US3217105A - Angular-sideband signal-forming transmitter - Google Patents

Angular-sideband signal-forming transmitter Download PDF

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US3217105A
US3217105A US82518A US8251861A US3217105A US 3217105 A US3217105 A US 3217105A US 82518 A US82518 A US 82518A US 8251861 A US8251861 A US 8251861A US 3217105 A US3217105 A US 3217105A
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phase
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Loy E Barton
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RCA Corp
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04H—BROADCAST COMMUNICATION
    • H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
    • H04H20/86—Arrangements characterised by the broadcast information itself
    • H04H20/88—Stereophonic broadcast systems

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  • the present invention relates to amplitude-modulation (AM) signal transmission systems, and more particularly to phase-shifted or angular double-sideband two-channel amplitude-modulation (AM) signal transmission systems for radio broadcast and other communication purposes.
  • a signal transmission system of this type provides twochannel or stereophonic information in the form of angular or phase-shifted double-sideband modulation on a single carrier-wave or RF signal, for two-channel or stereophonic reception, and compatible single-channel or monophonic reception.
  • One channel has double sidebands leading the carrier wave or signal by a given angle and the other channel has double sidebands laggin-g the carrier wave or signal by the same angle.
  • the two modulation signals are each on both upper and lower sidebands.
  • the two-channel or stereophonic program material or modulation such as two stereophonically-related A and B audio-frequency signals, or the sum and difference thereof,
  • (A+B) and (A-B) is applied to angular components of the single carrier wave and transmitted on the carrier-wave to receivers which translate the phase-shifted or angular double-sideband AM modulation and derive the A and B signals, for respective application to separate sound reproducing means, or for other uses.
  • a quadrature system for stereophonic AM broadcasting ot this angular-modulation type, has been proposed in which the linal phase-shifted sideband angles are :L45 from the carrier wave, or 90 between stereo channels.
  • the quadrature system appears to have certain disadvantages including harmonic distortion problems for monophonic reception and decoding problems for stereophonic reception.
  • the signal-forming transmitter or exciter of the present invention is adapted for use in such an angular-sideband system for modulated signal transmission, and includes means for generating or deriving the basic carrier signal, and means for separating the basic carrier signal into two carrier signal components for two-channel modulation and translation.
  • the components are each amplitude modulated by dilerent modulating signals, generally at audio frequency. The latter may .be stereophonically related.
  • Each carrier signal component thus is provided with double sidebands, and means are included in circuit with each channel for shifting the phase of the modulated carrier components 30 with respect to the phase of the basic carrier signal, thereby to shift the sidebands substantially 60 apart.
  • Means are also included for combining the carrier components to provide the single formed carrier signal having i-SO" phase-shifted double sidebands. This Carrier and the two double sidebands are applied to the output power amplifier for broadcast transmission.
  • the formed angular double-sideband AM signal is thus a composite carrier wave or signal having definite phase or frequency modulation information thereon for twochannel or stereophonic broadcast transmission.
  • the phase or frequency-modulation components must be faithfully translated or amplied and transmitted. Proper forming of the modulated RF carrier signal with phaseangle or frequency-modulation information, as well as amplitude-modulation, thereon is essential for undistorted reception and channel separation.
  • an object of the present invention to provide an improved low-level signal-forming amplitudemodulation (AM) transmitter or exciter, for a composite RF carrier wave or signal having phase-shifted or angular double sidebands, for two-channel or stereophonic signal transmission, which is effective to establish and maintain desired phase relations and modulation depth in the formed signal.
  • AM amplitudemodulation
  • AM amplitude-modulated
  • the percent modulation possible without appreciable distortion, in a system of this type, is normally relatively low and less than 20% Therefore, it has been considered to be virtually impossible to obtain a signal output from a forming transmitter or exciter in a system of this type which would have modulation and effectively utilize the capabilities of available electronic equipment. This is due in part to the vector form of the two angular carrier signal components and the resultant carrier signal with its excess carrier signal amplitude. This excess carrier signal amplitude precludes the possibility of obtaining 100% modulation without distortion.
  • AM amplitude-modulation
  • this is ⁇ accomplished by reducing the excess amplitude of the in-phase resultant of two angular (60) carrier signal components to that required for 100% modulation, in an improved forming transmitter or exciter system which provides simplified, direct and economical means for obtaining a two-channel or stereo double-sideband angular-modulated Signal.
  • This improved system includes means for producing three carrier signals or signal components in three branch circuits, the first and second of which signals or signal components are symmetrically angularly related to the third.
  • the first and second carrier signals may be angularly separated from each other by substantially 60, or i30 with respect to the third carrier signal.
  • the system further includes means for amplitude modulating the rst and second carrier signals or signal components, and means for combining the three carrier signals to provide a single resultant angular-modulated output carrier signal.
  • the third carrier signal or component is caused to be in phase opposition with the resultant of the irst and second carrier signals, which resultant is in phase with the carrier signal and of excess amplitude.
  • the amplitude of the third carrier signal is then adjusted to reduce the excess amplitude and produce a resultant differential output modulated signal or carrier wave, to be transmitted or applied to a high power transmitter, which is thus adapted for 100% modulation.
  • FIGURE 1 is a schematic circuit diagram of an amplitude-modulated (AM) signal transmitter for two-channel angular double-sideband signals provided with a low-level signal-forming transmitter or exciter system embodying the invention, and
  • AM amplitude-modulated
  • FIGURES 2 and 3 are graphs showing vector-diagram representations and curves illustrating the operation and certain features of the signal-forming transmitter or exciter system shown in FIGURE 1.
  • a crystal oscillator stage V1 provides a crystalcontrolled basic RF signal or carrier wave Co at a predetermined frequency as indicated in the graph 5.
  • the oscillator stage includes an oscillator tube 6 having a grid circuit 7 with a frequency-control crystal 8, and an anode output circuit lead 9 between which and common or chassis ground 10, for the system, the oscillator signal output is derived.
  • the frequency of the crystal, and of the basic carrier wave or signal C may be considered to be 1170 kc. and within the present AM broadcast band.
  • 'lhe oscillator stage V1 represents any suitable or conventional means for obtaining a stable carrier wave or signal frequency, and is the basic carrier-wave source for the sys ⁇ l tem shown.
  • the oscillator is coupled to a signal-forming circuit or amplifier which includes three substantially parallel stages V2, V3 and V4 comprising, respectively, three amplifier tubes 12, 13 and 14 connected as signal translating devices in three separate branch circuits or channels which include respectively circuit leads 15, 16 and 17. Chassis or common ground for the system serves as the common return circuit element.
  • the signal-forming amplifier stages V2 and V4 are, effectively, converter or modulator stages, and in the present example the tubes 12 and 14 therein are of the pentagrid converter type having respectively, grounded cathodes 20 and 21, first control grids 22 and 23, screen grids 24 and 25, second control grids 26 and 27, suppressor grids 28 and 29, and output anodes 30 and 31.
  • the control grid 22, for the converter or modulator stage V2 is coupled through a capacitor 35 with the signal channel lead 15, thereby providing a signal input circuit, in conjunction with the grounded cathode 20.
  • Bias potential e is applied to the grid 22 through a suitable grid resistor 36.
  • the control grid 23, for the converter or modulator stage V4 is coupled through a capacitor 37 with the signal channel or branch lead 17, thereby completing the input circuit for the stage V4, in conjunction with the grounded cathode 21.
  • Bias potential e for the grid 23 is applied thereto through a suitable grid resistor 38 similar to that for the grid 22.
  • the amplifier stage V3 of the signal-forming amplifier operates as a straight signal amplifier and thus may include any suitable amplifier device.
  • the tube 13 l is of the pentode type having a control grid 40 connected directly with the signal channel lead 16 and having a cathode 41 connected through a variable gain-control bias resistor 42 to system ground 1t).
  • the screen grid 43 together with the screen grids 24 and 25, is connected with a source of positive operating potential with respect to common ground, represented by a D.C. supply lead 44.
  • the anode of the tube 13 is indicated at 45, and the suppressor grid 46 is connected to the cathode as shown.
  • the output circuit 9-10 of the carrier wave source V1 is connected to the tuned primary winding 47 of an RF coupling transformer T1 through a coupling capacitor 48.
  • the winding is provided with a shunt tuning capacitor 49 and is variably tunable, as indicated, to the oscillator frequency.
