US2186099A - Radio receiving apparatus - Google Patents

Description

Jan. 9, 1940. F. CUTTING El AL RADIO RECEIVING APPARATUS Filed Spt. 15, 1937 7 Sheets-sheaf 1 A 1 RE 405N200 UZEDZ F m |u my? wokwmamn MsEzEEuwHQ ME L 6 w 11 w N C. M in u w M F n H Homhzoo Uwo V whim MHVGZ mH #w Jan. 9, 1940. F. CUTTING ET AL RADIO RECEIVING APPARATUS I 7 Sheets-Sheet 2 Filed Sept. 15, 1937 L u a Jan. 9, 1940. I u ALv 2,186,099

I RADIO RECEIVING APPARATUS Filed Sept. 15, 19 57 7 Sheets- Sheet 4 TO FILHMENTS our PUT 53 LINE III].

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RADI-0 RECEIVING- APPARATUS Filed Sept. 15, 1957 7 Sheets-Sheet 5 Jan. 9, 1940. CUTTING r AL 2,186,099

RADIO RECEIVING APPARATUS Filed Sept. 15, 1957 7 Shets-Sheet a QR w. W *QN W mozmzommm 29E mwsammmw dmmw ZDHIIIOA o Jan. 9, 1940. F. CUTTING ET AL 2,186,099

RADIO RECEIVING APPARATUS Filed Sept. 15, 1957 TSheets-Sheet 1 Patented Jan. 9, 1940 PATENT OFFICE 2,186,099 7 RADIO RECEIVING APPARATUS Fulton Cutting, Bufialo, and Henry 0. Forbes and Hulburt 0. Tittle, Eggertsville, N. .Y., assignors to Colonial Radio Corporation, Bufialo, N. Y., a

corporation of New York Application September 15, 193?,Serial No. 163,944

7 Claims. (01. 250-20) This invention relates to radio receiving apparatus and more particularly to improvements in radio receivers disclosed in Matzner Reissue Patent No. 18,796, in which a flashing stop sig- M nal is provided, showing when the tuning appaany one or moreof a number of chosen stations for whichthe receiver has previously been adjusted to give such a signal, applied to receivers or" the super-heterodyne type.

For the purpose of this description, such stations are herein termed flash stations, because they may be selected by a flash signal of the receiver without reference to logs, newspaper guides, or the like, afterhaving once been adjusted or keyed in the flash mechanism of the receiver.

The increasing power and crowding of transmitting stations in the ether channels, together 20 with the increased amplification and selectivity of receivers, making increased accuracy and exactness of tuning necessary, has introduced difficulties in the manufacture and operation of vflash tuning receivers. Among these may be 26 mentioned the necessity for greater accuracy and greater flexibility in adjustment of the flash controlling mechanism, resulting from the reception of stations at points considerably closer together on the dial, and the liability of the apparatus to give a signal when no station is received, or even a signal for a different station from that being received, resulting from drifting of the oscillator frequency away from its assumed value, with" consequent mistuning of the desired flash station.

It is an object of this invention to provide a receiver with generally improved flash tuning operating characteristics, particularly of the superheterodyne type. More specifically, it is an object of this invention to provide such a receiver in which mistuning is reduced and a-greater tuning tolerance provided; with which a larger number of both local and distant stations may be easily and quickly keyed for flash tuning re- 45 ception; to provide a receiver which, when operating by flash tuning, will not respond to stations other than those previously adjusted or keyed for flash tuning, and which will be silent except when receiving a flash station, even when 50 being tuned through flash stations; to provide for simplified manufacture and adjustment of the receiver for flash tuning operatiomboth originally and in case it is desired to change the adjustment of the receiver from'one previously 55 made, as to any one or more of the transmitting ratus has arrived at theproper position to select .ing apparatus for rendering the receiver silent between flash tuning stations;

stations for which a flash tuning signal .is desired; to provide a generally improved mechanical andelectrical structure facilitating the adjustment of the receiver for a large number of flash stations and better observation of the adjustment of the receiver to any particular flash station, as well as improved observation of the entire choice of flash tuning stations, and to provide such a receiver which will operate either with or without the flash tuning characteristics,

as desired.

Still other objects and advantages of our invention not specifically stated above will be apparent from the specification.

. The features of novelty which we believe to be characteristic of our invention are set forthwith particularity in the appended claims. Our invention, however, both as to its fundamental principles, andas to its particular embodiments, will best be understood by reference to the speciflcation and accompanying drawings, in which:

Fig. 1 is a schematic or block diagram of a receiver according to our invention;

I Fig. 2 (parts a, b and c) is a detailed circuit diagram of a receiver in accordance with our invention;

. Fig. 3 is a front view of a dial of areceiver in accordance with our invention;

Fig. 4 is a sectional view of the dial of Fig. 3;

Fig. 5 is a detailed circuit diagram of the mut- Fig. 6 is an elevation view of the contact mechanism. for producing the flash signal at desired dial settings;

Fig. '7 is a top plan view thereof;

Fig. 8 is a sectional elevation of 1ines-8-8 of Fig. 6; and

Fig. 8a is a perspective view of a'tool which may be used for logging flash stations; 40

- Figs. 9 and 10 are curves illustrating the op erations of the discriminator network.

