US2262218A - Radio receiver - Google Patents

Description

Nov. 11, 1941. E. F. ANDREWS RADIO RECEIVER Filed July 18, 1958 4 Sheets-Sheet l iv m. a

III l e 5 I QWA; w Jifarzgg Nov. 11, 1941. ANDREWS 2,262,218

RADIO RECEIVER Filed July 18, 1938 4 Sheets-Sheet 2 MJWA, WZQ? Nov. 11, 1941. E. F. ANDREWS 2,252,213

RADIO RECEIVER Filed July 18, 1938 4 Sheets-Sheet 5 I62 I73 I76 I74 177 Mora? HMC idea 22.-

Nov. 11, 1941. ANDREWS 2,262,218

RADIO RECEIVER :5 Filed July 18, 1938 4 Sheets-Sheet 4 Patented Nov. 1 1, 1941 UNITED STATES PATENT OFFICE RADIO RECEIVER Edward F. Andrews, Chicago, Ill. Application July 18, 1938, Serial No. 219,713

- without taking his hand from the wheel, while 20 Claims.

This invention relates to devices for tuning radio receivers in which tuning is effected by power means adapted to be set in operation by manually actuated means and adapted automatically to be rendered inoperative when the receiver has been tuned to the carrier wave of a broadcasting station received with sufllcient strength. I call this general type of station selection stop-oncarrier tuning. The manually actuated means suitably comprises means controlling the change of an electric current or voltage and may be located at a point remote from the receiver. For example, it may be a manually actuated switch which is preferably located in remote relation to the receiver, being connected thereto by means of a cable.

The invention also relates to means for securing the proper timing and for equalizing and narrowing the electrical impulses which cause automatic stoppage on the carrier to effect more exact and uniform tuning.

The invention is very advantageous for tuning all varieties of radio receiver. It facilitates remote control and provides simple automatic tuning which does not require manual adjustments for setting up pre-selected stations.

The invention is very advantageous for effecting automatic tuning for automobile or other portable radio receivers where the receiver may be moved out of the vicinity of certain broadcasting stations and into the vicinity of others. As the form of automatic tuning of this invention will tune in the stations whose carrier waves are of sufllcient strength to cause stoppage of the power means driving the tuning element, it is not necessary to re-set the device to tune in a new set of stations when the geographical location of the receiver is changed. The device automatically tunes in the stations broadcasting carrier waves of suflicient strength, regardless of what particular stations they may be, within the tuning range of the receiver.

As tuning from one station to another is effected merely by pressing a button, the tuning operation may be performed by the driver of an automobile without taking his eyes from the road. He may simply continue to operate the tuning button until he hears the desired station. This greatly enhances the safety of radio receiver operation by the driver of an automobile. As only a button or switch connected to the receiver by two small flexible wires is required for performing the tuning operation, this can be very conveniently mounted directly on the steering column, where the driver may operate it the receiver may be mounted at any other suitable location in the automobile.

The invention is, of course, also adapted to the automatic tuning of stationary or home types of receiver, and also may be remotely operated in other ways. Also, many of the features described in connection with automobile sets are similarly advantageous for home receivers.

The invention will readily be understood from the following description of preferred embodiments thereof, taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a wiring diagram of a radio receiver embodying my invention.

Fig. 2 is a graphical illustration of tuning curves illustrating voltages obtained in certain circuits of the receiver in Fig. 1, shown plotted against frequency.

Fig. 3 is a partial wiring diagram illustrating tuning control means adapted to start the rotation of the condensers in either of two directions, and showing a modification of part of the circuit shown in Fig. 1.

Fig. 4 is a modification of the arrangement of Fig. 1, in which the motor circuit is opened by the relay spring.

Fig. 5 is a further modification of this invention Employing very powerful automatic gain conrol.

Fig. 6 is a partial wiring diagram of an alternating current radio receiver embodying a combination of features of Figs. 1 and 5.

Referring to Fig. 1, the receiver shown is a superheterodyne receiver. Specifically, it represents the Philco superheterodyne receiver built expressly for the 1938 Ford automobile. It will be understood that this receiver is shown by way of example only, since the present invention may be applied to any superheterodyne or to any other radio receiver.

The receiver comprises an antenna ID, a radio frequency amplifying tube II, which is a No. 78 tube; a first detector and oscillator tube l2, which is a No. 6A7 tube; an intermediate frequency tube l3, which is a No. 78 tube; a diode detector and first audio tube H, which is a No. tube; a power tube H, which is a No. 42 tube; a speaker l6; and a "78" power supply, designated by the reference numeral 11, which includes a rectifying tube ll, which may be a No. 84 tube. Energy is supplied to the set from the battery it, being controlled by a switch 20, which is physically connected to the volume control 2|. The set includes transformers and other radio devices of conventional nature which need no particular description. The set is tuned by a gang 3! of three condensers which serve to tune the antenna circuit, the grid circuit of the first detector i2, and the oscillator circuit. The rotors of the condensers are mounted on a shaft 23 which rigidly carries a gear 21. The gear 24 is driven by a. worm 23 mounted on a shaft 23, which may beprovided. with a knob 21 for manual tuninc. r

To provide for the mechanical drive of the condensers, I rigidly mount on the shaft 26 a gear 23, which gear meshes with a pinion 23 which is carried by a short shaft 30. The shaft 30 carries projecting clutch elements 3| which are adapted to be engaged by corresponding clutch elements 32 on the shaft 33 of a reversible motor 34. The armature of the motor 34 is biased away from the shaft 34. This may suitably be done by brushes 34' which bear'resiliently against the armature. When the motor 34 is energized, the flux moves the armature against the tension of the brushes 34' so that its clutch elements 32 are moved into the path of the clutch elements 3|. Immediately the motor is de-energized, the brushes 34- move the clutch elements 32 out of the path of the clutch elements 3| so that the inertia of the armature does not tend to make the condenser overrun. In this way, the tendency of the condenser to overrun is substantially limited to the inertia of the condenser rotor and the drive means connected therewith.

While any type of reversible motor 34 may be employed, in the embodiment shown I employ a direct current reversible motor having two windings 35 and 34, both of which are connected by a lead 31 to the battery lead 33. This connection is located on the side of the switch 20 remote from the battery I9. I prefer to connect a grounded condenser 33 to the lead 31 to attenuate high frequency disturbances. The other ends of the windings 35 and 36 are connected by means of conductors 40 and 4! respectively to a single pole, double throw snap switch 42. This switch is also connected by a conductor 43 to a contact 44 of a relay 45. The snap switch 42 serves to connect the conductor 43 to one or the other of the windings 38 and 36 so as to cause one or the other of these windings to be energized to rotate the motorin one direction or in the opposite direction. The switch 42 is adapted to be thrown in one direction or the other by means of pins 48 and 41. Thus, when the switch 43 is in the position shown in Fig. 1, the winding 35 willbe energized so as to cause the motor to drive in the direction corresponding to the arrow shown on the gear 24. When the motor has thereby moved the condensers almost to their extreme position, the pin 46 engages the switch 42 and snaps it so as to connect the conductor 43 to the winding 36. Consequently, the direction of rotation of the motor 34 is reversed and the drive will occur continuously or intermittently, as will hereinafter be more fully explained, until the pin 41 throws the switch 42 back into the position in which it is shown in Fig. 1, again reversing the direction of rotation of the motor. It may here be noted that the movements of the condenser are interrupted when the set is tuned to stations of predetermined strength and are resumed by manual actuation. The movement of the condensers occurs, however, in progressive steps until they arrive at an extreme pomtion, whereupon the direction of rotation of the motor is reversed and the successive step-by-step movements of the condensers are executed in the opposite direction.

The armature 48 of the relay 4! is adapted to engage the contact 44 and also the contacts 49 and 53 when it is in the position shown in Fig. i.

'It is biased to this position by a'spring 5!. When the relay 45 is energized to a sufilcient degree, the armature 43 is withdrawn from the contacts 45, 4!, and Ill. The armature 48 is grounded and the contact 44 is connected through a resistor 52 and condenser 53 to ground to prevent arcing and sticking at the contact 44.

