Title:
Automatic interrupter for broadcast receivers
United States Patent 2055164


Abstract:
This invention relates to an automatic interrupter for broadcast receivers and it comprises in combination with a conventional receiving set, a unit connected to the antenna system thereof and adapted to respond to vibrations of a selected radio frequency different from that to which the conventional...



Inventors:
Wichman Jr., Ralph D.
Mcclellan, Robert T.
Application Number:
US64725632A
Publication Date:
09/22/1936
Filing Date:
12/14/1932
Assignee:
Emmett, Peterson J.
James, Littlehales H.
Carl, Hellmann A.
Primary Class:
Other Classes:
455/227, 455/229, 455/289, 455/355
International Classes:
H03G11/00
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Description:

This invention relates to an automatic interrupter for broadcast receivers and it comprises in combination with a conventional receiving set, a unit connected to the antenna system thereof and adapted to respond to vibrations of a selected radio frequency different from that to which the conventional receiver is tuned, said interrupter unit utilizing the incoming signal of different frequency automatically to block the electron flow in the radio frequency tubes of the said conventional receiving set, whereby when a signal is received of the predetermined frequency to which the interrupter unit is responsive it is made audible while the initial signal is blocked, but upon cessation of such signal the initial signal will again be rendered audible; all as will be described more fully hereinafter.

It is an object of our invention to provide a receiving set for signals of different frequencies and so arranged that when signals of a predetermined frequency are received the reception of other signals is automatically blocked and such audible reception is automatically resumed upon cessation of the signals of such predetermined frequency.

Another object is to provide an interrupter unit which can be compactly housed within the cabinet of any conventional receiving set, and which utilizes the incoming signal of a frequency dif:ferent from that to which the conventional receiving set is tuned for automatically rendering audible the signal of predetermined different frequency and simultaneously blocking the broadcast signals as received on the conventional receiving set, while automatically permitting such broadcast signals to resume to produce audible sounds when the predetermined different frequency signals have ceased.

Referring to the drawing wherein is shown in diagram a circuit embodying our invention: The variable condenser C1 acting as a high frequency blocking condenser and in conjunction with the radio frequency choke L1, blocks all signals to the conventional receiving set from shorting to ground.

The condenser C1 is adjusted to tune the aerial circuit including also the inductance Li to the desired frequency and when a signal of that frequency is picked up by the receiving set antenna it is impressed upon the grid of tube T1, a 58 type alternating current variable mu radio frequency pentode tube.

R1 is a variable resistor, the portion of which to the left of the slider is by-passed by a fixed condenser C3 for adjusting the bias on T1 to give the correct volume when the interrupter unit is operating through the audio system of the receiving set. R2 is a resistor which acts as a bleeder between R3 and R1. R3 is a voltage drop resistor between the plate lead and screen grid lead for the screen grid potential. C4 is a fixed by-pass condenser for the screen grid lead.

The tube T1 amplifies the received signal which, upon passing through the plate lead to the radio frequency coil L2 is again tuned by a variable condenser C2 to obtain greater amplification, and upon passing through the voltage blocking condenser C7 is impressed upon the grid of tube T2, a type 56 alternating current detector and amplifier. C5 is a fixed by-pass and voltage blocking condenser for the plate lead of tube T'.

The tube T2 is arranged to act as a detector, and the resistor R7 and fixed by-pass condenser C7 give the necessary bias. The resistor R8 is 25 a grid-to-ground bleeder. The tube T2 changes the signal from radio frequency to audio frequency and passing through the plate lead P it is connected with the plate lead of the first audio stage in the conventional receiving set as at P' to be further amplified. Such connection is the same for a resistance coupled first audio stage receiver of conventional circuit.

A radio frequency choke I with a fixed bypass condenser C9 in the plate lead of tube T2 serves to prevent radio frequency signals from going through to the audio amplifiers.

When a signal is being received by the interrupter unit receiver the following change occurs.

Tube Ti amplifies the incoming signal and impresses this amplified incoming signal upon the detector of the said receiver circuit. This amplified signal also comes through condenser C6 to the grid of tube T3, the signal acting as an applied voltage, alternating in character. Thus tube T3 acts as a rectifier. During the positive half of each cycle of alternation, the plate of tube T3 will draw current, and during each negative halfcycle the tube T3 will not pass current. The resistor R5 is adjusted to such a value that it will not permit excessive current to flow from the plate of tube T3 to the ground (chassis). The resistor R5 also permits a complete circuit from the grids of tubes I and 2 of the cooperating conventional broadcast receiving set. The resistor Re acts as a radio-frequency choke, preventing the leakage of any radio frequency enerI gies which otherwise might leak through tube T3, and keeping the aforesaid radio frequencies from being applied to the grids of tubes I and 2 of the said conventional receiving set.

The grids of the radio frequency tubes in the conventional receiving set become more negative with reference to the cathodes of the same tubes at the time the signal is received on the other receiving set, due to the rectified voltage output from tube Ta. The said output will tend to cut off the plate current from the radio frequency tubes in the conventional receiving set. The tube characteristic of such tubes is completely changed by this and all amplification in the conventional receiving set will cease.