  • the transformer is provided with a secondary Winding 50 having end terminals 51 and 52 which provide instantaneous signal potentials respectively opposite polarities with respect to an intermediate grounded terminal 53.
  • the terminal 51 is connected directly with the channel lead 16 and the terminal 52 is connected indirectly with both channel leads 15 and 17.
  • the terminal 52 is connected first to voltage-divider means cornprising two series resistors 54 and 55 connected between the terminal 52 and common ground and having an intermediate output terminal 56.
  • the terminal 56 is connected through a lead 57 with a branch circuit terminal 58 to which the branch circuit leads 15 and 17 are connected through respective phase-shift networks 59 and 60.
  • the phase-shift network 59 comprises a series resistor 61 and capacitor 62 connected between the terminal 58 and common ground 10, with the branch-circuit lead 1S connected at a terminal 63 at the junction of the resistor and the capacitor.
  • the phase-shift network 60 likewise comprises a series capacitor 65 and resistor 66 connected between the terminal 58 and common ground 10, with the branch circuit lead 17 connected with a terminal 67 at the junction of the resistor and capacitor.
  • the resistors 61 and 66 may be assumed to be 470 and 800 ohms, respectively, and the capacitors 62 and 65 may be assumed to have values of 150 and 300 microfarads, respectively.
  • the secondary Winding 50 of the transformer T1 is relatively tightly coupled to the tuned primary winding and provides an output voltage at the terminal 52 which is reduced by means of the voltage divider 54-55 at the output terminal 56 and the branch-circuit terminal 58.
  • the latter terminal is connected as described, to the input circuits and first control grids of the signal-forming modulator stages V2 and V4 through the phase-shifting networks 59 and 60.
  • the phaseshift network 59 provides a 30 or lagging phase angle from the carrier or oscillator signal output at the terminal 52 and of the tuned primary winding 47.
  • the phase-shift network 60 provides a +30 or leading phase angle from the carrier or oscillator signal output at the terminal 52 and of the tuned primary Winding 47.
  • the V2 stage signal output has a 30 lagging phase angle with respect to the generated carrier signal and the V4 stage has a +30 leading phase with respect to the generated carrier signal.
  • the forming-amplifier stages V2 and V4 are converters or modulators and include, in the present example, pentagrid amplifier tubes, each having two signal input grids.
  • the two-channel or stereophonic modulation signals may be applied to the input grid 26 of the amplifier tube 12 and to the input grid 27 of the amplifier tube 14, that is, to the second control grid of each tube, through suitable two-channel or stereophonic modulation signal supply circuits as now will be described.
  • the grid 26 for the modulator stage V2 is connected through an input grid-circuit lead 73 and a coupling capacitor 74 with the variable output terminal or contact 75 of a potentiometer resistor 76 which is connected in one modulation-signal supply circuit 77 from any suitable source of audio-frequency modulation (not shown). As indicated by the legend, this may be considered to be a channel A modulation signal, with an instantaneous frequency of 1000 cycles.
  • the potentiometer device -76 represents any suitable gain-control means for adjusting the amplitude or signal level of the modulating signal which is applied to the modulator stage V2.
  • Bias potential for the grid 26 issupplied through a grid resistor 79 connected with a biassupply lead 80 negative with respect to ground.
  • An R-F by-pass capacitor 81 is also connected with the grid circuit 73 in shunt relation thereto as shown.
  • the modulation-signal input grid 27 of the modulator stage V4 is connected through an input grid-circuit lead 83 and a coupling capacitor 84 with a variable output terminal or contact 85 of a potentiometer resistor 86 which is connected in the other modulation signal supply circuit 87 from any suitable second signal source of audio-frequency modulation (not shown).
  • this may be considered to be a channel B modulation signal at an instantaneous frequency of 500 cycles.
  • the channel A and channel B signals may be stereophonically related.
  • the potentiometer device 85-86 represents any suitable gain-control means for adjusting the amplitude or signal level of the modulating signal which is applied to the modulator stage V4.
  • Bias potential for the grid 27 is provided through a grid resistor 89 connected with the bias supply lead 80, and an R-F by-pass capacitor 90 is connected between ground and the grid-circuit lead 83, similar to that provided for the grid-circuit lead 73.
  • the signal-forming amplifier is provided with a common signal output coupling transformer T2 for all three branch circuits and the amplifier or modulator stages V2, V3 and V4 therein.
  • the branch circuit anode output leads '70 and 71 and a branch circuit output anode lead 92 for the amplifier tube 13 are connected in corrnnon to a signal input terminal 93 of the primary winding 95 of the transformer which is tuned to the carrier signal frequency by a shunt tuning capacitor 96.
  • the low-potential terminal 97 of the primary winding is connected with the positive anode-potential supply-circuit lead 44 as indicated, whereby the anode currents for the three branch circuit amplifiers, and the tubes 12, 13 and 14 therein, flow through the primary winding 95.
  • the resultant RF output signal is derived from the secondary winding 99 and applied to signal output terminals 1130-101 through a suitable linear buffer-amplifier stage V5 and a tuned output coupling transformer T3 therefor.
  • the linear amplifier includes an electronic screengrid tube 103 having a signal input grid 104 coupled to the high potential side of the secondary 99 through a coupling capacitor S, and having a cathode 106 connected to common ground or chassis through a cathode resistor 107, to complete the grid input circuit through the grounded end of the secondary winding 99.
  • the bias circuit for the grid is completed through a grid resistor 10S.
  • a variable capacitor 109 representing any suitable variable gain-control device for the buffer-amplifier stage VS, is interposed in circuit between the grid 104 and the secondary winding 99.
  • the anode output circuit 110 for the buffer-amplifier stage V5 is connected to a variably-tunable primary winding 111 for the coupling transformer T3, and through a supply lead 112 to a source of positive anode operating potential.
  • the transformer secondary winding 113 is connected directly with the output terminals 100 and 101 of the signal-forming transmitter or exciter.
  • the formed RF signal available at the terminals 1013-101 may be utilized for any suitable purpose. In the present example, for a broadcast transmitter, it is applied to an output power amplifier 114 of any suitable type which is coupled to a suitable transmitting antenna 115 and earth ground 116 as shown.
  • the carrierwave source V1 provides the crystal-controlled basic RF signal or carrier wave, CO, at a predetermined fixed frequency, such as ll70kc. as referred to hereinbefore.
  • This output signal is applied to the signal-forming amplifier stages V2, V3 and V4 through the tuned transformer T1.
  • the secondary terminal 52 of the transformer has a signal output on one side of the ground tap or terminal 53, of a predetermined voltage which is reduced by the voltage divider means and applied through the terminal 58 and the phase-shift networks 59 and 60 to the branch circuits 15-10 and 17-10 and the modulator stages V2 and V4.
  • Two separate channel carrier-signal components, C1 and C2 are thus derived at the output circuits 70 and 71, the former lagging the basic carrier or crystaloscillator output signal by substantially 30, and the latter leading the basic carrier or crystal-oscillator signal output by substantially 30, as represented in the graphs 120 and 121 shown on FGURE 1.
  • the channel A modulated-signal output of the V2 stage appears at the tuned transformer T2, having the carrier component C1 with its tWo-sidebands due to the channel A modulation.
  • the modulated signal output of the V4 stage appears at the tuned transformer T2, having the carrier component C2 with its two sidebands due to the channel B modulation.
  • the channel A sidebands for the 1000 cycle modulation of the carrier component C1, and the channel B sidebands for the carrier component C2 modulated at 500 cycles are indicated.
  • the other end of the secondary winding 50 that is the terminal 51, is connected to the grid 40 of the third branch-circuit amplifier stage V3, and the signal voltage at the terminal 51 thus has an approximately 180 phase angle from that at the terminal 52, both with respect to system ground.
  • the output circuits of all three of the signal forming amplifier branches are connected to the common broad-tuned RF output transformer T2.
  • the common carrier-frequency signals of all three branches add vectorially to obtain a resultant carrier signal C at approximately Zero phase angle with respect to the reference phase of the carrier-wave source at the transformer T1.
  • sideband output components only occur at the output circuits 70 and 71 from the modulators V2 and V4. Therefore they retain their phase and amplitude identity in the output of the three stages V2, V3 and V4 through the transformer T2, as represented in the graph 122.