The winding of the relay 45 isconnected to one of the plates 54 of a tube 55, which is a 6F8-G, having two cathodes 53 and 51, a plate II which is associated with the'cathode 56, a grid II which cooperates with the cathode 56, and another grid 80 which cooperates with the cathode I1 and plate 54. This tube is employed as a diode-triode tube, the plate 33 being connected to the cathode 56 which is connected through a condenser 61 to ground. The grid 43 is by-passed through a condenser 33 toground and is connected through a resistor 63 to the cathode 53. The cathode 53 and the resistor 63 are connected through a resistor 84 to the contact II. The contact 53 and the resistor 84 are connected through a resistor 33 to a resistor 66, which is connected to the cathode of the tube 15. The cathode of the tube I5 and the resistor 86 are connected to a conductor $1. The other end of the resistor 66, that is, the end which is connected to the resistor 35, is connected to a re sistor 63, which is grounded. The cathode 5'! is connected to a conductor 39.

The conductors 61 and 63 pass through a cable II which may be of any suitable length to provide a suitable location for one or more operating switches 'H These switches are normally closed and they are effective so that when either of them is opened, the motor 34 is started and it continues to operate as long as the switch or ceivers in the home, and the cable 14 may be of any desired length so that the radio listener may occupy any position and still have complete control of the timing of the receiver.

A transformer 12, located between the intermediate frequency tube l3 and the diode detector and first audio tube i4 comprises, the usual windings 13 and 14 in close-coupled relationship, and an additional winding II in relatively loose-coupled relation thereto. One end of the winding I! is connected to the grid 53. The other end I of the winding 15 is connected to one end of the winding 14, that is, the end which is remote from the end which is connected to the two diode plates of the tube II. The winding II. is tuned by an adjustable fixed condenser 16 to the intermediate frequency.

The resistors 11 and 13 are ccnnectedby a conductor I3 to the grids of the tubes 1 i and 12 so as to apply a negative voltage thereto to automaticaliy control the volume. Resistors 73 and ll" may be included in the circuits as shown.

The effect of the automatic volume control thus applied to the tubes I l and i! has the eifect of leveling to a large degree the voltages depicted on Fig. 2, which are derived from signals of varying strength. Thus, the voltages shown in the right hand part of Fig. 2 may be derived from a signal having a signal strength at the antenna of the order of a hundred times that of the signal from which the voltages shown on the left-hand side of Fig. 2 are derived. Thus, the application of automatic volume control renders the curves 8! very similar and mults in a relatively uniform intermediate frequency s al from all received stations, irrupective of very great diif'erences in signal strength. By the use of especially powerful A. G. C., such as will be described with reference to Fig. 5, weak and strong stations may be made to produce signals of substantially similar appearance. However, when this is done, the condenser will stop with equal facility on relatively weak and strong stations alike. Therefore, some difference must be preserved between the signals if it is desired to have the condenser stop only on the stronger carriers. A sensitivity control Ill for adjusting the stop-on-carrier system to stop only at stations of a greater than predetermined signal strength is shown in Fig. 1. Moving the adjustable contact H8 upward causes the condenser to stop on weaker stations, while moving the contact H8 downward causes the condenser to stop only on stations giving a more powerful signal.

The operation is as follows:

When the set is inoperative, the relay 45 is de-energized and the armature 48 is in the position shown in Fig. 1. When the switch 28 is closed, the motor circuit is complete through the conductor 31, one or the other of the windings 88 or 86, the switch 42, conductor 43, contact 44, and armature 48 to ground. Consequently, the condensers are rotated in one direction or the other. At the end of their movement, the direction is reversed, and this condition continues until the tubes warm up to energize the relay 45 with sufficient strength to attract the armature 48 from its initial position. This occurs when the condenser is tuned to a station which will provide a signal of greater strength than a predetermined minimum. If desired, a manually operated or time delay switch 31" may be included in the conductor 8! to prevent the motor 84 from operating until the filaments have warmed up and current flows in the relay 45. The diode detector elements of the tube l4 will pass current in one direction between the cathode and twin plates of the diode, owing to their connection through the resistances I1 and 18, thus establishing a voltage drop across these resist ances. Consequently, the diode detector i4 supplies to the plate 58 a negative bias. This negative bias is shown graphically for two different stations of different strength on Fig. 2, being designated by the reference numeral 19. On the graph shown in Fig. 2, the position of resonance of the intermediate frequency signal with the natural resonance of the circuits containing the windings II and is shown on the abscissa at zero.

To provide high fidelity reception from the loud speaker it, the curve 19, which represents the selectivity characteristics of the intermediate frequency circuits supplying the detector l4, must be fairly broad at the top. The addition of the winding Ii establishes a mutualinductance between this winding and the winding 18. The

result is that the curve 18 tends to have a dual peak, as shown in Fig. 2. The depth of the depression between the dual peaks may be regulated by the degree of coupling between the windings l5 and I3. Closer coupling will accentuate this central depression. The strength of the effective signal is increased thereby, but too close a coupling will cause distortion.

It will be understood, of course, that the negative bias applied to the grid 88 which is used as the plate of the diode element in the tube 85, from the diode detector I4, does not cause current to flow in the circuit containing the diodecathode 58 and the diode plate 59. In order for such current to flow, it is necessary to apply a positive voltage to the plate 58, which is greater than the negative voltage supplied from the diode l4. This requisite positive voltage is derived from the winding 15 which is loosely coupled to the winding 18, and it is shown graphically on Fig. 2, being designated by the reference numeral 88. Owing to the fact that the winding 15 is part of a low loss circuit, loosely coupled to the windings I8 and 14 and tuned to the intermediate frequency, the curve is quite sharp. It will be understood that the curve 80 corresponds to the selectivity characteristics of the tuned circuit containing the winding 15; therefore,the positive portion of the intermediate frequency signal is impressed on the plate 59 in accordance therewith. This positive voltage is the effective voltage.

In Fig. 2, the curves 82 represent the algebraic sum of the negative and positive voltages indicated by points on the curves 1! anti 80, respectively, on the same vertical line. It will thus be seen that the curves 82 represent the voltage effective for causing rectification in the diode section of the tube 55 to impress a positive bias on the grid 60.

Referring to the left hand side of Fig. 2, it will be noticed that up to approximately two kilocycles on each side of the optimum tuning position, that is, the position of the condensers corresponding to zero position on this graph, there is no possibility of current flowing in the rectifier circuit connected to the plate 58 and the cathode 56. The same is substantially true with the case of a much stronger signal, as shown on the right hand side of Fig. 2. The horizontal line 8| on this figure corresponds to the minimum positive voltage necessary to be applied to the plate 59 to cause rectification to occur and suiiicient current to pass resulting in a suflicient positive voltage being applied to the grid 68 to cause the armature 44 of the relay 45 to break the motor circuit and stop the rotation of the tuning condenser. It is apparent that this line intersects the two curves 82 at points 83, which are close to the same distance from the optimum tuning position indicated by zero. It will thus be seen that the curves of effective voltage 82 are made of substantially equal width at the base and of fairly similar widths at an operating level indicated by the line 8| by means of this invention. The wide sloping base portion of the curve 80 is cancelled by the similar portion of the curve 19, thus completely eliminating this broad, inexact portion of the signal. It thus becomes possible to approach similar widths of signal by reducing the height of the operating level 8| by increasing the sensitivity of the relay or varying thebias on the grid 68.

It may here be pointed out that the sensitivity control H6 functions in the following manner:

When the slider H8 is moved downwardly, the

. control grid of the tube I I made more negative.

signal of certain weak stations will correspond to a curve 82 which is not high enough to reach the operating level line 8|. These stations will then not be tuned in by the stop-on-carrier system. If, on the other hand, the slider H8 is raised to a higher level, the weaker stations will produce curves 82 projecting above the operating level line 8| and will then cause the relay 48 to stop the condenser on their carrier waves. Thus. the sensitivity control 8 functions to cause the condenser to stop or fail to stop on the weaker stations, as desired.

