US2066970A

US2066970A - Controlled carrier wave system for signaling

Info

Publication number: US2066970A
Application number: US746812A
Authority: US
Inventors: George W Fyler
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1934-10-04
Filing date: 1934-10-04
Publication date: 1937-01-05
Anticipated expiration: 1954-01-05
Also published as: FR797885A; GB453732A; DE690729C

Description

7 Jan. 5, 1937. v G. w. FYLER I 2,065,970 CONTROLLED CARRIER WAVE SYSTEM FOR SIGNALING @Fil ed 001;. 4, 1954 2 Sheets-Sheet 1 70 CURRL-NT sa /ac:

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Filed Oct. 4, 1954 2 Sheets-Sheet 2 fomL PLA r5 VOL7J46 A moss MODULA 70/? I A/VDAMPL mm.

' CARR/ER WAVE AMPL #vaz VOLTA a5- ACROSS A400ozAnaQ Inventor: Gecr ge \Nfl ler H is' Attcv'n' Patented Jan. 5,1937

onireo sTArEs PAT CONTROLLED CARRIER WAVE SYSTEM FoR SIGNALING George W. Fyler, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York My invention relates to carrier wave signaling systems, particularly to methods of and means for obtaining modulated and amplified carrier waves in such systems, and its object is to provide 5 a controlled carrier wave'system for signaling whereby the energy required for the modulator and amplifier devices is substantially reduced while the advantages of constant carrier systems of modulation are retained.

10 Various methods have been proposed heretofore for modulating an amplified carrier wave of superaudible or radio frequency with signal currents. The most efficient prior method known of obtaining a modulated radio frequency carrier 15 Wave is probably the constant carrier modulation method which comprises Class B modulation of a Class C radio frequency amplifier. In Class B modulation the electron discharge devices comprised in the modulator apparatus operate as Class B amplifiers, wherein the anode or output current has a relatively low value when the control grid excitation voltage is zero, and wherein, upon application of alternating excitation voltages to the control grids, pulses of anode or output current are produced corresponding to each positive half-cycle of grid excitation voltage variation. In Class C amplifiers the circuit arrangements are such that the anode or output current is substantially zero when no excitation 0 voltages are applied to the control grids, alternating excitation voltages being applied to the control grids such that relatively large amplitudes of anode or output current flow during a fraction of each positive half cycle of the grid 35 excitation voltage variation.

In a radio, or other system, in which the above mentioned carrier Wave modulation method of the prior art is employed a carrier wave is impressed on amplifier apparatus comprising a. Class 40 C amplifier, signal currents are impressed on a modulator apparatus comprising Class B amplifiers, and means including the modulator are provided to modulate the carrier wave in the amplifier. In certain portable or mobile radio 45 transmitter installations in which the above described modulating method has been employed the difiiculty has been encountered that the power required for the electron discharge devices of the transmitter has been excessive.

50 In accordance with my invention the above and other disadvantages encountered in the use of the above-mentioned and other methods of obtaining a modulated carrier wave are obviated by a series arrangement of the modulator and 55 amplifier with the power current source. In the improved arrangement in general of a modulating and amplifying system in accordance with my invention, voltage from a direct current source having a constant high voltage is impressed in series on the output circuit of a modulator ap- 5 paratus comprising Class B amplifiers arranged in push-pull relation and on a means included in a carrier wave amplifier apparatus to vary the amplifier output current in accordance with signal currents.

In a preferred form of a system in accordance with the invention the high constant voltage is impressed in series on the output circuit of the modulator apparatus comprising Class B pushpull amplifiers and on the output circuit of the Class C carrier Wave amplifier.

My invention will be better understood from the following description when considered in connection with the attached drawings and its scope will be set forth in the appended claims.

Referring to the drawings, Fig. 1 is a circuit diagram illustrating a modulated carrier wave system in which my invention has been embodied, Fig. 2 illustrates voltage relations in output circuits of the system shown in Fig. 1, Fig. 3 illustrates signal voltage and output current characteristics of the system shown in Fig. l, and Fig. 4 is a circuit diagram illustrating a modulated carrier wave system in which a modification of my invention has been embodied.

In Fig. 1 the numeral it! indicates a suitable source of carrier waves of superaudible, or radio, frequency comprising for example an electron discharge device ll having circuits arranged to produce oscillations. These carrier waves are impressed on an amplifier apparatus l2 comprising a Class C amplifier electron discharge device 13 having a cathode I l, grid i5 and anode it, the cathode l4 being supplied with suitable heating, current, for example through a transformer i1 from an alternating current source.