  • T he signal output from the transformer T3 at the terminals 10G-101 thus becomes the formed double-sideband two-channel or stereo signal which may be applied to any particular utilization means, such as the input circuit of the transmitting power amplier 114 for any degree of amplification to the transmitting antenna 11S.
  • the audio-frequency channel A and channel B modulation applied to the third grids 26 and 27 of the modulator or converter tubes 12 and 14, respectively, in the signal forming amplifier cannot produce 100% modulation of the RF signal output (C1 and C2) of the modulator stages V2 and V4 without appreciable distortion. Consequently when the signal output of the modulator stages V2 and V4 are vectorially added at the output transformer T2 in the tuned primary circuit 94, as represented in FIGURE 2, the resultant carrier signal, CR, will have excess carrier amplitude.
  • the signal phase input to the V3 amplifier stage is substantially from the phase of the resultant RF signal from the stages V2 and V4, due to the circuit-connections with the tapped secondary winding 50 as hereinbefore described.
  • This relation is shown in FIGURE 2 wherein the carrier signal from the V3 stage, designated as C3, is substantially 180 out of phase with the resultant carrier signal CR from the two carrier components C1 and C2.
  • Means are provided for making slight adjustments in the phase relation of the two signals C1 and C2, and is represented in the present example by the variable capacitor 124 connected between the common branch-circuit lead 57 and ground for the system, preceding the phase shift networks 59 and 60.
  • the percent modulation available through the modulator stages V2 and V4 without distortion may be considered to be a maximum of 20%, as indicated on the carrier components C1 and C2 in FIGURE 2.
  • the resultant carrier signal change in amplitude is indicated by the in-phase vector 125.
  • the carrier signal amplitude varies as the sum of these variations or changes, as indicated,
  • the excess carrier signal amplitude, with respect to the zero or reference line, is also indicated in FIGURE 2.
  • the third branch signal from the terminal 51 as applied to the amplifier V3 at the signal input grid 40 is substantially equal to the signal at the grids 22 and 23 as derived from the voltage divider means 54-55.
  • the third signal output from the amplifier stage V3 is in reverse phase to the resultant CR of the two carrier components C1 and C2 derived through the modulators V2 and V4.
  • the gain control means 42 for the third branch signal amplifier V3 permits a signal output therefrom of sufhcient amplitude to cancel the excess amplitude of the resultant of the V2 and V4 stage output carrier signals, that is, the resultant carrier signal CR, to permit 100% modulation of the output signal from the output transformer T2.
  • the cancelled excess carrier signal amplitude is represented in FIGURE 3 between a line 126 and the zero or reference line.
  • the required carrier signal amplitude is indicated by the arrowed line 127 and the new carrier signal C is indicated by the arrowed line 128.
  • the carrier amplitude variation resulting from the modulation, and as represented by the sine-wave lines 129 now provides for substantially 100% modulation of the new carrier signal C. This is shown for the new carrier C, by the wave form 129 between limits represented by the zero or reference line and the dotted line 130.
  • the output signal from the modulator stages V2 and V4 will be the vector sum of the carrier and the sidebands.
  • the gain of the third channel stage V3 is increased to apply the bucking carrier signal C3 to the mixing .transformer T2 -until the depth of modulation at the transformer T2 reaches the zero axis and the peaks of the modulation are equal to double the carrier wave amplitude, as represented in the lower portion of the graph of FIGURE 3.
  • This is a normal monophonic 100% modulated envelope that occurs when the signals to the A and B channels produce equal modulation land are of the same frequency, and in phase.
  • the formed output signal at the .terminals G-101 is a phase-:shifted or angular double-sideband two-channel amplitude-modulation signal on one carrier wave and substantially free of phase shifts due to modulation.
  • the sidebands ⁇ due to the channel A modulation will have substantially 30 angle with respect to the carrier signal C and the sidebands due to the channel B modulation have substantially a - ⁇ -'30 phase angle with respect to the carrier ysignal C.
  • the two channel A and B signals may be separated in a receiver for ⁇ stercophonic signal output, or for other uses.
  • substantially 100% modulation of a phase-shifted angle-modulation two-channel or stereo RF signal may be attained with relatively low-cost and simple circuitry.
  • means are provided for producing three carrier signal components, C1, C2 and C3, the first and second of which are symmetrically angularly related to the third.
  • the system involves the use of a basic carrier signal coupling transformer or like coupling means having a grounded intermediate terminal between the ends of the inductive coupling element or secondary Winding thereof, and the phase-shift networks are connected between one terminal and each of the modulators while the bucking-signal amplifier stage is connected with the other terminal of the said inductive coupling element, thereby, with simplified circuitry, to establish the phase relation between the resultant and ⁇ bucking carrier signals or s-ignal components.
  • the means for amplitude modulating .the first and second carrier signal components, C1 and C2, is readily provided by relatively simple and stable pentagrid-converter or like modulator means.
  • the means for combining the three carrier signal components C1, C2 and C3, with the third carrier signal component, C3, -in phase opposition with the resultant, CR, of the first and second carrier signal components, is attained through the common tuned primary winding of the output transformer T2.
  • the linear buffer amplifier stage V5 serves to prevent any interaction between the utilization means coupled to the output circuit at the terminals 10Q-101 and the signal-forming amplifier mixing circuit 94.
  • the use of the formed RF output signal for 'further power amplification and broadcast transmission represents .a present effective use for the Signal forming transmitter or exciter of the present invention. It may yalso be used directly as a signal source to test stereo receivers of the angular-modulation type.
  • a signal-forming transmitter for use in angular-sideband systems for modulated signal transmission, comprising in combination, means for producing three carrier signal components, the first and second ⁇ of which are angularly related to the third, means for modulating the first and second carrier signal components, and means for combining said three signal components, the third signal component being of opposite phase with the resultant of the first and second ⁇ signal components and of ⁇ an amplitude to reduce the resultant of the first and second signal components to provide a composite carrier signal having a relatively-wide modulation range.
  • a two-channel angular-sideband signal transmitter means for producing three carrier signals, the first and second of which are substantially symmetrically ⁇ angularly related to the third, means for amplitude modulating the first .and second carrier signals, and means for combining said three carrier signals, with the third carrier signal in phase opposition with the resultant of the first and second carrier signals to reduce the resultant of the first land second signal components to provide a composite differential output carrier signal adapted for substantially full modulation depth.
  • a signal-forming transmitter for use in angular-sideband systems for modulated signal transmission, comprising in combination, means for producing three carrier signal components the first and second of which are substantially symmetrically angularly related t-o the third, means for amplitude modulating the first and second carrier signal components with two modulating signals, a common tuned signal -output circuit, and means for combining said three signal components in said output circuit, with the third signal component in phase opposition with the resultant ⁇ of the first and second signal components yand of an amplitude to reduce the resultant of the first and second signal components to produce a differential output carrier signal adapted for substantially ⁇ full modulation depth.