It will readily be seen that the endwise moving parts of the motor 84 andthe gang of condensers 22 have a certain inertia which causes the condensers to continue to move for a brief interval after the motor circuit is broken. These parts can be readily constructed so that the overrun brings the condenser substantially to the position of optimum tuning; that is, the position corresponding to the zero line in Fig. 2. When the curve 82 is very narrow, it is desirable to construct the condenser drive mechanism, the disengaging clutch 8 I' and 32, and the rotating parts of the motor 34 so that the condenser will come to a stop as quickly as possible after the opening of the contacts 44. It is also desirable under these circumstances that the relay armature 48 be of small inertia and the relay as a whole be constructedior quick operation.

When the motor is running, that is, when the armature 48 is in the position shown in Fig. l, the grid 88 is about ground potential. At the same time, the cathode 51 is at a potential higher than ground, owing to the drop across the resistors 88 and 88. When, however, a voltage greater than that corresponding to the line 8I on Fig. 2 is applied to the plate 58, a current flows in the rectifier circuit, including the oathode 58 and the plate 89, which renders the grid 60 positive to a suillcient degree to induce a plate current through the winding of the relay 48 which is sufllcient to attract the armature 48 and open the motor circuit. As previously explained, the opening of the motor circuit corresponds to a point such as one of those indicated at 83 on Fig. 2, and the inertia carries the condensers on to a slight extent so that they are located very substantially to the optimum tuned position corresponding to the zero position on When the relay 48 moves away from its position shown in Fig. 1. the circuit of the contact 58 is broken, with the result that the grid 88 is made strongly positive, thus ensuring the energization of the relay 45 while that station is tuned in, notwithstanding that the signal of the station may fade below that corresponding to the line 8| on Fig. 2, or even if the station ceases broadcasting entirely.

It .will be noted that when the motor 48 is operating, the grid of the power tube I is grounded, and consequently the receiver is muted until the relay 48 is again energized to withdraw the armature from the contacts 44, 49 and 88.

terrupting the plate circuit which was energizing the relay 48. Consequently, the spring 8| moves the armature 48 into the position shown in Fig. 1 and the motor operates as long as the switch II is held open. After the-switch II is closed. the motor continues to operate until a carrier of suflicient strength to actuate the relay 45 is again received, whereupon the receiver will receive that station until the set is turned off or one of the switches II is opened. v

. The embodiment of the invention illustrated in Fig. 3 is intended to exemplify an A. C. set in which an alternating current motor 84 is employed. The windings of this motor are connected to a contact 88 of the relay 88, which is comparable to the relay 48 of the embodiment shown in Fig. 1. One pair of windings of the motor 84 are connected to a conductor 81 which is connected to a leaf 88 of a reversing switch 89. The other pair of windings are connected by a conductor 88 to another leaf M of the switch 89. Between the leaves 88 and 8| is a leaf 82 which is actuated by the armature 98 of a relay 94. The armature 93 is biased awayi'rom the relay 84 by a spring so that the leaf 92 normally makes contact with the leaf 88. The leaf 92 is connected to one end of the secondary of a transformer 88, the other end of which is grounded. The primary of the transformer 9 is supplied by alternating current from the mains, the object of the transformer 98 being to reduce the voltage to suitable proportions for the operation of a small split phase capacitor motor, such as 84. The armature 93 is also rigidly connected to a leaf 91 which is adapted to cooperate with a leaf 98. The leaves 81 and 98 are out of contact when the relay 94 is de-energized, and they are in contact when the same is energized.

The two sets of windings of the motor 84, that is, the sets which are connected to the conductors 81 and 88, respectively, are connected through a capacitor 99. It will readily be understood that when current is supplied to the lead 81, the motor 84 will rotate in one direction. whereas when current is supplied to the lead 88, the motor will rotate in the opposite direction. Consequently, the direction of rotation of the motor depends primarily on the state of energization or de-energization of the relay 94. It may here be noted that in the embodiment of the invention illustrated, the motor 84 tends to rotate the gang of condensers 22 in the clockwise direction or to the right'when the relay 84 is de-energized. When this relay is energized. the motor tends to operate to the left or in the counterclockwise direction, as viewed in Fig. 3.

The secondary of the transformer 98 is also connected to the winding of the relay 84 and this winding is also connected to a leaf I88. The leaf I88 is normally in contact with the shorter leaf III, which is connected by a conductor I82 to the leaf 81. The conductor I82 is also connected to a conductor I88, which may be one of three long conductors which may pass through a cable I84. the other two conductors being designated'lll and I88. The cable "4 may be of any suitable length and it may be provided at its end with a remote control unit designated generally by the reference numeral I81. This remote control unit may comprise any suitable container having'two leaves I88 and I88, which are normally biased into engagement with contacts III and II I respectively. The con- H2. The two leaves I03 and I33 are adapted to be actuated by two buttons H3 and H4 respectively in such a manner that when the buttons are pushed inwardly, the leaves I33 and I03 move away from the contacts III and III, respectively. When the button H3 is thus depressed, it brings the leaf I03 into engagement with a contact II5. Preferably, the contact III is somewhat resilient so that it follows the leaf I03 to a limited extent, remaining in engagement therewith until the leaf I33 has engaged the contact H5. The leaf I03 is connected to the conductor I05 and this conductor is preferably grounded at the set. The contact H5 is connected to the conductor I03. The leaf I33 is connected to the conductor I05. The conductor I06 is connected to a resistance I35, the opposite end of which is grounded.

The gang of condensers is indicated by the reference numeral 22, as in the previous embodiment of the invention. The shaft 23 of the gang carries opposite arms I I1 which carry pins H3 and H3 which are analogous to the pins 43 and 41 of the embodiment of the invention shown in' Fig. 1. It will be noted that when the condenser rotors move in the counterclockwise direction, as viewed in Fig. 3, into one extreme position, the pin H3 engages the long leaf I 00 and sepaq rates it from the leaf IOI, thereby breaking the circuit of the relay 34, allowing the leaves 32 and 31 to attain the position shown in Fig. 3 which has, as will hereinafter be more fully explained, the effect of reversing the direction of rotation of the motor and causing the condenser shaft 23 to turn in the clockwise direction. When the shaft is thus rotated in the clockwise direction nearly to the full movement of the gang of condensers, the pin II3 engages the long leaf I00 and carries the contacting leaf I 0| into contact with a leaf I20, which is normally out of' engagement with the leaf I M grounded.

The leaf 98 is connected to a contact I2I by a conductor I22. A contact I23 is located adjacent the contacts 35 and I2I so as to be engaged by the armature I24 of the relay 36 when that relay is disengaged. The armature I24 is biased into engagement with these contacts by a spring I25. The armature I24 is grounded. The contact I23 is analogous to the contact 43 of the previously described embodiment and it serves to mute the set when the armature I24 is in engagement with the contacts 85, I2I and I23 during the operation of the motor 84.

In this embodiment of the invention, I provide a diode I26, which may be regarded as one of the diodes of a No. 6H6 tube, and a D. C. amplifying tube I21, which may be a No. 76 tube instead of the diode-triode tube 55 of the embodiment shown in Fig. 1. The elements of the tubes are given the same numbers as in Fig. 1. The plate 59 of the tube I26 is connected to the tuned winding 15, which is loosely coupled to the winding 13. This, together with the closely coupled winding 14, constitutes the transformer 12 between the intermediate frequency tube and diode detector and first audio tube, as in the previously described embodiment.

The conductor I22 is connected through a resistor I23 to the cathode 56 of the tube I23. This cathode is connected to the grid 30 of the tube I21 and is by-passed to ground through a condenser I23. The cathode 51 of the tube I21 is connected through a resistor I30 to a conduc- The leaf I20 is tor I 3|, which is connected to the B supply I32 and the winding of the relay 33. The winding of the relay 36 is also connected to the plate 54 of the tube I21. The cathode 51 of the tube I21 is connected to ground through resistors I33, I34, and I35 in series. The conductor I22 is connected by the resistor I36 to the adjacent ends of the resistors I33 and I34. The conductor I33 is connected by a conductor I31 to the common ends of the resistors I34 and I 35.