Our invention is disclosed herein by way of example, as embodied in a super-heterodyne allwave receiver arranged to operate from a com- 1 mercial source of alternating current. It will be understood, however, that this is by way of example, as certain of the principles of our invention may be'applied to battery operated receivers,.as well as to those designed to cover a greater or smaller range of frequencies, and those not involving the superheterodyne principle.

In accordance with our invention we prefer to provide a receiver having a dial of the clock type,

which a pointer moves over a-dial, all of which is exposed to view, with means for mounting tabs showing the call letters of the various stations, and a travelling flash signal light mounted in position to selectively illuminate any one only of the call letter tabs at a time; with means for controlling the oscillator frequency to provide for exact and precise tuning of the desired signal over a considerably greater dial setting than would otherwise be possible; with simple means for preventing or reducing response of the loud speaker except when the receiver is tuned'to a flash sta tion (herein called muting) with selective controls for eliminating or affording flash tuning as may be desired; with the circuits arranged to prevent sudden and violent crashes of sound when a station is tuned in, but to cause it to build up to desired volume relatively slowly; and with improved correlation of controls to permit the desired features of operation to be obtained with a simple set of operating controls.

For purposes of clarity, the receiver will first be described as a whole, and its operation described generally, after which the various parts will be described more in detail.

Referring now more particularly to Fig. 1, l designates any suitable form of antenna from which a signal voltage is drawn, and which may be amplified at its own frequency in an amplifier with which there may be associated selecting circuits of any desired type. After the desired amount of amplification, the signals are fed to a mixer or first detector tube and mixed there with beat or heterodyne currents from an oscillator, and from which they emerge at a lower frequency (so-called beat or intermediate frequency) and are then amplified by lower frequency amplifier to the desired extent at the beat frequency.

These further amplified signals are then applied to a discriminator and detector network, the construction and operation of which will hereafter be described in greater detail. At this point, it sufiices to note that the discriminator and detector network has a pair of output circuits, to one pair of which it supplies audio frequency or Voice currents derived from a second detection or demodulation of the signal, and to the other of which it supplies a direct current voltage similarly derived, herein termed oscillator frequency control voltage, Ed, the magnitude of which is proportional, within limits, to the deviation of the intermediate or beat frequency being received from the calculated or design value, and the sign of which corresponds to the direction of such deviation.

For example, if the predetermined value of the intermediate frequency is 465,000 cycles, and the oscillator frequency so adjusted with reference to the incoming signal that the difference is exactly 465,000 cycles, the oscillator control voltage Ed will be zero. If the frequency difference between the signal and oscillator frequencies increases, because of drifting of either or both or if the dial be slightly mis-tuned, the voltage Ed will become, say, positive, and will increase in magnitude with increase of frequency difference, within limits Which may be chosen as hereinafter explained.

On the other hand, should the frequency diiference between the incoming signal and oscillator decrease, because of such drifting, or mistuning, Ed will become negative, and its magnitude will increase in value with the amount of departure, within the limits for which the design is chosen.

This oscillator control voltage is applied to an oscillator frequency control circuit, operating in a manner to be hereafter described in detail, to cause a correction of the oscillator frequency by an amount such as to keep the intermediate frequency always at or very near the value to which the intermediate frequency portion of the receiver is resonant for any particular station.

The audio frequency output of the detector and discriminator network is. supplied to a suitable audio frequency amplifier and after amplification, to the extentdesired, to a suitable signal indicator such as loud speaker L. S.

For flash tuning, the dial H is constructed to receive a plurality of tabs Ila, lib, I la, etc., at various positions on the dial at which flash stations are received, as indicated by the pointer II, and these tabs carry the call letters of the particular station received at that dial setting.

In addition, we prefer to provide flash control apparatus, in the form of a dummy dial or comb l3, and a dummy pointer l3 carrying spring finger l3a, relatively movable with respect to each other, and synchronized with the dial and pointer, upon which the user may setup the adjustments to operate the flash signal at any desired dial settings.

Carried by the dummy dial or comb there are provided a number of contact fingers l3'a, [3b, H30, etc., arranged to make contact with spring finger l3'a carried by the dummy pointer and thus to close a circuit between the comb and the spring finger at predetermined dial positions. The position of the various fingers ISa, b, 0, etc., is selected to correspond to the dial settings at which various flash stations are received, so that a circuit is closed between the dummy dial l3 and spring finger l3a at each position of the dial at which a flash station is received, there being one such position only for each flash station, and the position of each flash station being different from that of other flash stations, as will be understood.

When the circuit between comb and finger is closed at the position corresponding to that of a flash station, a circuit is operated including the flash indicator, which may be a lamp l6 whose movements are synchronized with those of the that point.

Preferably, the apparatus is constructed, in ways which will be described in more detail hereafter, so that the receiver is mute when adjusted for flash tuning, except when the dial is set for a flash tuning station. When the circuit is closed between comb and spring finger, the flash indicator lamp IE is energized, and circuits are operated which voice the receiver, so that when a tab is illuminated to show a particular flash station being received, the loud speaker will reproduce the program of that particular station.

