US2019481A - High frequency modulation system - Google Patents

Description

Nov. 5, 1935. I L. M. APPLEGATE HIGH FREQUENCY MODULATION SYSTEM Filed April 5, 1930 source 0/ FIGURE I ZZZ/emf m? any cm 72 k f FIGURE. 1!!

ZZZ/emf V INVENTOR: LINDSAY M. APPLEGATE,

BY f M,-

. ATTORNEYS.

Patented Nov. 5, 1935 UNITED STATES HIGH FREQUENCY MODULATION SYSTEM Lindsay M. Applegate, Seattle, Wash., assignor,

by mesne assignments, to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Delaware Application April 5, 1930, Serial No. 441,961

10 Claims.

My invention relates to the use of small changes in electrostatic capacity forthe control of electric circuits. The purpose of my invention is to produce a circuit in which the magnitude and changes. in magnitude of electrostatic capacity of two adjacent conducting plates control, respectively, the magnitude and changes in magnitude of an electric current.

While my invention is broadly related to electrical control systems generally, I have selected the application of my invention to high frequency modulation systems as one method of illustrating my invention.

The basic and other features of my invention will be described in the specification to follow and will be succinctly defined in the appended claims.

In the accompanying drawing,

Figure I is a diagrammatic view illustrative .of my invention in an arrangement for the control of 2 magnitude of current.

Figure 11' is a similar view showing, for purposes of illustration, my invention in an arrangement for the control of magnitude and direction of current.

25 Figure III is a similar view illustrative of an application of my invention in a balanced circuit arrangement for the control of the magnitude of current varying from zero.

Referring to the numerals on the drawing, l

30 indicates a source of high frequency alternating current, preferably of a frequency of the order of 1,000,000 cycles per second or any other con venient high frequency, 2 indicates a resistor, preferably noninductive, which, in connection 35 with the high frequency source I, provides for a definite regulated voltage at its terminals. This voltage is impressed upon a circuit embracing a condenser 3 and a resistor 4, preferably noninductive;

Condenser 3 consists, preferably of two plates in electrostatic relationship arranged so that the distance, and hence the electrostatic capacity between them is variable. High frequency electric current will flow in the part of the circuit embracing condenser 3 and resistor 4. The intensity and phase of this current will be dependent upon the capacity of condenser 3 in accordance with well known electrical laws. Furthermore, if the current that flows through resistor 2 is large in 50 comparison with that flowing through condenser, 3 and resistor 4 and the impedance of condenser 3 is large relative to the impedance of resistor 4, the current through 3 and 4 will be approximately proportional to the capacity of condenser 3, hence,

55 proportional to the distance between the plates of condenser 3. The high frequency voltage between the terminals of resistor 4 will be proportional to the current in resistor 4. The voltage of resistor 4 is impressed on the grid of an amplifier 5. Resistor 4 provides for maintaining the 5 grid bias of amplifier 5 as well as providing the high frequency alternating voltage.

The usual appurtenances of amplifiers are understood to be present although not shown in Figure I. l0

Amplifier 5 delivers energy through a transformer 6 to a detector 1. The output of amplifier 5, when properly adjusted, is substantially proportional to the high frequency alternating voltage impressed upon its grid by the resistor 4. 15 The output of detector l is substantially proportional to the envelope of the high frequency alternating voltage of resistor 4, and hence to the distance between the plates of condenser 3.

The intensity of the current of detector 1 is indicated or recorded by a terminal apparatus 8. The result of the action of the arrangement shown in Figure I is to provide an indication by mechanical action in the terminal apparatus 8 proportional to the movement in the relative position of the plates of condenser 3.

The action of this form of my invention may be summarized as follows.

The relative position of the plates of condenser 3 is represented in the output circuit of the detector 1 by the intensity of the output current. The rate of change in the relative position of the plates of condenser 3 is represented in detector 1 by the rate of changeof output current. This may be expressed in the statement that the output current of detector I is modulated by the relative movement of the plates of condenser 3. Any movement, oscillation, pressure, or impact within the range of the apparatusca-pable of changing the relative position of the plates of condenser 3 can be measured or recorded'by the arrangement shown in Figure I.

If the relative movements of the plates of condenser 3 in Figure I are of the nature of oscillation resulting from the action of impinging sound waves, the output of the detector I may be used in conventional audio circuits. This is indicated in Figure I in which the output of deoriginal sound by a telephone receiver. It is obvious that the telephone receiver could be replaced by any other apparatus requiring audio frequency current.

In another form of my invention, illustrated in Figure 11, variations in the relative positions of the plates of condensers l3 or 23, or both, produce changes in polarity and consequent reversal of action as well as changes in magnitude of current in the terminal apparatus.

In Figure 11, l is a source of high frequency electric energy. l2 and 22 are resistors, preferably noninductive. l3 and 23 are condensers aranged so that when the capacity of one increases the capacity of the other decreases or remains fixed. i4 and 24 are resistors preferably noninductive. l5 and 25 are amplifiers. I8 is a coupling between amplifiers l5 and 25, and detectors I1 and 21. I8 is a polarized relay arranged in such a way that if the magnetomotive force of the coil associated with detector I1 is equal to that of the coil associated with detector 21, the contacts l9a and I9?) are open. If the magnetomotive force of the coil associated with detector I I is greater than that of the coil associated with detector 21 the contact lSa is closed, if less contact 1% is closed. Under most conditions of application, the action of the circuit shown in Figure 11 will be to close either contact lea or contact I9b, depending upon the relative capacities of condensers l3 and 23. It is obvious that if half the duplicated elements in Figure 11 are removed, the circuit will then be the same as that of Figure I, except that the indicating device 8 will have been replaced by a relay.