When the set is inoperative, the relay 34 is deenergized and the armature 33 is in the position shown in Fig. 3. The armature I24 is in engagement with the contacts 35, I2I and I23. When energy is supplied to the receiver, which may be done by means of a switch corresponding to the switch in the previously described embodiment, current is supplied from the transformer 33 through the leaf 32 and leaf 33 to the conductor 31, motor coils, contacts 35 and I24 to ground. Consequently, the motor operates to drive the shaft 23 to the right or in the clockwise direction, as viewed in Fig. 3. When the pin I I3 is thus brought into engagement with the leaf I00, the leaf I00 and the leaf IOI are brought into conductive relation with the grounded leaf I20. The result is that the armature 33 is attracted and current is now supplied to the conductor of themotor 34, thus causing the motor to operate in the reverse direction; that is, to the left. The leaves IN and I20 separate immediately this reverse direction begins, but the relay. remains energized through the leaves I00 and IN, which are connected to ground through the conductor I02, leaves 31 and 33, conductor I22, contact I2I, and armature I24. The movement of the gang of condensers to the left is thus maintained until the pin I I3 separates the leaves I00 and IN, thus breaking the circuit of the relay 34 and allowing the armature 33 to attain the position shown in Fig. 3, which adapts the device for condenser operation in the clockwise direction. Consequently, the tuning device moves from one extreme position to the other until the tubes are heated up sufficiently to bring in a station with suiiicient strength to stop the motor, in substantially the same manner as described in connection with the embodiment of Fig. 1.

As in the previously described embodiment, no current flows between the plate 53 and the cathode 56 until the plate 53 becomes positive relative to the cathode 53. When plate current flows through the resistor I23 to ground through the contact I2I and armature I24, a certain positive potential is applied to the grid 30 so that it may become more positive. When a signal which gives a curve 32 (Fig. 2), which is greater than the voltage corresponding to the line 3|, is received, sufficient current flows through the relay 36 to energize it and the armature I24 is withdrawn from the contacts I23, I2I, and 35, and the motor circuit is broken. When the armature I24 moves away from the contact I2I, B voltage is applied through resistor I30, resistor I33, resistor I36, and resistor I23 to the grid 60, so that a still larger current flows through the relay 33, maintaining this relay energized indefinitely even if the received signal fades or ceases. The resistor I is preferably quite large in comparison to the resistors I33 and I34, but is quite small compared with the resistor I30. The resistor-I35 is not normally in the circuit of the cathode 51, since the resistor I34 is grounded through conductors I31, I06, 2, and "5, Thi ground circult is interrupted when either of the two buttons H3 and ill ispressed, with theresult that the relatively large'resistor I35 is introduced into the plate circuit, reducing the current through the relay 86 to such an extent that the armature I! is released. Itwill be noted that the switches II in the previously described embodiment open theplate circuit. In the present embodiment,

'10 this transformer, which is closely coupled tothe the introduction of the high resistance III into the plate circuit is distinctly analogous and has the same effect.

When the button H4 is pressed inwardly, it merely has the eifect of introducing the resistor E35 into the plate circuit of the tube i2'l. Consequently, the motor will operate towards the right, and if the button Ill is held inwardly, the rotor of the condenser 22 will be driven to the right, until at last the pin 8 comes in contact with the leaf Ill and starts the motor to the leit in the manner previously described; that is, through the energizatlon of the relay 94. when this relay is energized, the button ill, being still pressed inwardly, it is locked in energized relation through leaves III, III, conductor ill, leaves 91 and 98, conductor [22, contact ill, and armature [24. I! the button Ill is still maintained pressed, the pin ill breaks the circuit of the relay 84 and movement of the condenser to the right is again resumed. If, at any point of so the cycle thus described, the button Ill had been released. the motor would continue to tune thesetuntilanarresting carrierwastunedin. Thisarrestingcarrierwouldresultinencrgila tion of the relay 8', the stopping of themoior II, and the de-energization of the relay ll, if it were in a state of energization.

Ashaspreviomlybeenremarkedthe contact I preferably follows the leaf Ill when the button illispressedinwardlyuntilthe leaf "I hasengagedthecontact Ill. Whenthebutton H3 is pressed inwardly, the relay is energiaed.the circuit beingas follows: secondaryof transformer a, relay, conductor III, conand Ill again brought into contact. Thus,

any'chanceofinjuiytothemotorisprevented byprovidingforthereversalofthemotorat bothends of the throw of thegang of condensers.

It will be understood. of course, that lithe button 3 is pressed inwardly and then released, the gang of condensers will start moving to the left and the, motor will be arrested when a carrier wave of suflicient strength isbrought in.

Itwillbeunderstood that the contact ill may be stationary so-that the motor can be started to the rightby depressing the button ill sufilclently to disengage the pole Ill from the contact III. I! the button 3 is further depressed I may be omitted, the conductor. 2 being connected directly to the conductor I".

In the embodiment of theinvention shown in Fig. 4, the reference numeral ill indicates the lastintermediate frequency tube, the plate of which is connected to the primary I of a transformer I, which is analogous to the transformer I! or the previously described embodiments of the invention. The secondary ill of primary I, is connected to the diode plate I42 and through resistors M3 and I to the cathode Eli, which is located in the tube Hi with the diode plate I. The tube I also includes the triode elements, that is, the grid I and the plate I". The grid M! is connected to the adjacent ends of the resistors I and I. The secondary winding I and the resistor ill are connected through a resistor m, condenser I58,

and a volume control III to the grid of the first winding I", which is loosely coupled to the transformer I, being analogous to the winding 15 of the previously described embodiments.

The winding I53 istuned to the intermediate frequency by the condenser Ill. The end of the winding I53 remote from its connection to the plate is connected through a resistor iii to ground and is also connected to the grid I of the tube H1. The cathode II. of the tube i5! is connected through resistors I59 and I to ground. The common ends of the resistors I59 and I" are connected by the conductor It! 5 to a contact I82. A plate I of the tube ii! is connected through the relay I" to the B supply "I. The end of the winding of the relay remote from its connection to the 3 supply l6! isconnectedthrougharesistor Ill toapole '40 ill of the normally open switch "2. When the pole "I is manually depressed, the resistor I'll is grounded. A contact. [1}, which is located adjacent the contact I82, is connected by a conductor ill to the grid circuit of the audio fre- 5 quency tube, not shown. A contact I'll, which is located in alignment with the contacts In and "I, is connected by a conductor III to the motor (not shown). when the relay I" is energiaed, the armature I" is moved into engage- 5 ment with the contacts m; m and Hi, thereby mnting the receiver, driving the motor, and increasing the energisation of the relay i". It will thus be seen that this relay I" is-quite analogoustotherelay 4i oftheiirstdescribed embodiment, but it operates in the opposite direction.

when the button "I is depressed, the motor starts operating, and when a carrier of sufllcient strengthisreceivedtheiiuxoftherelay I decreases and the armature I" is moved away from it by a spring I'll. The removal of the armature H! from the contact It! decreases still further the flux of the relay I, thus providing a locking elect. This locking effect can,

however, be obtained in other ways; for example,

the armature i'll'may be arrested by a' stop l'll' sumciently far away from the relay I" so that thecurrentnecessarytoenergizethe'relay ill soastomovethearmamre i'l'l towardstheree soastobringtheleaflllintoengagementwith 7o lamismuch greaterthanthe current strength the contact Hi, the motor will start to the left. Consequently, I may have one button 3 or a plurality of similar buttons arranged in parallel, each of which can start the motor to the right at which therelay Ill releases the armature I" under the action of the spring vI'll. The operation is as iollows;

when energy is supplied ,to the set, the conor the left, as desired. In this case, the button denser remains inoperative until the t bes w r up. If the condenser is tuned for the reception of a station of sufllcient strength, that station will be received. If the switch I" is closed, B current fiows through the relay coil I55 and resistor I10, and the grounded relay armature I11 will be brought into engagement with the coniiacts I52, I15 and I15, and the motor will operate as long as the contact is depressed. It will be understood that the motor may be reversed in the manner described in connection with Fig. 1. If the switch IN is opened after being pressed momentarily or for a longer period, the motor continues to operate until a carrier wave of sufficient strength is received, which carrier wave has the effect of decreasing the plate current of the tube I51, so that the spring I15 opens this relay and terminates the operation of the motor.

