US2039618A - Automatic control circuits - Google Patents

Description

Ma 5, 193a.

F'i led Feb. 21, 1934 J. YOLLES AUTOMATIC CONTROL CIRCUITS [.F. AMPl/F/ER INVENTOR JACOB LLES ATTORN EY Patented May 5, 1936 UNITED STATES AUTOMATIC CONTROL CIRCUITS Jacob Yolles, Brooklyn, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application February 21, 1934, Serial No. 712,289

10 Claims.

My present invention relates to automatic control circuits for high frequency transmission systems, and more particularly to an improvement in automatic noise suppressor circuits for radio receivers utilizing automatic volume control arrangements.

In my co-pending application Serial No. 638,514, filed October 19, 1932 there is disclosed a background noise suppressor arrangement for a radio receiver employing automatic volume control. The noise suppressor arrangement utilizes a voltage operated condenser for variably attenuating the'audio frequency currents flowing between the demodulator of the receiver and the reproducer in response to variations in received carrier intensity. The voltage operated condenser in the aforesaid application specifically takes the form of the input capacity of an electron discharge tube, the magnitude of the input capacity being varied by changing the gain of the tube in response to variations in received signals.

Improvements in the circuits disclosed in the aforesaid application are shown in my co-pending application Serial No. 696,670, filed November 4, 1933, and in this latter application there is disclosed a circuit arrangement for suppressing undesired noise impulses in a radio receiver employing automatic volume control, the magnitude of the input capacity of the electronic condenser being controlled from a. diode demodulator circuit.

It may be stated that it is one of the main objects of my present invention to further improve the background noise suppressor arrangement disclosed in my last named co-pending application so that the improved circuit arrangement not only functions to substantially eliminate background noise when the radio receiver is operating at maximum sensitivity, but also functions as an automatic tone control circuit.

Another important object of the invention is to provide a noise suppressor circuit for a radio receiver of the type utilizing a diode demodulator circuit for automatic volume control operation, the input capacity of an electron discharge tube being effectively connected between a point of audio frequency potential on the demodulator circuit and ground for providing an audio attenuation path, the magnitude of the said input capacity being varied in response to changes in received carrier intensity.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically one circuit organization whereby my invention may be carried into 5 effect.

In the accompanying drawing there is shown a superheterodyne receiver in conventional manner, the receiver embodying the usual antenna circuit A, a radio frequency amplifier network, a local oscillator feeding a first detector, the radio frequency amplifier also feeding the first detector. The intermediate frequency amplifier 40 has its input electrodes coupled to the output of the first detector through a coupling transformer M which has its primary and secondary windings each tuned to the operating intermediate frequency. The tube 55, a tube of the duplex diode triode type well known to those skilled in the art at the present time, has its diode demodulator circuit coupled to the anode circuit of amplifier tube 4 through a coupling transformer'Mi which has its primary and secondary windings tuned to the intermediate frequency.

The multiple duty tube 55 has its two diode anodes strapped together and connected to the cathode lead through a path which includes in series the tuned input circuit 4|, the radio frequency choke 2, and the load resistor 3. A radio frequency by-pass condenser I is connected in '30 shunt with the choke 2 and resistor 3, and the cathode lead of tube 55 is connected to ground through the usual grid bias network 6. The grounded side of the grid bias resistor of network 6 is connected to the point at the junction of choke 2 and resistor 3 through a path which includes the resistor 5 and condenser 4 in series. The grid of tube 55 is connected to any desired suitable point on resistor 5 through a variable tap 5', and the latter functions as the manual volume control instrumentality since it functions to vary the intensity of the audio energy transferred from the diode demodulator circuit to the audio amplifier section of tube 55.

The diode anodes of tube 55 are disposed outside the electron stream to the grid and plate of the tube, and the audio component of the demodulated voltage developed across resistor 3 is impressed upon the grid of the audio section of tube 55, amplified therein, and then transmitted to the succeeding audio network through the resistance-capacitor network 8, l. The succeeding audio network may comprise one or more audio amplifier tubes and/or a reproducer. The resistor 8, the plate side of which is connected to 55 of tube l2 a condenser II.

ground through a by-pass condenser l0, connects the plate of tube 55 to the +B terminal of the voltage supply source.

The direct current voltage component of the demodulated Voltage developed across resistor 3 is utilized to perform the automatic volume control function. This is accomplished by connecting the grid circuits of the radio frequency amplifier, first detector and intermediate frequency amplifier to the negative side of resistor 3 through the path designated AVC which specifically includes the conductor 6 l as well as the conductors connected to the lead 6| through filter resistor 60.

