US2235859A - Single-sideband modulated-carrier receiver - Google Patents

Description

AMardi 25, 1941. J, Q WILSON SINGLE-SIDEBAND MODULATED-CARRIER RECEIVER Ich ATTORN EY llff) Patented Mar. 25, 1941 UNITED STATES man PATENT cerros John C. Wilson, Bayside, N. Y., assignor to Hazeltine Corporation, a corporation of Delaware Application February 2, 1940, `Serial No. 316,873

1t Claims.

This invention relates to modulated-carrier signal receivers adapted for single-sdeband reception and, more particularly, to such receivers capable of reproducing a received signal with uniform response over the modulation-frequency band.

Under some circumstances, it is desirable to provide a modulated-carrier signal system `adapted for single-sideband transmission and reception. inasmuch as the effective band Width of such 1a system is much less than that of a system adapted for double-sideb-and operation, the noise input tothe receiver is much less. Furthermore, it is frequently impossible, in the case of double-sideband transmission, to receive one sideband of a transmitted signal for the reason that there may be interference Within such sideband due to a station on an adjacent channel. While the adjacent station may preclude doublesideband reception, it may `not unduly interfere With the reception and satisfactory reproduction of the other sideband of the transmitted signal.

In single-sideband modulated-carrier systems, it is generally impracticable to provide cutoi characteristics, either at the receiver or at the transmitter, which are steepgenough so that only one sideband and the carrier Wave are present in the translated signal While Iall of the other sideband components ci the signal are suppressed. Therefore, in most practical single-sideband systems, the translated signal comprises doublesideband components of a given `frequency range and single-sideband components of frequencies outside of the given frequency range. If both sidebands of a signal are translatedvby the receiver over a portion of the Inodulation-sideband range of the signal and only one sideband is translated over .the remaining portion of the range, in a receiver having uniform gain over its entire pass band, the signal components corresponding to the portion over which both sidebands are translated are reproduced with double amplitude and thus effectively provide an amplitude distortion of the reproduced signal.

In order to eliminate the amplitude distortion described above, it has been customary to provide an amplification of the signal components corresponding to double-sideband reception half that of the components of the received signal corresponding to single-sideband reception. Specifically, it has been the general practice in the design of prior art single-sideband receivers .to locat-e the signal-carrier` Wave at the half-amplitude point on the slope of the carrier-frequency band-pass characteristic of the selective circuits' of the receiver and to cause the frequency range `covered by the sloping portions ci the characteristics on opposite sides of the carrier frequency to correspond to the frequency range of the received signal in which both sidebands Which are to be reproduced are present. Such prior-art systems, however, are subject to the disadvantage that a critical tuning of the receiver is necessary to ensure location of the signal-carrier vtave at the half-:amplitude point or the sloping portion of the band-pass characteristic of the selector circuits. The design of such receivers is further made critical by the fact .that the shape of the band-pass characteristic of the carrier-frequency selective circuits of the receiver must be so adjusted that the sloping part of the band-pass characteristic, upon which the signal-carrier frequency is located, substantially corresponds With the frequency range of the double-sideband components of the signal which are to be reproduced.

It has also been proposed, in order to eliminate the above-mentioned amplitude distortion in a single-sideband receiver, to provide a uniform amplification in the carrier-frequency portions of the receiver and to provide the necessary amplitude compensation in the modulation-frequency portion of the receiver. However, in such receivers, it is necessary to provide a particular modulation-frequency band-pass characteristic in order to secure the desired compensation and such shaped characteristic is more complex in design and more critical in adjustment than the simple uniform response characteristic. It is desirable, therefore, to provide a single-sideband receiver in which uniform gain may be provided in both the carrier-frequency portions of the receiver and modulation-frequency portions of the receiver and which includes a simple arrangement to eliminate amplitude distortion of the type mentioned above.

