US2264782A - Modulated-carrier signal receiver - Google Patents

Description

Dec. 2, 1941. I H. A. WHEELER MODULATED-CARRIER SIGNAL RECEIVER Filed Sept. 14, 1939 'uuodua 0 among Y NQE NE Emmi INVENTOR AROLD A. WHEEL ATTORN EY Patented Dec. 2, 1941 MGDULATED- CARRIER SIG-N RECEIVER Harold A. Wheeler, Great Neck, N. Y., ass'ignor to. Hazeltinc Corporation, a corporation of Delaware- Application September 14, 1939, Serial- No. 294,848

6 Claims.

This invention relates generally to modulatedcarricr signal receivers and particularly to such receivers adapted to receive asignal of relatively highv carrier frequency and having a relatively narrow band of modulation-frequency components.

There are several inherent diificulties encountered in the reception of a modulated-carrier signal having a relatively high carrier frequency and a relatively narrow band of modulation-frequency components which are not encountered in receiving signals having relatively wide modulation bands. For instance, it is impracticable to maintain in alignment the several tuned circuits in the selector channel of a receiver having a response characteristic sufiicien-tly' sharp to select a particular station separated by only 1'0 kilocycles from adjacent stations, as is customary in the broadcast band. The reason for this is that the difficulty in aligning the selective circuits increases with decreasing relative band Width, that is, the ratio of the width of the pass band to its mean frequency. In brief, it is diificult to maintain sharply-tuned circuits in alignment with the degree of accuracy which is necessary to provide an operative receiver due to the fact that the tuning of the individual circuits is subject to frequency shifts due to aging of the circuit elements, temperature rise, and other causes.

Therefore, it is a practical necessity to increase the width of the channels allotted transmitting stations operating at very high frequencies in order that the receivers utilized for reception of the signals transmitted may be, designed for operation with some practicable relative band width. While receivers designed to operate with a. practicable relative band width have. sufficient. selectivity toseparate signals on adjacent channels, the incoming noise. tov which the. receiver is responsive is a function of the width of the pass band of the receiver. It is, therefore, desirable to provide such a receiver with at least one sharply-selective circuit in its channel, thereby eliminating as much noise as possible. However, such a receiver must be very critically tuned, rendering an automatic tuning control means a practical necessity. The automatic tuning control means for such a receiver must also be very sharply selective; that is, it must be at least as selective as the sharply-selective circuit in the signal-translating channel of the receiver. However, if the selective circuit of the automatic tuning control means is not accurately aligned with the mostselective circuit of the signal-translating channel of the receiver, the automatic tuning means will be useless. As brought. out above, it is difficult to maintain in alignment two such selector circuits having very narrow relative band widths.

It is an object of the present invention, therefore, to provide a modulated-carrier signal receiver in which one or more of the above-mentioned diiiiculties of receivers of the prior art are eliminated.

It is a further-object of the invention to provide a modulated-carrier signal receiver having an automatic tuning control, in which a single highly-selective circuit in the signal translating channel is also utilized asthe selective circuit, of the automatic tuning or frequency control means.

In accordance with the invention, a modulatedcarrier signal receiver comprises a carrier-frequency band-pass selecting system adapted to translate a desired signal-carrier wave and having an output circuit and including only one sharplytuned stage having a response peal; imparting to the selecting system an effective pass band substantially narrower than that of any of the other portions. of said system and perhaps comparable in width to the width of the carrierfrequency and sideband-frequency components of the signal to be translated by saidsystem. Signal-detecting and reproducing means are coupled to the output circuit of the selecting system so they are subject to the full selectivity of the sharply-tuned stage and there is also provided means including the single sharply-tuned stage of the selecting system and dependent mainly on the selectivity characteristic thereof for deriving an automatic frequency con-trol effect. There are provided also means for utilizing the derived control elfect to adjust the frequency difference between the signal-carrier wave and the response peak of the sharply-tuned stage to maintain the receiver accurately in tune. Y

A sharply-tuned stage of the kind under consideration provides an effective pass band which is subject to frequency shifts due to agingof circuit elements, temperature rise, and other causes. Preferably, one or more broad-band selectors are also included in the selective system, having apassv band sufiiciently wide to include at least the effective pass band of the sharplytuned stage and the frequency shifts of all the selective circuits. Preferably, several or all of the broad-band selector or selectors are included in the signal-translating channel of the receiver ahead of the sharply-tuned stage. Also, in accordance with a preferred embodiment of the invention, the means for deriving an automatic frequency control effect comprises means for rectifying voltages dependent on the sum and difference of voltages across a preceding broad-band selector and the single sharply-selective circuit included in the sharply-tuned stage in the signaltranslating channel of the receiver.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the accompanying drawing, Fig. 1 is a circuit diagram, partly schematic, of a modulatedcarrier signal receiver of the superheterodyne type incorporating the invention, while Fig, 2 comprises a series of curves utilized to illustrate certain of the operating characteristics of the receiver of Fig. 1.

