US1789364A - Method and means for combining and for eliminating frequencies - Google Patents

Method and means for combining and for eliminating frequencies Download PDF

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Publication number
US1789364A
US1789364A US71890A US7189025A US1789364A US 1789364 A US1789364 A US 1789364A US 71890 A US71890 A US 71890A US 7189025 A US7189025 A US 7189025A US 1789364 A US1789364 A US 1789364A
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United States
Prior art keywords
tubes
carrier
modulation
push
pull
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Expired - Lifetime
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US71890A
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English (en)
Inventor
Clarence W Hansell
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RCA Corp
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RCA Corp
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Filing date
Publication date
Priority to NL22927D priority Critical patent/NL22927C/xx
Application filed by RCA Corp filed Critical RCA Corp
Priority to US71890A priority patent/US1789364A/en
Priority to GB27844/26A priority patent/GB262076A/en
Application granted granted Critical
Publication of US1789364A publication Critical patent/US1789364A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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
    • H03C1/54—Balanced modulators, e.g. bridge type, ring type or double balanced type

Definitions

  • the present invention relates to an improved circuit for the control of one wave by another for signalling or other purposes.
  • Circuits and arrangements of this general type commonly known in the art are modulators, and demodulators, according to the use to which they are put.
  • the invention relates particularly to a novel form of balanced modulator or detector in which preferably a pair of three elect-rode discharge devices are connected so as to emphasize the production of certain wave components and to neutralize or lessen the production of other components.
  • a microphone circuit acting through a suitable transformer is used to produce a low frequency voltage which will change the grid bias potentials differentially so as to unbalance the output from the to es and result in anoutput from the system. If this is done the resulting output contains only the two side bands of the modulated carrier. This represents the ordinary push-pull modulating system shown in the patent to Hartley 1,494,905.
  • modulation is defined as the ratio of the maximum change away from the normal carrier current, produced by the side band currents, to the steady unmodulated carrier current.
  • modulation is defined as the ratio of the maximum change away from the normal carrier current, produced by the side band currents, to the steady unmodulated carrier current.
  • 100 ampere carrier current in an antenna and 100% modulation the antenna current will vary from 0 to 200 amperes.
  • 200% modulation the antenna current will vary from 100 amperes to 300 amperes, the significance of the minus sign being a 180 reversal in phase. Modulation in excess of 100% is analogous to a dearth of carrier frequency energy, and consequently distortion will be produced in an ordinary receiver.
  • the use of the balance principle makes it unncessary to modulate the tubes over the whole range of their characteristics from twice the steady value down to dynamic cutoff and so avoids the discontinuities and distortion usually caused as soon as the peak of the high frequency excitation and the modulation reaches dynamic cut-off, at which time arts of the excitation and modulation are a ruptly cut-01f, and distortion suddenly increases rapidly.
  • the amplification characteristic of a great many ordinary vacuum tubes as actually operated follows approximately a threehalves power law, and the rate of change of the slope of the amplification characteristic, which expresses the modulation characteristic, then follows a squareroot power, when the output impedance is small.
  • the modu lation characteristic of a single tube is therefore curved and as a result the modulation in the output, for large amplitudes of modulation, will be distorted by the addition of a very large second harmonic frequency.
  • the use of the two balanced tubes balances out this second harmonic, giving a resulting modulation characteristic which is more nearly straight. This correction of the distortion is the most important characteristic of the balanced modulator.
  • the modulator of this invention is of the same mechanical construction as the balanced modulator units which have been developed for use in sin le side band and multiplex equipments, and its use is a simple but radically different application of standard equipment
  • the vintra-inter-stage push-pull circuit shown in Fig. 3 is an improvement over the simple modulator.- Although the circuit shown in Fig. 1 eliminates even harmonics of the modulation it does not eliminate the fundamental and odd harmonics of the modulation nor the even harmonics of the radio frequency output caused by the curvature of the tube characteristics. I obviate these defects by using two complete sets of pushpull modulators which themselves are arranged to cooperate in push-pull.
  • the circuit consists of two balanced modulator units so arranged that their desired outputs add in a common output circuit but the second and other even multiple harmonic radio frequencies are balanced out.
  • This circuit is of considerable importance in a multiplex transmitter where an extremely large band of frequencies is required because of the waste frequency spectrum which would otherwise be taken up by the harmonics.
  • This system also will produce an appreciable reduction in the radiation of undesired and interfering harmonic frequencies from transmitters by preventing the formation of the harmonics before they can enter the amplifier system.
  • Fig. 1 shows a simple modification of my arrangement.
  • Fig. 2 shows a slightly different arrangerimary winding 3 windings 4 and 5.
  • the oscillator 9 is coupled through the transformer 8 to the rid cirunits of the tubes 10 and 11.
  • the Eias batteries 6 and 7 are disposed in opposite directions so that opposite potentials are impressed upon the grids of the tubes.
  • Fig. 2 the bias batteries 6 and 7 of Fig. 1 are replaced by a common battery .16 and the different potentials which are applied to the grids are determined by variable potentiometers 17 and 18 which are used to pick-off the desired potential.