This same output current from tube Ti flowing through the detector of its receiver or interrupter unit will change this signal, initially of the frequency to which the interrupter unit is tuned, from radio frequency to audio frequency, due to the action of the detector tube Tz, and the interrupter unit, being connected in the usual manner to the first audio transformer of the con30: ventional broadcast receiver, the signal is amplified and ultimately changed to sound in the usual way. During this time there is no interference from the signal energy of the conventional receiver. The resistor R4 is a limiting resistor to hold the output of tube T3 to a predetermined value.

The alternating current voltage impressed upon the grid of tube T3, of course, initially is of radio frequency which becomes rectified the same as any other alternating voltage. The rectified or direct current voltage from the plate of T3 is conveyed through the resistor R6 to the low potential end of the tuning coil or coils in the said conventional radio receiving set.

R6 is a high resistance connected from the plate of Ta to the chassis or ground of the conventional radio receiver. Its purpose is to avoid a direct short circuit of any current flowing from the plate of tube T3 and also to permit the tubes of the conventional radio receiving set to operate with their customary grid bias whenever no signal is passing through the interrupter unit.

When a signal is received through the interrupter unit the rectifying action of tube T3 is established immediately and when such signal ceases the rectification also stops at once.

The tube Ta which is thus used as a control tube, is preferably of the same type as tube T2.

The plate or anode of tube Ti is connected to the grid of tube T3 through the coupling condenser C6. When a signal is passing through the tuned circuit of the interrupter unit, said signal produces a small current flow between the cathode and the anode of tube T3, thus producing a small voltage drop. This voltage drop is applied to the grids of tubes 2 and 3 of the conventional: receiving set and serves to provide a high negative bias which will cut off the anode current in these tubes and thereby effectively prevent said tubes from acting as radio frequency amplifiers in the radio frequency portion of the said conventional receiving set.

The lead wire from the tuning coil L2 to condenser Co which is in series in the circuit, and from the condenser Co to the grid of tube T3, feeds the signal frequency only during the operation of the interrupter unit, which interrupter unit includes Ts, R4, R9, Rs, and Ro as shown in the drawing.

Thus when no signal is coming through the grid of T3, no rectification takes place; the only voltage present on the grid of tube T3 is a negative voltage supplied by resistor Ri which is connected to the grid of tube T3, and the resistor Ro which, in turn, is supplied by this negative voltage from the power supply (negative end of Ra), When no signal is being received on the auxiliary receiver, the interrupter unit is not in operation, but because resistor R5 (which is connected to resistor R6 and to the plate of tube T3) is grounded to the chassis, a normal grid-bias voltage is allowed to flow through said resistor.

This bias voltage (approximately 2.5 volts) may be obtained from the conventional broadcast receiver in the manner specified and usual to all conventional broadcast circuits and is preferably obtained in this manner. Between the cathode of any detector or amplifier tube, of the type of tube T3, and the ground (chassis) is inserted a resistor, the value of the resistance being determined by the tube characteristic. One side of this resistor, which is negative, is connected to the ground (chassis) and will permit the cathode to become positive. This is due to the current flowing through the tube, the grid of this tube being connected to a coil which is connected to the ground (chassis) by means of a wire leading to the chassis of the receiving set, or else the said coil may be connected to a resistor, which is connected to the ground (chassis), so that the ground will then become negative with respect to the cathode of the same tube. The above explains the term "negative bias".

The voltage action between the grid and plate output of tube T3 results in the complete and instantaneous interruption of the receiving set on regular broadcast signals and allows the receiving set to function on another signal of a different frequency which is being received 4 through the interrupter unit, such voltage action further causing the receiver automatically and instantly to resume operation on the original signal when the signal to the interrupter unit ceases.

R4 is a high negative bias control resistor for the grid of tube T3 while R6 and RO0 are adjustable bleeder resistors, and R9 is a voltage drop resistor.

Cl0 and C11 are high capacity by-pass condensers to act as a direct radio frequency short circuit between condensers Ca and Cb to tune coils La and Lb of the receiving set.

The filament or heater leads Y from the tubes of the interrupter unit are connected to the Y leads of the receiving set which is of conventional circuit and for that reason is not here described in particular detail except insofar as the interrupter unit is connected to it.

The condensers C' and C2 are semi-adjustable and are initially tuned and set to the desired frequency for operation of the interrupter.

It is to be understood that although in its preferred form our invention includes an interrupter unit responsive to short wave signals such unit may, within the purview of the invention, be responsive to any wave length, either short or long, utilizing any frequency band. Further, the interrupter circuit shown is merely by way of illustration, and may, instead, be adapted for long distance reception by the addition of radio frequency or intermediate frequency amplification stages.