While the receiver is in a transition stage, being tuned away from one flash station to another, little or no response will be received, from other stations, or from static or noise. When the position for another flash station is reached the flash indicator will light, and the receiver will be voiced. However, in our preferred embodiment, it will not immediately begin to play, because a time lag is introduced by apparatus hereafter to be described, which does not permit the receiver to come instantly up to the volume level to which it is set, but delays and graduates its response for blasts of sound issuing suddenly from the loud speaker, and also permits tuning from one flash station through one or more intervening flash stations to the particular flash station then desired, without any-response from intervening flash stations.

The correlation of the design of the discriminator network and control tube with that of the closure range of the comb and finger permits the desired flash station to be perfectly tuned over a considerably greater dialrange than would be otherwise possible, and provides a latitude of adjustment-for each dial setting which would otherwise be impossible to obtain.

Referring now more specifically to Fig. 2,

I represents an antenna, which-may be of, the

usual T or L type, or'one section of a doublet,

. and 2 the other section of the doublet. 3a, 3b, 3c,

3d, 36, 3], 39, 372, and 32' represent various sections of the wave-change switch which are operated in synchronism by a common control, to select the wave band desired to be received, sections 3a and 3b being associated with the antenna system,

' 3c and 3d being associated with the antenna system, 30 and 3d being respectively associated with the input and output of the R F amplifier preceding the'mixer or translator tube, 3e with the input of the translator, '31 with the plate side of the oscillator, 3g with the grid side of the oscillator, and 3h and 3i with the flash tuning control. I

As shown, the switching system provides for four bands,-of which the broadcast is the lowest in frequency and they receiver is shown with the switches in position to receive that band. As the switches are rotated in acounterclockwise direction as observed in Fig. 2, the band frequency progressively increases, the inductances and and that such blades rotate with such angular reas a doublet, the current path to ground being opened by wave change switch 3b, and section 2 being merely tied to section I as a capacity through coil 50, which latter coil has no substantial effect at such frequencies. For the next higher band, the path to ground from section -2 is still opened by switch 3b, and section 2 is tied tosectionl through coil 5d. For-the two highest bands, however, the path to ground from section 2 is direct,'and it will be noted that circulating currents between the two sections I and 2 can .fiow through coils 50 or 512 for the two higher positions of thewavechange switch, whereas for the two lower frequency positions of switches 3a and 3b, the two sections I and 2 :feed in parallel to the set through coil 5a or 5b.

The feed from coils 5a, 5b, 5c, and5d is shown as by inductive coupling to coils 6a, 6b, 6c, and 6d respectively in the grid circuit of the r. f. amplifier tube I I, the tuning circuit in each case being formed by one of the latter coils and its associated trimmer condenser shown adjacent but not numbered, and by tuning condenser, section I M, in parallel therewith, which condensers'ectionis one of the sections ofthc three-gang tuning condenser, consisting of sections I la, 14b, and I 40, by

which the desired station is selected.

It will be-noted that for the two lower frequency bands,condenser I4'a" is short circuited'by the right hand segmentof switch section 30, but for the two higher hands, it is connected in series with condenser Ma between the control grid of amplifier tube II and ground, thereby reducing the effective capacity of condenser Ma.

Radio frequencyamplifier tube II is indicated as a pentode, but other typesof tubes may be employed if desired. The-anode or plate I Ie is preferably connected totheblade of wave change switch section-3d, thence through'coils .Ia, lb, 10, or Id, and to the conductor marked plus B line, depending on the position of the wave change switch. t

The cathode of tube It maybe connected to ground through resistances I5 and I6 in series and alternating currents by-passe'd to ground through condenser II. Resistance I6 may be short-circuited in one position ofthe section I'Ia of flash and selectivity control switch, the purpose and operation of which will be hereafter explained.

Control grid III) is preferably connected to the upperterminal of condenser Ida, whence it receives the signal voltage tobe amplified. The

screen grid He may be connected toa source of positive potential less 'positivethan the plate, and the suppressor grid I ll) to the cathode as customary; I

' Coils Ia, lb, 10, and Id are coupled, preferably inductively, to coils 8a, 8b, 8c, and 8d respectively, and, similarly to the input circuit of tube I I, each coil may have its" trimmer condenser associated with it, and be tuned by section Nb of the gang tuning condenser. Condenser It?) is arranged similarly to condenser Ma and has a simliar purpose. I 1 I I Aswillibe understood the circuit so far functions-as an amplifier of incoming signals at their own frequency, the various circuits being bandtuned or broadly made responsive to frequencies .in the desired band bythe Wave-change switch,

and the input circuits of tubes II and I2 being more or less sharply tuned by the sections of the gang tuning condenser. i I The frequency of the signals may be now lowered in tube I2, which is hereinshown as a tube of the known pentagrid converter type, having cathode I2a, electrodes I21), I20, IZd, .I2e, and,

I21, and anode or plate I2g. This tube is not connected in the usual manner for such tubes, but electrode I 273 may be connected "to function as a control electrode by being connected to the upper terminal of condenser 'I lb to receive signal voltage. Electrodes I20 and I2e may be connected together and to the screen return line, to which I I0 is connected. Electrode I2d may be connected to the oscillator and oscillator control circuit in a manner to be hereafter more fully described, and received therefrom the oscillator frequency, oscillations which are. mixed with the incoming signals to produce'the beat frequency currents.