When no signals are impressed upon the input circuit 4| the voltage developed across resistor 3 is practically negligible, and for this reason the controlled networks are operating at maximum sensitivity. This means that background noise impulses will be greatly amplified, and therefore be reproduced with great intensity. This will occur especially when the tuning means 10, which represents the usual tuning means of a radio receiver, is adjusted between desired station set tings. Furthermore, when receiving distant stations, which obviously are received with weak intensity, the background noise impulses lying in the upper region of the audio frequency spectrum will seriously mask the desired signal.

The direct current voltage developed across resistor 3 is therefore utilized to perform an additional function, and eliminate the disadvantages enumerated in the preceding paragraph. A voltage operated condenser, in the form of the input capacity C1, of tube I2, is varied in magnitude in response to variations of the direct current voltage developed across resistor 3. The input capacity C1 is the grid to cathode capacity of tube l2, and it has been found, as disclosed in my earlier one of the aforementioned co-pending applications, that its magnitude may be augmented by connecting between the grid and plate The augmenting condenser II is connected between the negative side of resistor 3 and the cathode side of resistor 6 through a radio frequency by-pass condenser I4. The condenser M has low impedance to intermediate frequency currents, and this is also true of condenser II and condenser I. The condenser l4, however, has a'high audio impedance compared to the condenser H so that the load resistor 9 in the plate circuit of tube l2 will not be short circuited.

The lead 61 connects the grid of tube l2 to the negative side of resistor 3, and thus a change in the potential value of the negative side of resistor 3 results in a corresponding change in the negative bias on the grid of tube 12. The latter istranslated into a gain variation of tube 12, and, as shown in my aforementioned applications,

this results in a variation 'in the magnitude of the capacity C1, which capacity is shown in dotted lines.

The automatic tone control arrangement as used in the aforementioned applications, and particularly the earlier one, involves a small degree of attenuation which is due to a minimum effect even when the tone control tube is cut off as when receiving strong signals. In some cases where extremely fine fidelity is required, or where the load impedances operated upon are high, it is desirable to eliminate such residual effects. The present arrangement accomplishes such residual effect elimination, and simultaneously permits the tone control grid to be excited by small audio signals to prevent overload.

The tube l2, connected to act as a variable capacity across the audio output of the diode demodulator, lowers the high frequency audio response of the set as the signal strength decreases, and therefore diminishes the noise background which tends to increase as the incoming signal becomes weaker. It will therefore be seen that it operates simultaneously with the automatic volume control so that when the sensitivity or gain of the receiver is increased to compensate for a weak or fading signal, the tube l2 eliminates the increased background noise by increasing its effective capacity C1 across the diode demodulator output.

While I have described one arrangement for carrying my invention into efiect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many modifications may be made without departing from the scope of my invention, as set forth in the appended claims.

What I claim is:-

1. In combination with a receiver provided with a high frequency amplifier and a diode demodulator network, said demodulator network including a load resistor across which is developed a direct current voltage and an audio frequency voltage, an electron discharge tube having its grid to cathode capacity connected to said load resistor and providing an audio frequency attenuation path, a direct current connection between the negative side of said load resistor and the grid circuit of said high frequency amplifier, and a direct current connection between the grid of said electron discharge tube and the said negative side of the load resistor.

2. Ina radio receiver provided with a high frequency amplifier and a multiple duty tube including a diode section and an amplifier section, a network connected to said diode section including a tuned input circuit and a. load resistor, a connection from the grid of said amplifier section to a point of audio potential on said load resistor, a tube independent of said multiple duty tube, said independent tube having its input electrodes connected across the said. load resistor, an augmenting condenser connected between the grid and plate of said independent tube, and a direct current connection between the said negative point on the load resistor and the control grid of said independent tube and the grid circuit of said high frequency amplifier.

3. In an arrangement as defined in claim 2, said augmenting condenser being connected in shunt with the said load resistor.

4. In an arrangement as defined in claim 1, a condenser connected between the grid and plate of the said electron discharge tube for augmenting the overall capacity value of the said grid to cathode capacity.