The numeral l8 indicates a source of signal currents such as a microphone, the currents of signal frequency from source l8 being impressed, through audio frequency amplifying apparatus 5 I9 comprising an audio amplifier tube 20 and an audio output transformer 2!, on a modulator apparatus designated by the numeral 22 comprising a pair of Class B amplifiers 23 arranged in push-pull relation and having an output circuit including anodes 24, cathodes 25, the primary 26 of an output transformer 27 the secondary of which is designated by the numeral 28, and a connection including a condenser 29 between the primary 26 and the cathodes 25.

The cathodes 25 are supplied with heating current, as from an alternating current source through transformer 30 and leads 3|.

A current source of constant and relatively high voltage, represented for purposes of illustration as a battery 32, is provided to supply anode current to the anodes of the several electron discharge devices of the system illustrated in Fig. 1. In order to impress the required plate or anode voltage on the carrier wave amplifier tube I3 and the modulator tubes 23, and to provide connections whereby the carrier wave is modulated by the signal currents, the high direct voltage source 32 is connected, in accordance with my invention, to the output circuits of the amplifier apparatus I2 and modulator apparatus 22 in series. This series connection can be traced from battery 32 through lead 33', secondary 28 of modulator output transformer. 21, output circuit 34 of tube I3, anode I6, cathode I4, leads 35, secondary 36 of heating transformer I'I, lead 31, primary 26 of modulator output transformer 21, anodes 24, cathodes 25, leads 3|, secondary 38 of heating transformer 30, and lead 39 back to battery 32.

In operation of the system illustrated in Fig. 1, under normal conditions of modulation throughout the range from minimum to maximum of the per cent of signal currents supplied from the source I8, that part of the impedance of the above-described series circuit constituted by the anode-cathode circuit impedance proper or plate impedance of the carrier wave amplifier tube I3 is substantially constant. The anode-cathode circuit impedance or plate impedance of the modulator 22, however, is not constant but Varies throughout the modulation range. When there is no modulation, no signal currents from signal source I8 being supplied for the modulation of the carrier, the modulator tubes 23 present a high impedance to the flow of plate current in the series circuit comprising the plate battery 32 and the plate circuits of the amplifier tube I3 and modulator tubes 23. Under these conditions that part of the total plate voltage, the-total being for example 600 volts across the terminals of battery 32, which is on the modulator plate circuit is relatively high and that part of the total voltage which is on the carrier wave amplifier plate circuit is low, as better shown in Fig. 2.

As the. per cent of signal current supplied from source I8 for modulation of the carrier wave is increased from zero upto as illustrated in Fig. 2,v the modulator tubes 23 present a progressively reducing impedance to the flow of plate current in the series circuit. Under these latter conditions, since the carrier wave amplifier impedance is substantially constant, the portion of the total voltage which is on the modulator tubes 23 decreases correspondingly with the decrease in modulator plate impedance, and that portion of the total voltage which is on the carrier wave amplifier l3 correspondingly increases.

The impression on the plate circuit of carrier wave amplifier I3 of a voltage from source 32 varying, as above described, correspondingly with the variation or per cent of signal current impressed on the modulator tubes 23 causes the wave of carrier frequency in. the output circuit of tube I3 to vary in accordance with the amplitude of the waves of signal frequency. Simultaneously, however, with the impressing of the above described varying plate voltages on the amplifier tube I3 which cause the carrier in the output circuit of carrier wave amplifier I3 to vary correspondingly in amplitude, modulation voltages corresponding to the oscillating signal voltages generated by source I8 are impressed on the anode I6 of carrier wave amplifier tube I3. The oscillating signal currents from source I8 are amplified by the audio amplifier I9 and by the pushpull amplifier tubes 23, and, in the embodiment of the invention illustrated in Fig. 1 the modulation voltages are then transmitted to tube I3 from the modulator by the modulator output transformer secondary 28 which is connected in series with the plate current source 32 and the anode circuit of the carrier wave amplifier tube I3.

It will be seen that the magnitude of the carrier wave in the output circuit of carrier wave amplifier tube I3 is a function of the plate current in this tube, which in turn is determined by the varying impedance of the modulator tubes 23 and by the magnitude of the signal current provided by source I8. It will be seen further that while the carrier wave in the output circuit of amplifier I3 will thus vary with the amplitude of the signal current at a syllabic rate the mod ulation envelope variations will have the same amplitudes as in the case of the constant carrier system of modulation, as illustrated in Fig. 3 wherein the signal wave represented by the curve 40 causes the envelope of the carrier frequency oscillations in amplifier tube I3 to be modulated,

as shown in curve 4|, in accordance with the signal Wave.