At this point, it may be noted that coils 6a, 6b, 6c and 6d may be connected through resistance 59 to the grid return line, connected to ground through by-pass condenser 19a. Similarly, coils 8a, 8b, 8c, and 8d may be connected to the grid return line on the opposite side of resistance 59. The connection of the gridreturn line and its operation will be described hereafter.

Electrode I'Zd may be connected to ground through resistance I9, andthe common point of coils 8a, 8b, 8c, and 8d maybe connected to the ground point ofresistance l9 through by-pass condenser 20.

The plate l2g may be connected through output coil 220., with its associated trimmer condenser, not numbered, to the plus B line, and through a by-pass condenser to ground.

The currents of lower or beat frequency are fed to coil 22b coupled to coil 22a, and which may have connected in series therewith coil 24 and re sistance 25. The trimmer condenser, not numbered, may be connected to the upper terminal of coil 22?), and to the blade'of section 11b of the flash and selectivity switch, the first and second (clockwise) contacts of which section are connected to the lower terminal of resistance 2601,, while the third is connected to the lower terminal of coil 22b. The effect of this is that when the flash and selectivity switch is on the first two contacts, the tuning is broader than when the switch is on the third contact. Itwill be understood that this circuit is tuned to the beat frequency instead of to the actual signal frequency.

The beat or intermediate frequency amplifier may comprise one or more stages such as tube 23, herein shown, like tube II, as a pentode, having cathode 23a, control grid 23?), screen 230, suppressor 23d, and anode 23c. Control grid 231) may be connected to the upper terminal of coil 22b, screen 230 to the screen return line, the suppressor 23d to the cathode, and anode 23c through coil 24a and its associated trimmer condenser to the plus B line. Cathode 23a may be connected through self-biasing resistance 26a shunted by by-pass condenser 2b to ground.

The intermediate frequency currents flowing in coil 24a are supplied to coil 2% in the well known manner, and thence to the discriminator and detector network, through coilMc connected in series with coil 2%, and adjustable tuning condenser 25, and the common point of condensers 25 and coil 24c maybe connected to the grid return line. Coils 2t and 21 (which are preferably identical) may be connected in series, and shunted by adjustable condenser 28 and by adjustable condensers 29 and 38 in series, the intermediate point between said condensers being grounded. Coil 2&0 may be inductively and reversely coupled to coils 26 and 21 respectively and a direct connection may be provided between the upper terminal of condenser 25 and the common point of coils 26 and 21.

Two rectifiers may be provided; 1 .e., tubes 3| and 32, here indicated as triodes, although diodes may be employed. The tubes may comprise cathodes em and 32a, control grids 3i?) and 32b, and anodes tic and 320, the cathodes being connected through condenser 33, and the anodes through resistance 3d and 35. The anode of tube 32 may be grounded as indicated, and the anode of tube 3i connected to the oscillator control tube line and to switch contact it, which latter circult is described. later. The anode of tube 2! supplies the oscillator frequency control voltage Ed, through resistance 36, and the latter is connected to ground through by-pass condenser 3'].

The mid-point of resistors 34 and 35 supplies the audio frequency signal resulting from ilemodulation of the intermediate frequency signal, which audio frequency signal may be further amplified by the audio frequency amplifier.

The operation of the discriminator and detector network will now be described. The secondary system consisting of coils 24b, 24c and condenser 25 in series is tuned to the best frequency and the tertiary system, comprising coils *26 and Hand tertiary tuning condenser .28, in parallel with which are condensers 29 and 30 in .series and the various capacities of tubes 3| and 32, is likewise tuned to the beat frequency. f

In such an arrangement, the voltages developed at resonance in coils 2t and 21 are 180 displaced in phase (because the direction of coupling to coil 2 30 is reversed between them) and both said voltages are displaced with respect'to the voltage incoil 24b.

Because of the connections, it will be seen that tubes ti and 32 rectify respectively the vector sums of the voltages across coils 240, 2% and 25 (tube 32) and coils 2%,2417, and 2? (tube 32), which voltages are 90 displaced in phase. One of these voltages maximizes below resonance, as in curve A, Fig. 9; the other maximizes above resonance as in curve B, Fig. 9. Which does which depends on the direction of the respective couplings between secondary and tertiary systems.

If these two tertiary voltages be separately rectified and then combined, the resultant voltage curve has the form shown by the full and dotted line curves of Fig. 10, the direction of slope being determined by the direction of coupling between secondary and tertiary. This voltage, it will be seen, is proportional in magnitude and corresponds in sign to the directionof the departure of the beat frequency currents from the frequency to which the system is tuned; i. e., the design frequency of the secondary and tertiary system, which is the desired beat frequency.

This departure may be caused by drifting of the transmitter or oscillator frequency or both, or other causes but in any event, it may be utilized to control the oscillator frequency to cause a corresponding correction which will restore the beat frequency to thedesired value, and thus maintain the desired signal exactly in tune.

