US2174641A - Muting system - Google Patents

Description

Oct. 3, 1939.

D. V. SINNINGER MUTIHG SYSI'EI Filed Aug. 9. `195'7 M ATTORNEY Patented Oct. 3, 1939 UNITED STATES PATENT OFFICE MUTIN G SYSTEM poration of Illinois Application August 9, 1937, Serial No. 158,073

4 Claims.

This invention relates to radio receiving systems and more particularly to means for preventing response from a radio receiver while it is being adjusted to receive a desired signal.

5 In the past, in order to secure silent tuning with the conventional type of radio receiver it was necessary to retard the manual volume control prior to and during the tuning operation and to then advance it to the desired point upon completion of the operation. Thus three separate steps were necessary in order to avoid the annoyance of hearing a mixture of undesired signals and extraneous noise when changing from one setting of the station selector to another.

Since most modern radio broadcast receivers are provided with Visual means for indicating exact resonance with all signals of useful strength, it is generally unnecessary that the receiver produce any audible response during the tuning operation. It remains, therefore, to provide automatic means for muting the receiver while the station selector is actually in use, so that no sound will be heard until the tuning operation is Completed.

It is an object of this invention to provide simple means for automatically muting a radio receiver during the tuning operation.

A further object of the invention is to provide automatic muting means which will effect continuous muting during tuning operations of a radio receiver persisting through short interruptions that may occur in any of said tuning operations.

It is a further object of the invention to greatly 5 simplify the tuning operation in radio receivers,

by automatically preventing all extraneous noises during the operation, so that the user of the receiver may readily and without distraction adjust the instrument closely to exact resonance with,

and consequently to the position of best possible response to, the signal of the desired station.

It is also an object of the invention to greatly simplify the arrangements for producing satisfactory muting of the receiver during the tuning operation, and to thus reduce not only the cost but also the complication and liability to service failure thereof.

It is an additional object of the invention to 50 provide a muting arrangement by which the operator may listen momentarily at will to the signals from each of a number oi different stations as he tunes the receiver, to determine which of them he desires to listen to, without the annoy- 55 ance of static or other unwanted noises, and with- (Cl. Z-20) out hearing the signals of any stations except those which he elects to hear.

In accordance with a preferred form of the invention, contact of the operators fingers with the knob which actuates the station selector of 5 the receiver is utilized to actuate electrically operated means for muting the receiver. The muting is accomplished by rendering an audiofrequency amplifying vacuum tube substantially inoperative by biasing it beyond cut-off, so that 10 the response of the receiver is reduced practically to zero. In the arrangement according to the invention, the audio-frequency vacuum tube is either operating normally or is completely cut off, and thus no distortion of the signal is 15 introduced by the addition of my muting system.

The invention will be better understood by reference to the accompanying drawing, in which:

Fig. 1 is a schematic circuit diagram of a preferred form of the invention; and 20 Figs. 2, 3, 4 and 5 are elevations, partly in section, of various forms of selector or tuning knobs which may be employed in connection with the invention.

Referring to Fig. l of the drawing, block I 25 represents the high-frequency amplifying and selecting means, and the detector, of a radio receiver. Grid 2 of 'audio-frequency amplifying vacuum tube 3 is connected to the output of unit I by means of blocking capacitor 4. Cathode 5 30 of vacuum tube 3 is grounded through resistors 6 and 'I in series, which are shunted by capacitors 8 and 9, respectively. The lower terminal of grid-leak Il] is connected to the junction of resistors E and 'l through resistor II, which is 35 shunted by capacitor I2. Resistor Ill is connected between the junction of grid-leak I0 and resistor II and one terminal of the device I5, the other terminal of which is grounded. Device I5 may be a modified tuning knob presently to 40 be described. Device I 5 is indicated as being mechanically linked to unit I by dotted line I6. Which, in the usual case, Will be the driving shaft of a variable condenser gang or other tuning unit. A switch I3 may be provided between re- 45 sistors II and I4 to render the muting device inoperative if desired. The plate circuit of vacuum tube 3 includes load resistor Il, and bleeder resistor I8 is connected between the junction of resistors B and 'I and a source of positive plate 50 voltage, not shown. Resistors l and I8 are so chosen that the potential drop across resistor 'I due to current from the positive plate-voltage source is suicient at all times to bias vacuum tube 3 well beyond cut-off. When this potential 55 is applied to grid 2, the cathode current of vacuum tube 3 becomes practically zero and therefore the potential drop across resistor 6 is negligible, and under these conditions, vacuum tube 3 ceases to amplify.

In operation, grid 2 of vacuum tube 3 is normally provided with the correct bias voltage due to the potential drop across resistor 6 in its cathode circuit. The audio-frequency path from unit I to ground includes capacitor 4, grid-leak Il), capacitor I2, and capacitor 9. The drop in audiofrequency potential across grid-leak I is applied to grid 2 of vacuum tube 3, and appears in amplied form across load resistor I'I in the plate circuit of vacuum tube 3.

