- 0 ample, through a transformer. The cable thus becomes but an extension of the antenna and ground lead-in conductors.

This form of connection has, however, been r demonstratedin practice to introduce losses so 0 serious as greatly to impair performance of the apparatus as'a whole.I O'nelreason for this'is v that substantially' the entire open circuit signal '.Avoltage of, the antenna circuit is impressed.

between'the lcableconductors, which, due to the relatively' large capacity inherent between con-u 5 ductors, greatly attenuatesv the signals prior to applying them to the tuned input circuit.

In an effort to eliminate vthis defect, it has been proposed .further to couple the antenna cir-v cuit tothe cable through a step-down trans- 10 4 .former and ,additionally to employ a `step-up transformer coupling between the cable and the tuned input to the receiver. vThe-thought here is to convert the 'relatively high voltage-low current energy of the antenna lcircuit, to low.15

' voltage-high current for transmission over the A cable, thereby to minimize the aforementionedY high frequency cable losses, the signals being. thereafterv reconverted by' the jstep-up transformer to the high voltage-low current required 20 by they tuned input. With this arrangement the coupling efficiencyvaries markedly with fre- -quen'cy despite the introduction of dispropor-1 tionally expensive and complicated `circuits in an effort to offset this effect. This variation in 25 efficiency, which is particularlyv noticeable inthe successive'wave bands of a multi-wave band re-l ceiver, results from the well understood Aaction `'of the antenna coupling transformer and antenna impedance relations as follows: 30

The antenna impedance is in general capacitively reactive throughout the frequency range or ranges of operation. The transformer impedance, on the other hand, vis inductively reactive.

the antenna circuit is most responsive. Accordingly as the reception `frequency is varied by tuning with respect Ato the fixed frequency of antenna circuit resonance, thel effectiveness of 40 signal transfer to the tunedginput circuit will vary correspondingly. Although this variation in effectiveness of coupling with reception frequency may be minimized to some extent by suitable design, as by most 4effectively allocating the xed resonance of the wave .band receivers employing the mentioned The antenna circuit will thus be' subject 35 to resonance at some fixed frequency at which transformer couplings to the cable, to provide at the tuned input in the remote control unit, separate step-up transformers individually suitable for each wave band of operation. 'Not only is this an unduly expensive construction, but in addition further complication and expense are necessarily incurred by the requirement for suitable switching apparatus in the control unit adapted to con- Vnect the transformers individually in the receiver circuit both as to their primary and secondary coils for selection of a given waveband.

For most effective operation asimilar arrangement of transformers and switching should be employed at the main receiver chassis to couple the antenna circuit to the cable. 'Since this additional switching at the main receiver chassis would, however, destroy the feature of remote control operation, the practice has been to eniploy a permanently tapped coil in the antenna circuit despite the resultingl loss in eiiiciency at the lower frequency bands of operation.

I propose, and it is upon this that my invention is predicated, to eliminate the mentioned disadvantages inherent in arrangements heretofore suggested, by capacitively coupling the antenna circuit to the cable and over the cable tothe tuned input of the receiver. To this end I propose, in the preferred modification of my invention, to interpose fixed condensers of suitably chosen values in both the antenna circuit and the tuned input circuit. I further propose to bridge these condensers respectively between opposite ends of a cable conductor and the metallic sheath housing the conductors.

Withinvthe operating range of the receiver the cable usually will be electrically short -and its distributedl capacity thus effectively lumped. Hence the capacities of the mentioned coupling condensers and that of the cable are equivalently that of a single lumped condenser having a ca` pacity equal to the sumof the capacities of the coupling condensers and of the cable. The antenna ,circuit is thus in eil'ect coupled to the tuned input circuit through a single lumped coupling condenser of appropriately chosen value.

With this arrangement -the coupling impediance assumes the same character as that of the antenna, that is, both are substantially pure capacities throughout 'the operating frequency range. 'I'hus the fraction of the total signal voltageimpinging on the antenna which is impressed on the coupling impedance, tends to be substantially constant and independent of frequency and equal to the ratioof ythe coupling capacity to sum of the antenna and coupling capacities.

`Moreovensince in the tuned input circuit the capacity of the tuning condenser is now in series with the coupling capacity, the coupling from` the antenna circuit to the tuned input will be the same for a given dial setting of the tuning condenser for all wave bands of operation in a multi-wave band receiver. 'I'his results from the fact that the coemcient of coupling depends exclusively on the antenna capacity, capacity, and the tuning capacity in accordance with the well understood definition for coeiiicient of capacitive coupling. -For a given setting of the tuning condenser the coeii'icient of coupling will therefore be the same for all wave bands of operation.