How this may be done will now be explained. The local oscillations may be generated by oscilla tor tube 38, which may be a triode, or other type oi tube, herein shown as having a cathode 38a,

The grid may control grid 33b, and anode 380. be provided with grid leak 3Q connected to grid, cathode and ground, and grid condenser ii).

The grid circuit may comprise any one of coils 8a, 9b, 90, or 9d, selected by section 3g of the wave-change switch, and the plate circuit the appropriate one of coils llla, lb, [60, and llld similarly selected by section 3 of the Wavechange switch. Each of these coils may be grounded through its appropriate adjustable condenser and shunted by its appropriate trimmer condenser, not numbered, and each may be inductively coupled to its corresponding grid coil 9a, 9b, 90, or tel.

This system as will be understood, forms a feed back oscillator, and it will be noted that it is tuned on the plate side, rather than the grid side, as customary. This has been found to increase stability of the oscillator and lessens the disturbance which We call motor-boating.

It will be noted that variable tuning of the oscillator frequency for station selection is obtained through small capacity condenser 69, to the third section Me of the three-gang tuning condenser, which is in parallel with the oscillator plate coil. In the lowest frequency position of the wave-change switch, (farthest clockwise) adjustable condenser 4| is in series with tuning condenser section Mc and serves to reduce its effective capacity, and in the next two higher positions it is shorted out, having no efiect while in the highest frequency position (farthest counterclockwise) it is again in series with the tuning condenser section Mc, reducing its effective capacity.

The anode of the oscillator tube '38 is preferably connected to the plus B line through resistances 42 and43, the mid-point of which is grounded through condenser 44.

stant at all times in spite of drifting of either signal oros-cillator frequency, or both, or of inaccurate tuning.

- While-various types of tubes maybe used for this purpose, we prefer to use a pe'ntode, comprising cathode ,.control grid45b, screen grid 45c, suppressor 45d, and anode 45a, The anode 45c may be connected to the upper terminal of coil Him and to the cathode 45b: through resist-, ance 45 and condenser 48. I I

Condenser 41 may be connected from control grid 45b tothe common point .of' condenser 48 and resistance 46, and said-grid may be likewise connected through resistance 52 to the anode of tube 3i which furnishes the oscillator frequency control voltage. Cathode 45w may begrounded through resistariceld forself-biasing, by-passed by condenser 50.

The operation of tube 45 is as follows: Assum ing a voltage across inductance Illa, that voltage will also be across resistance 46 and condenser 48, which are in "effect in' paralleltherewith (the series condensers between coil Illa and cathode 45a and ground being in. effect of no impedance for the oscillator frequency) and the phase will be the sameas thatacross condenser 41, which has oneterminalqconnected to con denser 43. Condenser 48 may be very small compared to condenser 41 (1,000 m. 'm'. f. for it and 15 m. m. f. for 48) and resistance 46 of the order of 50,000 ohms.

Under such conditions, the-voltage across coil and condensers 41 and 48;, and thecurrent through coil Ida will lag the voltage across coil Illa by substantially but: the 'current through resistance iti and condenser 48 will be substantially in phase with the impressed voltage (the resistance of 45 being high with respect to the impedance of condenser 48. The voltage across condenser 48,.and also condense'r 41 will lag the current in those condensers by substantially 90. The voltage across condenser 41' is in effect that between the cathodeand control grid,

of oscillator frequency controltube 45,-and is therefore, out of phase with-the current in coillfla. i

The tube plate current is in phase with the control grid voltage, since the tube plate impedance may be regardedasa resistance, andthe voltage drop across it due to change in they plate current is in phasewith the control voltage, and

hence with the volta'ge across inductance inc. 1

Illa. will also be in effect acrossresistance .46

The current through tube 45 is, however, conv trolled by thevoltageE increasing or decreasing as that voltagedeparts from zero,

Thus, the tube may be effect regarded as either a variable inductance or a variable condenser, the inductance" or capacity of which varies with the voltage impressed upon it, and as such, corrects any; deviation in the oscillator frequency produced by oscillator 38, or changes the oscillator frequency when the beat frequency .19,

changes" because of drift of signal frequency, within limits determined by the circuit constants, and thus maintains the beat frequency at or very near the desired value, and preserves exact tuning under conditions whereit would otherwise not existr It will ordinarily e desirable to control the gain of the radio frequency amplifier end of the I receiver inversely in proportion to the strength speaker, This maybe done by separatingcthe audio frequency currents to some extent from the demodulated current output of the discriminator and detector network, and thus obtaining applied as a bias voltage to the control grids of tubes H and I2 to-regulate their gain.

This may be done by filtering the demodulated output of the discriminator and detector network, by feeding the demodulated currents through resistance-capacity filter made up of resistance 55, shunted by condensers 56 and 51 in series, the common point of condensers 56 and '5? being grounded. .-Audio frequency currents may .then be drawn from the common point of resistance 55 and condenser 51, while morenearly pure direct current may be drawn from the common point of resistances 35 and 55, and ap-' plied as agrid bias to tubes H and 12, through the conductor marked grid return line, in series in ,whichmaybe provided resistances 58 and, 59. Resistance 58 may be very high, as 1" megohm, resistance '59 somewhat lower, as- 100,000 ohms.j I

As will be understood, the stronger the signal, a

the greater will be the negative bias applied to the control grids of tubes l l and 1-2 and the lower their gain will be.

