US2012321A - Receiver selectivity control arrangement - Google Patents

Description

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RECEIVER SELECTIVITY CONTROL ARRANGEMENT Filed May 29, 1933 Riff/F158 BY gm A O NEY Patented Aug. 27, 1935 PATENT orrler.

RECEIVER SELECTIVITY CONTROL ARRANGEMENT Rudolf Rechnitzer, Berlin, Germany, assignor to Telefunken Gesellschaft fur Drahtlose Telegraphic in. b. H., Berlin, Germany, a corporation of Germany Application May 29, 1933, Serial No, 673,347 In Germany May 2, 1932 8 Claims. (01. 25020) The present invention relates to radio receivers, and especially to selectivity control arrangements for receivers.

In radio reception it is often necessary to artificially weaken the reproduction of the high side band frequencies in order to avoid disturbance of reception by Waves of other transmitting stations with adjacent transmitting frequencies. To this end receivers are often equipped with a so-called tone control consisting of means for suppressing of high frequencies of the modulating energy obtained by the rectification.

In accordance with the present invention these tone controls are directly coupled with means serving for the change of the sensitivity of the receiver. Experience shows that the suppression of high modulating frequencies in order to avoid disturbances by other stations will only become necessary in the case of reception of weak stations, 1. e. if the receiver is to operate with a high amplification. The organization of broadcasting is such that closely situated stations do not transmit adjacent frequencies; transmitting stations of approximately the same transmitting frequency can generally only then be received with'equal intensity if both transmitters are situated at a far distance, and approximately at equal distances from the place of reception whereby their receiving intensity becomes low.

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, as to both 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 several circuit organizations whereby my invention may be carried into efiect.

In the drawing,

Fig. 1 shows a receiver circuit embodying the invention,

Fig. 2 shows a modified form of the invention,

Fig. 3 is still another modification.

The present invention can be practically executed in various manners. In its simplest embodiment it consists of a mechanical coupling between the volume control device and the tone control device as represented in Fig. 1. In this figure HF is a high frequency amplifier tube, and E is the end, or audio power, tube. The volume control is obtained by a resistance 0 inserted in the grid circuit of the high frequency amplifier tube. The tone control consists of a variable shunt to the useful circuit of the output tube. For the purpose of controlling the shunt a variable resistor R is connected in series with a block condenser C; the variable resistor R is mechanically coupled with the operating means of the grid voltage resistance 0, as shown by the dotted line 3.

According to the embodiment of Fig. 2, an iron choke D, through which the anode current of the high frequency amplifier tube flows, is placed in series to the shunt of the tone control. The iron choke varies its impedance for the speech frequency in accordance with the direct current of the high frequency tube HF by which it is premagnetized, and whichon the one hand depends on the amplification of the arrangement. A conventional automatic volume control (AVC) arrangement is shown connected between the rectifier and the amplifier HF to reduce the sensitivity of the latter as the receiver carrier intensity increases.

According to Fig. 3, the shunt for. the useful circuit of the end tube E comprises an additional electron discharge tube H placed in series with condenser C. Connected in parallel to the auxiliary tube is a resistor W passed by the direct current of the high frequency amplifier tube HF. The variable anode current of the high frequency amplifier produces the anode potential for this auxiliary tube, and varies the resistance of the auxiliary tube in accordance with the amplification of the high frequency amplifier.

The present invention is particularly suited for its application to receivers with automatic volume control in that it weakens considerably the disturbing noises which occur during tuning of such receiving sets between tuning positions. Such AVC arrangements are conventionally shown in Figs. 2 and 3. As is well known, the rectifier anode current may be used to provide a control potential drop across an impedance in the rectifier anode circuit.

It is obvious that in series with the automatically varying means for the tone control in Fig. 3, additional manually operated means may be provided, in order to limit, or eliminate, at will the efiectiveness of the automatic control. As means for this purpose the use of a manually operated shunted resistor R, is suitable. Also, it is to be understood that the tube HF may be an intermediate frequency amplifier of a superheterodyne, and the rectifier the usual second detector, or both may be tuned radio frequency and tuned detector of a tuned radio frequency receiver.

What is claimed is:

1. A radio receiver comprising a tunable radio frequency amplifier, means for varying the grid bias of the latter to regulate the amplification of said amplifier, a detector, an audio amplifier, a tone control path connected to the output circuit of the audio amplifier, a connection from the output circuit of the radio amplifier to the tone control path, the latter including means for varying the transmission of currents of higher audio frequency therethrough in the same direction as the change in amplification of said radio amplifier.

2. In a receiver, as defined in claim 1, said grid bias varying means including an automatic volume control arrangement.

, 3. In a receiver, as defined in claim 1, a source of voltage for the anode of said radio amplifier, said connection from the radio amplifier output circuit being additionally connected to a positive potential point on the source, and an element of variable impedance to audio frequency currents having one side connected to said positive point and its other side to said connection and tone control path.

4. In a receiver, as defined in claim 1, said grid bias varying means including an automatic volume control circuit, a source of energizing voltage for the anodes of the. radio and audio amplifiers, and an element of variable impedance to audio currents connected on one side to said source and on its other side to said radio amplifier output circuit connection and said tone control path.

5, Inaradio receiver of the type including a tunable radio frequency amplifier, a demodulator and an audio network, means for automatically regulating the gain of the amplifier in a sense to maintain the signal input substantially constant regardless of fluctuations in the signal input to said amplifier, an audio frequency attenuation path connected to said audio network, said path including as a control means thereof an element arranged in the anode circuit of said amplifier, said element having an impedance to audio frequency current which varies to increase the flow of the higher audio frequencies through said path as the flow of direct current through said amplifier anode circuit increases.

6. In a receiver, as defined in claim 5, said element consisting of a choke coil.

'7. In a receiver, as defined in claim 5, said element consisting of an electron discharge tube whose space current path is arranged in series with said attenuation path.

8. In a radio receiver comprising a high frequency amplifier having tuning means, a demodulator and an audio amplifier, an automatic volume control circuit for varying the sensitivity of the amplifier to maintain the signal input to the demodulator constant, and means for rendering the receiver response to the higher audio frequencies inefficient when the signal input to the tuned amplifier falls below a desired intensity level, the last means comprising an audio frequency by-pass path connected to the audio amplifier, said path including as an element thereof an impedance arranged in the tuned amplifier anode circuit and whose audio conductivity varies in response to the variation of direct current flow through the said anode circuit.

RUDOLF RECHNITZER. 35

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