Owing to the relatively high eiiiciency of this type of coupling for the various wave bands of reception, the necessity -for switching operations at themain receiver chassis is avoided, and those at the remote controlunit reduced to them1nlthe couplingof the receiver circuit requisite to full understanding Jof the invention is shown in the form of a circuit diagram.

The system Aof the drawing comprises broadly a main receiver unit I, a remote control unit 2, and a shielded cable 3 containing conductors such as 4 and 5, housed in a metal sheath `6 andappropriately connecting the main receiver unit to the remote control unit.

Thereceiving system includes an antenna 'l and ground 8 arranged in a circuit coupled, in a manner to be explained, over `the cable to the tunable input circuit 9 of a vacuum tube II) constituting a stage of tuned radio 'frequency amplification. The reception frequency output of tube I0, is selectively applied `by a tunable circuit II, generally similar to 9, to the input of a multi-grid vacuum tube I2 operating as a combined oscillator-modulator, the former by virtue of a tuned impedance I3 regeneratively coupling certain of its electrodes. The intermediate frequency output of tube I2 is selectively applied, in a manner to be explained, over cable conductor 5 to the input of a vacuum tube I4 operating as a stage of intermediate frequency amplification in the main receiver unit, vthe remainder of which,

comprising additional stages of intermediate frequency amplification,- detector and audio frequency amplification, i's indicated .schematically by rectangles I5, IB and I1 respectively. The

terminating loud speaker I8 may be mounted on densers 22 and 23 respectively, bridged in series across a variable condenser 24fconnected between the contro1grld'25 and cathode 26 of tube I 0. 'I'he circuit is tunable by condenser 24 throughout two distinct frequency bands, selection 'of either of which is under control of a switch ,21 adapted to/short circuit the lower coil 2l'. Receptionv occurs -within the upper frequency band withswitch 21 closed, and at the lower frequencyband with the switch open.

Tuned circuits II and I3 are generally similar in construction and arrangement to circuit 9. The band selection switches corresponding to 2l and the rotors of the Variable condensers corresponding to 24, are, for the mentioned tuned circuits, mechanically ganged to unitary controls 28 and 29 respectively. for simultaneously adjusting the reception band and the tuning respectively of the several circuits. The padding condensers of tuned. circuits II and I3v correspending to condensers 22 and 23 of 'circuit 9,

are semiadjustable and serve to align' the circuits for'single dial tuning. Condenser 55, having a capacity about ,equal to the `sumof the combined capacities C1 and the distributed capacity, C,l of the cable, provides at least approximate alignment between circuits III' and 9.

The/output or plate circuit of tube II'I` is coupied capacitively through condenser 30, and inductively through transformer'3l, to'circuit .II bridged between theV signal control grid of tube I2 and the common cathode lead 32. The design is such that the capacitive coupling opposes the .inductive coupling for reception at the lower frequency band, the couplings being, however, additive for reception at the'upper frequency band. In this way the gain or amplification is maintained reasonably uniformthroughout both reception bands;

For generating heterodyne oscillations, circuit I3 is connected between the inner grid of tube I2 and the cathode lead 32,A a combined induc-l l tive and capacitive regenerative coupling to the -by-pass Condensers, such as 40, 4I, 42 andI 43,

for suitably 'adjusting the potentials of the tube electrodes, by-passing and filtering high frequency currents, etc. 4

The common cathode lead 32 is grounded to the metallic sheath 6 of cable 3, this sheath in turn being grounded at 44 at the main receiver chassis. as are directly involved in the present invention. They are conductors 4 and 5 connectedfto the grid circuit of tube I8 and to the plate circuit of tube I2 respectively, as is explained hereinafter. It will b'e understood, however, that there will be present' in the cable other conductors for suitably energizing the electrodes of tubes I and I2, and for securing at the control unit such operations as switchingjon and oir-of the power supply, volume control, etc.

For purposes of this invention the antenna I is connected to ground 8 through a resistance 45, and to cable conductor 4 through a blocking condenser 46, the latter in order to preventgrounding at 8 of negative biasing voltage applied by the power unit over conductors 41 and 5 to the grids of tubes I0 and I2.