The audio frequency currentsmay be further amplified bythe first A. F. amplifier tube 60, which may be a triode if desired. Manual volume control may be obtained in an'y suitable mannenfor instance by passing the audio frequency currents to ground through condenser 25, va more nearly pure direct current, which may be 6| and resistance 62 in series, and tapping'ofi the desired-part of the audio frequency voltage drop through resistance '62 by adjustable contact 63, connected through condenser 66 to the con-' trol grid of tube 60. i

,A second stage of audio frequency amplification may be providedby tube 64, also shownas a triode, although anysuitable type may be .em-

ployed, coupled to tubeBB in any suitable man-'- ner, as by condenser 65 and resistance 66,'which latter may be grounded as 'tshownl Tonecontrol maybe provided by condenser 61 connected between ground and an adjustable point on resistance (i6 and operating in the known manner.

A third or outputstage of amplification has been shown, employing a phasechanger tube 61 and avpair'of output tubes of the 6N6G type, 10

and ll feedinga-loud speaker 12, but since these Wheaten se, and their circuit connections are of received signals, to maintain amore or less constant volume output level from the-loud well known in the art, they are not described in detail.

A rectifier and filter system for supplying direct current to the various tube electrodes is also shown on the drawings, but since this part of the operation of the discriminator and oscillator fre-" quency control tube affords more latitude in the dial settings without mistuning than would otherwise be possible. How this is correlated with the flash tuning apparatus, and how that apparatus is constructed and operated, will now be described.

The dial II is diagrammatically illustrated in Fig. 1, traversed by a pointer l I, to indicate the adjustment of the tuning elements. Positioned on the dial face at appropriate positions we provide a plurality of tabs I! a, i lb, II to, etc, each of these tabs being preferably transparent, or translucent, and having marked thereon the call letters of the transmitting station which isreceived when the pointer Il points to that particular tab, and arranged to be illuminated only at that position of the pointer.

At the same time, sufficient illumination of the dial as a whole is provided to see the setting of the pointer at all times, but without detracting from the flash signal which is given when the dial pointer reaches the position for a flash station. The details of construction by which this is made possible are shown in Figs. 3 and 4., and will now be described. 1

V In order to eliminate parallax in reading the position of the pointer, mirror zones are provided on the dial. In Fig. Sannular zones 1) and (1 may be mirror surfaces, while the other zones may be opaque in appearance. The various graduations and indications to be shown by the dial, with the exception of the call letters of flash stations, may

be etched on the rear surface of the front dial glass I39, and filled with a suitable pigment.

The front surface of the rear dial glass I36 I may then be sprayed lightly with a suitable paint,

' such as bronze, except over the areas where other coloration is desired. The layer of paint is made just sufiiciently thick so that such portions of the of the dial is preferably completely shielded against extraneous light by a housing I35, the inside of which may be painted black. To provide the mirror surface for the mirror zones, a brightly polished disk of suitable metal I3I may be mounted behind the front glass dial I39, and both may be backed up by the rear glass disk I32.

General illumination of the dial may be secured by edge effect by placing a lamp 136 within the hollow shaft 89, which is provided with narrow circumferential slotsat the plane of, the dial. Stray light is prevented from escaping the outer end of the shaft by the pointer, which is held on the end of the shaft by a cap which fits snugly in position around the shaft.

ith the dial so constructed, all figures and graduations are plainly. observable when the receiver is positioned so that the dial is'illuminat'ed is adjusted to the corresponding position.

when the room is dark and the only light is that furnished by the center light I36, which, although not observable itself, nevertheless renders the dial and pointerclearly readable.

Behind the dial, and carried by the shaft 30 there maybe provided a bracket 8! extending parallel to the pointer Iiv The outer extremity of this bracket carries a lamp socket 83, in which there is mounted a small lamp It.

A demountable opaque hood or thimble Illa may be mounted upon lamp it, and this hood 1 may be provided with a longitudinal narrow slit It?) facing the dial, to permit the light from lamp It to shine through the dial and illuminate the particular tab which is in front of lamp It, at the time it is lighted.

Extending around the rim of the dial We may provide a U-shaped strip having spring fingers 85a extending inwardly on the face of the dial, andv similar, fingers 85b extending inwardly on the rear of the dial. Preferably fingers 851) are staggered or offset with reference to fingers 85a, and the spacing and angular relation of the slots between the fingers is so arranged that the tabs may he slipped under the fingers 35a at any point on the 'periphery of the dial at which a desiredstation is received.

The outer section of the dial where the tabs are placed preferably appears opaque except at the area in front of the slit Ilia, when the lamp i6 is lighted, at which area enough light passes through the dial to render the call letters on the tab clearly legible and the appearance of such light signals that the receiver is tuned to that station.