It will be understood that the cathode I45 and the plate I42 constitute the second detector of the receiver. This diode circuit creates a voltage drop across the resistors I45 and I44, with the result that the grid I41 is more negative than the cathode I45. The signal strength is proportional to the drop of potential across the resistor I44, so that the stronger the signal, the

greater is the negative voltage applied to the grid I41 relative to the voltage of the cathode I45. Thus, the stronger the signal, the greater is the tendency for the grid I41 to oppose the passage of plate current between the plate I45 and the cathode I45. The negative voltage applied to the grid I41 varies in the general manner shown by the curve 15 on Fig. 2, it being understood, however, that the curve '15 involves the ampliflcation factor of the triode elements I45, I41 and I45, which constitute a grid controlled rectifier. The positive component of the loosely coupled winding I53 is applied to the plate I45 and has a characteristic corresponding to the curve 50 of Fig. 2. Consequently, the plate current, corre-. sponding in magnitude to the curve 52 of Fig. 2, will flow between the plate I45 and the cathode I45 when a station of sufficient magnitude is brought in. This plate current passing through the resistor I55 lowers the voltage of the grid I55 so that the plate current of the tube I51 is reduced sufficiently to effect the withdrawal of the armature I11 from the contacts I52, I15 and I15 under the action of the spring I15. It will be understood that the station thus received may fade or sign off without the relay I55 being energized sufficiently to again attract the armature I11. The reason for this is that the contact I52 is no longer grounded and has the effect of increasing the positive bias of the cathode I55, thereby decreasing the current flowing through the relay I55, and furthermore, the armature I11'is removed from the position of strongest flux of th relay I55.

In the previously described embodiments, a certain negative automatic gain control or A. G. C. voltage' is applied to the grids of certain of the earlier tubes of the receiver for the purpose of varying their gain or amplification to secure automatic gain or volume control. Since the resulting reduction of the gain on stronger signals reduces the A. G. C. voltage, the various received signals, while rendered very much more uniform in strength, still show considerable differences after'amplification between the signals produced by a weak and a strong station. This is exemplified in Fig. 2, where the strength of the signal illustrated on the right is approximately double curves of the left of this figure.

I have discovered that I can attain much greater uniformity of signal for stop-on-carrier tuning by applying the negative A. G. 'C. voltage to the grid of a radio frequency or intermediate frequency amplifier not located in front of the circuit in the amplifier supplying energy to the A. G. C. rectifier. In other words, a more powerful A. G. C. effect can be obtained from a tube which does not contribute to the amplification of the signal operating the A. G. C. rectifier. This is true because the reduction of amplification of this tube does not reduce the A. G. C. voltage as is the case when the tube precedes the A. G. C. rectifier. I call this form of automatic'gain control "after A. G. C." to differentiate it from the ordinary A. G. C. applied to a tube which is before the A. G. C. rectifier and through which the signal operating the A. G. C. rectifier must pass. -By employing both before and -after automatic volume control, I may obtain control voltages for stop-on-carrier which are very close to uniformity for all received stations. By operating in this manner, I produce a stop-on-carrier receiver such as that illustrated in Fig. 5, which may cause all the signals, both weak and strong, which will affect the stop-on-carrier system, to operate very much alike.

Referring to Fig. 5, the reference numeral I15 designates the last intermediate frequency tube,

which is coupled'by a transformer I50 to the second detector and first audio frequency tube Ill. The detector circuit of the tube I5I includes resistors I52 and I55 from which are derived negative voltages which are applied by conductors I54 to the grids of certain of th earlier tubes in the receiver. A conductor I 55 is connected to the two resistors I52 and I55 and to a coil I55 which consists of a few turns tightly coupled to the primary of the transformer I50. The coil I55 is connected to the grid of an intermediate frequency amplifying tube I51, which is outside the radio receiver circuit. That is, the tube I51 and the tube I55 to which it is connected through the transformer I55, have no part in the conveyance or amplification of the audible signal. The transformer I55 is loosely coupled and its windings are sharply tuned to the intermediate frequency, which has the effect of narrowing the resonance curve for the signal passing through the tube I51. Consequently, the tube I will onlydraw substantial plate current when the intermediate frequency signal is near the resonant frequency of the transformer I55. Furthermore, on account of the before and after" A. V. C.,

. the maximum value of the signal of the tube I55 is substantially the same for all effective stations. The current delivered by the tube I55 passes through a relay I50, which controls the motor circuit I5I.

The relay I50 is biased open by a spring I52, and when the relay I50 is opened, its armature I55 makes contact with the motor circuit I5I. It may here be noted that the motor circuit may be completed as in the modification of Fig. 1. When the motor circuit is closed, an armature I55, which is grounded, engages a contact I54 which is connected by a conductor I55 to the grid circuit of the second audio tube, not shown. Consequently, when the motor is operating, the set is mute. When the armature I 55 is in engagement with the motor circuit I5I and the contact I54, it opens a switch I55. This switch is arranged to close when the relay I50 is energized. One side of the switch I55 is connected through a 5 resistor I51 to the plate of the tube I55 and to one end of the winding of the. relay I98. The other end of the winding of th relay I98 is connected to the B supply. The cathode of the tube I88 is connected through a resistor I98, to the other side of the switch I98. The common point and to the speaker. The automatic volume conof the latter tube to other audio frequency tubes trol applied by the conductors I84 to the earlier tubes of the receiving set has the eifect of reducing very greatly the difference of strength of signal reaching the tube 18 I. The after A. G. C. voltage applied by the conductor I85 to the tube I81 may be adjusted to render substantially equal signals appearing in the tube I88 from all stations above a certain signal strength. Substantial equality may 'be obtained by properly proportioning the resistors -I82 and I83 to impress the desired portion of the-voltage drop across these resistors on the grid ofthe tube I81. These resistors may also be proportioned so as to get any desired ratio less than equality between the signals produced by the strongest and the weakest stations to be received. It is even possible to make the signal of a strong station produce a smaller signal in the tube I88 than would be produced by a weaker station. It is generally desir-' able to approach equality between weak and strong stations for the purpose of very exact tuning, In addition to the equalizing effect of'40 the after A. G. C., the loose coupling and sharp resonance of the primary and secondary circuits of the transformer I89 may be adjusted to make the stop-on-carrier signal highly selective; that is, to narrow the width of .the motor stopping signal in terms of degrees of condenser rotation.

It will be understood that when the plate current of the tube I88 is sufllcient; that is, when of suflicient signal strength closely approaches the adjusted frequency of the transformer I89, the armature I93 is moved away from the motor contact and from the contact I94. so that the motor stops and the station may be audibly received. When the relay: I98 is energized, the.

plate current flows from the B supply through the winding of the relay 198, the tube I88, the

resistor I98, and the switch I99. The relay I98 is energized during the reception of a station. The switch I96 is then closed and a parallel cir-' cult is completed from the B supply through the winding of the relay I98, the resistor I81, the switch I98, and the switch I99. Consequently, when the switch I99 is opened, both of these circuits are interrupted and the relay'I98 is deenergized so that the motor tunes in another station. -It will be understood that the additional circuit just referred to has the effect of locking the relay I98 during the reception of a station until the switch 199 is'opened manually.