Referring now more particularly to the drawing, the receiver illustrated comprises a carrierfrequency selector Ill having an input circuit coupled between an antenna H and ground I2 and an output circuit coupled to an intermediate-frequency amplifier I3. The carrier-frequency selector Ii] may comprise the conventional radio-frequency and oscillator-modulator units of a conventional superheterodyne receiver circuit and preferably incorporates push-buttons M for tuning the receiver to predetermined selected stations. Connected in cascade with the output circuit of intermediate-frequency amplifier |3 in the signal-translating channel of the receiver are a carrier-frequency band-pass selecting system I5, a detector IS, an audio-frequency amplifier I1, and a sound reproducer l8. An automatic volume control 8 is provided having an input circuit coupled to inductance 9, inductively coupled to inductance 20, and an output circuit coupled to one or more of the tubes of carrier-frequency selector l and intermediate-frequency amplifier l3 to control the gain of the receiver in a conventional manner.

Considering first the operation of the receiver as a whole, without regard to the details of the portion of the receiver constituting the present invention, presently to be described, a desired received signal is selected, amplified, and converted to a modulated intermediate-frequency signal by carrier-frequency selector H). all in accordance with conventional practice. The signal as thus converted is further amplified in unit l3, selected in signal-selecting system l5, and translated therethrough to detector l6, wherein the audio-frequency modulation components are derived. The audio-frequency components are, in turn. amplified in audio-frequency amplifier l1 and reproduced by sound reproducer IS. The automatic volume control 8 serves to maintain the signal input to detector l6 within relatively narrow limits for a wide amplitude range of received signals.

Referring now to the portion of the system constituting the present invention, there is provided in the carrier-frequency band-pass selecting system l5, which is adapted to translate a desired intermediate-frequency signal carrier wave, a band-pass selector IQ for passing a relatively wide or broad band of frequencies and including transformer 21], 2| having its windings respectively tuned by condensers 22, 23 to the intermediate-carrier frequency. A terminal resistor 24 is coupled across the winding 2| to increase the uniformity of response of the selector. There is also provided in selective systern l5 2. sharply-tuned stage comprising a parallel-connected inductance 25 and condenser 25, and an output circuit comprising an inductance 21 inductively coupled to inductance 25 and effectively coupling the sharply-selective resonant circuit 25, 26 to the input circuit of detector l6 with full sharpness of selectivity.

In order to provide an automatic frequency control for the receiver, there is provided means separate from the signal-detecting means l6 and including the sharply-tuned stage 25, 2B and dependent primarily on the selectively characteristic thereof for deriving an automatic frequency control effect. This means comprises a pair of rectifiers 3|], 3| coupled to the signal-translating channel of the receiver by means of an inductance 32 inductively coupled to inductance 20 and an inductance 33 inductively coupled to sharply-tuned circuit 25, 26. The connections are such that there is applied to one of the rectifiers a voltage dependent on the sum, and to the other a voltage dependent on the difference, of the voltages across the broadly-tuned circuit 2 2|, 22, 23 and the sharply-tuned circuit 25, 26. The rectifiers and 3| are provided with load resistors 35 and 36 shunted by condensers 3'! and 38, respectively, in order to derive therefrom an automatic frequency control effect. The receiver includes means for utilizing the derived automatic frequency control effect automatically to adjust the frequency difference between the intermediate-frequency signal-carrier wave and the response peak of the sharply-tuned stage 25, 25 comprising a frequency-control unit 42. The difference of the output voltages of the rectifiers 38, 3| is applied through a modulation-rejecting filter network including a series resistor 40 and a shunt condenser 4| to the input circuit of the frequency-control unit 42, effective upon variation of its control bias derived from rectifiers 3|], 3| to adjust the tuning of the carrier-frequency selector unit If] in a conventional manner. It will be understood that the selector circuits of carrier-frequency selector l0 and intermediate-frequency amplifier I3 have relatively wide pass bands in order that they may be properly aligned and maintained in alignment dur ing the life of the receiver.

