US2167722A - Sideband modulation - Google Patents

Sideband modulation Download PDF

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Publication number
US2167722A
US2167722A US131828A US13182837A US2167722A US 2167722 A US2167722 A US 2167722A US 131828 A US131828 A US 131828A US 13182837 A US13182837 A US 13182837A US 2167722 A US2167722 A US 2167722A
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United States
Prior art keywords
circuit
band
load
filter
output
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Expired - Lifetime
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US131828A
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English (en)
Inventor
Nils E Lindenblad
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RCA Corp
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RCA Corp
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Priority to BE427063D priority Critical patent/BE427063A/xx
Application filed by RCA Corp filed Critical RCA Corp
Priority to US131828A priority patent/US2167722A/en
Priority to GB6465/38A priority patent/GB512065A/en
Priority to FR835441D priority patent/FR835441A/fr
Application granted granted Critical
Publication of US2167722A publication Critical patent/US2167722A/en
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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

  • This application concerns an improvement in methods of and means for producing single sideband modulation of a carrier wave in accordance with television signals.
  • a 3 to 5 percent band with an impedance or admittance variation corresponding to less than l db. is about the average obtainable with simple radiating structures without additional artificial loading.
  • a modulation band width of 3% of the carrier efficiently with radiating systems in present use.
  • a carrier of 50 megacycles is selected and after amplification, is modulated by energy characteristic of 30 frames of 343 line pictures.
  • the modulation output is then impressed on two sideband pass filters tuned to the upper and lower side frequencies respectively.
  • One lilter is terminated in an artificial load, the other in a radiating structure.
  • the changes in response of the power amplifier tank circuit and of the radiating structure or load for the different frequencies of the wide frequency band covered by one sideband results in variations in load on the filters, the power amplifier, etc., and these variations produce reactions through the power amplifier to the succeeding amplifiers and cause 1937, Serial No. 131,828
  • the object of my present invention is to provide a new and improved sideband modulation system which eliminates the defects enumerated above and by means of which a single sideband modulated by a wide modulating potential band may be produced, amplified, and impressed on appropriate radiating structure.
  • This invention therefore, in its broadest aspect, concerns a new and improved means for transferring from one tuned circuit in which wave energy covering a relatively wide frequency spectrum flows to a second circuit, wave energy covering a portion only of said spectrum and so loading said first circuit as to improve its impedance characteristic over the entire range of the frequency spectrum.
  • the transferred frequency spectrum is characteristic of the entire band.
  • FIG 1 illustrates the essential elements of the improved single sideband modulator as described hereinbefore;
  • Figure la is a modification of a portion of the circuit of Figure 1.
  • plate modulation is used.
  • grid modulation is used;
  • Figure 2 is a curve illustrating the character of the output of the modulator as impressed on the band pass filters and also the character of the output, the power amplifier as impressed on the load or transmission line; while Figures 3, 4, 5 illustrate band pass filters of different character which may be utilized in place of the band pass filters of Figure l.
  • l5 is a modulator comprising a pair of electron discharge devices having their control grids connected by reactance I2 which may be coupled for excitation to any source of carrier wave energy of the desired frequency and amplitude.
  • the anodes of the modulator tubes are connected together by a tuned tank circuit I, a ⁇ point on which is connected to the anode of a modulator tube l2, the control grid of which is connected to a source of modulating potentials I4 and the anode of which is connected by a reactor I6 to a source of direct current potential.
  • the anode of each of the carrier wave amplifier tubes in the stage I0 may be connected to ground as shown by external tank loading impedances.
  • 'Ihe modulated output from tank circuit I is impressed on the inputs 20, 22 of a high band pass filter and a low band pass filter respectively.
  • This arrangement permits susbtantially complete separation of the upper and lower sidebands except for possibly the lowest modulation frequencies.
  • the output of the high band pass filter is connected as shown to the control or other input electrode of the initial tube in a power amplifier 24.
  • This power amplifier may be of any type but is preferably of a type such that changes in load in the output thereof cannot react therethrough to affect the high band pass filter.
  • a neutralized power amplifier is appropriate for use here or an amplifier wherein tubes of the screen grid type wherein the screen grid shields the output electrodes from the inputk electrodes.
  • amplifiers of the electron coupled type may also be used.
  • the terni amplifiers one or more tube stages in cascade or stages comprising parallel tubes in cascade, is contemplated.
  • the output of the power amplifier 24 is connected directly to a radiating structure or by lines to any utilization circuit.
  • the low band pass filter is terminated in an artificial load such as, for example, an absorbing resistance 30 wherein the energy representative of the lower sideband frequencies is expended.
  • the gain from this procedure lies in the fact that thanks to the neutralizing in the power amplifier 24 or the un-coupling between the output and input thereof, the impedance from antenna, line 3E, and cross talk filter is uri-coupled from the modulated stage Il).