Also, it is Well known that distortion is minimized by the use of a linear detector for doublesideloand reception While distortion is minimized for single-side band reception by the use of a square-law detector. A linear detector may be used Without undue detector distortion in a single-sideband system only Where the percentage of modulation is small. It is desirable, therefore, to provide a receiver adapted to receive doublesideband components of a given frequency range of the received signal and to receive single-sideband component-s outside of this range, in which detector distortion is minimized for the detection of modulation components or each oi the two types.

It is an object of the invention, therefore, to provide an improved receiver adapted to receive double-sideband components of .a received modulated-carrier signal corresponding to a given frequency range and single-sideband components of the signal outside of the given frequency range.

It is a further object of the invention to provide a receiver adapted to receive double-sideband components of a received modulated-carrier signal corresponding to a given frequency range and single-sideband components of the signal outside the given frequency range, in which a simple arrangement is provided to compensate for amplitude distortion due to the reception of both double-sideband components and singlesideband components of the received signal.

It is still another object of the invention to provide a receiver adapted to receive doublesideband components of a received modulatedcarrier signal corresponding to a particular frequency range and single-sideband components of the signal outside of the given frequency range, in which detector distortion is minimized in the detection of the received signal components of each type.

In accordance with the invention, a modulatedcarrier signal receiver comprises means for detecting only double-sideband components of a given frequency range of the signal and means for detecting single-sideband components of the signal outside of the given range. The two detecting means include means for deriving, from a signal input of given amplitude,detectoroutputs therefrom of predetermined relative amplitudes. Means are further provided for combining and reproducing the detected signal components. Also in accordance with a modification of the invention, the two detecting means are of types adapted to minimize distortion for both the double-sideband components and the single-sideband components.

For a better understanding of the present 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 television receiving system including detector circuits embodying the invention; Fig. 2 comprises a graph illustrating certain of the operating characteristics of the receiver of Fig. l; Figs. 3 and 5 are circuit diagrams of modifications of the portion of the system of Fig. 1 embodying the present invention; while Figs. 4 and 6 comprise graphs illustrating, respectively, certain of the operating characteristics of the circuits of Figs. 3 and 5.

Referring now more particularly to Fig. 1 of the drawing, the system illustrated comprises a receiver of the superheterodyne type including an antenna system Ill, II connected -to a radiofrequency amplifier I2 to which are connected in cascade, in the order named, an oscillator-modulator i3, an intermediate-frequency amplifier I4, a signal-selecting and detecting system I5 designed in accordance with the present invention, a video-frequency amplifier I6, and a signalreproducing device I'I preferably of the cathoderay tube type. A line-scanning generator I8 and a field-scanning generator I9 are also coupled to detector I5 through a synchronizing-signal separator 25 and connected to the scanning elements of the signal-reproducing device I'I through terminals 2I and 22. respectively, in a conventional manner. The stages or units I-I4, inclusive, and II-2Il, inclusive, may all be of conventional well-known construction so that detailed illustrations and descriptions thereof are unnecessary herein.

Referring briefly, however, to the operation of the system described above, television signals intercepted by the antenna circuit I 0, I'I are selected and amplified in radio-frequency amplier I2 and applied to the oscillator-modulator I3 wherein they are converted to intermediate-frequency signals which, in turn, are selectively amplified in the intermediate-frequency amplifier I 4 and delivered to the signal-selecting and detecting system I5. The modulation components of the signal are derived by unit I5 in a manner to b described more fully hereinafter and supplied to the video-frequency amplifier I6 wherein they are amplified and from which they are supplied, in the usual manner, to a brightness-control electrode of the signal-reproducing device I'I. Synchronizing signals derived from detector I5 are applied through synchronizing-signal separator 20 to line-scanning generator I8 and fieldscanning generator I9. The intensity of the electron beam of the signal-reproducing device I 'I is thus modulated or controlled in accordance with the video-frequency voltages impressed upon the brightness-control electrode of the device II, for example, the control grid of a cathode-ray tube, in the usual manner. Saw-tooth current or voltage scanning waves are generated in the linescanning and field-scanning generators IS and I9, respectively, which are controlled by synchronizing voltage pulses applied from detector I5 through synchronizing-signal separator 20, and are applied to the scanning elements of signal-reproducing device I1 to produce electric scanning fields, thereby to defiect the ray in two directions normal to each other so as to trace a rectilinear scanning pattern on the screen of the device, thereby `to reconstruct the transmitted image.