5. In a receiver of the superheterodyne type, a multiple function stage comprising a tube provided with an amplifier section and a diode section, both of said sections having a common cathode, a resonant input circuit, tuned to the operating intermediate frequency, connected between the diode electrodes of said diode section, a resistor connected between the cathode of said diode section and the low alternating potential side of said resonant input circuit, a network preceding said input circuit for producing the intermediate frequency energy impressed on the input circuit, a connection between the input grid of said amplifier section and a desired point on the diode circuit resistor, said connection being variable, coupling elements arranged in the output electrode circuit of said amplifier section for transmitting energy amplified by said amplifier section to a following utilization network, an auxiliary electron discharge tube including a control grid connected by a direct current connection to a point of negative direct current potential on said diode circuit resistor, a direct current path between the cathode of said multiple section tube and the cathode of said auxiliary tube, and an automatic gain control connection between said preceding network and the direct current connection between the control grid of the auxiliary tube and said diode circuit resistor.

6. In a receiver of the superheterodyne type, a multiple function stage comprising a tube provided with an amplifier section and a diode section, both of said sections having a common cathode, a resonant input circuit, tuned to the operating intermediate frequency, connected between the diode electrodes of said diode section, a resistor connected between the cathode of said diode section and the low alternating potential side of said resonant input circuit, a network preceding said input circuit for producing the intermediate frequency energy impressed on the input circuit, a connection between the input grid of said amplifier section and a desired point on the diode circuit resistor, said connection being variable, coupling elements arranged in the output electrode circuit of said amplifier section for transmitting energy amplified by said amplifier section to a following utilization network, an auxiliary electron discharge tube including a control grid connected by a direct current connection to a point of negative direct current potential on said diode circuit resistor, a direct current path between the cathode of said multiple section tube and the cathode of said auxiliary tube, and an automatic gain control connection between said preceding network and the direct current connection between the control grid of the auxiliary tube and said diode circuit resistor, and a condenser connected between the anode of said auxiliary tube and the control grid thereof.

'7. In a receiver of the superheterodyne type, a multiple function stage comprising a tube provided with an amplifier section and a diode section, both of said sections having a common cathode, a resonant input circuit, tuned to the operating intermediate frequency, connected between the diode electrodes of said diode section, a resistor connected between the cathode of said diode section and the low alternating potential side of said resonant input circuit, a network preceding said input circuit for producing the intermediate frequency energy impressed on the input circuit, a connection between the input grid of said amplifier section and a desired point on the diode circuit resistor, said connection being variable, coupling elements arranged in the output electrode circuit of said amplifier section for transmitting energy amplified by said amplifier section to a following utilization network, an auxiliary electron discharge tube including a control grid connected by a direct current connection to a point of negative direct current potential on said diode circuit resistor, a direct current path between the cathode of said multiple section tube and the cathode of said auxiliary tube, and an automatic gain control connection between said preceding network and the direct current connection between the control grid of the auxiliary tube and said diode circuit resistor, a control grid bias resistor disposed in the cathode circuit of said auxiliary tube, and a common source of positive voltage connected to the output electrode of said amplifier section and the anode of said auxiliary tube.

8. In a receiver of the superheterodyne type, a multiple function stage comprising a tube provided with an amplifier section and a diode section, both of said sections having a common cathode, a resonant input circuit, tuned to the operating intermediate frequency, connected between the diode electrodes of said diode section, a resistor connected between the cathode of said diode section and the low alternating potential side of said resonant input circuit, a network preceding said input circuit for producing the intermediate frequency energy impressed on the input circuit, a connection between the input grid of said amplifier section and a desired point on the diode circuit resistor, said connection being variable, coupling elements arranged in the output electrode circuit of said amplifier section for transmitting energy amplified by said amplifier section to a following utilization network, an auxiliary electron discharge tube including a control grid connected by a direct current connection to a point of negative direct current potential on said diode circuit resistor, a direct current path between the cathode of said multiple section tube and the cathode of said auxiliary tube, and an automatic gain control connection between said preceding network and the direct current connection between the control grid of the auxiliary tube and said diode circuit resistor, a bias resistor in the space current path of said amplifier section, and a direct current connection between a point of negative direct current potential of said bias resistor and the input electrode of said amplifier section.

9. In combination with a high frequency signal transmission tube and a diode demodulator netadapted to develop a direct current voltage and an audio voltage from impressed signals, an audio frequency attenuation path comprising the capacity between at least two electrodes of an electron discharge tube, said capacity being connected to a point on said load impedance, a direct current connection, functioning as a gain control connection, between a gain control electrode of the transmission tube and a point on said impedance, and means for varying the gain of said attenuation tube in response to variations in magnitude of said direct voltage.

10. In a system as defined in claim 9, a reactance operatively associated with said attenuation tube for increasing the magnitude variation range of said capacity.

JAQOB YOLLES.

work, the latter including a load impedance

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