In considering the operation of the circuit of the invention, it will be assumed that the overall frequency-response or selectivity characteristic of the signal-translating channel of the receiver up to the point at which tuned circuit 20, 2|, 22, 23 is coupled is as represented by curve A of Fig. 2 and has an approximately uniform response between cutoff frequencies f1 and f2 over a relatively wide frequency band. The fre-v quency-response characteristic of the single sharply-tuned selector circuit 25, 26, included in the signal-translating channel of the receiver at a point succeeding the broadly-tuned circuit 20, 2|, 22, 23, is illustrated by curve B of Fig. 2. The sharply-tuned stage comprising the selector circuit 25, 26 thus has a response peak imparting to the band-pass selecting system l5 an effective pass band substantially narrower than that of any other portion of this system. The selectivity characteristic illustrated by curve A, therefore, is designed to be only sufficiently sharp to eliminate interference due to stations on adjacent signal channels, while the selectivity characteristic illustrated by curve B is designed to be highly selective at frequency in in order to redues to a minimum the effect of incoming noise,

which. is a function of the pass band of the selector. Thus, the signal-detecting and reproducing means, comprising the units Hi, l1 and I8, which are coupled to the output of the bandpass selector system l are completely subject to the selectivityof the sharply-tuned. stage com;-

prising the sharply-tuned circuit 25, 2'6. Tuned circuit 25, 26: will be subject to some unpredictable frequency shifts due to changes in the capacitance value of condenser 26 and other causes but, due to the broad pass band of" the other circuits of the selective system of the receiver, an operative alignment is at all times maintained. The over-all effect is as though the peak of the selectivity curve B rode across the top of the curve A, resulting in no change in the over-all selectivity of the receiver;

It will be seen that a voltage varying in accordance with the vectorial sum of the voltages shown by curves A and B is applied to one of the rectifiers and that a voltage varying in accordance with the vectorial difference of these voltages is applied to the other of the rectifiers. The difference of the output voltages of the rectifiers 30, 3| is applied to frequency control unit 42 and varies in accordance with curve C of Fig. 2. Thus, the rectifiers 30, 3!, the inductances 32, 33, the load resistors 35, 36 and the condensers 31, 38 comprise means for deriving and rectifying voltages individually dependent on the sum and difference of voltages of the broad-band selector 20, 2!, 22, 23 and the sharply-tuned circuit 25, 26 to drive an automatic frequency control bias. That is, the inductances 32 and 33 comprise means for deriving and applying with opposite polarity to each of the rectifiers 38, 3i a voltage varying in accordance with the output of the broad-band selector 20, 2|, 22, 23 and for deriving and applying to each of the rectifiers 38, 3| in series with the last-named voltage and with the same polarity a voltage varying in accordance with the voltage across the sharply-tuned circuit 25, 2B in order to derive an automatic frequency control bias for the receiver. It is seen that the control voltage applied to frequency control unit 42 and illustrated by curve C is very steep in the vicinity of the frequency in to which the sharply-selective circuit 25, 25 is tuned and that this steep portion of the curve is subject to any frequency shift to which tuned circuit 25, 26 is subjected. The automatic frequency control bias is, therefore, effective to adjust to a minimum the frequency difference between the intermediate-frequency signal and the response peak of the sharplytuned circuit 25, 26. Due to the fact that there is only a single sharply-selective circuit, namely 25, 26, included in the signal-translating channel of the receiver and in the automatic frequency control arrangement of the receiver, there is present no problem of aligning a plurality of sharply-tuned circuits.

It will be understood that the system is so designed that the difference between the intermediate-carrier frequency of the signal and the peak frequency of sharply-tuned circuit 25, 26 is maintained substantially at zero for doublesideband operation, or at the proper value for single-sideband operation if desired.

It will be understood that the system described above may be utilized in the sound channel of a television receiver and that the frequency control unit 42 may be used to control an oscillator which operates on the entire received signal, both sound and picture. When the system is so employed, the unit 42 controls the frequency of both the sound and picture channels at once. In this way, the sound channel furnishes a sharp frequency control for the picture channel even though the picture channel does not include any sharply-selective circuits suitable for this purpose.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that Various changes and modifications maybe made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope" of the invention.