Referring now more particularly to the portion of the system of Fig. 1 embodying the present invention, the signal-selecting and detecting system I5 is coupled to the output of the carriersignal translating channel of the receiver which comprises means for uniformly translating the received carrier wave and its sideband components to be reproduced. The detecting system I5 comprises a filter A coupled to intermediate-frequency amplifier I4 for selecting therefrom only the carrier wave and the doublesideband components of the signal to be reproduced. A diode detector 25 is coupled to the output circuit of filter A and thus comprises means for detecting only double-sideband components of a given frequency range and has associated therewith a load circuit including an adjustable resistor 26 Icy-passed for carrierfrequency signals by a condenser 21. The unit I5 also comprises a filter B coupled to the output circuit of intermediate-frequency amplifier I4 for deriving therefrom the carrier wave component and the single-sideband components of the received signal which are to be reproduced and which are outside of the frequency range of the double-sideband components of the signal which are to be reproduced. A diode detector 28 is coupled to the output circuit of filter B and, therefore, comprises means for detecting single-sideband components outside the range of the double-sideband components detected by de- .tetor 25 and has associated therewith a load resistor 29 by-passed for carrier-frequency currents by condenser 3l). The signal outputs of detectors 25 and 28 are connected in series with additive polarity and applied to the input circuit of video-frequency amplifier I6 so th'at means are thus provided for deriving from a carrier-signal input of given amplitude detector outputs of predetermined amplitudes, preferably of equal amplitudes, and for combining and reproducing the detected signal components,

Reference is made to Fig. 2 for an explanation of the operating characteristics of the portion of the system of Fig, 1 constituting the present invention. Fig. 2 illustrates certain of the frefluency-amplitude characteristics of the circuit of the invention.. It Will be assumed that the frequency of the carrier wave to be received is fc, that the double-sideband components of a given frequency range to be reproduced lie Within the range f1 to fz, and that the single-sideband components of the signal to be reproduced lie Within the range fz to f3. Filter A is designed to have a band-pass characteristic, such as represented by curve by, so that only the carrier-Wave component and the sideband components of the signal between frequencies f1 and f2 are applied to detector 25. Filter B is designed to have a bandpass characteristic, such as represented by the curves a and c of Fig. 2, so that only the carrier- Wave component andthe single-sideband components to be reproduced are transmitted to detector 28. Therefore, detector 25 is effective to operate substantially purely as a double-sideband ldetector and detector 28 is effective to operate substantially purely as a single-sideband detector. Ii the signal-input amplitudes of detectors 25 and 28 were identical, and they were provided with identical `output circuits, an undesired amplitude distortion of the reproduced signal would result for the reason that each of the two corresponding sideband components of detector 25 contributes to the amplitude of the reproduced signal corresponding to these sideband components as explained above, while only a single sideband contributes to the signal output of detector 2B. Therefore, it is necessary to provide a signal input for detector 25 which, for a given signal input to the system, is effectively half theamplitude of the signal input to detector 28 in order to develop an output from detector 25 substantially equal to that developedby detector 25. Resistor 25, included in the output circuit of detector 25, can also be varied to adjust the relative amplitude of the signal outputs of detectors 25 and 28.

Furthermore, lilter B may be effective to increase the amplitude of the carrier Wave a relative to the amplitude of the sideband signals represented by curve c so that the carrier-Wave output is large in amplitude compared to the single-sideband components and detector distortion is minimized in the linear detector 28 even though the received signal originally did not have a high modulation coefficient.

The input signal to synchronizing-signal separator 2l) is taken only from detector 25 for the reason that the fundamental and all of the necessary harmonic components of the synchronizing signal are Within the frequency range f1 and fz.

