US2044645A - Radio receiving system - Google Patents

Description

* J1me 19.36. A. w. STAPLETON ET'ALYQ 2,044,545

RADIO RECEIVING SYSTEM 2 Sheet-Sheet 1 Original Filed Jan. 25, 1955 AH huv Will (a m 'u fin June 16, m6,

. A. W. STAPLETON ET AL RADIO RECEIVING SYSTEM .2 Sheets-Sheet 2 Original Filed Jan. 23, 1935 nun;

lNvENT E-S Patented June 16, 1936 "UNIT D STATES PATENT OFFICE 1 RADIO RECEIVING SYSTEM Arthur William Stapleton and Rodney Herbert Hatfield, London, England Application January 23, 1935, Serial No. 2,982.

Renewed November 20. 1935.

January 13, 1934 3 Claims. (Cl. 250- 40) V erator.

With the above objects in view, the invention resides in a' radio receiving system comprising means active to vary progressively the resonance of the tuned circuit or circuits thereof, means for rectifying radio-frequency signal cutrent in the system, and a relay device responsive to the rectified current therefrom when the system is in tune with respect'to an incoming signal to render inoperative the resonance-varying means.

In a convenient form of the invention the system, which preferably incorporates automatic volume control, comprises a variable tuning device or devices for a'radio frequency circuit or circuits, a motor having a driving connection with such device or devices for progressively.

varying the same, and a relay device responsive as above stated for rendering the motor inoperative.

Further objects, features, and advantages of the invention will be apparent on consideration,

of the following description and attached drawings, which have reference to two of the many practical forms which In the drawings, 1

Figure 1 is a circuit diagramshowing an applithe invention may take.

cation of the invention to a"straight type of radio receiver,

Figure 2 shows an application of the invention to a supersonic heterodyne receiver, and

Figure 3 is'a graphical illustration of a feature of operation of the arrangement shown in Fig- In Figure 1, L1C1represents a radio-frequency circuit tunable, by means of the variable condenser C1 to resonance with an incoming carrier wave of any frequency within a certain range. Oscillations from this circuit are transferred in the known manner, with or without amplification, to the control grid of a rectifying thermionic tube V1 and the audio frequency currents passed from the anode thereof through a condenser C2 a p yi g system at Art" 1 'In Great Britain Now it is well known that the rectified carrier wave appears as a component of the steady anode current of the tube V1, being added to or subtracted from the no-signal value of such current according to the characteristics of the grid circuit of this tube. In other words the steady anode current of the tube V1 rises to a maximum or falls to a minimum when the rectified carrier component reaches its maximum; i. e., when thecircuit L101 and kindred circuits, if any, are correctly tuned with respect to the incoming signal. In the present arrangement there is also incorporated automatic volume control indicated at AVC, according to which a voltagetapped from a resistance R1 in the cathode lead of the rectifier :is incorporated in the grid bias of a preceding radio-frequency tube or tubes to control their sensitivity, the net result being that the maximum or minimum value above referred to of the anode current of the rectifier V1 is substantially predetermined and independent of the actual weakness or strength of the signal in the aerial system of the receiver.

The anode current of V1 passes to the high tension source at HT via one winding L2 of a differentially-wound relay indicated generally at M1, the opposed winding L3 of which is separately energized from the high tension source via a resistance consisting of or including sections R2 The ends of these sections are connected and R3. with a two-pole three-position switch S1 in such a way that, as is apparent in the figure, R3 is short-circuited when the switch is in the neutral' position shown, R2 and R: are both short circuited when the switch is in one extreme position (down), and R2 and R3 are both in circuit when the switch is in the other position (up).

Now the arrangement is such that when R:

7 only 'is short-circuited the field L3 of the relay winding is equal, and of course opposite, to that of the winding L2 when energized by the anode current corresponding to a correctly-tunedcarrier wave, consequently according as to whether the switch S1 is thrown up or down while the receiver is so in tune with a signal the armature A1 will be moved to one side or the other from its central neutral position;

Reverting now to the tuned circuit L101; the variable condenser, C1, alone or coupled or ganged with corresponding condensers in other tuned circuits, is adapted to be slowly rotated in either direction by a reversible electric motorM through an electromagnetic clutch device indicated generally at D. The device D is such as to throw the motor M into and out of driving ing one of a pair of clutch plates or friction wheels of which the other is mounted on the condenser shaft. Thus when the motor is energized its armature moves longitudinallyto engage the clutch plates or friction wheels, and when it is switched off the reverse movement takes place. In either case, when the supply of current is broken the condenser is instantaneously freed of any overrunning inertia of the armature.