Figure III shows a modification of my invention in which a source of high frequency energy i is connected with a balanced circuit which includes resistors 32 and 42 and condensers 33 and 43 arranged so that under certain conditions the voltage impressed on a resistor 34, which may be inductive, is substantially zero. With a change in either condenser 33 or 43, or both, the balance will be disturbed so that a voltage will appear at the terminals of resistor 34 which will be am-' plified by a relay 35, whose output will be delivered by a transformer 36 to a rectifier 31 whose output will operate a relay 38. This arrangement is capable of responding to very small changes in distance represented by changes in the spacing of the plates of condenser 33 or of condenser 43, or preferably, both for maximum of effect, or the increase of one and decrease of the other, or by changes in capacity due, for example, to changes in pressure, temperature, or composition of the dielectric of condenser 33 or of condenser 43.

What I claim is:

l. The method of modulating a high frequency alternating current which comprises delivering an unmodulated high frequency current to an aperiodic branched circuit containing conducting and phase shifting elements, said unmodulated high frequency current being divided between a first branch of said circuit and a second branch of said circuit, the current in the: said first branch being large in comparison with the current in the said second branch, altering the impedance of said phase shifting elements by differential variation thereof in accordance with signal energy for effecting modulation of said high frequency current in said second branch of said circuit.

2. A modulating system comprising a source of high frequency alternating current, a branched modulating circuit including a multiplicity of resistors and a pair of differentially variable condensers, said source of high frequency alternating current supplying an unmodulated current to a plurality of said resistors, said pair of differentially variable condensers operative to produce a modulated high frequency current in each of a 5 second plurality of said resistors, an amplifier circuit and a detector circuit connected with each of said second plurality of resistors, means for combining the outputs of said detector circuits, and a utilization circuit connected with said combining means.

3. In a system for utilizing the variations of a pair of differentially variable phase shifting elements the combination of a circuit containing a first pair of resistors of low impedance, a second 15 pair of resistors of relatively high impedance and a pair of differentially variable phase shifting elements, means for delivering to said first resistors unmodulated'high frequency altemating current, means including said phase shifting elements for delivering modulated currents to said second resistors, and means including said second resistors for impressing modulated voltages on the input elements of a pair of utilizing circuits.

4. In a system for utilizing the variations of a pair of difierentially variable phase shifting elements the combination of a circuit containing a first pair of resistors of low impedance, a second pair of resistors of relatively high impedance and 30 a pair of difierentially variable phase shifting elements, means for delivering to said first resistors unmodulated high frequency altemat-. ing currents, and means including said second resistors for impressing modulated voltages on 35 the input elements of a pair of utilizing circuits, said second resistors acting as biasing connections for said utilizing circuits.

5. The method of modulating a high frequency alternating current which consists of delivering 40 an unmodulated high frequency current to a branched circuit containing conducting and differentially variable phase shifting elements, causing one of said branches to carry a substantially unmodulated high frequency current and another 45 of said branches to carry a high frequency current modulated by the action of said differentially variable phase shifting elements, producing thereby a usable modulated high frequency potential'difl'erence across a conducting element 50 of said latter-branch.

6. A modulating system comprising a pair of parallel circuits, a first of said parallel circuits including a pair of resistance elements, a second of said parallel circuits including a pair of dif- 55 ferentially variable condensers, means for impressing a high frequency alternating currenton said'parallel circuits, and means comprising said differentially variable condensers-for modulating said high frequency current. 60

'7. A modulating system comprising a pair of parallel circuits, a first of said parallel circuits including a pair of resistance elements, a second of said parallel circuits including a pair of differentially variable condensers, means for im- 65 pressing a high frequency alternating current on said parallel circuits, an output circuit resistively coupled with said second parallel circuit, means comprising said differentially variable condensers for modulating said high frequency 7 current, and means for delivering said modulated current to said output circuit.

8. A modulating system comprising a pair of parallel circuits, a first of said parallel circuits including a pair of resistance elements, a sec- 15 0nd of said parallel circuits including a pair of differentially variable condensers, means for impressing a high frequency alternating current on said parallel circuits, a pair of balanced output circuits coupled to said second parallel circuit, means comprising said differentially variable condensers for modulating said high frequency current, and means for delivering said modulated current to said output circuits.

9. A modulating system comprising a Wheatstone bridge-arrangement, a pair of relatively low resistances composing two of the arms ofsaid bridge, a pair of difierentially variable condensers composing the other two arms of said bridge, a separate source of high frequency alternating current, means for supplying said source to opposite terminals of said bridge arrangement, a relatively high resistance element, means comprising said differentially variable condensers for modulating said high frequency current, and means for delivering said modulated high frequency current to the terminals of said high resistance element and to a utilizing circuit.

10. A modulating system comprising a pair of parallel circuits, a first of said circuits containing resistance of relatively low value, a second of said circuits including at least one variable condenser and resistance of relatively high value, an external source of unmodulated high frequency alternating current, means for supplying said high frequency current to said parallel circuits, means including said variable condenser for modulating the high frequency current in said second parallel circuit, and means including said 15

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