The modification of the `invention represented in Fig. 3 is generally similar to that of Fig. 1 and similar circuit elements have identical reference characters. It will be understood that the remaining portions of the receiver of Fig. 3, which are not illustrated, may be identical with those of Fig. 1 and that the circuit of Fig. 3 can be connected into the receiver circuit of Fig. 1 by connecting terminals A and B to corresponding terminals of Fig. 1 and connecting the terminals of the synchronizing-signal, separator and scanning generators to corresponding terminals of the receiver of Fig. 1. The circuit 0f Fig. 3 comprises a detector 35 corresponding generally to detector 25 of Fig. 1. A triode detector 38 is provided which corresponds generally to detector 28 of Fig. 1, the detector 38 being of the biased triode type to provide anode-circuit detection of the square-law type. A suitable grid leak 32 and bias source 33 are provided for detector 38. Unidirectional operating potentials are provided for detector 38 through load circuit 39, and resistor 36 is adjustable in order that the amplitude of the output of detector 35 may be adjusted. The outputs of detectors 35 and 3B are combined in video-frequency amplifier l5 Which comprises a double-triode tube with a common output circuit, the signal output of detectors 35 and 38 being applied individually to the input circuits of the triode sections of the tube.

Reference is made to Fig. 4 for an explanation of certain of the operating characteristics of the circuit of Fig. 3. The curves of Fig. 4 are identical with those of Fig. 2 and the general operation of the circuit of Fig. 3 will be readily understood from the description given above with reference to the operation of the circuit of Fig. 1. It will be understood that the adjustable resistor 36 may be adjusted to provide the proper amplitude of the signal output of detector 35 in order.

to minimize amplitude distortion of the type mentioned above. Also as brought out above, distortion is minimized in single-sideband de-l tection by the use of a square-law detector and is minimized in double-sideband detection by the use of a linear detector. Therefore, a suitable detector effective to minimize distortion is provided in the circuit of Fig. 3 for each portion of the sideband range to be reproduced.

The circuit of Fig. 5 is generally similar to that of Fig. l and similar circuit elements have identical reference numerals. It Will be understood that the circuit of Fig. 5 may be connected into the receiver circuit of Fig, 1 by connecting the terminals of Fig. 5 to the terminals of Fig. 1 having corresponding reference numerals. The circuit of Fig, 5 differs from that of Fig. 1 only in the band-pass characteristics of filter B and in the relative polarity with which the signal outputs of detectors 25 and 28 are combined. Filter B' is so designed as to be effective to trans mit the carrier Wave and all sideband components of the signal to be reproduced.

Reference is made to Fig. 6 for an explanation of the operating characteristics of the circuit of Fig. 5. Curve c illustrates the band-pass characteristic of filter B. It is thus seen that lter B' is effective to pass sideband-signal components from frequency f1 to f3. Curve b represents the band-pass characteristic of the filter A of the circuit of Fig. 5 and is shown reversed for the reason that it is desired to combine difierentially the signal outputs of detectors 25 and 28.

`In considering the operation of the circuit of Fig, 5 with reference to the curves of Fig. 6, it will be seen that all signal components to be reproduced are translated by detector 28 and, in the absence of detector 25, an amplitude distortion of the type mentioned above would result for the reason that a portion of the reproduction is derived from double-sideband'components of the signal and a remaining portion of the reproduced signal is derived from single-sideband components of the signal, which has the effect of unduly increasing the amplitude of the reproduced signal within the range f1 to fz. Therefore, detector 25 is designed to develop an output corresponding only to the double-sideband components of the received signal and of half the amplitude of the signal output which would be developed from detector 28 from an identical signal input so that the double-sideband output components of detectors 25 and 23 are eifectively subtractive in the input circuit of videofrequency amplifier I6, thereby to eliminate the undesirable amplitude distortion of the type under consideration. In summary, therefore, it is seen that means including diode 25 of Fig. 5 are provided for detecting double-sideband components of a given frequency range and that means including diode 28 are provided for detecting the double-sideband components of the given range and,in addition, single-sideband components outside of the given range, the two detecting means including means for deriving from a signal input of given amplitude detector outputs of predetermined relative amplitudes. Furthermore, it is seen that by means of the load circuit connection of diodes 25 and 28, means are provided for differentially combining and reproducing the detected signal components.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such'changes and modiiications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A modulated-carrier signal receiver comprising, means for detecting only double-sideband components of a given frequency range of a received signal, means for detecting single-sideband components of said signal outside of said range, said two detecting means including means for deriving from a signal input of given amplitude detector outputs of predetermined relative amplitudes, and means for combining and reproducing said detected signal components.