  • the high pass filter is now clearly terminated for all frequencies in the high frequency sideband including those of the lower sidebands which may inadvertently get through the high pass filter.
  • the high pass filter now acts as a true filter whereas if its output impedance varies filter tuning conditions may arise if the high pass filter lets through portions of the lower sidebands. This condition might occur if the high band pass filter was located between the power amplifier and the antenna or lines 30, as has been the Case heretofore because the antenna impedance is of variable value for the lower sidebands, being adjusted for linear response over the higher sideband frequencies.
  • the tank circuit of the power amplifier 24 may now be given characteristics such as to amply take care of the upper side frequency when this amplifier is operated class A. While class A operation is not efiicient it gives high fidelity and is reliable. Obviously it would be very difficult to make this stage 24 broad enough to have a flat pass characteristic for both the upper and the lower sidebands.
  • stage Ie may have to be somewhat greater than normal since stage I0 will have to be loaded not only by some artificial loading of the high pass filter but also by the loading from the low pass filter and absorber resistance and, in general this stage EG, must be broad enough to pass both sidebands well.
  • the characteristic of the tank circuit I must be such as to pass substantially uniformly all of the frequencies covered by the carrier and both sidebands. Obviously, in order to obtain this characteristic excessive modulation in the stage ID must be avoided.
  • the high band pass filter and the low band pass filters of Figure i have been shown as comprising series and parallel reactances of the capacitive type, it will be understood that I contemplate the use of any appropriate filters in these circuits.
  • the high band pass filter of Figure l may be replaced by the high band pass filter of Figure 3.
  • the low band pass filter of Figure 1 may be replaced by the low band pass filter of Figure 4 and finally the high and low band pass filters of Figure 1 may be replaced by the high or low band pass filter of Figure 5 provided the elements thereof are given the proper values.
  • a transmission system comprising in combination a modulator, a source of carrier wave energy, and a source of modulating energy interconnected to produce modulated wave energy, a load circuit, a filter circuit tuned to the frequency range between the carrier and one maximum sideband frequency of said wave energy connected between the modulator and the load circuit, and a complementary lter terminated by an artificial load tuned to the frequency range between the carrier and the maximum sideband on the opposite side of said carrier relative to said first mentioned maximum sideband frequency connected with the modulator for balancing the modulator for all frequencies.
  • a single side band signalling system for transferring a portion only of the frequency spectrum of a wide frequency band comprising a carrier and side bands from a tuned circuit to a load circuit, a filter circuit coupling said load circuit to said tuned circuit, said filter circuit boing tuned ⁇ to pass a selected band of frequencies less than the total frequency spectrum but including a side band from said tuned circuit to said load circuit, and a network tuned to a selected band of frequencies not passed by said filter substantially coupled to said tuned circuit only, said network imposing on said tuned circuit impedance characteristics complementary to the impedance characteristic imposed on said tuned circuit by said filter circuit.
  • a filter circuit for selecting said portion only of the total band of produced frequencies which is connected between the load circuit and the modulator, the combination which comprises a complementary compensating circuit tuned to the remaining portion of the total frequency band and connected to said modulator only for loading said modulator at a portion of the remaining frequencies within the produced band so that said modulator is substantially uniformly loaded for all produced frequencies.
  • a modulated wave amplifier having an output coupled to said load circuit, said amplifier having an input, means for preventing reaction between the output and input of said amplifier, a carrier wave amplifier having its anode coupled to a tuned tank circuit, its control grid excited by wave energy to be modulated and one of its electrodes coupled to a source of modulating potentials to produce modulated energy comprising sideband frequencies, a filter tuned to pass a substantial amount of said modulated energy coupling said tank circuit to the input of said power amplifier, an artificial load, and a filter tuned to pass a substantial amount of said modulated energy coupling said tank circuit to said artificial load, said filters being tuned to pass wave energy of different frequency.
  • a load circuit a neutralized amplifier having an output coupled thereto, said neutralized amplifier having an input
  • a carrier wave amplifier having its anode coupled to a tuned tank circuit, its control grid excited by wave energy to be modulated and one of its electrodes coupled to a source of modulating potentials to produce modulated energy comprising sideband frequencies and impress the same on said tank circuit
  • a band pass filter coupling said tank circuit to the input of said power amplifier to supply modulated energy to said power amplifier from said tank circuit, and artificial load
  • a band pass filter coupling said tank circuit to said artificial load, said .last filter being tuned to pass energy not passed by said first filter to thereby ,load said tank circuit substantially uniformly for a selected band of frequencies.