  • a signal-forming transmitter for use in an angularsideband system for modulated signal transmission, comprising in combination, means providing a basic carrier signal source having an output circuit including a coupling winding having two end terminals and an intermediate tap connected to ground for said system, means providing first and second branch signal circuits connected jointly with one terminal of said coupling winding, phase shift networks in said branch circuits providing substantially equal phase shifts positively in one br-anch circuit and negatively in the other branch circuit for deriving two signal components having a predetermined phase differential in response to an applied carrier signal from said source through said winding, modulator means coupled to each of said branch circuits having a common output circuit wherein the carrier-signal components derived from said branch circuits are added vectorially to provide a resultant carrier signal, signal-translating means coupled between the other terminal of said coupling winding and said common output circuit for the modulator means for applying to said output circuit a carrier signal component substantially 180 out of phase with said resultant carrier signal and substantially equal to the excess amplitude of said resultant carrier signal above that required for
  • a signal-forming transmitter for use in an angularsideband system for modulated signal transmission, comprising in combination, means providing a basic carrier signal source having a tunable output circuit responsive to the carrier-signal frequency and including a coupling winding having two end terminals and an intermediate tap connected to ground for said system, means providing rst and second branch signal circuits connected jointly with one terminal of said coupling winding, a phase shift network in each of said branch circuits providing substantially 30 phase shift positively in one branch circuit and negatively in the other branch circuit for 4deriving two signal components with substantially 60 phase differential in response to an applied carrier signal from said source through said winding, means providing a pair of modulator stages coupled one to each of said branch circuits and having a common ⁇ output circuit tunable to the carrier signal frequency and wherein the carrier-signal components derived from said branch circuits are added vectorially to provide a resultant carrier signal, and means including a signal amplifier coupled between the other terminal of said coupling winding and said tunable output circuit for the modulator stages for applying to
  • a signal-forming transmitter for use in an angularsideband system for two-channel modulated signal transmission, comprising in combination, basic carrier-signal generating means having a tunable output circuit including a coupling winding having two terminals and an intermediate tap connected to ground for said system, means providing first and second branch signal circuits connected jointly with one of said terminals, means in said last named connection for reducing signal voltages applied to said branch circuits, a phase-shift network in each of said branch circuits providing substantially equal phase shifts positively in one branch circuit and negatively in the other branch circuit for deriving two signal components with a predetermined phase differential in response to an applied carrier signal from said source through said winding, means providing a pair of modulator stages coupled one to each of said branch circuits and having a common output circuit tunable to the carrier signal frequency and wherein the carrier signal components derived from said branch circuits are added vectorially to provide a Iresultant carrier signal, means for applying two-channel modulating signals to said modulator stages for modulating the first and second carrier signal components in said
  • a signal-forming transmitter for use in an angularsideband system for modulated signal transmission comprising in combination, a tunable oscillator providing a basic carrier signal source, a tunable output transformer therefor having a secondary winding with an intermediate tap connected to ground for said system, means connected with the secondary winding on opposite sides of said tap for producing therefrom three carrier signal components from said basic carrier signal, said last named means including first and second branch signal circuits connected with said secondary winding on one side of said tap for translating a first and second of said three carrier signal components and a third branch signal circuit connected with said secondary winding on the opposite side of said tap for translating a third of said three carrier signal components, the signal components applied to said first and second branch circuits thereby being substantially out of phase with said -third signal component, a phase-shift network i-n each vof said first and second branch signal circuits providing positive phase shift in one branch circuit and negative phase shift in the other branch circuit thereby to provide two signal components having a predetermined phase differential and substantially symmetrically ang
  • a signal-forming transmitter for angular-sideband modulated-signal transmission comprising in combination, signal generator means, output transformer means therefor having a winding with a grounded intermediate tap, rst and second branch signal circuits connected with said winding on one side of said tap and a third branch signal circuit connected with said winding on the opposite side :of said tap, whereby signal components from said generator means applied to said first and second branch circuits are substantially 180 ⁇ out of phase with a signal component from said generator means applied to said third branch signal circuit, a phase-shift network in each of said first and second branch signal circuits providing a positive phase shift in one branch circuit and a negative phase shift in the other branch circuit to provide two signal components having a predetermined phase differential and angularly related to said third signal component, means providing a pair of modulator stages coupled one to each of said rst Iand second branch signal circuits and having a common output circuit tunable to the carrier signal frequency, means for combining said three carrier signal components in said signal output circuit with the third carrier signal component
  • a signal-forming transmitter for angular-sideband modulated-signal transmission comprising in combination, signal generator means, output transformer means therefor having a winding with a grounded intermediate tap, first and second branch signal circuits connected with said winding on one side of said tap, a third branch signal circuit connected with said winding on the opposite side of said tap, a phase-shift network in each of said first and second branch signal circuits providing substantially a 30 positive phase shift in one branch circuit and substantially a 30 negative phase shift in the other branch circuit thereby to provide two signal components having a predetermined substantially 60 phase differential and substantially symmetricallyl angularly related to said third signal component, signal modulator means coupled to each of said first and second branch signal circuits having a common output circuit tunable to the carrier signal frequency, means for combining said three carrier signal components in said signal output circuit, with the third carrier signal component in phase opposite with the resultant -of the first and second carrier signal components, thereby to provide a resultant output carrier signal of reduced amplitude for increased effective modulation depth, means for applying
  • a signal-forming transmitter for use in an angularsideband system for modulated signal transmission, comprising in combination, means providing a basic carrier signal source, a tunable carrier-signal output transformer therefor having a secondary Winding with an intermediate tap connected to ground for said system, first and second branch signal circuits connected with said secondary winding on one side :of said tap, a third branch signal circuit connnected with said secondary winding on the opposite side of said tap, a phase shift network in each of said first and second branch signal circuits, means providing a pair of modulator stages coupled one to each of said first and second branch signal circuits and having a common output circuit tunable to the carrier signal frequency, means for combining carrier signal components from said branch signal circuits in said common output circuit, one carrier signal component from the third branch signal circuit being in phase opposition with the resultant of carrier signal components from the first and second branch signal circuits, signal utilization means coupled to said output circuit, means for applying different modulating signals to said modulator stages for differently modulating said first and second carrier signal components in the first and second branch

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Description

Nov. 9, 1965 E. BARTON 3,217,105
ANGULAR-SIDEBAND SIGNAL-FORMING TRANSMITTER Filed Jan. 115, 1961 2 Sheets-Sheet 1 Nov. 9, 1965 E. BARTON ANGULAR-SIDEBAND SIGNAL-FORMING TRANSMITTER v2 Sheets-Sheet 2 Filed Jan. 13, 1961 United States Patent O 3,217,105 ANGULAR-SDEBAND SlGNAL-FGRIVHNG TRANSMITTER Loy E. Barton, Princeton, Nd., assigner to Radio Corporation of America, a corporation of leiaware Filed gan. 13, 1961, Ser. No. 82,518 Claims. (Cl. 179-15) The present invention relates to amplitude-modulation (AM) signal transmission systems, and more particularly to phase-shifted or angular double-sideband two-channel amplitude-modulation (AM) signal transmission systems for radio broadcast and other communication purposes. A signal transmission system of this type provides twochannel or stereophonic information in the form of angular or phase-shifted double-sideband modulation on a single carrier-wave or RF signal, for two-channel or stereophonic reception, and compatible single-channel or monophonic reception. One channel has double sidebands leading the carrier wave or signal by a given angle and the other channel has double sidebands laggin-g the carrier wave or signal by the same angle. The two modulation signals are each on both upper and lower sidebands.
The two-channel or stereophonic program material or modulation, such as two stereophonically-related A and B audio-frequency signals, or the sum and difference thereof,
(A+B) and (A-B), is applied to angular components of the single carrier wave and transmitted on the carrier-wave to receivers which translate the phase-shifted or angular double-sideband AM modulation and derive the A and B signals, for respective application to separate sound reproducing means, or for other uses.
A quadrature system for stereophonic AM broadcasting, ot this angular-modulation type, has been proposed in which the linal phase-shifted sideband angles are :L45 from the carrier wave, or 90 between stereo channels. However the quadrature system appears to have certain disadvantages including harmonic distortion problems for monophonic reception and decoding problems for stereophonic reception.
An improved angular-modulation signal transmission system in which the two double sidebands respectively lead and lag a resultant formed carrier wave or signal by the same given angle and less than i45 is described in my copending application, Serial No. 809,025, now Patent No. 3,102,167, for Phase-Shifted Double-Sideband Two- Channel AM Communications System. This system provides for reception with reduced harmonic signal distortion and greater compatibility in conventional AM receivers. In this system, the phase shift of the sidebands from the resultant carrier wave, or the angular relation of the sidebands to the carrier wave, is reduced to *30 or less, and provides a higher degree of compatibility for both two-channel or stereophonic AM reception, and standard or monophonic AM reception.
The signal-forming transmitter or exciter of the present invention is adapted for use in such an angular-sideband system for modulated signal transmission, and includes means for generating or deriving the basic carrier signal, and means for separating the basic carrier signal into two carrier signal components for two-channel modulation and translation. The components are each amplitude modulated by dilerent modulating signals, generally at audio frequency. The latter may .be stereophonically related. Each carrier signal component thus is provided with double sidebands, and means are included in circuit with each channel for shifting the phase of the modulated carrier components 30 with respect to the phase of the basic carrier signal, thereby to shift the sidebands substantially 60 apart. Means are also included for combining the carrier components to provide the single formed carrier signal having i-SO" phase-shifted double sidebands. This Carrier and the two double sidebands are applied to the output power amplifier for broadcast transmission.
The formed angular double-sideband AM signal is thus a composite carrier wave or signal having definite phase or frequency modulation information thereon for twochannel or stereophonic broadcast transmission. The phase or frequency-modulation components must be faithfully translated or amplied and transmitted. Proper forming of the modulated RF carrier signal with phaseangle or frequency-modulation information, as well as amplitude-modulation, thereon is essential for undistorted reception and channel separation.
