US2186146A - Side band suppression system - Google Patents

Side band suppression system Download PDF

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Publication number
US2186146A
US2186146A US228923A US22892338A US2186146A US 2186146 A US2186146 A US 2186146A US 228923 A US228923 A US 228923A US 22892338 A US22892338 A US 22892338A US 2186146 A US2186146 A US 2186146A
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Prior art keywords
frequency
circuits
side band
resonant
phase
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US228923A
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English (en)
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Plebanski Jozef
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Radio Patents Corp
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Radio Patents Corp
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03C—MODULATION
    • H03C1/00—Amplitude modulation
    • H03C1/52—Modulators in which carrier or one sideband is wholly or partially suppressed
    • H03C1/60—Modulators in which carrier or one sideband is wholly or partially suppressed with one sideband wholly or partially suppressed

Definitions

  • I. F'. I J4 AMPLIFIER AMPLIFIER J2, IFREQUENO( CHANGER J5 20
  • I. F'. is AMPLIFIER I MO 35 glmws: E; 44 29 J1 zo 3 24 T AMPLIFI -ob FREQuEMC? f1 12 ANGER AMPLJFIER f 91 b QZ 30 e an z.
  • An object of the invention is to provide a simple and 'means and a method for selecting the upperor lower side band of a modulated carrier signal. 1 v
  • a more specific object is to provide a simple and efficient circuit arrangement in a radio re DCver for eliminating'or minimizing interference due to overlapping of the modulation side bands of adjacent signalling channels experienced in the reception of broadcast signals or the like.
  • Another object is the reduction or suppression of disturbing heterodyning signals or beat notes in a radio receiver caused by an adjacent carrier wave.
  • FIG. 1 is a circuit diagram for a radio receiver embodying a side band selecting system in accordance with the invention
  • Figure 2 shows a set of response curves ex planatory of the design and operation of the circuit according to Figure l
  • 7' Figure3 illustrates a preferred practical embodiment of a system constructed in accordance with the invention
  • Figures 4 and 5 are theoretical'diagrams explanatory of the design and operation of Figure 3,
  • Figure 6 illustrates a 1 and 3
  • FIG. 7 shows a diagram explanatory of the efiects and results obtained by means of a system according to Figure 6, and
  • Figure 8 shows a diagram illustrating a furmodification of Figures ther modification of the invention.
  • an antenna i0 connected in a known manner to ground 34 through a series coupling condenser H and acoupling coil l2.
  • the latter is arranged in inductive relation with a secondary coil l3 connected tothe input of a frequency changeror mixer device I4 as provided in' the conventional type of superheterodyne receiver.
  • a modulated high frequency signalreceived by the antenna is converted into a signal of intermediate or beat frequency portions of which are applied to a pair of separate.
  • intermediate frequency amplifiers l5 and I6, respec tively.
  • the output signal of'the amplifier I5 is impressed upon the grid of a further amplifying tube l9 including in its output a resonant circuit comprised of an induction coil 22 shunted by a condenser E! in series with a coupling coil 28.
  • the output signal of the amplifier I6 is impressed upon the grid of an amplifying-tube including in its output a resonant circuit comprised of an induction coil E l shunted by a condenser 23 in serieswith a coupling coil 29.
  • the 1 anodes of tubes l9 and 29 are supplied with high potential from a source indicated by the plus symbols in a manner well known, and the resonant circuits are returned to ground or cathode.
  • the high potential ends of the resonant circuits are further connected each to one of a pair of fixed contacts of a switch 39 having a movable contact connected to a detector andv audio frequency amplifier 32 through a coupling condenser 3
  • the output of the audio amplifier may serve to supply a translating device such as. a loud speakerv'i i.
  • , 22, 28 and 23, 2Q, 29 are tuned to the signal frequency, that is in the example illustrated the intermediate or beat frequency of the receiver.
  • bands of the impressed input signal may be selected and applied-to the detector or audio frequency, amplifier by connecting the switch 30 in the upper or lower position, respectively.
  • the received high frequency signal may be directly applied to the amplifier tubes I9 and 2d or tuned circuits El, 22 or 23, 24, respectively, i. e. in the manner of a straight high frequency receiver without changing to aninterm'ediate frequency as shown in the example illustrated.
  • the amplitude response characteristic of the amplifier l5,that is the amplitude of the output current I input as a function of frequency is shown at A in Figure 2, that is the amplitude response is substantially constant throughout the modulation frequency band.
  • the phase characteristics of this amplifier is assumed to be constant such as shown at P1 in Figure 2, or in other words no substantial phase displacement occurs during the passage of the signals from the input to the output.
  • the amplifier IS on the other hand is designed to have an amplitude response characteristic similar to the amplifier I5, that is as shown at A in Figure 2, and a phase response characteristic differing substantially from the phase response characteristic of the amplifier l5 as shown at P2 in Figure 2.
  • the time phase of all frequencies below the resonant frequency f0 (lower side band) is and the phase of all the frequencies above the resonant frequency Ju (upper side band) is +90 or, in other words, all frequencies of the left side band are shifted by 90 in respect to the same frequencies in the amplifier l5 and all frequencies of the right side band are shifted by +90 in respect to the corresponding frequencies in the amplifier l5.