  • This battery 16 is grounded at 19 and completes itscircuit through the ground 20 back to the-potentiometers. This also forms a convenient method of grounding the filaments of the tubes.
  • thefilaments are grounded at 53; ground 36 is connected to the bias battery and current is conducted from this battery to the potentiometers 37 and 38 back to the ground by means of wire 57.
  • potentiometers 37 and 38 are used to pick-off the respective bias voltages for the pairs of tubes 42, and 43, 46 respectively,
  • the grids of the tubes in the pairs being connected by wires 40 and 39 so that tubes of one pair will have a. different bias than the tubes of the other pair and the tubes of the upper push pull group and of the lower push pull group are differently biased by equal amounts.
  • the output coils 49 and 50 of the tubes are connected in opposition as before with the wire 54 connecting their middle points to the high potential battery 51 and back through the ground 52.
  • a master oscillator 41 is used, capacitatively coupled to the grids of the tubes through the inductive coupling 48 and the capacitive couplings 44 and 47.
  • the upper two tubes form one push-pull group and the lower two tubes another, and because of a fundamental property of a push-pull circuit, in each group the even harmonics of the modulating frequency are suppressed, and cannot appear in the output circuit, 55, 56.
  • the fundamental and the odd harmonics of the modulating frequency do appear in the coils 49 and 50, but are in phase, and therefore are eliminated by the reversed connection of the windings 55 and 56.
  • the carrier current from the source 41 is supplied to each push-pull group symmetrically, and, therefore, in each push-pull group, if the grids were equally biased, the carrier would be suppressed and could not appear in the coils 49 and 50.
  • the grids in each group are not at equal bias,and therefore a part of the carrier dependent upon the amount of inequality of bias appears in each of the coils 49. and 50.
  • the carrier is fed to the upper and lower groups in phase opposition, that is, when the carrier is positive at 44 it is negative at 47 In this way the carrier is supplied to the upper group and the lower group in pushpull, as'regards the pair of groups. For this reason the carrier components in the coils 49 and 50 are in phase opposition, but because of the reversed connection of coils 55 and 56,
  • 59 and 61 of Fig. 4 show the relative tube characteristics as they would be with their filaments connected together, the values above the abscissa being positive and those below being negative.
  • a characteristic would result as at which is the numerical sum of the instantaneous value of the two curves 59 and 61.
  • the modulation characteristic of each tube is a curve expressing the first derivative of the amplification characteristics 59 and 61, and adding these two modulation characteristic curves, a characteristic such as 58 results, and while working within the limits of the relatively straight portion of the curve, substantially straight line modulation is possible both in a positive and negative direction.
  • a method of reducing radio frequency harmonics in a carrier fundamental in order to make possible the use of more carrier frequencies in a given frequency spectrum which includes suitably directly balancing the outputs of two sets of simultaneously operated push-pull modulators by opposing them in phase, and supplying carrier. energy to the sets of modulators in phase opposition.
  • sets of vacuum tubes having cathodes, anodes and grids, each of said sets having their grids capacitatively coupled, their anodes inductively coupled and their cathodes conductively coupled, an oscillator coupled to each capacitative grid coupling, modulating means coupled to the grids, one grid of each set being conductively coupled to one grid of another set, means for conductively coupling the plates and applying a constant potential at the point of conductive coupling, a bias means for applying unlike potentials on each grid in a set and like potentials on all conductively coupled grids, means inductively associated with the inductive anode couplings so arranged as to counteract simultaneous equal oscillations and to be effective for simultaneous opposite oscillations.
  • sets of vacuum tubes having cathodes, anodes and grids, each of said sets having their grids capacitatively coupled, their anodes inductively coupled and their cathodes conductively coupled, an oscillator coupled to each capacitative grid coupling, modulating means coupled to the grids,one grid of each set being conductively coupled toone grid of another set, means for conductively coupling the anodes and applying a constant potential at the point of conductive coupling, a bias means for applying unlike potentials on each grid in a set and like potentials on all conductively coupled grids, means inductively associated with the inductive anode couplings so arranged as to counteract simultaneous equal oscillations.
  • the method of reducing harmonics produced by modulation of energy of one frequency by energy of another frequency which includes applying energy of one of the frequencies in push-pull to each of a pair of push-pull modulators, applying energy of the other frequency symmetrically to each modulator but in push-pull to the pair of energy to two pairs oftubes in phase and to each pair in push-pull, applying the carrier energy to the two airs o opposition and to eac pair symmetrically, differently normally biasing the tubes of each pair, and combming the outputs of each pair in push-pull, and of the two pairs in I phase opposition.
  • a plurality of pairs of electron emission tubes means to supply energy to each pair in series and to the pairs cophasially, means to supply energy to each pair in parallel and to the pairs in phase opposition, and means to subtractively combine energy from the tubes.
  • a plurality of pairs of electron emission tubes means to supply energy of one frequency to each pair in series and to the pairs cophasially, means to supply energy of another frequency to each pair in parallel and to the pans in phase opposition, and means to collect energy from each pair in series and from the pairs in phase opposition.
  • An arrangement for the elimination of undesired frequencies comprising, in combination, two push-pull stages, an input circuit coupled to the input circuits of the two stages cophasially, and an output circuit coupled to the output circuits of the two stages in phase opposition.