The embodiment of the invention illustrated in Fig. 6 comprises a radio frequency tube 288, an oscillator and first detector tube 28I, a first intermediate frequency tube 282, a combined diode 283 and second intermediate frequency elements the intermediate frequency produced by a station 284 enclosed in a single tube 285, a double diode 288, which may be a No. 61-16 tube, a first audio frequency tube 281, which is connected to other audio frequency tubes or the loud speaker, and a gas tube 288, which may be a No. 884 tube. The last named tube may be considered as being out of the set since it is merely used for the control of the relay 289. The set is tuned-by a motor 218 which controls the position of three condensers 21I, 212 and 213, which may be arranged in a gang, as in the first described embodiment of the invention. The condensers control a switch 214, which is analogous to the switch 42 of Fig. 1, and which is actuated at extreme positions of the condenserto reverse the motor, tlierebyreversing the direction of movement of the condenser. The motor 218 is supplied with current from power lines through a transformer 215. When the relay289 is de-energized, the armature 218 is retracted by a spring 211 so as to ground a conductor 218 which is connected to the motor 218 through the switch 214 and a conductor, 219, which has the eflect of muting the set v in the manner described with reference to the previously described embodiments. When the relay 269 is energized, the armature 218 is attracted and breaks the motor and muting circuits.

The plate of the diode 288 is connected through a winding 288, which is grounded through resistors 281 and 282, which provides a negative A. V. C. voltage. This voltage or part thereof is applied in the before" or after A. V. C. previously described. Thus, the maximum negative voltage isapplied through a resistor 288 to the grid of the tube 288. A lesser degree of negative voltage which corresponds to the voltage drop across the resistor 282 is applied through resistor 284 to the grids of tubes 28I and 282. A still lesser. amount of the negative voltage, being that corresponding to a part of the voltage drop across the resistor 282, is applied to the grid of the intermediate frequency tube elements 284, this being the position. at which the after'. A. V. C. is applied. The winding 288 consists of a few turns closely coupled to the primary of a transformer 288, which connects the plate circult of the tube 282 to the grid of the intermediate frequency amplifying elements 284 in the tube 285. v

For the reasons set forth above, the before and after" A. V. C. gives a signal in the plate circuit of the intermediate frequency elements 264 which can be made substantially equal for all received stations, strong or weak. This signal passes through the primary of a closely coupled transformer 288, the secondary of which is located in the plate circuit of one of the diodes 299 in the tube 288, this secondary being in series with a resistor 281. The diode 288 serves as the detector for the set, and the negative side of the resistor 281 is connected through a resistor 289, condenser 298, and volume control 29I to the grid of the first audio tube 281. The negative or plate side of the resistor 281 is also connected through a winding 292-to the plate of the diode 292 in the tube 288. The cathode of the diode 298 is grounded through a resistor 294. The positive side of the resistor 281 is also grounded. The

ground through a condenser It will readily be understood that the plate oi. the diode 288 is subjected to a negative voltage derived from the voltage drop across the resistor 281, which voltage drop corresponds to one of the curves 19 in- Fig. 2. The plate of the diode 298 also receives an intermediate frequency signal, the positive phase of which corresponds to one oi the curves 88 in Fig. 2. Consequently, the

positive phase of the voltage across the coil 292 impressed upon the plate of the diode 293 is indicated by one of the curves 82 on Fig. 2. It may here be noted that the eifect of the before and "after A. V. C. is to render the two sets of curves shown in Fig. 2 andthe corresponding curves for both strong and weak stations very much more uniform. The further result is that all of the curves 82 for received stations can be made practically uniform, both as to height and breadth. As previously described, it is also possible by applying various portions of the voltage drop across the resistors 28i and 282 as after A. V. C. to establish any desired ratio of signal between the strongest and weakest signals effective on the grid of the tube 288 to be received. For instance, the effective signal of the strongest station to be received might cause a voltage change only twice as great as the weakest signal to be received, although the corresponding signals, as received on the antenna of the set, may have a tremendously greater difference.

When a station is being received, current flows in the gas tube 288, the relay 289 is energized, the motor circuit is broken, and the mute circuit is open. When the switch 388 is opened, the plate circuit of the tube 288 is broken and the armature 218 is released. Consequently, the motor operates until the switch 388 is allowed to close again. After the switch 388 closes (and it may here be noted that it may be opened momentarily only), the motor continues to operate until a carrier wave of adequate strength is received, whereupon rectified current fiows through the resistor 298, thereby making the cathode end of the resistor 284 positive. This positive voltageis communicated through the resistor 298 to the grid of the tube 288. The resistor 298 and condenser 291 serve as time filter circuits which prevent the tube 288 from responding to static or other undesired electrical disturbances of extremely brief duration. It will be noted that the grid of the tube 288 does not need to become positive with respect to the cathode of this tube in order to start the current through the relay 288. It merely needs to have its negative bias reduced below a certain point determined by the characteristics of the tube, the plate voltage applied, etc. This reduction of negative voltage on the grid of the tube 288 is attained when a received carrier gives a signal corresponding to the curve 82 (Fig. 2) of magnitude greater than a certain value, for example, that corresponding to the line 8| on this figure.

As has been previously described, the opening of the switch 888 breaks the plate circuit of the tube 288, resulting in starting the motor 218.

tor continues to operate until the next station of suiilcient strength is tuned in.-

Itwill be understood that the tube as: passes its full plate current as soon as the negative voltage of its grid falls below the value which prevents ionization. In other words, the grid acts as a trigger controlling the plate current, but once ionization is established and plate current flows, the plate circuit must be interrupted, the plate voltage reduced below the ionization point,

orthe negative bias on the grid enormously in- Alter the switch 388 is allowed to close, the mocreased to stop the fiow of plate current. This quality of the gas tube therefore provides similar locking characteristics to those obtained in the other embodiments by special locking circuits. The action 01 the gas tube 288 is very rapid. Its time characteristics, however, can be controlled by means of the time constant of the filter circuit composed of the resistor 298 and condenser 291. Increasing the resistance of the resistors and the capacity of the condensers increases the time interval, and vice versa. The time filter circuit connected to the grid of the tube 288 should be so proportioned that the action of the tube 288 is as rapid as possible, but still slow enough so as to require a signal of appreciable duration to cause it to ionize. In other words, it should work as rapidly as possible on a continuous carrier wave, but should not respond to static or other undesired disturbances of negligible duration.

There are certain considerations pertaining to the time interval between the instant at which the signal is tuned closely enough to resonance to effect the interruption of the motor circuit and the instant that the condenser comes to a full stop, which should be considered for proper operation of this invention. Lag or delay tending to prolong this interval can occur in several ways. First, the filters employed in connection with rectifiers contributing to the stop-on-carrier signal must not have too long a time constant if the quickest possible stoppage is desired. Of course, the characteristics of the whole system must be considered. If a sharp selective stopon-carrier signal is employed, then the distance or time available between the effective stop-oncarrier signal and arrival at the peak of the carrier wave is very short and the time constants of all portions of the system must be" made very small to prevent passing the peak of the carrier before complete condenser stoppage occurs. On the other hand, if the stop-on-carrier signal is relatively broad, then too quick action will result in condenser stoppage before the peak of the carrier is reached. Accuracy and uniformity of tuning are, however, facilitated by sharp tuning of the carrier signal and corresponding reduction in the time lag all along the line. This procedure in connection with the equalization of the efi'ective width of strong and weak signals is the preferred arrangement.

When the time constants oi the rectifiers are sufliciently short, the next point of delay to be considered is the stop-on-carrier relay. The operation of the relay may be accelerated by reducing the inertia of the moving parts, by reducing hysteresis and eddy current eifects, and by supplying a large sudden increase of plate current to provide a powerful relay action. It is also generally desirable to close the magnetic circuit of the relay for quickest action rather than to open it. This means that fast action is obtained when energization of the relay stops the motor. It will be understood that it is desirable also to reduce 'permeability or reluctance.

the weight and inertia of the parts rotating with the rotor of the condenser.- A considerable 1nertia, however, is unavoidable in the armature or rotor of the motor employed in driving the condenser. It is therefore preferable to provide means whereby the condenser or other variable reactance can be brought to a full stop while the armature of the motor is still rotating. If a clutch is provided for this purpose, as shown in Fig. 1, it is desirable to reduce as faras possible the time required for the clutch to release. Other means of eliminating the effect of the motor armature inertia may also be employed, such as a friction drive between the motor and the condenser with provision for abruptly stopp n the condenser, while the armature may continue to rotate for a short interval by slippage of the friction drive.