The motor M has permanent or separately excited field magnets, and its armature is energized from a source indicated at B via the contacts of the relay M1 which, as will be clear from the figure, areadapted to pass current in one direction when the armature'A1 is in one extreme position and in the opposite direction when it is in the other extreme position, all the contacts being open and the motor M de-energized when the relay is in the balanced condition as illustrated.

The operation of the arrangement described in the foregoing is as follows:-

Assuming the rectifier tube V1 to be operating on the leaky grid principle and the receiver to be correctly tuned to an incoming carrier wave. The switch S1 is in the intermediate position shown, giving an intermediate value of resistance in the energizing circuit of the relay winding L3. The field of the latter balances that of the winding L2, which is energized by the steady anode current of the tube V, this current being reduced by the rectifiedcarrier component to the minimum value predetermined by the automatic volume control arrangement.

The armature A1 of the relay M1 is thus in the intermediate position shown and the motor M is therefore idle. V

If new it is desired to tune the receiver to another carrier wave, the switch S1 is moved to one or other of its extreme positions to render the field of the relay winding L3 stronger or weaker than that of the winding L2 and throw the armature A1 in one direction or the other, thus starting the motor M to tune the circuit L1C1 to a higher or lower frequency as may be desired. Whenthe wanted signal is heard, the switch S1 is released, the motor M continuing to turn the condenser Ci until the carrier wave is correctly tuned in,'when the steady anode current of the rectifier tube V1 will have become depressed to the minimum value corresponding to that in the winding L3 in the intermediate position of the switch S1, when the armature A1 of the relay M1 moves to the balanced intermediate position, switching off the motor M and simultaneously withdrawing the clutch. member D.

It will be realized from the foregoing that solely by movement of the switch S1, which may form or be incorporated in a remote-control unit, the receiver may be accurately tuned in to any existing carrier wave which it is capable of receiving, in which respect it is a notable advance on remote control arrangements, which are restricted to the selection of one of a limitednumberof predetermined resonant frequencies in the radiofrequency circuit or circuits.

It may be observed that in the particular arrangement above described, the motor will always rotate in the same direction when the receiver is off tune with the switch S1 in the intermediate position, owing to the fact that under these circumstances the field strength of the relay winding L2 is always greater than that of the winding L3, so that when searching in one direction it is necessary to pass through the optimum tuned position when a carrier wave is encountered before releasing the switch S1 to allow the apparatus to adjust itself to the optimum setting. Where this precaution proves an inconvenience, a modified arrangement may be adopted in which the means for reversing the motor M are associated with the switch S1, the relay M1 being of a simpler type serving only to break the motor circuit, when the anode current of the tube V1 falls In this figure, L4C4 and L505 represent the signal frequency and oscillator frequency circuits tuned by the variable condensers C4 and C5 respectively, these condensers being so coupled or ganged that the frequency difference between the circuits has always a fixed value, say in the present case kilocycles. Incoming carrier waves are thus converted by rectification, in the known way, to an intermediate frequency of 110 kilocycles and are thereafter treated in a manner analogous to the treatment of radio-frequency signal currents of such frequency in a straightforward receiver.

As in the arrangement of Figure 1, these condensers are simultaneously varied by a motor M through an electromagnetic clutch device D, the motor being energized, when required, from a source B. 1

In thisembodiment of the invention a portion of the intermediate frequency signal current is tapped from the receiver at IF and passed via a condenser C3 to an intermediate-frequency transformer, indicated generally by T1, tuned to 110 kilooycles. The secondary circuit of the transformer T1 incorporates a quartz or, equivalent crystal resonator X. As is well known, such a crystal may be arranged to have an electromechanical resonance period at any predetermined frequency, which in this case will be 110 kilocycles, and has moreover a very high decrement above and below such frequency, in other words is so sharply tuned as compared to an ordinary inductance-capacity resonant circuit as to resonate at substantially its natural frequency only. The advantage of this in the present connection is illustrated by Figure 3, in which the full curve shows the voltage-frequency characteristic of an ordinary circuit tuned to 110 kilocycles and the dotted line that of a quartz crystal arranged to resonate at this frequency. It will be apparent that a small variation from the correctly tuned position produces a much greater decrease in the amplitude of the intermediate frequency oscillations passed in the case of the crystal than in the case of the ordinary resonant circuit. In fact it may be said that the crystal will pass a substantial current only when the: receiver is correctly tuned, and that it is.- not therefore essential to. employ an automatic volume control arrangement to predetermine the maximum value of such current, since it is substantially non-existent when the receiver is oil tune. A similar efiect may be secured, although in a less simple manner, by employing a. sharply-tuned filter comprising a plurality of tuned circuits in cascade, and although, as above explained, it is usually not necessary to employ automatic volume control, it may nevertheless be incorporated with advantage.