2. A modulated-carrier signal receiver comprising, means for uniformly translating a received carrier wave and the sideband components to be reproduced, means coupled to said translating means for detecting only double-sideband components of a given frequency range of said components to be reproduced, means coupled to said translating means for detecting single-sideband components outside of said range, said two detecting means including means for deriving from a signal input of given amplitude detector outputs of predetermined relative amplitudes, and means for combining and reproducing said detected signal components.

3. A modulated-carrier signal receiver comprising, means for uniformly translating a received carrier wave and the sideband components to be reproduced, means coupled to said translating means for detecting only doublesideband components of a given frequency range of said components to be reproduced, means coupled to said translating means for detecting only single-sideband components outside of said range, said two detecting means including means for deriving from a signal input given amplitude a detector output from said lastmentioned detecting means of an amplitude substantially equal to that from said irst-mentioned detecting means, and means for combining and reproducing said Idetected signal components.

4. A modulated-carrier signal receiver comprising, means for detecting only double-sideband components of a given frequency range of a received signal, means for detecting singlesideband components of said signal outside of said range, said detecting means including means for adjusting the relative amplitudes of the outputs of said detecting means, and means for combining and reproducing said detected signal components.

5. A modulated-carrier signal receiver comprising, means for selecting and detecting only double-sideband components of a given frequency range of a received signal, means for selecting and detecting single-sideband components of said signal outside of said range, said two detecting means including means for deriving from a signal input of given amplitude detector outputs of predetermined relative amplitudes, and means for combining and reproducing said detected signal components.

6. A modulated-carrier signal receiver comprising, means for selecting the carrier wave and double-sideband components of a given frequency range of a received signal, means coupled to said selecting means for detecting said double-sideband components, means for selecting said carrier wave and single-sideband components of said signal outside of said range, means coupled to said last-mentioned means for detecting said single-sideband components, said two detecting means including means for deriving from a signal input of given amplitude detector outputs of predetermined relative amplitudes, and means for combining and reproducing said detected signal components.

7. A modulated-carrier signal receiver comprising, means for selecting the carrier wave single-sideband components, means coupled to said last-mentioned means including a linear detector for detecting said single-sideband components, said two detecting means including means for deriving from a signal input of given amplitude detector outputs of predetermined relative amplitudes, and means for combining and reproducing said detected signal components.

8. A modulated-carrier signal receiver comprising, means including a linear detector for detecting only double-sideband components of a given frequency range of a received signal, means including a square-law detector for detecting single-sideband components of said signal outside of said range, said two detecting means including means for deriving from a signal input of given amplitude detector outputs of predetermined relative amplitudes, and means for com- I bining and reproducing said detected signal components.

9. A modulated-carrier signal receiver` comprising, means for detecting only double-sideband components of a given frequency range of a received signal, means for detecting doublesideband com-ponents of said given range and single-sideband components outside of said range, said two detecting means including means ior deriving from a signal input of given amplitude detector outputs of predetermined relative amplitudes, and means for differentially combining and reproducing said detected signal components.

10. A modulated-carrier signal receiver comprising, means for detecting only double-sideband components of a given frequency range of a received signal, means for detecting doublesideband components of said given range and single-sideband components outside of said range, said detecting means being so proportioned that the output of said first-mentioned detecting means over the range of said doublesideband components is,` for a given signalinput amplitude, substantially half the amplitude of that of said last-mentioned detecting means, and means for differentially combining and reproducing said detected signal components.

JOHN C. WILSON.

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