US2061982A - Automatic sensitivity reduction system - Google Patents

Description

Nov. 24, 1936. w, VAN B. ROBERTS 2,061,982

AUTOMATIC SENSITIVITY REDUCTION SYSTEM Filed March 30, 1929 jwvemoz WALTER VAN .RoERTs Patented Nov. 24,'y 1936 UNITED STATES Y AUTOMATIC SENSITIVITY REDUCTION v SYSTEM Walter van B. Roberts, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application VMarch 30,

8 Claims.

This invention relates to receiver volume control, and, more particularly, to the automatic reduction of the sensitivity of a receiving circuit during thetuning of said circuit.

In radio reception, especially in the case of sensitive receivers, thereare present to a great extent, variations in the signal strength characterstics of various broadcasting stations, which render it diiiicult to obtain satisfactorily uniform reception volume, withoutthe use of special devices to maintain such a uniform volume.

Thus, in tuning a sensitive receiver, through a particular range of frequencies in order to pass fromv one extreme of the range to the opposite extreme, the listener lwill often be subjected to aural annoyance while traversing the frequencies intermediate the said extremes, it being understood that the intermediate frequencies very often include stations emitting powerful signals, or perhaps local stations with comparativelyi strong signal characteristics.

It is possible, o f course, to prevent the raucous and distorted noises, engendered by the traverse over these intermediate channels, by reducing the amplification of the receiver through manual manipulation of the volume control mechanism. However, experience has shown that the average radio broadcast listener regards the repeated resetting of the volume control mechanism as an annoyance, primarily because, when the volume is once set to his satisfaction, he regards the time taken for readjustment of the setting as a detraction from the time available for the enjoyment of the broadcast` program.

. Now, I have invented a method of, and means for, eradicating and obviating this source of annoyance to theowner of a broadcast receiver, by providing means vfor insuring automatic reduction of the receiving circuit sensitivity, and/or amplification, to a point where only a predetermined sound output occurs as the'tuning dial is manipulated past the position corresponding to the frequencies of powerful signals.

Briefly, the broad conception embodied in the present invention, involves the uni-control of volume control simultaneously with frequency selection so that receiver sensitivity is suiciently reduced, at frequencies of signals, which are abnormally loud in .the particular installation, so that only a predetermined sound output occurs when passing from one extreme of a predeterminedv range of frequencies to the opposite extreme, and additional means for rendering the above sensitivity reduction ,control inoperative When desired,

1929, serial NQ. 351,408

(ci. 25o-20) Y The vinvention will be better understood from the following Y description and thel accompanying drawing, in which,

Fig. 1 diagrammatically shows a radio receiver system embodying the principles of the invention,

Fig. 2 is a diagrammatic view of the detailsof the automatic sensitivity reduction mechanism,

Fig. 3 is a detailed viewof one ofthe circuit breaker members; and

Fig. 4 shows diagrammatically a modied form of the invention.

Referring to Fig. 1, there is shown a receiver, including a uni-control tuning means, and connectedvvto agrounded antenna circuitMG. The

type of receiver shown herein embodies the well known construction wherein signal volume is controlled by the introduction of a Variable resistance, the volume of sound from the receiver being increased or reduced by the rotation of an exposed dial,y the dial being connected on the interior of the setto arheostat which provides the aforesaid resistance.

'This resistance, V, may 'beinserted at any of several points in the receiver circuit, such as: (1) in the filament circuit of theradiofrequency amplier tubes, (2) in the plate circuit of the radio frequency amplier tubes,\(3) in the cathode lead wire common to both plate and grid circuits. It will be noted that in each casethe volume is reduced when the resistance is increased. All of these constructions and many others are well known in the art and need not be gone into Vin further detailat this point.

r,I 'he radio frequency amplifier is shown as embodying a uni-control tuning means, it being understood that this control is the conventional one dial gang condenser control. It is understood, of course, that any other type of tuning means may be employed, the invention depending upon the mechanical coupling between the tuning means and the volume control rather than upon the latter two members themselves. The invention as utilized in Fig. 2 embodies two main members comprising one or more normally short circuited resistances contained in a common circuit represented by the letter A in Fig. 1, the common circuit being adapted to be connected to the receivng circuit, in this case, in series with resistance V. In other words, I insert a number of series connected resistances in series with the resistance V.