In the design of a system as above set forth in connection with Fig. 1 it is advantageous to use zero bias and high MU tubes in the modulator.

With zero bias tubes the plate current at zero bias is low and increases at a low rate with increased plate voltage. The use of these tubes as modulators permits a reduction of the carrier wave level to about one-fifth or less of the value for 100% modulation, indicating a drop in power level in the carrier amplifier output to 4% or less of the maximum carrier wave value. This decrease in the carrier level can be controlled in accordance with the differing amplification factor of various i source ID to the carrier wave amplifier I3 must be modulated 100 in the usual case. The modulator tubes 23 must supply half of the maximum value in signal frequency power taken from the output terminals of the signal current transformer 2I. If the modulator overall plate circuit efficiency through the modulator output transformer 21 is assumed to be 50% for 100% signal current operation it will be seen that the platecircuit input power to the modulator tubes 23 will be equal to the plate circuit input power to the carrier wave amplifier I3. Since the plate current supplied from the direct current source 32 must be the same throughout the series circuit comprising the plate circuits of the modulator tubes 23 and carrier amplifier I3, the plate voltage will, therefore, divide equally between the modulator and carrier amplifier units for 100% signal. This latter condition is illustrated in Fig. 2 wherein at 100% signal voltage the voltage (E /I at 100% modulation) at the lowest signal frequency desired, since. if

this capacitor 29 were of too great capacity the rate of rise of the carrier wave would be limited and overmodulation would result. However it should be noted that the residual carrier wave takes care of a considerable amount of signal and the rate of rise of signal modulation is normally not sufficient to cause overmodulation of the carrier.

In the operation of a transmitter system comprising modulator tubes arranged in the Class B connection usually employed heretofore I have found that the plate power input to the modulator was approximately 10 milliamperes at zero signal and 300 volts, the plate current at 100% modulation being approximately 100 milliamperes. The total plate power input to the modulator and carrier wave amplifier in thissystem as heretofore arranged was 40 watts at 25% average modulation, a constant carrier wave amplifier input load of 100 milliamperes at 300 volts, or 30 watts, being included.

Comparing the operation of the above-mentioned system of the prior art, having Class B modulator connections as employed heretofore, with the operation of a similar system having connections in accordance withmy invention as illustrated in Fig. l, I have found that withthe described series output connection and variable carrier arrangement shown in Fig. 1 the power input to the modulator plate circuits and to the carrier wave amplifier plate circuit, for the same average modulation conditions as in the case of the above system employed heretofore, is 24 watts, or little more than one-half of the plate circuit input power required with the system as used heretofore.

In the modification of my invention illustrated in Fig. 4, the general arrangement of the parts, carrier source I0, carrier wave amplifier apparatus 43, signal source i8, signal amplifier l9, and modulator 22, is essentially the same as that of the corresponding parts in the system illustrated in Fig. 1. In the system of Fig. 4, however, the direct current source 32 supplies current to a series connection comprising, as in Fig. 1, the plate circuits of Class B modulator tubes 23, and in addition, instead of the output circuit of the carrier wave amplifier, a bias resistor 44 which is connected, preferably in series with a bias potential source or battery 45, in the grid-cathode circuit of the carrier amplifier 46. To impress signal frequency voltage on the bias resistor 44 to cause modulation of the carrier, the return connection from the resistor 44 includes the secondary 28 of the modulator output transformer 21.

The arrangement of connections shown in Fig. 4 thus constitutes a serially connected grid bias modulation system, the carrier amplifier tube 46 being one suitable for the grid bias method of modulation. In operation a steady bias potential *eimpressed on grid 41 of carrier amplifier I3 is varied, to produce modulation of the carrier wave, by reason of the drop through resistor 44, which varies in accordance with the signal frequencies impressed on the series circuit from modulator 22.

My invention has been described herein in particular embodiments for purposes of illustration. It will be understood, however, that the'invention is susceptible of various changes and modifications without departing from the scope and spirit of the invention as set forth in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In a carrier wave modulation system, an electron discharge device, means to transmit a carrier wave to be modulated through said device, a source of signal currents, a modulator having an output circuit including an element of a coupling device, a current source, means to modulate said carrier wave in accordance with the frequency of said signal currents comprising said -modulator and a second element of said coupling device adapted to be supplied with voltages from said first-named coupling element and means connected to said discharge device, and means including said second element of said coupling device to connect in series with said current source said modulator output circuit and said means connected to said device, whereby the intensity of the carrier wave is varied in accordance with the intensity of said signal currents.