It is therefore, an object of the present invention to provide an improved low-level signal-forming amplitudemodulation (AM) transmitter or exciter, for a composite RF carrier wave or signal having phase-shifted or angular double sidebands, for two-channel or stereophonic signal transmission, which is effective to establish and maintain desired phase relations and modulation depth in the formed signal.
It is also an object of the present invention to provide an improved amplitude-modulated (AM) signal transmitter or exciter which will faithfully form and translate a composite RF carrier signal having angular double-sideband amplitude modulation for broadcast stereophonic and like signal reception, without undesirable phase shift or amplitude distortion and with a high degree of eiciency.
The percent modulation possible without appreciable distortion, in a system of this type, is normally relatively low and less than 20% Therefore, it has been considered to be virtually impossible to obtain a signal output from a forming transmitter or exciter in a system of this type which would have modulation and effectively utilize the capabilities of available electronic equipment. This is due in part to the vector form of the two angular carrier signal components and the resultant carrier signal with its excess carrier signal amplitude. This excess carrier signal amplitude precludes the possibility of obtaining 100% modulation without distortion.
It is, therefore, a still further object of this invention to provide an improved signal-forming amplitude-modulation (AM) transmitter or exciter for an RF carrier wave or signal having phase-shifted or angular double sidebands, for two-channel or stereophonic signal transmission, which is eifective to establish predetermined signal-component phase relations and substantially 100% modulation in the formed signal, without excessive phase or amplitude distortion.
In accordance with the invention, this is `accomplished by reducing the excess amplitude of the in-phase resultant of two angular (60) carrier signal components to that required for 100% modulation, in an improved forming transmitter or exciter system which provides simplified, direct and economical means for obtaining a two-channel or stereo double-sideband angular-modulated Signal. This improved system includes means for producing three carrier signals or signal components in three branch circuits, the first and second of which signals or signal components are symmetrically angularly related to the third. For example the first and second carrier signals may be angularly separated from each other by substantially 60, or i30 with respect to the third carrier signal.
The system further includes means for amplitude modulating the rst and second carrier signals or signal components, and means for combining the three carrier signals to provide a single resultant angular-modulated output carrier signal. The third carrier signal or component is caused to be in phase opposition with the resultant of the irst and second carrier signals, which resultant is in phase with the carrier signal and of excess amplitude. The amplitude of the third carrier signal is then adjusted to reduce the excess amplitude and produce a resultant differential output modulated signal or carrier wave, to be transmitted or applied to a high power transmitter, which is thus adapted for 100% modulation.
The invention will be further understood from the following description when considered in connection with the accompanying drawings, and its scope is pointed out in the appended claims.
In the drawings, FIGURE 1 is a schematic circuit diagram of an amplitude-modulated (AM) signal transmitter for two-channel angular double-sideband signals provided with a low-level signal-forming transmitter or exciter system embodying the invention, and
FIGURES 2 and 3 are graphs showing vector-diagram representations and curves illustrating the operation and certain features of the signal-forming transmitter or exciter system shown in FIGURE 1.
Referring to FIGURE 1 and the transmitter shown therein, a crystal oscillator stage V1 provides a crystalcontrolled basic RF signal or carrier wave Co at a predetermined frequency as indicated in the graph 5. In the present example, the oscillator stage includes an oscillator tube 6 having a grid circuit 7 with a frequency-control crystal 8, and an anode output circuit lead 9 between which and common or chassis ground 10, for the system, the oscillator signal output is derived. In the present example the frequency of the crystal, and of the basic carrier wave or signal C may be considered to be 1170 kc. and within the present AM broadcast band. 'lhe oscillator stage V1 represents any suitable or conventional means for obtaining a stable carrier wave or signal frequency, and is the basic carrier-wave source for the sys`l tem shown.
The oscillator is coupled to a signal-forming circuit or amplifier which includes three substantially parallel stages V2, V3 and V4 comprising, respectively, three amplifier tubes 12, 13 and 14 connected as signal translating devices in three separate branch circuits or channels which include respectively circuit leads 15, 16 and 17. Chassis or common ground for the system serves as the common return circuit element. The signal-forming amplifier stages V2 and V4 are, effectively, converter or modulator stages, and in the present example the tubes 12 and 14 therein are of the pentagrid converter type having respectively, grounded cathodes 20 and 21, first control grids 22 and 23, screen grids 24 and 25, second control grids 26 and 27, suppressor grids 28 and 29, and output anodes 30 and 31.
The control grid 22, for the converter or modulator stage V2, is coupled through a capacitor 35 with the signal channel lead 15, thereby providing a signal input circuit, in conjunction with the grounded cathode 20. Bias potential e is applied to the grid 22 through a suitable grid resistor 36. Likewise the control grid 23, for the converter or modulator stage V4, is coupled through a capacitor 37 with the signal channel or branch lead 17, thereby completing the input circuit for the stage V4, in conjunction with the grounded cathode 21. Bias potential e for the grid 23 is applied thereto through a suitable grid resistor 38 similar to that for the grid 22.
The amplifier stage V3 of the signal-forming amplifier operates as a straight signal amplifier and thus may include any suitable amplifier device. As represented in the present example, the tube 13 lis of the pentode type having a control grid 40 connected directly with the signal channel lead 16 and having a cathode 41 connected through a variable gain-control bias resistor 42 to system ground 1t). The screen grid 43, together with the screen grids 24 and 25, is connected with a source of positive operating potential with respect to common ground, represented by a D.C. supply lead 44. The anode of the tube 13 is indicated at 45, and the suppressor grid 46 is connected to the cathode as shown.
The output circuit 9-10 of the carrier wave source V1 is connected to the tuned primary winding 47 of an RF coupling transformer T1 through a coupling capacitor 48. The winding is provided with a shunt tuning capacitor 49 and is variably tunable, as indicated, to the oscillator frequency. The transformer is provided with a secondary Winding 50 having end terminals 51 and 52 which provide instantaneous signal potentials respectively opposite polarities with respect to an intermediate grounded terminal 53. The terminal 51 is connected directly with the channel lead 16 and the terminal 52 is connected indirectly with both channel leads 15 and 17. The terminal 52 is connected first to voltage-divider means cornprising two series resistors 54 and 55 connected between the terminal 52 and common ground and having an intermediate output terminal 56. The terminal 56 is connected through a lead 57 with a branch circuit terminal 58 to which the branch circuit leads 15 and 17 are connected through respective phase- shift networks 59 and 60. The phase-shift network 59 comprises a series resistor 61 and capacitor 62 connected between the terminal 58 and common ground 10, with the branch-circuit lead 1S connected at a terminal 63 at the junction of the resistor and the capacitor.
The phase-shift network 60 likewise comprises a series capacitor 65 and resistor 66 connected between the terminal 58 and common ground 10, with the branch circuit lead 17 connected with a terminal 67 at the junction of the resistor and capacitor. In the present example the resistors 61 and 66 may be assumed to be 470 and 800 ohms, respectively, and the capacitors 62 and 65 may be assumed to have values of 150 and 300 microfarads, respectively.
The secondary Winding 50 of the transformer T1 is relatively tightly coupled to the tuned primary winding and provides an output voltage at the terminal 52 which is reduced by means of the voltage divider 54-55 at the output terminal 56 and the branch-circuit terminal 58. The latter terminal is connected as described, to the input circuits and first control grids of the signal-forming modulator stages V2 and V4 through the phase-shifting networks 59 and 60. At the input circuit of the stage V2 the phaseshift network 59 provides a 30 or lagging phase angle from the carrier or oscillator signal output at the terminal 52 and of the tuned primary winding 47. Likewise, at the input circuit of the stage V4 the phase-shift network 60 provides a +30 or leading phase angle from the carrier or oscillator signal output at the terminal 52 and of the tuned primary Winding 47. As a result of this simplified channel-dividing or branching and phase-shift circuit, the V2 stage signal output has a 30 lagging phase angle with respect to the generated carrier signal and the V4 stage has a +30 leading phase with respect to the generated carrier signal.