  • the invention by reason of the relative simplicity of the circuit and its adjustment has great advantages over the existing methods of side band suppression or selection requiring filters with sharp cut-off characteristics, the latter being complicated in design and as a result thereof bulky and costly.
  • transmitters or modulators it has become known to suppress one side band by modulating each of a pair of carrier waves having a quadrature phase relation by a corresponding pair of modulating waves also having a quadrature relation and by adding or subtracting the output products, whereby one of the modulation side bands is suppressed or neutralized.
  • Systems of this type are also expensive and complicated both in design and operation due primarily to the fact that a 90 phase shift of both the carrier and the components of the modulating signal is required.
  • FIG 3 there is illustrated a preferred practical circuit arrangement for obtaining an amplitude and phase characteristic in the signal channels feeding the coupled resonant circuits.
  • Figure 3 is described with reference to a transmitter, it is understood that the arrangement shown equally applies to a receiver or any other system for translating modulated carrier energy.
  • a generator or oscillator producing high frequency currents are applied to a modulator 31 of any known type There. is
  • the output circuits of the tube 39 contains a resistance capacity coupling arrangement comprising in the example shown a coupling condenser 46 in series with a coupling resistance 46. A suitable tap point of the latter is connected to the grid of the tube 38.
  • , 22, 28 and 23, 2d, 29 connected in the output circuits of the tubes l9 and 2t] and the side band selecting switch 38 are substantially similar to the arrangement shown in Figure 1.
  • nae tunedcircuit 42 as has a low damping which may be obtained by regen eration through the feed-backcoil 45 connected in the output circuit of the tube I9 and arranged in inductive coupling relation with the coil 43, the side band characteristics vA and Af' will assume ashape such as shown in Figured,
  • suitable regulating means are provided such as an input resistance 46 havingfa variable tapconnected to'the control grid of the tube 23 as described hereinabove.
  • the latter are symmetrical for the upper and lower side band in respect Ito-the carrier frequency, whereby either of the side bands may be selected for transmission or reception by means of switch M as shown in Figures 1 and 3.
  • the selected side band may be applied to any output or utilization circuit connected to point a in a manner wellunderstood from the above.
  • a characteristic of the circuit shown: in Fig ure 3 is the fact that if the damping of the resonant circuit 42, '43 is decreased one of the side bands will be reduced to a greater extent while the lower frequencies in the other side band will be accentuated which may be useful in some cases; Furthermore, by adjusting the system in such a manner that the carrieramplitude is substantially greater than :the side band amplitudes-as shown-in Figure 5 (by vary-.
  • FIG. 6 there is shown a modlfication of the. invention especially suited although not limitatively forsuppression of disturbing heterodyning signals produced by beating between twoadjacent carrier frequencies.
  • means are provided for producing an additional fixed phase shift between the potentials exciting the coupled side band suppression circuits through the amplifiers I5 and it.
  • aiphase shifting circuit ,,arran'gement connected between the frequency changingor mixer stage l4 and the amplifiers l5 and It and comprising an output transformer 49 of the frequency changerrM having a secondary tuned to the intermediate frequency by a parallel condenser 50.
  • the phase shifting arrangement comprises a pair of series networks connected acrossthe transformer sec ondary, the first of said-networks being comprised of a condenser 5
  • a pair of amplifying tubes 56 and 5? theinput'control grid of the former beingcon'nected to junction betweenthe resistance 5d and condenser 55 and the inputzgrid of the latter being connected to avariable tap point of the'resistance 52.
  • the amplified output currents of the tubes are further provided.
  • the freand c are connected to a sideband elimination quency f for whichcomplete'suppressiontakes place can be controlled by regulating the resistances' 52 and 53, that is by' adjusting both the initial phase shift and relative amplitude of the exciting potentials exciting the coupled resonant It will be evident from the foregoing that the presentinvention provides a simple means and I method for suppressing one side band ina modulated carrier signal and has great advantages compared with known methods and circuits of side band. elimination requiring filters with sharp cutoff characteristics'or other circuit arrangejustment.
  • the invention may be further used advantageously for providing ultra-selective circuits, that is circuits having extremely sharp out-off frequencies at both sides of the resonant frequency.
  • two arrangements of the type disclosed are connected in cascade and adjusted in such a manner that the cut-off frequency f1 in the first arrangement is above and the cut-off frequency fiff of thesecond circuit is below the resonant frequency fo aS shown in Figure 8 in such a manner that the overall side band characteristic A1 and A2 overlap resulting in a narrow frequency band characteristic with sharp cut-off frequencies shown by the hatched area in the drawing. In this manner, a resultant band-pass characteristic of extreme selectivity is obtained.
  • a translation system for modulated carrier energy comprising a pair of transmitting channels having substantially constant input-output amplitude response over a range encompassed by the modulation side bands, means for applying substantially equal portions of said energy to the inputs of said channels, one of said channels having a substantially constant input-output phase characteristic in dependence upon frequency and the other channel adapted to change the phase of the modulation frequencies below and above the carrier frequency between the limits of 90 to +90", respectively, resonant circuits tuned to the carrier frequency connected to the outputs of said channels, mutual reactive coupling means between said resonant circuits, and a utilization circuit connected to one of said resonant circuits.