2. In a carrier wave modulation system, an electron discharge device having an output circuit, means to transmit a carrier wave to be modulated through said device, a source of signal currents, a modulator having an output circuit including an element of a coupling device, a current source, means comprising said modulator and a second element of said coupling device adapted to be supplied with voltages from said first-named coupling element to modulate said carrier wave in accordance with the frequency of said signal cur rents, and means including said second coupling element to connect in series said output circuits and said current source, whereby the level of said carrier wave is varied in accordance with the intensity of said signal currents.

3. In a carrier wave modulation system, a carrier wave amplifier apparatus comprising a Class C amplifier having an output circuit, means to supply a carrier wave to be amplified to said amplifier, a source of signal currents, a modulator comprising a pair of Class B amplifiers and having an output circuit including an element of a coupling device, a current source, means comprising said modulator and a second element of said coupling device adapted to be supplied with voltages from said first-named coupling element to modulate said carrier wave in accordance with the frequency of said signal currents, and means including said second coupling element to connect in series said current source and said output circuits, whereby the intensity of said carrier wave is varied in accordance with the envelope of said signal currents.

4. In a carrier wave modulation system, an electron discharge device having an anode-cathode circuit, means to transmit a carrier wave to be modulated through said device, a source of signal currents varying from zero to a maximum intensity, a modulator having an anode-cathode circuit including an element of a coupling device, a current source of substantially constant voltage,

means comprising said modulator and a second element of said coupling device adapted to besup f. plied with voltages from said coupling element to modulate said carrier wave with said signal currents, and means including said second coupling element to connect in series said output circuits and said current source, the impedance of said amplifier anode-cathode circuit being substantially constant throughout the modulation range, the impedance of said modulator anode-cathode circuit varying from a relatively high value to a predetermined lower value as the intensity of said signal currents varies from zero to maximum of the modulation range, whereby the voltage in said anode-cathode circuit has a relatively high value at the maximum of the modulation range and is reduced to a low value at zero of the modulation range.

5. In a carrier wave modulation system, an electron discharge device having an output circuit, means to transmit a carrier wave to be modulated through said device, a source of signal currents, a modulator including a pair of Class B electron discharge amplifiers arranged in push-pull relation and having an output circuit including an element of a coupling device, a current source, means comprising said modulator, a second element of said coupling device adapted to be supplied with voltages from said first-named coupling element, and means connected to said device to modulate said carrier wave in said output circuit of said device in accordance with the frequency of said signal currents, and means including said second coupling element to connect in series with said source said modulator output circuit and said means connected to said device.

6. In a carrier wave modulation system, an electron discharge device, means to transmit a carrier wave to be modulated through said device, grid-bias means including a resistor connected in the grid-cathode circuit of said device, a source of signal currents, a modulator having an output circuit including a coupling means, a current source, means to modulate said carrier wave in accordance with the amplitude and frequency of said signal currents comprising said modulator and said resistor, and means including said coupling means to connect in series with said source said modulator output circuit and said resistor.

7. The combination, in a carrier wave modulation system, of a pair of electron discharge devices, means to transmit the carrier wave to be modulated through one of said devices, the other of said devices having an output circuit including an element of a coupling device, means to vary the impedance of the other discharge device in accordance with signal currents, and means including a second element of said coupling device to connect the space paths of said discharge devices in series, said second element being adapted to be supplied with voltages from said first-named coupling element, thereby to modulate said carrier wave in accordance with the frequency of said signal currents and so to vary the intensity of the carrier wave with respect to the intensity of said signal currents as to maintain a constant unmodulated component of carrier wave during variation in intensity of said signal currents.

8. The combination, in a carrier wave modulation system, of a pair of electron discharge devices, means to transmit the carrier wave to be modulated through one of said devices, the other of said devices having an output circuit including the primary of a coupling transformer, means to vary the impedance of said other of said devices in accordance with signal currents, and means including the secondary of said transformer to connect the space paths of said devices in' series, thereby to modulate said carrier wave in accordance with the amplitude and frequency of said signal currents and to vary the intensity of said carrier Wave in accordance with the envelope of said signal currents.

9. The combination, in a carrier wave modulation system, or an electron discharge device, means to transmit the carrier wave to be modulated through said device, a modulator apparatus comprisingv an electron discharge device having an output circuit including the primary of a coupling transformer, means to vary the impedance of said modulator electron discharge device in accordance with signal currents, and means including the secondary of said transformer to connect the anode circuits of said electron discharge devices in series, thereby to modulate said carrier wave in accordance with the amplitude and frequency of said signal currents and to vary the level of said carrier Wave in accordance with the intensity ofv said signal currents.

GEORGE W. FYLER.