Bridged between the conductor 4 and ground at the main receiver chassis, is a condenser C1 similar' to condenser C1 serially included at the remote control unit 2 in the tuned input circuit 9, and connected thereat between cable conductor 4 and the grounded sheath 6. Condensers C1 together with the distributed capacity inherent between-cable conductor 4 and grounded sheath 6, indicated by capacities C, serve to couple the antenna circuit 1, 8 capacitively to the tuned circuit 9 in accordance with the invention.

In the usual installation cable 3 will be electrically short with respect to the wavelengths toy Only such cable conductors are shown cuit 9 through a single capacity equal to the sum of capacities C1, and the total distributed capacity inherent between conductor 4 and metallic sheath 6.

In'a capacitively coupled circuit, such as that -under consideration, the coeflicient of coupling depends onlyl on the resultant capacities indi'- vidual to the antenna and tuned circuits and the mutual coupling capacity. All of these capacities are substantially fixed with the exception of thev variable tuningr capacity 24 which, however, for

a given dial setting, introduces the same capacity into the tuned circuit for operation in either the upper or lower frequency bands of reception. It

follows from this that the coupling coefficient,

and` hence the eiiiciency of signal transfer from the antenna circuit l, 8 to the tuned input cir-` cuit9, will be substantially the same in both thel upper and lower receptionbands forlike dial settings of condenser 24.` 1 4 Resistance 45, arranged in the antenna circuit effectively in shunt to the antenna. coupling cajustment-of the tuning condenser 24, and also to by-pass interfering currents of relatively low frequencies, such as may be picked up by'the antenna.

A coupling-of the same character as that described above, is employed to couple the intermediate frequency output of the oscillator-modulator tube I2 over cable conductor 5 vto the input of the intermediate frequency amplifier tube I4. To this end there is directly connected between the anode of tube I2 and the grounded cathode lead 32, a tuned circuit 48 consisting of a semi-adjustablecondenser 49 bridged across a coil 50 and a xed condenser C2 in series. Condenser Cz is in turn bridged between cable conductor 5 and the grounded metallic sheath 6. A similar condenser C2 is in turn bridged between conductor 5 and ground at the main receiver chassis. This latter condenser Cz is serially in eluded in a resonant circuit 5I inductively coupled by the mutual inductance M to a secondl resonant circuit 52 connected between grid and y,

cathode of tube I4.

The system comprising circuits 48, 5I and 52 4constitutes a triple tuned coupling system couthe total distributed capacity C inherent between cable conductor 5 and sheathv 6, considered as a lumped capacity. v

The magnitudes of Condensers C1 and Cz, will, of course, depend upon the cable capacity, the design of the circuits to be coupled and the degree of coupling required. For example, capaci-V ties of 500 micro-microfarads (auf) 'were found suitable for each of condensers C1 and C2 for a.4

particular installation incorporating the circuit of the drawing. The total coupling capacity was therefore in each instance that of the cable conductors plus 1000 auf.

1. In a wave signaling system: a signal translatinglcircuit tunable throughout a plurality of frequency bands, an antenna circuit spaced therefrom, said antenna circuit being capacitively rcactive at the frequencies of tuning of said tunable circuit, a pair of cable conductors extending between said circuits, and means capacitively coupling said circuits comprising, the capacity inherent between said cable conductors supplemented by capacities individual to said circuits and bridged between said conductors thereat respectively. i

`2. In a wave signaling system, a circuit, means for tuning saidcircuit throughout a plurality of frequency bands, an antenna circuit remote therefrom, said antenna circuit being capacitively reactive at the frequencies of tuning of said tunable eircuit, a pair of cable conductors extending between said circuits,- and means capacitively.

coupling said circuits comprising, the capacity inherent between said cable conductors supplemented by the capacityA of condensers individual to said antenna and tuned circuits respectively,

said condensers being bridged between oppositei terminals of said cable conductors. f 3. In a wave signaling system, a circuit tunablethroughout a plurality of frequency bands by a variable condenser, a plurality of coils and switching means for connecting in said circuit a coil appropriate to each of said frequency bands,

- an antenna circuit remote from said tuned circluding two conductors surrounded by a third conductor, means capacitivelycoupling said antenna circuit to the input circuit of one of said units comprising the capacitance between one of said two conductors and said third conductor and additional capacitance bridged between said one of said two conductors' and said third conductor,

and means capacitively coupling the output circuit of said one of said units to the input circuit of the other of said units comprising the capacitance between the ,othenof said two conductors and said third conductor and additional capacitance bridged between lsaid other of said -two conductors and said third conductor.

JOHN vKELLY JOHNSON.

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