As hereinbefore referred to, the forming-amplifier stages V2 and V4 are converters or modulators and include, in the present example, pentagrid amplifier tubes, each having two signal input grids. Thus the two-channel or stereophonic modulation signals may be applied to the input grid 26 of the amplifier tube 12 and to the input grid 27 of the amplifier tube 14, that is, to the second control grid of each tube, through suitable two-channel or stereophonic modulation signal supply circuits as now will be described.
The grid 26 for the modulator stage V2 is connected through an input grid-circuit lead 73 and a coupling capacitor 74 with the variable output terminal or contact 75 of a potentiometer resistor 76 which is connected in one modulation-signal supply circuit 77 from any suitable source of audio-frequency modulation (not shown). As indicated by the legend, this may be considered to be a channel A modulation signal, with an instantaneous frequency of 1000 cycles.
The potentiometer device -76 represents any suitable gain-control means for adjusting the amplitude or signal level of the modulating signal which is applied to the modulator stage V2. Bias potential for the grid 26 issupplied through a grid resistor 79 connected with a biassupply lead 80 negative with respect to ground. An R-F by-pass capacitor 81 is also connected with the grid circuit 73 in shunt relation thereto as shown.
In a similar manner, the modulation-signal input grid 27 of the modulator stage V4 is connected through an input grid-circuit lead 83 and a coupling capacitor 84 with a variable output terminal or contact 85 of a potentiometer resistor 86 which is connected in the other modulation signal supply circuit 87 from any suitable second signal source of audio-frequency modulation (not shown). In the present example, this may be considered to be a channel B modulation signal at an instantaneous frequency of 500 cycles. The channel A and channel B signals may be stereophonically related.
The potentiometer device 85-86 represents any suitable gain-control means for adjusting the amplitude or signal level of the modulating signal which is applied to the modulator stage V4. Bias potential for the grid 27 is provided through a grid resistor 89 connected with the bias supply lead 80, and an R-F by-pass capacitor 90 is connected between ground and the grid-circuit lead 83, similar to that provided for the grid-circuit lead 73.
The signal-forming amplifier is provided with a common signal output coupling transformer T2 for all three branch circuits and the amplifier or modulator stages V2, V3 and V4 therein. For this purpose, the branch circuit anode output leads '70 and 71 and a branch circuit output anode lead 92 for the amplifier tube 13 are connected in corrnnon to a signal input terminal 93 of the primary winding 95 of the transformer which is tuned to the carrier signal frequency by a shunt tuning capacitor 96. The low-potential terminal 97 of the primary winding is connected with the positive anode-potential supply-circuit lead 44 as indicated, whereby the anode currents for the three branch circuit amplifiers, and the tubes 12, 13 and 14 therein, flow through the primary winding 95.
The output signals from the three branch circuits at the output circuit leads 70, 71 and 92 vectorially add in the primary winding of the tuned output circuit 94 of the broadband transformer T2 as provided by the primary winding 95 and the shunt capacitor 96. The resultant RF output signal is derived from the secondary winding 99 and applied to signal output terminals 1130-101 through a suitable linear buffer-amplifier stage V5 and a tuned output coupling transformer T3 therefor. In the present example, the linear amplifier includes an electronic screengrid tube 103 having a signal input grid 104 coupled to the high potential side of the secondary 99 through a coupling capacitor S, and having a cathode 106 connected to common ground or chassis through a cathode resistor 107, to complete the grid input circuit through the grounded end of the secondary winding 99. The bias circuit for the grid is completed through a grid resistor 10S. A variable capacitor 109, representing any suitable variable gain-control device for the buffer-amplifier stage VS, is interposed in circuit between the grid 104 and the secondary winding 99. The anode output circuit 110 for the buffer-amplifier stage V5 is connected to a variably-tunable primary winding 111 for the coupling transformer T3, and through a supply lead 112 to a source of positive anode operating potential. The transformer secondary winding 113 is connected directly with the output terminals 100 and 101 of the signal-forming transmitter or exciter. The formed RF signal available at the terminals 1013-101 may be utilized for any suitable purpose. In the present example, for a broadcast transmitter, it is applied to an output power amplifier 114 of any suitable type which is coupled to a suitable transmitting antenna 115 and earth ground 116 as shown.
The operation of this system is such that the carrierwave source V1 provides the crystal-controlled basic RF signal or carrier wave, CO, at a predetermined fixed frequency, such as ll70kc. as referred to hereinbefore. This output signal is applied to the signal-forming amplifier stages V2, V3 and V4 through the tuned transformer T1. The secondary terminal 52 of the transformer has a signal output on one side of the ground tap or terminal 53, of a predetermined voltage which is reduced by the voltage divider means and applied through the terminal 58 and the phase- shift networks 59 and 60 to the branch circuits 15-10 and 17-10 and the modulator stages V2 and V4. Two separate channel carrier-signal components, C1 and C2, are thus derived at the output circuits 70 and 71, the former lagging the basic carrier or crystaloscillator output signal by substantially 30, and the latter leading the basic carrier or crystal-oscillator signal output by substantially 30, as represented in the graphs 120 and 121 shown on FGURE 1. The channel A modulated-signal output of the V2 stage appears at the tuned transformer T2, having the carrier component C1 with its tWo-sidebands due to the channel A modulation. Similarly the modulated signal output of the V4 stage appears at the tuned transformer T2, having the carrier component C2 with its two sidebands due to the channel B modulation. The channel A sidebands for the 1000 cycle modulation of the carrier component C1, and the channel B sidebands for the carrier component C2 modulated at 500 cycles are indicated.
The other end of the secondary winding 50, that is the terminal 51, is connected to the grid 40 of the third branch-circuit amplifier stage V3, and the signal voltage at the terminal 51 thus has an approximately 180 phase angle from that at the terminal 52, both with respect to system ground.
As noted, the output circuits of all three of the signal forming amplifier branches are connected to the common broad-tuned RF output transformer T2. As a result, the common carrier-frequency signals of all three branches add vectorially to obtain a resultant carrier signal C at approximately Zero phase angle with respect to the reference phase of the carrier-wave source at the transformer T1. However sideband output components only occur at the output circuits 70 and 71 from the modulators V2 and V4. Therefore they retain their phase and amplitude identity in the output of the three stages V2, V3 and V4 through the transformer T2, as represented in the graph 122. T he signal output from the transformer T3 at the terminals 10G-101 thus becomes the formed double-sideband two-channel or stereo signal which may be applied to any particular utilization means, such as the input circuit of the transmitting power amplier 114 for any degree of amplification to the transmitting antenna 11S.
Referring now to the graphs shown in FIGURES 2 and 3, along with the circuit of FIGURE l, the audio-frequency channel A and channel B modulation applied to the third grids 26 and 27 of the modulator or converter tubes 12 and 14, respectively, in the signal forming amplifier, cannot produce 100% modulation of the RF signal output (C1 and C2) of the modulator stages V2 and V4 without appreciable distortion. Consequently when the signal output of the modulator stages V2 and V4 are vectorially added at the output transformer T2 in the tuned primary circuit 94, as represented in FIGURE 2, the resultant carrier signal, CR, will have excess carrier amplitude.
The signal phase input to the V3 amplifier stage is substantially from the phase of the resultant RF signal from the stages V2 and V4, due to the circuit-connections with the tapped secondary winding 50 as hereinbefore described. This relation is shown in FIGURE 2 wherein the carrier signal from the V3 stage, designated as C3, is substantially 180 out of phase with the resultant carrier signal CR from the two carrier components C1 and C2. Means are provided for making slight adjustments in the phase relation of the two signals C1 and C2, and is represented in the present example by the variable capacitor 124 connected between the common branch-circuit lead 57 and ground for the system, preceding the phase shift networks 59 and 60.
The percent modulation available through the modulator stages V2 and V4 without distortion may be considered to be a maximum of 20%, as indicated on the carrier components C1 and C2 in FIGURE 2. The resultant carrier signal change in amplitude is indicated by the in-phase vector 125. When this is applied to the resultant carrier signal CR, as indicated at 125a and 125b, the carrier signal amplitude varies as the sum of these variations or changes, as indicated, The excess carrier signal amplitude, with respect to the zero or reference line, is also indicated in FIGURE 2. The third branch signal from the terminal 51 as applied to the amplifier V3 at the signal input grid 40 is substantially equal to the signal at the grids 22 and 23 as derived from the voltage divider means 54-55. Through this circuit connection with the secondary 50, the third signal output from the amplifier stage V3 is in reverse phase to the resultant CR of the two carrier components C1 and C2 derived through the modulators V2 and V4. The gain control means 42 for the third branch signal amplifier V3 permits a signal output therefrom of sufhcient amplitude to cancel the excess amplitude of the resultant of the V2 and V4 stage output carrier signals, that is, the resultant carrier signal CR, to permit 100% modulation of the output signal from the output transformer T2.