Lamp I6 is lighted only when the tuning control is adjusted to receive any one of a number of flash stations for which the flash control is previously set or keyed. This flash control is provided by fiash control apparatus shown diagrammatically in Figs. 6, .7, and 8, and comprises a comb or dummydial I3, from the periphery of which there extend, at the positions corresponding to the dial setting for each desired flash station, teeth 53a, I31); I30 etc.

Rotatable with pointer I I we may provide a dummy pointer I3, carrying at its extremity a spring finger I3a, arranged to engage each of the teeth I311, I31), 430 etc., when the tuning control The comb I3 may conveniently be mounted on the rear plate 88 of the gang tuning condenser, as sembly by bolts 86 and 89, and the finger or dummy pointer may be secured to the rear end of the condenser shaft *3? which may project through the plate 85 for thatpurpose.

The comb is preferably constructed of two identical stampings having a periphery a little more than a "semi-circle. The periphery is notched to provide a multiplicity of teeth, I 3a, b, e, etc., and the teeth are bent over at substantially right angles to the plane of the stamping. The peripheral width of the teeth and the spacing between them is, so chosen that when the complete comb-is formed, by rivetting two stamp ings tcgetherback. to back, the teeth of each stamping lie opposite the space between the teeth of the other. I

The spring finger I3'a may be mounted on bracket 9!! angularly adjustable on arm I4 and held in adjusted position by bolt 9|. This adjustment permits the obtaining of good contact between contact v finger I3'a and such of the fingers I3a, I31), I30, etc., as may be bent out into the plane of the comb, while preventing conpractically tact between finger I3'a' and the other fingers. The closure of the circuit so made energizes the lamp I6 to give the flash tuning signal, and may the procedure is as follows: the receiver is allowed to operate for a sufficient length of time to reach temperature equilibrium. Then, with the receiver controls set for non-flash operation, the dial settings for the various stations for which flash operation are determined, the particular tooth on the comb I3 which is opposite contact portion of spring finger Ma is marked for each flash station.

The marked teeth are then bent until they extend-outwardly in the plane of the comb, and for this purpose the tool illustrated in Fig. 8a willbe found useful. It may comprise a strip of 'metal having its opposite extremities bent at right angles: in opposite directions as at- 9! and 94. A narrow slot 92 may be formed in the end Ella, which slot fits over and embraces a single tooth at a time of the comb, and permits it to be bent into contacting position to engage finger i3'a, without danger of bending teeth other than the one desired. a

With the selected teeth bent outward as ex-- plained, the receiver controls may now be set for flash operation, and the appropriately marked tabs placed under spring fingers 85a at the previously determined dial settings for the flash stations for which the receiver has been keyed. It may be noted that additional stations may be keyed at any time, in the same way, or if it is desired to eliminate from flash operation a previously keyed station, this may be done by simply bending down its tooth on the comb, and removingits tab from the dial.

It will be understood that without the use of the discriminator and detector network and'the oscillator frequency control system, the flash control system would be very critical in adjustment, because even a slight mistuning would result in side band suppression, and corresponding distortion, and this in turn would require razor edge adjustment of the spring finger I3a' with reference to the comb, which would in turn render the receiver more sensitive to drifting of the oscillator or signal frequency. The apparatus herein disclosed eliminates these difiiculties, and permits a relatively coarse adjustment of finger lt'a with reference to the comb, permitting the incoming signal to be received perfectly, without mistuning, over an appreciable width on the dial, much wider than would otherwise be possible, and thus permits quicker and easier tuning, while it eliminates the possibility of distortion resulting from mistuning. i

The circuits by which the receiver is muted between flash stations will now be described. While these circuits are included in the complete diagram of Fig. 2, for clarity they are separately shown in Fig. 5. v

The various circuitchanges which occur when a flash station is tuned in are made by the relay 1 having an actuating winding IOI, movable blades to the opposite side ofwinding 10!.

and moved into front contact (mute) position by energizing coil Il.'

The receiver is voiced when the relay is on back contact position, and mute in front contact position. When the circuit is open between finger I3a and comb I3 (mute), a circuit exists from B through the field winding I50 of the loud speaker, thence through actuating winding IfiI of the relay and resistance I03 in parallel, and through resistance I02 to ground. This attracts the relay to front contact (mute) position.

In this position, the oscillator frequency control voltage output Ed of the discriminator and detector network is grounded by blade I04, against front contact I03, the energizing circuit of lamp i6 is opened by blade I04, and blade I closing against front contact I09 applies a relatively high muting bias to the grid of the first audio frequency amplifier tube 60 through the circuit from B through resistance H0, front contact IE9, blade I05 to the lowest frequency contact of section 3h of the wavechange switch, to the blade of said section, to flash contact I2I. of section I20a-of flash and'selectivity control switch E20, to the blade thereof, thencethrough resistances I22 and I26 to the point between winding and resistance I02.