If switch I3 is absent, however, or if it is present and closed, and the circuit is completed through device I in a manner to be described below, grid 2 of vacuum tube 3 is effectively at ground potential from the direct-current standpoint. Therefore the effective grid-bias voltage becomes equal to the potential drop across resistor I, and vacuum tube 3 ceases to function as an amplifier because it is biased beyond cut-off. Device I5 is preferably so arranged that the fingers of the operator when he touches the knob which actuates the station selector provide a relatively low-resistance path from resistor I4 to ground. In this way, the receiver is muted during the tuning operation.

It will be understood that switch I3 may be operable from the front panel of the receiver, so that the muting system may be rendered inoperative if desired. It is also within the scope of the invention, when applied to a receiver adapted to cover more than one band of frequencies, to prol vide means for actuating switch I3 simultaneously with the band-selecting device of the receiver, in such a manner that the muting system is automatically rendered inoperative in one or more of the frequency bands covered by the receiver.

Although the muting system of the invention operates substantially instantaneously upon completion of the circuit by device I5, it is desirable that the muted condition be maintained for a short period of time after the tuning knob is released, so that it is unaffected by momentary interruptions of contact by the operators hand, as for example to secure a new grip on the knob for further rotation. In accordance with the invention, this desirable delay may be realized by so choosing the values of resistor II and capacitor I2 as to provide a suitable time delay in the restoration of normal bias voltage to grid 2.

Since in some forms of my invention, the conductive connection which is established by device I5 includes a portion of the operators fingers, resistor I I is preferably of high resistance relatively to the resistance of the conductive path established by device I5 under these conditions, and thus the provision of a suitable time delay requires the use of only a small value for capacitor I2. Resistor I4 functions merely to isolate device I5 from potentials greater than ground, in order to avoid the possibility of the operator receiving a slight shock during the tuning operation.

Referring now to Figs. 2, 3, l and 5, each of these figures shows a possible form of device I5 of Fig. l. Figs, 2, 3 and 4 each show arrangements which may be utilized as the tuning knob which actuates the shaft that drives the variable condensers or other ganged tuning devices.

Fig, 5 shows an arrangement which may be used independently of the tuning knob.

In Fig. 2, I9 is a knob of wood or other insulating material. Around that portion of the knob I9 with which the ngers of the operator come into direct contact are two coaxial conductive rings 2l] and 2I, of Wire, fiat strip or other suitable material. Rings 29 and 2I may be molded into knob I9, or may be applied in suitable grooves after the knob is made. Ring 29 is connected to shaft 22 upon which knob I9 is mounted. Ring 2l is connected to a slip-ring 23 mounted on the rear surface of knob I9, and a connection to ring 2l is secured through brush 24 which bears on slip-ring 23. Shaft 22 is journaled in bushing 25 in the front panel of the receiver, which provides a connection to ring 2U.

In Fig. 3, shaft 22 carries at its outer end punched or deep-drawn metal knob 25 which has a knurled periphery. Bushing 2'I extends in front of the receiver panel and carries insulating sleeve 23 upon which is mounted stationary conductive knob-shaped member 29 which has a smooth periphery, and is of substantially the same diameter .as knob 26. Member 29 and knob 26 are so positioned that the fingers of the operator readily bridge the small gap separating them` and provide a relatively low-resistance connection between them. When the operator attempts to rotate knob 2G and member 29, knob V2t is rotated by virtue of its knurled periphery but member 29 remains stationary, since it is not free to rotate, and its smooth periphery exerts practically no restraint against the operators turning effort. A connection 30 is provided through a suitable hole in the receiver panel to member 29.

In Fig. 4, shaft 22 carries at its outer end punched or deep-drawn conductive knob 3l, which has a knurled periphery. Secured to shaft 22, for example by a forced t, there is an insulating sleeve 32 upon which is mounted, also preferably by a forced t, conductive member 33 which has a knurled knob-shaped flare 34 of substantially the same diameter .as knob 3l at its outer end and a small shoulder 35 as shown. Member 33 is positioned so as to leave a small air-gap to knob 3l. Parts 22, 3|, 32 and 33 together constitute av rotatable knob and shaft, the knob having two insulated peripheral surfaces. Member 33 is journaled in bushing 3G in the panel of the receiver, which provides a connection thereto. Post 31 mounted on the rear of the receiver panel carries brush 38 which bears on shaft 22 and provides a connection to knob SI.

In Fig. 5, Contact fingers 39 .and 4E! are arranged to be closed by pressure on knob 4I, but are normally held out of contact by spring 42. In this arrangement, when the operator desires to tune the receiver, he depresses knob 4I, thus closing contacts 39, 49, and when the tuning operation is completed and the receiver is accurately tuned to the desired station, he releases knob 4I. It will be understood that by suitable mechanical arrangements knob 4I may be the tuning knob of the receiver, so that upon rotation it actuates the tuning device in the receiver.