Each of the resistances R, and in Fig. 2 I only show three resistances R1, R2, R3, is normally short circuited by a spring switch I, 2, 3. A switch 9 is Cil shunted across all the resistances, for a purpose to be later described. The circuit A may be so constructed, that it is readily inserted into a receiving circuit of conventional design, which includes means to receive the plugs of the circuit A, it being understood that slight changes or additions would have to be made in the mechanical design of the receiving circuit.

Each of the switches I, 2, 3 are opened successively by means of a series of breaker members C, mounted upon a shaft 5. The shaft may be threaded at one of its endsv for facilitating the attachment thereof to the interiorly threaded hub I0 of a conventional uni-control tuning shaft.

Fig. 3 shows one of the many possible mechanisms C which may be used as a breaker for each of the switches I, 2, 3, it being understood that these mechanisms need not be shaped as shown herein, nor need even be cams. Each of the members C is preferably made of a poorly conducting material, such as fiber, hard rubber, etc., and is provided at one end thereof with a hub 'I, whereby the members C may be mounted upon the shaft 5. The hub is bored as at 3, to receive a positioning pin I I whereby the members C may be disposed in any predetermined position.

As shown in Fig. 2, each member C is positioned so that each of the switches I, 2, 3 will be opened by the corresponding breakers C1, C2, C3, the switch I being shown in open position due to the disposition of the breaker C1 therebetween.

The operation of the mechanism is readily understood by reference to the above description, it being understood that as the tuning dial 4 rotates, past a given point on the exterior of the set, each of the switches I, 2, 3 are successively opened by its respective breaker C1, C2, or C3. For example, suppose stations WJ Z and WOR are the two strongest stations in a given locality, and assume that the operator of the receiving set has been listening to station WABC which is a weak station requiring maximum volume control setting, and it is desired to listen to station WEAF. (It should be understood that WABC and WEAF represent the two extremes of a range of frequencies of which stations WJZ and WOR are intermediate frequencies.)

If the volume control setting were not disturbed, and my present invention were not in use in the receiving circuit, then as the dial 4 traversed the angle between the settings of WABC and WEAF, stations WJZ and WOR would be heard extremely loud. Consequently, raucous and distorted sounds would be heard as the dial moved past the positions representing stations WJZ and WOR.

With my invention, however, as the dial reaches the position where station WJZ begins to be heard the breaker C1 moves in between the points of switch I and separates them, thereby opening the short circuit around resistance R1 and effectively inserting more resistance in series with resistance V. This results in a reduction of the receiver sensitivity at that position, it being understood that the resistance R1 is so designed that it adds sufficient resistance to resistance V that station WJZ is of a desired loudness. When the dial has passed the furthest setting where WJZ would be heard, breaker C1 leaves switch I and R1 is again shortcircuited.

As the dial is rotated still further towards position WEAF the dial position representing station WOR is reached. As position WOR is reached the short circuit around resistance R2 is opened, in a similar fashion, and the, predetermined sound output at this position is not exceeded. It is understood, of course, that this arrangement is applicable to as many stations as may cause signals which are exceedingly loud when the volume control V is set for maximum. It is also possible to use the same breaker member C for breaking a series of vertically superposed short circuiting switches so that each switch is opened as the breaker member travels downward or upward through an arc.

In case it is known that a broadcasting station emitting weak signals, for the particular locality in which reception is being employed, possesses the same Wave length as one of the strong stations already referred to, and it is desired to receive this weak station when the locally strong station is not transmitting, I provide a master switch 9. This switch allows the receiver to operate on all wavelengths with the maximum sensitiveness determined by the setting of the volume control V.