From the common point of resistances I22 an 526 to ground there may be provided condenser I24, from the opposite terminal of resistance I22 'cc-ndenser I23 to ground, and from the common point of resistances I22 and I 25 a connection through resistance I25 to the control grid of tube 60, the first audio frequency amplifier. With the muting relay on front contact position, and flash fingers I311, 13, 0, etc., of the comb, relay actuating winding IIlI is short-circuited as follows: from winding IOI through resistance I02 to ground, to the comb, to finger I3a, to low frequency contact of band switch section 32', to the blade thereof, to blade of flash and selectivity switch section I2ilb, to fixed contact in position shown, The relay is thereupon closed by spring action against its back contacts, opening the muting bias circuit at front contact I09, ungrounding the Ed line at contact 208, and closing the circuit through lamp it as follows: ground, blade I04, back contact Mil, lamp I6, secondary I08 (which may be a special transformer separate from the power value, fo-r example, one second. The effect of this is that in tuning rapidly, one may pass through one or-more flash stations in reaching the desired'flashstation, and the receiver will not respond to such stations because there is not time for condenser I24 to discharge. 7

When the desired station is reached, and the station selector left on the position for the desired station, this condenser gradually discharges and the station gradually builds up to the volume determined by the setting ofthe'volume control.

Wave change switch section 3h serves to open the muting bias circuit at positions other than the lowest frequency band, while section 32 opens the circuit around the relay actuating. winding which otherwise would be closed at flash positions of the dial, and the relay is continuously held in front contact position. This renders lamp I6 inoperative to give a flash signal, but while the relay is in muting position the muting bias circuit is now open and the receiver is voiced at any position of the dial, and the Ed line is grounded, and the correction voltage is not applied to the oscillator control tube.

Flash and selectively switch sections I2Ila and I202) which are arranged for gang operation with switch sections Fla and H17, likewise open the muting bias circuit and the circuit around the relay actuating winding respectively, just as with wave change switch sections 3h and 31', although the flash and selectivity gang switch is operable independently of the wave change switch.

S0 arranged, flash tuning is available only on the broadcast band, but it will be understood that switches, 3h and 3i may be omitted if flash tuning is desired on all bands.

It will be observed that in the arrangement shown, flash tuning is available only in the broadly tuned condition, as established by switch section Ill), and that with flash operation, the receiver operates at maximum sensitivity as established by switch section Ila, but it will be understood that we may omit switch sections I291; and I20b if desired, or arrange them so that flash operation may be had for both broad and sharp tuning, or either, as desired.

While we have disclosed certain preferred embodiments of my invention, it will be understood that modifications and changes may be made Without departing from the spirit and scope of our invention, as will be understood by those skilled in the art.

We claim:

1. In a tuning indicator for a radio receiver or the like, a tuning element, means for adjusting said tuning element, a luminous indicator carried by said adjusting means for movement there'- with, means for silencing the receiver during tuning operations, and means actuated by said adjusting means for simultaneously energizing said luminous indicator to indicate the tuned condition of the receiver and rendering said silencing means inoperative.

2. In a tuning indicator for a radio receiver or the like, a tuning element, means for adjusting said tuning element, a luminous indicator carried by said adjusting means for movement therewith, means for silencing the receiver during tuning operations, means actuated by said adjusting means for simultaneously energizing said luminous indicator to indicate the tuned condition of the receiver and rendering said silencing means inoperative, said last mentioned means having a time delay means incorporated therein whereby the receiver may be tuned through a relatively strong signal without producing audible response thereto.

3. In a tuning indicator for a radio receiver or the like, a tuning element, means for adjusting said tuning element, a luminous indicator carried by said adjusting means for movement therewith, means for silencing the receiver during tuning operations, means actuated by said adjusting means for simultaneously energizing said luminous indicator to indicate the tuned condition of the receiver and rendering said silencing means inoperative, electrical means for maintaining the tuning of the receiver at the frequency selected initially by operation of the tuning element and operating automatically to correct for frequency drift.

4. In a tuning indicator for a radio receiver or the like, a tuning element comprising an oscillator, means for adjusting said tuning element, a luminous indicator carried by said adjusting means for movement therewith, means for silencing the receiver during tuning operations, means actuated by said adjusting means for simultaneously energizing said luminous indicator to indicate the tuned condition of the receiver and rendering said silencing means inoperative, and

means inoperative, said last mentioned means comprising an electro-magnetic relay.

6. In a tuning indicator for a radio receiver or the like, a tuning element, means for adjust?- ing said tuning element, a luminous indicator carried by said adjusting means for movement therewith, means for silencing the receiver during tuning operations, means actuated by said adjusting means for simultaneously energizing said luminous indicator to indicate the tuned condition of the receiver and rendering said silencingmeans inoperative, said last mentioned means including an electro-magnetic relay, biased to voice the receiver and electro-magnetically actuated to silencing position.

'7. In a tuning indicator for a radio receiver or the like, a tuning element, means for adjusting said tuning element, a luminous indicator carried by said adjusting means for movement therewith, a switch having an element carried by said adjusting means for movement therewith and arranged to be closed at predetermined positions of said adjusting means, means for silencing the receiver during tuning operations, means actuated by said adjusting means -for simultaneously energizing said luminous indicator to indi-- cate the tuned condition of the receiver and rendering said silencing means inoperative, said last mentioned means including an electro-magnetic relay having an energizing coil short circuited by closure of said switch.

FULTON CUTTING.

HENRY C. FORBES.

HULBURT C. TITTLE.

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