  • a load circuit an amplifier having an output coupled thereto, said amplifier having an input, means for preventing said output circuit and load from reacting on the input of said amplifier, a carrier wave amplifier having its anode coupled to a tuned tank circuit, its control grid excited by wave energy to be modulated and its anode electrodes coupled to a source of modulating potentials to produce modulated energy and impress it on said tank circuit, a high pass filter coupling said tank circuit to the input of said power amplifier to supply modulated energy thereto for signalling purposes, and means for substantially uniformly loading said tank circuit over the modulated energy frequency range comprising, an artificial load, and a low pass filter coupling said tank circuit to said artificial load.
  • a power amplifier adapted to repeat voltages in one direction only having an output coupled to said load circuit, said amplifier having an input, a low pass filter coupled at its input to said tuned circuit and at its output to an articial load, and
  • a high pass lter coupled at its input to said tuned circuit and at its output to the input of said power amplifier, said filters together imposing a .load on said tuned circuit which is substantially uniform over the wide frequency band to improve its characteristic and prevent reaction between diiferent frequencies of the wide band.
  • an electron discharge device having a control electrode on which said ultra-high frequency wave energy may be impressed, said tube having an output electrode, an output circuit connected to said output electrode, means for impressing modulating potentials which cover a wide frequency band on the impedance of said device to modulate said high frequency wave in accordance with said wide band of modulating potentials, a power amplifier having an output connected to a load, said power amplifier having an input, a filter for passing the upper sideband connecting said output electrode to said power amplifier input and a filter for passing the lower sideband coupling said output electrode to an artificial load, said two filters imposing on said tube output complementary impedance characteristics to thereby improve its linearity of operation over the wide band of frequencies through which said ultra-high frequency wave energy is modulated.
  • an electron discharge device having a control electrode on which said ultra-high frequency wave energy may be impressed, said device having an output electrode, means for modulating the impedance of said device in accordance with modulating potentials, a tank circuit connected to said output electrode and tuned to the mean frequency of said ultra-high frequency wave energy, an external .load connected with said output electrode to broaden the frequency range to which said tank circuit responds linearly, a power ampliiier having an output connected to a load, said power amplifier having an input, a band pass filter operating over a first band of frequencies connecting said output electrode to said power amplifier input and a band pass iilter operating over a second band of frequencies coupling said output electrode to an artificial load.
  • an electron discharge device having a control electrode on which said ultrahigh frequency Wave energy may be impressed, said device having an output electrode, means for impressing modulating potentials on the anode of said device whereby carrier and side bands are produced in said device, a tank circuit connected to said output electrode and tuned to the mean frequency of said Wave energy, an external load connected with said output electrode to broaden the frequency range to which said tank circuit responds linearly, a neutralized or equivalent power amplifier of the class A type having an output connected to a load, said power amplifier having an input, a filter for passing the upper sideband connecting said output electrode to said power amplifier input and a filter for passing the lower sideband coupling said output electrode to an artificial load.
  • a pair of electron discharge devices each having a control grid, a cathode, and an anode, means for impressing wave energy in phase opposition on said control electrodes, a tank circuit connecting said lanodes in push-pull relation, a tube having an anode, a cathode, and a control electrode, a connection between the anode of said tube and a point on said tank circuit, a source of modulating potentials connected with the control grid of said tube, a load circuit, an amplifier having an output coupled to said load circuit, said ampliiier having an input, an artificial load circuit, and band pass filters operating over diierent frequency ranges coupling said tank circuit to said amplifier input and to said load circuit respectively.
  • a pair of electron discharge devices each having a control grid, a cathode, and an anode, means for impressing wave energy in phase opposition on said control electrodes, a tank circuit connecting said anodes in push-pull relation, a tube having an anode, a cathode, and a control electrode, a connection between the anode of said tube and a point on said tank circuit, a source of modulating potentials connected with the control grid of said tube, a load circuit, a neutralized amplifier having an output coupled to said load circuit, said neutralized amplifier having an input, an artificial load circuit, and high and low pass filters coupling said tank circuit to said amplifier input and to said load circuit respectively.
  • a pair of electron discharge devices each having a control grid, a cathode, and an anode, means for impressing wave energy in phase opposition on said control electrodes, a tank circuit connecting said anodes in push-pull relation, an external impedance connecting the anode of each device tothe cathode of each device to broaden the characteristic of said tank circuit, a tube having an anode, a cathode, and a control electrode, a connection between the anode of said tube and a point on said tank circuit, a source of modulating potentials connected with the control grid of said tube, a load circuit, a neutralized amplifier having an output coupled to said load circuit, said neutralized amplifier having an input, an artiiicialload circuit, and high and loW passvfilters of different character coupling said tank circuit to said amplifier input and to said load circuit respectively.