In other words, the switch 9 renders the auxiliary volume control A inoperative when desired. Various manually operable switches may also be employed to restore maximum sensitivity at the frequency of any one or more intermediate stations, while maintaining reduced sensitivity at other angular positions of the tuning dial.

For example, each of the resistances R1, R2, Rf1 may be provided with a small manually operable 'short circuiting switch which may be shunted o around each resistance. As stated heretofore, it is not essential to this invention that the main volume control V be inserted at any particular part of the circuit, for the broad concept of the invention, which is illustrated by the drawing, involves the method of maintaining a low sensitivity in a receiving circuit over certain predetermined narrow bands of frequencies, which consists in reducing the circuit sensitivity through a predetermined narrow range of frequencies simultaneously` with the tuning of the circuit to said frequencies.

It Should be noted that in some cases the volume control resistance may be so located in the receiver circuit that volume is reduced by increasing the control resistance. An example yof this is shown in Fig. 4 where a resistance is inserted between antenna and ground. In such a case switches I, 2' and 3 connect R1, R2, and R3 respectively, in parallel with the volume control resistance V' when operated by the cams Ci, C2, C3. The master switch 9 is opened in this case to restore normal sensitivity at all frequencies.4 The switches I', 2 and 3 are normally maintained open by springs I5.

It will be obvious that the general principles herein disclosed may be embodied in many organizations and constructions widely different from those illustrated herein without departure from the spirit of the invention as defined in the following claims.

What I claim is:

1 In a radio receiving set of the uni-control tuning type, including a variable resistance for controlling signal Volume, means including a plurality of normally short-circuited resistances in series, adapted to be connected to said Variable resistance, and means, operative simultaneously with the uni-control tuning means, for successively breaking the short circuits within predevfrequencies in the said range.

3. In a tunable amplifier of the type provided with a continuously variable signal energy selecting means, a Signal Volume control means including a Variable resistor device, a plurality of normally disconnected auxiliary resistance elements and means for connecting said resistance elements to said variable resistor device in a predetermined sequence to produce additional volume controlling effects upon said amplifier, said last named means being simultaneously operative with said signal energy selecting means.

4. In the operation of radio receiving apparatus having one or more circuits tunable by adjustment ofthe movable elements of tuning devices associated therewith, the method which comprises moving said elements continuously to change the resonant frequency of said circuits in search of signals from a. desired station, and utilizing the movement temporarily to depress the sensitivity of the apparatus as the resonant frequency of thecircuits passes through transmission frequency of nearby or powerful stations.

tus having means to adjust sensitivity and one f or more circuits tunable by adjustment of the tus having one or more circuits tunable by adjustment of the movable elements of tuning devices associated therewith, and impedance controlling the amplitude of reproduced signals, the method lwhich comprises moving said elements continuously to change the resonant frequency of said circuits in search of signals from a desired station, and utilizing the movement to effect temporary change in the effective magnitude of said impedance as the resonant frequency of the circuits passes through the frequency df' transmission from nearby or powerful stations, in a sense reducing the amplitude of signals therefrom. n

'7. Radio receiving apparatus comprising thermionic tubes, circuits including tuning devices having elements adjustable to tune said circuits to all frequencies Within a range of. frequencies,

a calibrated operating dial therefor, an imped-V ance adapted to control the sensitivity of said apparatus, and means movable in unison with said adjustable elements throughout their range of movement varying the effective magnitude of said impedance in a sense to depress sensitivity when said dial is at a setting corresponding to the frequency of transmission from a powerful station.

8. In the operation of radio receiving apparatus having one or more circuits tunable by adjustment of the movable elements of. tuning devices associated therewith and volume control means, the method which comprises moving said elements to continuously change the resonant frequency of said circuits from one point within a range of frequencies to another point. thereof in search of signals from a desired transmitting station and utilizing the movement temporarily to operate the volume controlling means so as to maintain the receiving apparatus output substantially constant as the resonant frequency of the circuits passes through certain predetermined values.

WALTER VAN B. ROBERTS.

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