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  • Electric Propulsion And Braking For Vehicles (AREA)
  • Amplifiers (AREA)
US71890A 1925-11-28 1925-11-28 Method and means for combining and for eliminating frequencies Expired - Lifetime US1789364A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
NL22927D NL22927C (enrdf_load_stackoverflow) 1925-11-28
US71890A US1789364A (en) 1925-11-28 1925-11-28 Method and means for combining and for eliminating frequencies
GB27844/26A GB262076A (en) 1925-11-28 1926-11-05 Improvements in or relating to modulation systems applicable to wireless signalling

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US71890A US1789364A (en) 1925-11-28 1925-11-28 Method and means for combining and for eliminating frequencies

Publications (1)

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US1789364A true US1789364A (en) 1931-01-20

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Country Status (3)

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US (1) US1789364A (enrdf_load_stackoverflow)
GB (1) GB262076A (enrdf_load_stackoverflow)
NL (1) NL22927C (enrdf_load_stackoverflow)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2441964A (en) * 1944-05-19 1948-05-25 Standard Telephones Cables Ltd Compensating circuit
US2505670A (en) * 1947-11-28 1950-04-25 Raytheon Mfg Co Transceiver for multichannel radio communication systems
US2839728A (en) * 1956-02-06 1958-06-17 Donald L Jacoby Pulse code modulation system
US3725786A (en) * 1970-03-05 1973-04-03 Int Standard Electric Corp System for discrete marking and detecting a predetermined point in time within the envelope of a pulse modulated carrier

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2441964A (en) * 1944-05-19 1948-05-25 Standard Telephones Cables Ltd Compensating circuit
US2505670A (en) * 1947-11-28 1950-04-25 Raytheon Mfg Co Transceiver for multichannel radio communication systems
US2839728A (en) * 1956-02-06 1958-06-17 Donald L Jacoby Pulse code modulation system
US3725786A (en) * 1970-03-05 1973-04-03 Int Standard Electric Corp System for discrete marking and detecting a predetermined point in time within the envelope of a pulse modulated carrier

Also Published As

Publication number Publication date
GB262076A (en) 1927-05-19
NL22927C (enrdf_load_stackoverflow)

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