  • a translation system for modulated carrier of transmission channels having substantially constant input-output amplitude response over the modulation side band range means for impressing substantially equal amounts of said energy upon the inputs of said 'channela'one of said channels having a substantially constant input-output phase characteristic in dependence upon frequency and the other channel adapted to change the phase of modulation frequencies below and above the carrier between the limits of -90 to +90, respectively,
  • a translation system for modulated carrier energy comprising a pair of amplifying channels each comprising at least two amplifying stages in cascade, a resonant circuit tuned to the carrier frequency forming a coupling element between successive amplifying stages in said first channel, a resistance-capacity network forming a coupling element between successive amplifying stages in said second channel, a pair of further resonant circuits tuned to the carrier frequency and each connected to the output of one of said channels, inductive coupling means between said resonant circuits, and a utilization circuit connected to one of said resonant circuits. 4.
  • a translation system for modulated carrier energy comprising a pair of amplifying channels each comprising at least two amplifying stages in cascade, a resonant circuit tuned to the carrier frequency forming a coupling element between successive stages in said first channel, a resistance-capacity network forming a coupling element between successive stages in said second channel, a pair of further resonant circuits tuned to the carrier frequency and each connected to the output of one of said channels, a coupling transformer interconnecting said resonant circuits, the ohmic impedances of said last resonant circuits being substantially equal to each other and to the mutual reactance of said coupling transformer to effect suppression of the upper and lower modulation side bands, respectively, in each of said resonant circuits respectively, and a utilization circuit energized from one of said resonant circuits.
  • a system as claimed in claim 4 including means for adjusting the relative amplitude of the energies impressed upon said last resonant circuits.
  • a system as claimed in claim 4 including means for reacting upon said first mentioned resonant circuit with currents derived from a point at a relatively higher level of amplification in said first amplifier.
  • a system as claimed in claim 4 including means for regeneratively reacting upon said first resonant circuit with currents derived from a point at a higher amplification level in said first amplifier.
  • a translation system for modulated carrier energy comprising a pair of transmitting channels having substantially constant amplitude response over the modulation frequency range to be transmitted, one of said channels being substantially aperiodic and the other channel including a resonant circuit tuned to the carrier frequency and adapted to effect a phase shift between the lower and upper side band frequencies between the limits from 90 to +90", respectively, a pair of further resonant circuits each connected to the output of one of said channels,
  • a system as claimed in claim 8 including means for selectively connecting said utilization 11.
  • a translation system for modulated carrier energy comprising an aperiodic amplifier, a periodic amplifien comprising at least one resonant circuit tuned to the carrier frequency, means for impressing equal portions of the energy to be translated upon said amplifiers, a pair of further resonant circuits tuned to the carrier frequency and connected each to the output of one of said amplifiers, mutual reactive coupling means between said last resonant circuits, and a utilization circuit energized from one of said resonant circults.
  • t 12 In a system as claimed in claim 11 in cluding means for adjusting both the relative amplitude and phase; of the energies impressed upon said amplifiers.
  • a translation system for modulated signal energy comprising a pair of transmitting circuits, means for feeding portions! of the energy to be translated to said circuits, one of said circuits adapted to maintain the time phase position of the individual frequency components of the energy transmitted substantially constant and the 'theoutput of one of said transmitting circuits,
  • a system as'claimed in claim 13 including means for initially adjusting the relative time phase between corresponding components of like frequency of saidenergy portions before impression upon said transmitting circuits.

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US228923A 1938-03-08 1938-09-08 Side band suppression system Expired - Lifetime US2186146A (en)

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2646499A (en) * 1948-02-28 1953-07-21 James L A Mclaughlin Single-sideband radio equipment
US2846573A (en) * 1956-10-23 1958-08-05 Rca Corp Heterodyning receiving system
US2906831A (en) * 1956-08-07 1959-09-29 Texas Instruments Inc Convertible amplifier to plural channel and to push-pull
US2964622A (en) * 1957-10-21 1960-12-13 Sylvania Electric Prod Image suppressed superheterodyne receiver

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2646499A (en) * 1948-02-28 1953-07-21 James L A Mclaughlin Single-sideband radio equipment
US2906831A (en) * 1956-08-07 1959-09-29 Texas Instruments Inc Convertible amplifier to plural channel and to push-pull
US2846573A (en) * 1956-10-23 1958-08-05 Rca Corp Heterodyning receiving system
US2964622A (en) * 1957-10-21 1960-12-13 Sylvania Electric Prod Image suppressed superheterodyne receiver

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Publication number Publication date
FR851173A (fr) 1940-01-04

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