The intermediate-frequency current at 110 kilocycles, after passing the crystal X, is amplified by a screened-grid thermionic tube V2 and transformer T2 and rectified by a diode V3, appearing as a steady voltage acrossa resistance R4 in the diode circuit. This voltage is transferred as a negative voltage to the grid of an amplifyingcontrol tube V4 forming, with an electromechanical relay M2 in its anode circuit, a relay unit. The arrangement is such that when no appreciable negative voltage is being transferred from the diode V3 to the grid of the control tube V4 the normal anode current of the latter is sufficient to hold the armature A2 of the relay up to the core, the high tension supply to this tube then passing through one of the two closed pairs of contacts of the relay. The other pair of contacts complete the circuit to the motor M, which is thus in the arrangement as illustrated, active to vary the tuning of the receiver.

At the moment that the receiver becomes correctly tuned with respect to an incoming carrier wave, the crystal resonator X passes the resulting 110 kilocycle current which is amplified by the tube V2, rectified by the diode V3 and is applied as a negative voltage to the grid of the control tube V4. Theanode current of this tube therefore falls sharply in value, the armature A2 is released, and the two pairs of contacts of the relay M2 open, breaking the anode circuit of V4 and the motor energizing circuit respectively.

When it is desired to de-tune from the received carrier wave it is only necessary to restore the anode current of tube V4 to its normal value'by short-circuiting the resistance R4 and shunting the pair of relay contacts through which the anode voltage is applied to the tube V4. These two operations are conveniently performed by a press-button double-pole single-throw switch S2,

which maybe incorporated in a remote-control unit. On pressing this switch the normal anode current will be restored to the tube V4, the relay M2 will close and the motor will be started to vary the tuning. The apparatus will immediately I be detuned from the carrier wave, and the switch S2 may be released; The condensers C4 and C5 will continue to be progressively varied until another carrier wave is picked up and fully tuned in, when the relay M2 will release its armature and the motor M be switched off as before. In order to pass over an unwanted carrier wave it is only necessary to hold down the switch S2 thus preventing the relay system V4Mz from being deswitch S3 is associated in the remote control unit with the restarting switch S2.

It is to be noted that the apparatus enclosed by the dotted line in Figure 2 and the remote control unit embodying the switches S2 and S3 are particularly well adapted to constitute auxiliary units for connection to or incorporation in existing supersonic heterodyne receivers, and that this is regarded as a valuable and important aspect of the invention.

In all cases where a remote-control unit is employed, it may be desirable to incorporate therein means remotely controlled by the variable condensers for indicating the frequency to which the system is tuned at any instant. Such means may readily be devised in a number of ways by competent persons, and it is therefore unnecessary to describe or illustrate the same in detail.

We claim:-

1. In a radio-receiving system, the combination of tuning means, motor means for progressively operating the same, a relay, means for energizing the same comprising a circuit including a pair of contacts, signal receiving means constructed and connected to vary the strength of magnetization of said relay at a moment when incoming signals are in tune with said system, to thereby open said contacts, an energizing circuit for said motor means including contacts held closed so long as the magnetization of said relay is not varied by said signal receiving means and broken by said relay when the magnetization thereof is so varied, and means operable at the will of the operator at any time, and including a circuit shunting said first named contacts, for re-energizing said relay.

2. In a radio-receiving system, the combination of tuning means, motor means for progressively operating the same, a relay, means for energizing the same comprising a circuit including a pair of contactsfsignal receiving means constructed and connected to vary the strength of magnetization of said relay at a moment when incoming signals are in tune with said system, to thereby open said contacts, an energizing circuit for said motor means controlled by said relay and broken thereby at the moment when incoming signals are in tune with said system, means whereby said motor energizing circuit remains broken unless closed by a positive act of the operator, and means operable at the will of the operator at any time, and including a circuit shunting said contacts, for restoring said relay to a condition in which it closes said motor energizing circuit.

3. In' a radio receiving system, tuning means, means for progressively moving said tuning means to tune said system, means responsive to an incoming signal, when the system is in tune, to stop the motion of the tuning means, said stopping means including a thermionic tube, a relay connected in the plate circuit thereof, and means for impressing on the grid of said tube a voltage derived from the incoming signal, and means,

operable at any time at the will of the operator, for causing said relay to restart the motion of said tuning means, said last mentioned means including manual means'for altering the voltage impressed on said grid.

ARTHUR WILLIAM STAPLETON. RODNEY HERBERT HATFIELD.

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