What is claimed is:

l. A modulated-carrier signal receiver comprising, a carrier-frequency band-pass selecting system adapted to translate a desired signalcarrier wave and having an output circuit and including only one sharply-tuned stage having a response peak imparting to said selecting system an effective pass band substantially narrower than that of any other portion of said system, signal-detecting and reproducing means coupled to said output circuit of said selecting system and completely subject to the selectivity of said sharply-tuned stage, means including said sharply-tuned stage and dependent primarily on the selectivity characteristic thereof for deriving an automatic frequency control effeet, and means for utilizing said effect automatically to adjust the frequency difference be-' tween said signal-carrier wave and the response peak of said sharply-tuned stage.

2. A modulated-carrier signal receiver comprising, a carrier-frequency selecting system adapted to translate a desired signal-carrier wave and having an output circuit and including only one sharply-tunedv stage having a response peak imparting to said selecting system an effective pass band substantially narrower than any other portion of said system, said effective pass band being subject to frequency shifts, a broad-band selector in said system having a pass band wider than sufiicient to include said effective pass band notwithstanding said frequency shifts, signaldetecting and reproducing means coupled to said output circuit of said selecting system and completely subject to the selectivity of said sharplytuned stage, means including said sharply-tuned stage and depending primarily on the selectivity characteristic thereof for deriving an automatic frequency control effect, and means for utilizing said effect automatically to adjust the frequency difference between said signal-carrier wave and the response peak of said sharply-tuned stage.

3. A modulated-carrier signal receiver comprising, a carrier-frequency selecting system adapted to translate a desired signal-carrier wave and having an output circuit and including only one sharply-tuned stage having a response peak imparting to said selecting system an effective pass band substantially narrower than any other portion of said system, said effective pass band being subject to frequency shifts, a broad-band selector in said system at a point preceding said sharply-tuned stage and having a pass band sufficient to include said effective pass band notwithstanding said frequency shifts, signal-detecting and reproducing means coupled to said output circuit of said selecting system and completely subject to the selectivity of said sharplytuned stage, means including said sharply-tuned stage and depending primarily on the selectivity characteristic thereof for deriving an automatic frequency control effect, and means for utilizing said effect automatically to adjust the frequency difference between said signal-carrier Wave and the response peak of said sharply-tuned stage.

4, A modulated-carrier signal receiver comprising, a carrier-frequency selecting system adapted to translate a desired signal-carrier wave and having an output circuit and including only one sharply-tuned circuit having a response peak imparting to said selecting system an effective pass band substantially narrower than any other portion of said system, said effective pass band being subject to frequency shifts, a broad-band selector in said system having a pass band sufficient to include said effective pass band notwithstanding said frequency shifts, signal-detecting and reproducing means coupled to said output circuit of said selecting system and completely subject to the selectivity of said sharplytuned circuit, means for deriving and rectifying voltages individually dependent on the sum and difference of voltages of said broad-band selector and said sharply-tuned circuit to derive an automatic frequency control bias, and means for utilizing said bias automatically to adjust the frequency difference between said signal-carrier wave and the response peak of said sharplytuned circuit.

5. A modulated-carrier signal receiver comprising, a carrier-frequency selecting system adapted to translate a desired signal-carrier wave and having an output circuit and including only one sharply-tuned circuit having a response peak imparting to said selecting system an effective pass band substantially narrower than any other portion of said system, said effective pass band being subject to frequency shifts, a broad-band selector in said system having a pass band sufficient to include said effective pass band notwithstanding said frequency shifts, signal-detecting and reproducing means coupled to said output circuit of said selecting system and completely subject to the selectivity of said sharplytuned circuit, two rectifiers, means for deriving and applying with opposite polarity to each of said rectifiers a voltage varying in accordance with the output of said broad-band selector and for deriving and applying to each of said rectifiers in series with said last-named voltage and with the same polarity a voltage varying in accordance with the voltage across said sharplytuned circuit in order to derive an automatic frequency control bias for said receiver, and means for utilizing said bias automatically to adjust the frequency difference between said signalcarrier wave and the response peak of said sharply-tuned circuit.

6. A modulated-carrier signal receiver comprising, a carrier-frequency band-pass selecting system adapted to translate a desired signalcarrier wave and having an output circuit and including only one sharply-tuned stage having a response peak imparting to said selecting system an effective pass band substantially narrower than that of any other portion of said system, signal-detecting and reproducing means coupled to said output circuit of said selector system and completely subject to the selectivity of said sharply-tuned stage, means separate from said signal-detecting means and including said sharply-tuned stage and dependent primarily on the selectivity characteristic thereof for deriving an automatic control effect, and means for utilizing said effect automatically to adjust the frequency difference between said signalcarrier wave and the response peak of said sharply-tuned stage.

HAROLD A. WHEELER.

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