From the foregoing it will be apparent that our invention provides an efficient and compact but inexpensive means for automatically receiving signals of different frequency from that of the receiving set to which it is connected, and without necessitating the use of a separate antenna system, such means functioning automatically to block the signals of one frequency while those of a selected different frequency are being received and translated into sound, and further functioning automatically to resume the audible reception of the signals of the one selected frequency when those of the other selected frequency have ceased. The center tap of the power transformer is negative with relation to the ground (chassis) due to the resistor Ra. The difference in voltage depends upon the current drawn through the resistor Ra and on the resistance of the said resistor.

What we claim is: 1. In combination wtih an antenna and a receiver connected thereto, responsive to signals of a selected frequency and comprising radio frequency and audio, frequency stages, a second receiver circuit responsive to a predetermined signal of different frequency and also connected to said antenna, a control tube in said second receiver circuit, said control tube having a grid, a cathode and an anode, means normally impressing on said grid a potential negative with respect to the cathode and means whereby the negative potential of the said grid is removed when said second receiver is fed with such predetermined signal energy of different frequency, whereby electron flow from the cathode to the anode of said control tube takes place, thus providing an output of current from the said anode, and connections for applying a negative bias derived from the anode current of said control tube to the grids of the radio frequency tubes of the first receiver, thereby automatically blocking the electron flow in such radio frequency tubes and interrupting the audible reception of the signals to which the first receiver is responsive, during the reception of signals of the selected frequency to which the second receiver circuit is tuned. 2. In combination with an antenna and a receiver connected thereto, responsive to relatively long wave length signals and comprising radio frequency and audio frequency stages, a second receiver circuit responsive to a predetermined relatively short wave length signal and also connected to said antenna, a control tube in said second receiver circuit having cathode, grid and anode electrodes, means for normally maintaining said grid negative with respect to said cathode, means for providing a positive voltage on the said grid responsive to passage of a signal through the said second receiver circuit, thereby establishing a relatively large anode-cathode current in said tube, means including a resistance traversed by such current whereby a voltage drop is provided, and means for applying such voltage drop as a negative bias to the grids of the radio frequency tubes of the first receiver, to temporarily prevent such tubes from amplifying, so as to interrupt the audible reception of the long wave length signals during reception of the selected short wave length signals, and a detector tube in said second receiver circuit, the anode lead of which is connected with the anode lead of the first audio stage in said first-named receiver to cause the latter to amplify and render audible the signals impressed upon the short wave length receiver circuit.

3. The combination of two radio receivers tuned to be responsive to signals of different radio frequencies, each receiver including tubes having cathode, anode and grid electrodes, certain of said tubes acting as radio frequency amplifiers, an antenna common to said receivers, a control tube having cathode, anode and grid electrodes and connected in circuit with one of said receivers and having an anode connected to at least one of the grids of the radio frequency amplifier tubes of said other receiver, means for applying a voltage on the grid of said control tube produced by and in response to a signal impressed upon the circuit containing such tube, and thus controlling the action of said radio frequency amplifier tubes through their said connection with the anode of said control tube, whereby when a signal is received by the circuit containing the control tube, audible reception by said other receiver will be interrupted.

4. The combination of two radio receivers tuned to be responsive to signals of different radio frequencies, each receiver including tubes having cathode, anode and grid electrodes, certain of said tubes acting as radio frequency amplifiers, an antenna common to said receivers, a control tube having cathode, anode and grid electrodes and connected in circuit with one of said receivers and having an anode connected to at least one of the grids of the radio frequency amplifier tubes of said other receiver, means for applying a voltage on the grid of said control tube produced by and in response to a signal impressed upon the receiver with which the control tube is in circuit, thereby to produce a gridblocking voltage output from the anode current of said control tube which, being applied through said connection to at least one of the grids of said radio frequency amplifier tubes, interrupts the audible reception of said other receiver.

5. The combination of a plurality of radio receivers tuned to be selectively responsive to signals of different radio frequencies, an antenna common to all of said receivers, a control tube in circuit with one of said receivers and having a grid which is normally maintained at a negative potential with respect to the cathode, but which, when a signal of proper frequency is impressed upon such circuit, produces a corresponding variation of effective impedance of the control tube whereby a pulsating rectified anode current is provided, means to produce a voltage drop from said current, connections between the anode of such tube and the grids of the radio frequency tubes of another receiver, thereby to interrupt the electron flow in said radio frequency tubes and, consequently, to interrupt audible reception through such receiver, by applying said voltage drop as a grid-blocking negative bias on the grids of such tubes through said connections when the anode current in said control tube is increased by the impression of a radio frequency signal upon the circuit in which the control tube is connected, together with an audio amplification system common to all of said receivers.

6. The process of controlling the operation of a first radio receiving set by a second, which consists in tuning the first set to a wave length of signals which are substantially continuously available, whereby said set normally produces an audible response corresponidng to said signals, tuning the second set to a wave length of signalmodulated carrier wave signals which are available only at relatively infrequent intervals, causing said second set to produce an audible response corresponding to said relatively infrequent signals, and at the same time causing the second set to produce a unidirectional voltage upon receipt of said signals, and applying said voltage as a blocking bias in the first set, to interrupt the production of audible response to the continuously available signals thereby, during such infrequent periods of activity of the second set, whereby the second set alone then produces audible sounds.