It will be further understood that the importance of eliminating the stopping lag increases with the speed at which the motor turns the condenser. If this speed is quite slow, requiring for instance, ten or twenty seconds for a half revolution of the condenser rotor, the time lag may not need to be especially reduced. It might even be necessary to increase it. Butit is desirable to drive the condenser at relatively high speed so that only a brief interval is required to tune from one station to the next. This facilitates selecting the desired station by tuning from one station to the next in the shortest period of time. It is thought desirable for this purpose to turn the condenser one-half revolution in from two to not over five seconds, and it is desirable to work closer to the lower figure.

To achieve the most rapid operation with exactand uniform tuning, it is desirable that a given number of degrees of condenser rotation should result in changing the tuning by a given number of kilocycles alike from the high to the low frequency ends of the tuning range. For this purpose, a condenser having a substantially straight line frequency characteristic, at least to within a short distance of the low frequency end, may be employed. To keep the straight line frequency characteristic all the way to the low frequency end might involve too great a structural disadvantage in the condenser, although it isdesirable otherwise. A variable inductance may also be employed for tuning, for instance, one in which the inductance is changed by va y g the In this case, a uniform change of frequency with rotation is of similar advantage. 'With slower tuning, this straight line frequency characteristic is of lesser importance.

Although the invention has been described in ing a power actuated tuning element, a grid controlled gas tube having a cathode and plate, means for supplying a steady direct current voltage to the plate of the gas tube, fast acting direct current means in the plate circuit of said tube actuated by' a change in the direct plate current of said gas tube to stop the movement of said tuning element substantially at resonance, rectifying means and means for impressing a voltage from said rectifier on the gridof said gas tube to stop said tuning element.

2. In combination with. a radio device having an adjustable control, electric power means for driving said control in both directions, a source of electric current therefor, relay means for stopping and starting said power means, a second relay means for reversing said power means biased to normally operate said power means in one direction, switch means for energizing said step and start relay means, switch means for energizing said reversing relay means, and means for manually operating one switch means to start in one direction and both said switch means to start in the other direction. 7

3. In combination with a radio receiver, a tuning element, means actuated by a change in the plate current of a grid controlled electron tube to stop the movement of said tuning ele ment substantially at resonance, electric power means for driving said tuning element, a source of electric current therefor, relay means for stopping and starting said power means, a second relay means for reversing said power means biased to normally operate said power means in one direction, switch means for energizing said stop and start relay means, switch means for energizing said reversing relay means, and means for manually operating one switch means to start in one direction'and'both said switch means to start in the other direction.

4. In combination, in a superheterodyne radio receiver having an intermediate frequency section and a second detector, a shielding container, second detector coupling means within said container, a power actuated tuning element, a

grid-controlled electron tube, means actuated by a change in the plate current of said electron tube to stop said tuning element when the intermediate frequency signal is in substantial resonance with said intermediate frequency section, means including a pair of circuits tuned to the intermediate frequency housed within said container and having mutual coupling adapted to produce a first control voltage having a selectivity curve with two peaks and a depression therebetween, means for deriving from said receiver a second control voltage having a single peak coinciding with said depression and exceeding said first control voltage when a carrier signal is closely tuned in, and means including rectifying means for applying a voltage depending upon the diflerence between said first and second control voltages to said electron tube adapted to produce a change in the plate current .of the electron tube.

5. In a radio receiver, in combination, a variable tuning element, a motor for operating said tuning element, a clutch connecting said motor to said tuning element, an ionizing gas tube having a grid and plate, electrical means in the plate circuit of said gas tube for controlling said clutch, tuned coupling means deriving from said receiver a first control voltage having a seiec-- tivity curve with two peaks and a depression therebetween, tuned coupling means deriving from said receiver a second control voltage having a selectivity curve with a single peak coinciding in frequency with said depression and exceeding first said control voltage when a carrier signal is closely tuned in, means including rectifying means for applying a voltage depending upon the difference between said first and second control voltages to said grid to ionize said tube when a carrier signal is closely tuned, thereammo by to cause said electrical means to disengage said clutch and stop said tuning means closely on said carrier signal.

6. In a radio receiver having a variable tuning element, in combination, power means for driving said tuning element, relay means controlling said power means and tuning element, said relay means being operable when deenergized to render said power means effective to drive the tuning element and when energized to stop said power means and tuning element, an ionizable gas tubehaving an output circuit connected to said relay means and a control grid, means connected to said grid to supply it with a control voltage from the receiver for ionizing said tube and energizing said relay when a carrier signal is closely tuned in, a source of direct current connected to said plate circuit for maintaining said tube ionized and said relay means energized, and normally closed switch means in said plate circuit operable to open said plate circuit for deionizing said gas tube and deenergizing said relay'means.

7. In a superheterodyne receiver having variable tuning means, in combination, a motor for actuating said tuning means, switch means controllable by an operator for starting said motor, an intermediate frequency transformer having a primary winding tuned to intermediate frequency, a tuned circuit coupled to the primary of said intermediate frequency transformer, said circuit being tuned to intermediate frequency and having a degree of mutual coupling to the primary of said transformer such that the selectivity curve of the primary has two peaks with a depression therebetween and the selectivity curve of said tuned circuit has a single peak coinciding in frequency with said depression and the voltage of said tuned circuit exceeding that of said primary only when a carrier signal is closely tuned in, a rectifier having a plate and a cathode, one terminal of said tuned circuit being connected to supply said plate with an intermediate frequency voltage, other rectifying means energized from the primary of the intermediate frequency transformer and delivering a negative rectified voltage to said plate, a tube having a grid and plate with its grid connected to said cathode, and a relay operated by the plate current of said last tube for stopping the motor and movement of said tuning means when the positive phase of th intermediate frequency voltage exceeds the negative voltage by a definite amount.

8. In a radio receiver having a variable tuning element, in combination, power means for driving said tuning element, relay means adapted when energized to stop said power means and tuning element, an ionizable gas tube having a plate circuit connected to said relay means and a control grid, means connected to said grid to supply it with a control voltage from the receiver for ionizing said gas tube and energizing said relay means when a carrier signal is closely tuned in, a source of direct current connected to the plate circuit of said tube for maintaining said tube ionized and said relay means energized, and a time delay circuit connected between said grid and control voltage source having a time constant short as compared to the time of operation of said relay and long as compared to the duration of static impulses.

9. In a radio receiver having variable tuning means, in combination, electrically actuated means for stopping and starting said timing means, an electron tube having a plate circuit v connected to said electrically actuated means and a grid controlling the plate current for operating said electrically actuated means, means including a pair of circuits tuned to the same frequency associated with said receiver and having a mutual coupling adapted to produce a first control voltage having a selectivity curve with two peaks and a depression therebetween, means for deriving from said receiver a second control voltage having a single peak coinciding with said depression and exceeding said first control voltage when a carrier signal is closely tuned in, means including rectifying means for applying a voltage depending upon the difference between said first and second control voltages to said grid when said carrier signal is closely tuned to operate said electrically actuated means and stop said tuning means closely on said carrier signal, and means actuable by an operator to operate said electrically actuated means to restart said tuning means.

10. In a radio receiver having power actuated tuning means, in combination, a transformer having a tuned primary circuit and a tuned secondary circuit coupled thereto to cause the voltage selectivity curve of said primary to have two peaks and to cause the voltage selectivity curve of said secondary to have a single sharp peak located with respect to frequency at the depression between the two peaks of the primary selectivity curve and exceeding the voltage of the double peaked selectivity curve when a station is closely tuned in, a thermionic tube having a grid and controlling said power actuated tuning means, and means including rectifying means for applying a control voltage dependent on the difference between the single peaked and double peaked voltages to the grid of said thermionic tube to stop said tuning means when a station is closely tuned in thereby.