The various structures shown in Figs. 2, 3, 4 and 5 are given merely by way of illustration of suitable devices for use in carrying out my invention, and other structures for securing an electrical circuit through the lingers of the operator or as the result of his actuation of the controls of the receiver will readily occur to thdcse skilled in the mechanical arts and are to be taken as the full equivalents of the structures shown. Additionally, electrically operated contacts, actuated for example by a relay device, may also be substituted.

The operation of a receiver equipped with muting arrangements according to the invention is highly pleasing and successful. When the operator decides to tune the receiver to a new station, he places his fingers upon the tuning knob or other suitably arranged control, and the receiver is immediately muted, that is, the signal from the station to which the receiver was previously tuned becomes inaudible, and the loud speaker is silent. The operator then turns the knob to tune to the new statio-n, watching the visual tuning indicator, or, if no indicator is provided, then the markings on the receiver dial, until he is sure that the receiver is now properly tuned to the new station. He then takes his fingers off the knob, and, after a very short delay due to the time constant of the circuit, as eX- plained above, the signal of the new station bccoines audible.

If, during the tuning operation, the operator removes his fingers from the knob toV get a new grip upon it to make further rotation possible, the time constant of the circuit may be and preferably is arranged to be such that during the short interval in which the operators fingers are not in contact with the knob, the receiver remains muted and no sound is heard from the loud speaker.

An additional advantage of the invention is that with a receiver so equipped it is readily possible for the operator to listen momentarily to the signal from each of a number of stations as he tunes from one end of the frequency range to the other, by merely removing his ngers from the tuning knob, to determine whether the content of the signal from any one of them interests him particularly at the moment, or to decide which of the available stations he will listen to, all without the distraction of unpleasant noises and sounds from unwanted stations during the tuning operation.

Having thus described my invention, what I claim is:

l. A radio receiver including tunable circuits; a station selector for tuning said circuits; an audio-frequency amplifying vacuum tube having a grid, a cathode and a plate; two adjacent mutually insulated conductive surfaces upon the ringer-grip portion of said station selector; two grid-circuit resistors in series between said grid and one of said surfaces; two cathode resistors in series between said cathode and the other of said surfaces; by-pass capacitors across each of said cathode resistors; two plate-circuit resistors in series between said plate and the junction of said cathode resistors; a connection from the junction of said plate-circuit resistors to a source of plate potential; and a path through the fingers of the operator between the junction of said grid-circuit resistors and the junction of said cathode resistors having high direct-current resistance and low impedance.

2. A radio receiver including tunable circuits; a station selector for tuning said circuits; an audio-frequency amplifying vacuum tube having a grid, a cathode and a plate; two adjacent mutually insulated conductive surfaces upon the finger-grip portion of said station selector adapted to be electrically connected through the 1ingers of the operator; two grid-circuit resistors in series between said grid and one of said surfaces; two cathode resistors in series between said cathode and the other of said surfaces; bypass capacitors across each of said cathode resistors; two plate-circuit resistors in series between said plate and the junction of said cathode resistors; a connection from the junction of said plate-circuit resistors to a source of plate potential; and a resistor and a capacitor connected in parallel between the junction of said grid-circuit resistors and the junction of said cathode resistors.

3. A radio receiver including tunable circuits; a station selector for tuning said circuits; an audio-frequency amplifying vacuum tube having a grid, a cathode and a plate; two adjacent mutually insulated conductive surfaces upon the finger-grip. portion of said station selector adapted to be electrically connected through the nngers of the operator; two grid-circuit resistors in series between said grid and one of said surfaces; two cathode resistors in series between said cathode and the other of said surfaces; bypass capacitors across each of said cathode resistors; two plate-circuit resistors in series be tween said plate and the junction of said cathode resistors; a connection from the junction of said plate-circuit resistors to a source of plate potential; and a resistor and a capacitor connected in parallel between the junction of said grid-circuit resistors and the junction of said cathode resistors; said resistors being of such value as to provide efcient operating bias upon said grid but such as to materially increase the negative bias upon said grid upon manual grasping of said station selector.

4. A radio receiver including tunable circuits; a station selector for tuning said circuits; an audio-frequency amplifying vacuum tube having a grid, a cathode and a plate; two adjacent mutually insulated conductive surfaces upon the finger-grip portion of said station selector adapted to be electrically connected through the fingers of the operator; two grid-circuit resistors in series between said grid and one of said surfaces; two cathode resistors in series between said cathode and the other of said surfaces; bypass capacitors across each of said cathode resistors; two plate-circuit resistors in series between said plate and the junction of said cathode resistors; a connection from the junction of said plate-circuit resistors to a source of plate potential; said resistors being of such value as to provide efficient operating bias upon said grid but such as to materially increase the negative bias l,

upon said grid upon manual operation of said station selector; and a resistor and a capacitor connected in parallel between the junction of said grid-circuit resistors and the junction of said cathode resistors and of such values as to maintain said bias at said increased value during momentary interruption of said manual operation.

DWIGHT V. SINNINGER.

Images