The cancelled excess carrier signal amplitude is represented in FIGURE 3 between a line 126 and the zero or reference line. The required carrier signal amplitude is indicated by the arrowed line 127 and the new carrier signal C is indicated by the arrowed line 128. It will be seen that the carrier amplitude variation resulting from the modulation, and as represented by the sine-wave lines 129 now provides for substantially 100% modulation of the new carrier signal C. This is shown for the new carrier C, by the wave form 129 between limits represented by the zero or reference line and the dotted line 130.
To adjust the value of the bucking signal or carrierwave component from the third channel amplifier V3 of the signal-forming amplifier, a practical -limit of audio voltage for modulation is applied individually to the modulators V2 and V4 from the signal input circuits 77 and 87 for channels A and B. When the modulators V2 and V4 are modulated equally, and the same audio-frequency signal is applied to each channel, the output signal from the modulator stages V2 and V4 will be the vector sum of the carrier and the sidebands. The gain of the third channel stage V3 is increased to apply the bucking carrier signal C3 to the mixing .transformer T2 -until the depth of modulation at the transformer T2 reaches the zero axis and the peaks of the modulation are equal to double the carrier wave amplitude, as represented in the lower portion of the graph of FIGURE 3. This is a normal monophonic 100% modulated envelope that occurs when the signals to the A and B channels produce equal modulation land are of the same frequency, and in phase.
When different or stereophonically-related audio signals are supplied through the channel modulation circuits 77 and 87, the formed output signal at the .terminals G-101 is a phase-:shifted or angular double-sideband two-channel amplitude-modulation signal on one carrier wave and substantially free of phase shifts due to modulation. The sidebands `due to the channel A modulation will have substantially 30 angle with respect to the carrier signal C and the sidebands due to the channel B modulation have substantially a -{-'30 phase angle with respect to the carrier ysignal C. In this case, the two channel A and B signals may be separated in a receiver for `stercophonic signal output, or for other uses.
By this system, substantially 100% modulation of a phase-shifted angle-modulation two-channel or stereo RF signal may be attained with relatively low-cost and simple circuitry. In the forming transmitter, it will be `seen that means are provided for producing three carrier signal components, C1, C2 and C3, the first and second of which are symmetrically angularly related to the third.
The system involves the use of a basic carrier signal coupling transformer or like coupling means having a grounded intermediate terminal between the ends of the inductive coupling element or secondary Winding thereof, and the phase-shift networks are connected between one terminal and each of the modulators while the bucking-signal amplifier stage is connected with the other terminal of the said inductive coupling element, thereby, with simplified circuitry, to establish the phase relation between the resultant and `bucking carrier signals or s-ignal components.
The means for amplitude modulating .the first and second carrier signal components, C1 and C2, is readily provided by relatively simple and stable pentagrid-converter or like modulator means. The means for combining the three carrier signal components C1, C2 and C3, with the third carrier signal component, C3, -in phase opposition with the resultant, CR, of the first and second carrier signal components, is attained through the common tuned primary winding of the output transformer T2. The linear buffer amplifier stage V5 serves to prevent any interaction between the utilization means coupled to the output circuit at the terminals 10Q-101 and the signal-forming amplifier mixing circuit 94. The use of the formed RF output signal for 'further power amplification and broadcast transmission represents .a present effective use for the Signal forming transmitter or exciter of the present invention. It may yalso be used directly as a signal source to test stereo receivers of the angular-modulation type.
Having described the invention, what is claimed is:
1. A signal-forming transmitter for use in angular-sideband systems for modulated signal transmission, comprising in combination, means for producing three carrier signal components, the first and second `of which are angularly related to the third, means for modulating the first and second carrier signal components, and means for combining said three signal components, the third signal component being of opposite phase with the resultant of the first and second `signal components and of `an amplitude to reduce the resultant of the first and second signal components to provide a composite carrier signal having a relatively-wide modulation range.
2. In a two-channel angular-sideband signal transmitter, means for producing three carrier signals, the first and second of which are substantially symmetrically `angularly related to the third, means for amplitude modulating the first .and second carrier signals, and means for combining said three carrier signals, with the third carrier signal in phase opposition with the resultant of the first and second carrier signals to reduce the resultant of the first land second signal components to provide a composite differential output carrier signal adapted for substantially full modulation depth.
3. A signal-forming transmitter for use in angular-sideband systems for modulated signal transmission, comprising in combination, means for producing three carrier signal components the first and second of which are substantially symmetrically angularly related t-o the third, means for amplitude modulating the first and second carrier signal components with two modulating signals, a common tuned signal -output circuit, and means for combining said three signal components in said output circuit, with the third signal component in phase opposition with the resultant `of the first and second signal components yand of an amplitude to reduce the resultant of the first and second signal components to produce a differential output carrier signal adapted for substantially `full modulation depth.
4. A signal-forming transmitter for use in an angularsideband system for modulated signal transmission, comprising in combination, means providing a basic carrier signal source having an output circuit including a coupling winding having two end terminals and an intermediate tap connected to ground for said system, means providing first and second branch signal circuits connected jointly with one terminal of said coupling winding, phase shift networks in said branch circuits providing substantially equal phase shifts positively in one br-anch circuit and negatively in the other branch circuit for deriving two signal components having a predetermined phase differential in response to an applied carrier signal from said source through said winding, modulator means coupled to each of said branch circuits having a common output circuit wherein the carrier-signal components derived from said branch circuits are added vectorially to provide a resultant carrier signal, signal-translating means coupled between the other terminal of said coupling winding and said common output circuit for the modulator means for applying to said output circuit a carrier signal component substantially 180 out of phase with said resultant carrier signal and substantially equal to the excess amplitude of said resultant carrier signal above that required for effective 100% modulation.
5. A signal-forming transmitter for use in an angularsideband system for modulated signal transmission, comprising in combination, means providing a basic carrier signal source having a tunable output circuit responsive to the carrier-signal frequency and including a coupling winding having two end terminals and an intermediate tap connected to ground for said system, means providing rst and second branch signal circuits connected jointly with one terminal of said coupling winding, a phase shift network in each of said branch circuits providing substantially 30 phase shift positively in one branch circuit and negatively in the other branch circuit for 4deriving two signal components with substantially 60 phase differential in response to an applied carrier signal from said source through said winding, means providing a pair of modulator stages coupled one to each of said branch circuits and having a common `output circuit tunable to the carrier signal frequency and wherein the carrier-signal components derived from said branch circuits are added vectorially to provide a resultant carrier signal, and means including a signal amplifier coupled between the other terminal of said coupling winding and said tunable output circuit for the modulator stages for applying to said output circuit a carrier signal component substantially 180 out of phase with said resultant carrier signal and substantially equal to the excess amplitude of said resultant carrier signal above that required for effective 100% modulation.
6. A signal-forming transmitter for use in an angularsideband system for two-channel modulated signal transmission, comprising in combination, basic carrier-signal generating means having a tunable output circuit including a coupling winding having two terminals and an intermediate tap connected to ground for said system, means providing first and second branch signal circuits connected jointly with one of said terminals, means in said last named connection for reducing signal voltages applied to said branch circuits, a phase-shift network in each of said branch circuits providing substantially equal phase shifts positively in one branch circuit and negatively in the other branch circuit for deriving two signal components with a predetermined phase differential in response to an applied carrier signal from said source through said winding, means providing a pair of modulator stages coupled one to each of said branch circuits and having a common output circuit tunable to the carrier signal frequency and wherein the carrier signal components derived from said branch circuits are added vectorially to provide a Iresultant carrier signal, means for applying two-channel modulating signals to said modulator stages for modulating the first and second carrier signal components in said first and second branch circuits, and means including a signal amplifier coupled between the other terminal of said coupling winding and said tunable output circuit for the modulator stages for applying to said output circuit a carrier signal component substantially 180 out of phase with said resultant carner signal and substantially equal to the excess amplitude of said resultant carrier signal required for effective modulation, thereby to provide a resultant output carrier having an amplitude adapted for substantially full modulation.