11. In a radio receiver having variable tuning means, in combination, power means driving said tuning means, relay means for stopping and starting said power and tuning means, an electron tube having a plate circuit connected to said relay means and a grid for controlling said plate current for operating said relay means to stop said tuning means, tuned coupling means deriving from said receiver a first control voltage having a selectivity curve with two peaks and a depression therebetween, tuned coupling means deriving from said receiver a second control voltage having a selectivity curve with a single peak coinciding in frequency with said depression and exceeding said first control voltage when a carrier signal is closely tuned, means including rectifying means for applying a control voltage depending upon the difference between said first and second control voltages to said grid when said carrier signal is closely tuned to operate said relay means and stop said tuning means closely on said carrier signal, means including a circuit controlled by said relay upon operation thereof to stop said tuning means for applying additional grid bias voltage to said grid to prevent a decrease in carrier signal strength from operating said relay means, and means actuable by an operator for operating said relay means to restart said power and tuning means.

12. In a radio receiver having a variable tuning element, in combination, power means fordriving said tuning element, relay means adapted when energized to stop said power means and tuning element, an ionizable gas tube having a plate circuit connected to said relay means and a control grid, means connected to said grid to supply it with a control voltage from the receiver for ionizing said gas tube and energizing said relay means when a carrier signal is closely tuned in, and a source of direct current connected to the plate circuit of said tube for maintaining said tube ionized and said relay means energized.

13. In a radio receiver having variable tuning means, in combination, power means driving said tuning means, relay means for stopping and starting said power and tuning means, an electron tube having a plate circuit connected to said relay means and a grid controlling the plate current for operating said relay means to stop said tuning means, tuned coupling means deriving from said receiver a first control voltage having a selectivity curve with two peaks and a depression therebetween, tuned coupling means deriving from said receiver a second control voltage having a selectivity curve with a single peak coinciding in frequency with saiddepression and exceeding said first control voltage when a carrier signal is closely tuned,vmeans including rectifying means for applying a voltage depending upon the diife'rence between said first and second control voltages to said grid when said carrier signal is closely tuned to operate said relay means and stop said tuning means closely on said carrier signal, and means actuable by an operator for operating said relay means to restart said power and tuning means.

14. In a superheterodyne radio receiver having an intermediatefrequency section and variable tuning means, in combination, power means driving said tuning means, relay means for stopping and-starting said power means, an electron tube having a plate circuit connected to said relay means and a grid controlling the plate current for operating said relay means to stop said tuning means, means coupled to said intermediate frequency section and tuned to intermediate frequency for deriving from said receiver a first control voltage having a selectivity curve with two peaks and a depression therebetween, means coupled to said intermediate frequency section and tuned to intermediate frequency for deriving from said receiver a second control voltage having a selectivity curve with a single peak coinciding in frequency with said depression and exceeding said first control voltage when a carrier signal is closely tuned, means including rectifying means for applying a voltage debeing energizable to stop and deenergizable to start said power means, an ionizable gas tube having a plate circuit connected to said relay means, said tube being non-conductive during operation of said tuning means and having a control grid adapted to be supplied with a control voltage to render said tube conductive to energize said relay means, means coupled to said intermediate frequency section and tuned to intermediate frequency for deriving from said receiver a first control voltage having a selectivity curve with two peaks and a depression therebetween, means coupled to said, intermediate frequency section and tuned to intermediate frequency for deriving from said receiver a second control voltage having .a selectivity curve with a single peak coinciding in frequency with said depression and exceeding said first control voltage when a carrier signal is closely tuned, means including rectifying means for applying a control voltage depending upon the difference between said first and second control voltages to said grid when said carrier signal is closely tuned to render said tube conductive and energizesaid relay means to stop said tuning means closely on said carrier signal, and means actuable by an operator for deionizing said tube and deenergizing said relay means to restart said power and tuning means.

16. In a superheterodyne receiver having an intermediate frequency section, an amplifying tube preceding said section, and variable tuning means, in combination, power means driving said tuning means, relay means for stopping and starting said power means, an electron tube having a plate circuit connected to said relay means and a grid controlling the plate current for operating said relay means to stop said tuning means, means coupled to said intermediate frequency section and tuned to intermediate frequency for deriving from said receiver a first control voltage having a selectivity curve with two peaks and a depression therebetween, means coupled to said intermediate frequency section and tuned to intermediate frequency for deriving from said receiver a second control voltage having a selectivity curve with a single peak coinciding in frequency with said depression and exceeding said first control voltage when a carrier signal is closely tuned, means including rectifying means for applying a control voltage depending upon the difference between said first and second control voltages to said grid when said carrier signal is closely tuned to operate said relay means and stop said tuning means closely on said carrier signal, means controlling the grid bias of said amplifying tube for preventing operation of said relay in response to carrier signals below intensities determined by said grid bias controlling means, and means actuable by an operator for operating said relay means to restart said power and tuning means.

17. In a radio receiver having a variable tuning element, in combination, power means for driving said tuning element, relay means controlling said power means and tuning element, said relay means being operable when deenergized to render said power means effective to drive the tuning element and when energized to stop said power means and tuning element, an ionizable gas tube having a cathode, plate and control grid, a source of direct current voltage, said source being connected across the plate and cathode of said tube in series with said relay means, means including a grid bias resistor connected between said cathode and the negative side of said voltage source and a second resistor connected between the positive side of said voltage source and said cathode for biasing said control grid to deionize said tubewhen said means is deenergized, and means connected to 18. In a radio receiver having a variable tuning element, in combination, power means for driving said tuning element, relay means controlling said power means and tuning element, said relay means being operable when deenergized to render said power means eifective to drive the tuning element and when energized to stop said power means and tuning element, an ionizable gas tube having a cathode, plate and control grid, a source of direct current voltage, said source being connected across the plate and cathode of said tube in series with said relay means, means including a grid bias resistor connected between said cathode and the negative side of said voltage source and a second resistor connected between the positive side -of said voltage source and said cathode for biasing said control grid todeionize said tube when said relay means is deenergized, means connected to said grid to supply it with a control voltage from the receiver for ionizing said tube and energizing said relay when a carrier signal is closely tuned in, and normally closed switch means in the plate-cathode circuit of said tube for deionizing said tube and deenergizing said relay means.

'19. In a radio receiver having variable tuning means operable between predetermined limits, in combination, a reversible electric motor for driving said tuning means in opposite directions, a source of power for said motor, means including a relay and switch means operated thereby controlling the connections of the motor to said power source for starting and stopping said power means, means including limit switch mechanism actuated by said tuning means and controlling the connections 01' said motor to said power source for automatically reversing the motor at the limits of movement of said tuning means, means including an electron tube having its plate circuit connectedto said relay for operating said relay to effect disconnection of said motor from said power source when a carrier signal is tuned in, and switch means operable by an operator controlling said relay and connections of the motor to said power source for reversing said motor when said tuning means is between the limits of its movement.

20. In a radio receiver having variable tuning means, .operable between predetermined limits, in combination, a reversible electric motor for driving said tuning means in opposite directions, a source of power for said motor, means including a relay and switch means operated thereby controlling the connections of the motor to said power source for starting and stopping said power means, means including a reversing switch controlling the connections of said motor to said power source, a second relay controlling said reversing switch and limit switch mechanism actuated by said tuning means adapted to energize said relay at one limit and to deenergize said relay at the other limit of movement of said tuning means for automatically reversing said motor, means including an electron tube having its plate circuit connected to said first relay for operating said relay to eflect disconnection of said motor from said power source when a carrier signal is tuned in, and switch means operable by an operator for energizing said second relay independently of said limit switch mechanism for initiating operation of said motor in a direction opposite to that determined by said limit switch mechanism. EDWARD ,1". ANDREWS.

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