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US131828A 1937-03-19 1937-03-19 Sideband modulation Expired - Lifetime US2167722A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
BE427063D BE427063A (de) 1937-03-19
US131828A US2167722A (en) 1937-03-19 1937-03-19 Sideband modulation
GB6465/38A GB512065A (en) 1937-03-19 1938-03-01 Improvements in or relating to modulated carrier wave transmitters
FR835441D FR835441A (fr) 1937-03-19 1938-03-19 Système de modulation

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US131828A US2167722A (en) 1937-03-19 1937-03-19 Sideband modulation

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US2167722A true US2167722A (en) 1939-08-01

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US131828A Expired - Lifetime US2167722A (en) 1937-03-19 1937-03-19 Sideband modulation

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BE (1) BE427063A (de)
FR (1) FR835441A (de)
GB (1) GB512065A (de)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2658992A (en) * 1945-12-10 1953-11-10 John F Byrne Single side band jamming system
US2676304A (en) * 1951-01-11 1954-04-20 Hartford Nat Bank & Trust Co Wave modulator to produce a single sideband signal

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2658992A (en) * 1945-12-10 1953-11-10 John F Byrne Single side band jamming system
US2676304A (en) * 1951-01-11 1954-04-20 Hartford Nat Bank & Trust Co Wave modulator to produce a single sideband signal

Also Published As

Publication number Publication date
GB512065A (en) 1939-08-29
FR835441A (fr) 1938-12-21
BE427063A (de)

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