'7. A signal-forming transmitter for use in an angularsideband system for modulated signal transmission, comprising in combination, a tunable oscillator providing a basic carrier signal source, a tunable output transformer therefor having a secondary winding with an intermediate tap connected to ground for said system, means connected with the secondary winding on opposite sides of said tap for producing therefrom three carrier signal components from said basic carrier signal, said last named means including first and second branch signal circuits connected with said secondary winding on one side of said tap for translating a first and second of said three carrier signal components and a third branch signal circuit connected with said secondary winding on the opposite side of said tap for translating a third of said three carrier signal components, the signal components applied to said first and second branch circuits thereby being substantially out of phase with said -third signal component, a phase-shift network i-n each vof said first and second branch signal circuits providing positive phase shift in one branch circuit and negative phase shift in the other branch circuit thereby to provide two signal components having a predetermined phase differential and substantially symmetrically angularly related to said third signal component in response to an applied carrier signal from said oscillator through said secondary winding, means providing a pair of modulator stages coupled one to each of said iirst and second branch signal circuits and having a common 4output circuit tunable to the carrier signal frequency, means connecting said third branch signal circuit with said common output circuit for combining said three carrier signal components, with the third carrier signal component in phase opposition with the resultant of the first and second carrier signal components in said output circuit, thereby to effect a reduction in the resultant carrier signal amplitude for increased eifective modulation depth, means for applying different modulating signals to said modulator stages for differently modulating said first and second carrier signal components in the first and second branch signal circuits, buffer linear signal amplifier means, and signal utilization means coupled to said output circuit through said amplifier means.
8. A signal-forming transmitter for angular-sideband modulated-signal transmission, comprising in combination, signal generator means, output transformer means therefor having a winding with a grounded intermediate tap, rst and second branch signal circuits connected with said winding on one side of said tap and a third branch signal circuit connected with said winding on the opposite side :of said tap, whereby signal components from said generator means applied to said first and second branch circuits are substantially 180 `out of phase with a signal component from said generator means applied to said third branch signal circuit, a phase-shift network in each of said first and second branch signal circuits providing a positive phase shift in one branch circuit and a negative phase shift in the other branch circuit to provide two signal components having a predetermined phase differential and angularly related to said third signal component, means providing a pair of modulator stages coupled one to each of said rst Iand second branch signal circuits and having a common output circuit tunable to the carrier signal frequency, means for combining said three carrier signal components in said signal output circuit with the third carrier signal component in phase opp-osition with the resultant of the first and second carrier signal components, thereby to provide a resultant output carrier signal of reduced amplitude for increased effective modulation depth, and means for applying different modulating signals to said modulator stages for differently modulating said first and second carrier signal components in 1 1 the first and second branch signal circuits at relatively low amplitudes.
9. A signal-forming transmitter for angular-sideband modulated-signal transmission, comprising in combination, signal generator means, output transformer means therefor having a winding with a grounded intermediate tap, first and second branch signal circuits connected with said winding on one side of said tap, a third branch signal circuit connected with said winding on the opposite side of said tap, a phase-shift network in each of said first and second branch signal circuits providing substantially a 30 positive phase shift in one branch circuit and substantially a 30 negative phase shift in the other branch circuit thereby to provide two signal components having a predetermined substantially 60 phase differential and substantially symmetricallyl angularly related to said third signal component, signal modulator means coupled to each of said first and second branch signal circuits having a common output circuit tunable to the carrier signal frequency, means for combining said three carrier signal components in said signal output circuit, with the third carrier signal component in phase opposite with the resultant -of the first and second carrier signal components, thereby to provide a resultant output carrier signal of reduced amplitude for increased effective modulation depth, means for applying different modulating signals to said modulator means for differently modulating said first and second carrier signal components in the first and second branch sign-al circuits at relatively low amplitudes, buffer linear signal amplifier means, and signal utilization means coupled to said output circuit through said amplifier means.
10. A signal-forming transmitter for use in an angularsideband system for modulated signal transmission, comprising in combination, means providing a basic carrier signal source, a tunable carrier-signal output transformer therefor having a secondary Winding with an intermediate tap connected to ground for said system, first and second branch signal circuits connected with said secondary winding on one side :of said tap, a third branch signal circuit connnected with said secondary winding on the opposite side of said tap, a phase shift network in each of said first and second branch signal circuits, means providing a pair of modulator stages coupled one to each of said first and second branch signal circuits and having a common output circuit tunable to the carrier signal frequency, means for combining carrier signal components from said branch signal circuits in said common output circuit, one carrier signal component from the third branch signal circuit being in phase opposition with the resultant of carrier signal components from the first and second branch signal circuits, signal utilization means coupled to said output circuit, means for applying different modulating signals to said modulator stages for differently modulating said first and second carrier signal components in the first and second branch signal circuits, buffer linear signal amplifier means, and signal utilization means coupled to said output circuit through said amplifier means.
References Cited by the Examiner UNITED STATES PATENTS 1,608,566 11/26 Potter 179-15 1,666,158 4/28 Offel 179-15 1,854,247 4/32 Brand 179-15 2,611,036 9/52 Norgaard 179-15 3,007,005 10/61 Moore et al. 179-15 OTHER REFERENCES Electronic Circuits and Tubes, Cruft Electronics Staff, 1947; McGraw-Hill.
DAVID G. REDINBAUGH, Primary Examiner,
ROBERT H. ROSE, Examiner,

Claims (1)

1. A SIGNAL-FORMING TRANSMITTER FOR USE IN ANGULAR-SIDEBAND SYSTEMS FOR MODULATED SIGNAL TRANSMISSION, COMPRISING IN COMBINATION, MEANS FOR PRODUCING THREE CARRIER SIGNAL COMPONENTS, THE FIRST AND SECOND OF WHICH ARE ANGULARLY RELATED TO THE THIRD, MEANS FOR MODULATING THE FIRST AND SECOND CARRIER SIGNAL COMPONENTS, AND MEANS FOR COMBINING SAID THREE SIGNAL COMPONENTS, THE THIRD SIGNAL COMPONENT BEING OF OPPOSITE PHASE WITH THE RESULTANT OF THE FIRST AND SECOND SIGNAL COMPONENTS AND OF AN AMPLITUDE TO REDUCE THE RESULTANT OF THE FIRST AND SECOND SIGNAL COMPONENTS TO PROVIDE A COMPOSITE CARRIER SIGNAL HAVING A RELATIVELY-WIDE MODULATION RANGE.
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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4182932A (en) * 1978-10-26 1980-01-08 Fisher Charles B A-m stereo system
US4236042A (en) * 1979-03-12 1980-11-25 Harris Corporation Compatible AM stereo system employing a modified quadrature modulation scheme
US4406922A (en) * 1980-05-19 1983-09-27 Motorola Inc. Stereo broadcast system

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1608566A (en) * 1925-12-31 1926-11-30 American Telephone & Telegraph System for binaural transmission of sound
US1666158A (en) * 1925-12-31 1928-04-17 American Telephone & Telegraph System for binaural transmission of signals
US1854247A (en) * 1928-10-30 1932-04-19 American Telephone & Telegraph Multiplex phase discrimination transmission system
US2611036A (en) * 1947-11-12 1952-09-16 Gen Electric Selective sideband transmission and reception system
US3007005A (en) * 1959-02-12 1961-10-31 Philco Corp Transmitter for stereophonic information signals

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1608566A (en) * 1925-12-31 1926-11-30 American Telephone & Telegraph System for binaural transmission of sound
US1666158A (en) * 1925-12-31 1928-04-17 American Telephone & Telegraph System for binaural transmission of signals
US1854247A (en) * 1928-10-30 1932-04-19 American Telephone & Telegraph Multiplex phase discrimination transmission system
US2611036A (en) * 1947-11-12 1952-09-16 Gen Electric Selective sideband transmission and reception system
US3007005A (en) * 1959-02-12 1961-10-31 Philco Corp Transmitter for stereophonic information signals

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4182932A (en) * 1978-10-26 1980-01-08 Fisher Charles B A-m stereo system
US4236042A (en) * 1979-03-12 1980-11-25 Harris Corporation Compatible AM stereo system employing a modified quadrature modulation scheme
US4406922A (en) * 1980-05-19 1983-09-27 Motorola Inc. Stereo broadcast system

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