US1750579A - Modulator for radiotelephones - Google Patents

Description

March 930. H. H. c. DUNWOODY 1,750,579

MODULATOR FOR -RADIOTELEPHONES Filed April 20, 1926 l i l l l l l l l l l P INVENTOR WITNESSES Z EH61 Dunn 00%,

J" ATTORNEYS Patented Mar. 11, 1930 PATENT OFFICE HENRY H. C. DUNWOODY, F INTERLAKEN, NEW YORK MODULATOR FOR RADIOTELEPHONES Application filed April 20, 1926. Serial No. 103,397.

This invention relates to improvements in radio telephony, and one of the objects thereof is to provide an improved modulator for use in connection with the telephone transmitter, use being made of the property of certain substances to vary in electrical conductivity under the action of heat or light in producing a changing current in the talking circuit.

Other objects and advantages appear in the following specification, reference being had to the accompanying drawings, in which Figure 1 is a diagram of an oscillator circuit illustrating the use of the improved mod- 35 ulator.

Figure 2 is a detail sectional view of the improved modulator, the associated talking circuit being indicated diagrammatically.

Figure 3 is a diagrammatic and sectional view of a slight modification.

The principle of radio telephony, telegraphy and the like consists fundamentally of changing the amplitude of the high frequency transmitting or antenna current.

The frequency of the diaphragm (using the telephone for illustration herein) is impressed upon the foregoing antenna current,

and inasmuch as it produces said change in amplitude is known as the modulating frequency. v

WVithout encumbering the present description with unnecessary details, it is suflicient to say that practice has demonstrated the nonfeasibility of impressing the transmitter diaphragm frequency directly upon the antenna current or carrier frequency, because the lat ter will be changed but little so that both the quality and distance of transmission will be poor. Again, it is deemed suflicient to say that practice has demonstrated the need for a modulating device by which the maximum effect of the diaphragm can be imposed upon the antenna.

As is known, modulating devices exist in a number of shapes. An oscillating vacuum tube is commonly employed in the required capacity. Magnetic modulators are employed to good advantage also. As previously stated, the herein improved modulator employs the peculiar property of variable conductivity under the action of light or heat of certain substances, for example carborundum, selenium, magnetite, etc. Figure 1 illustrates an oscillator circuit of more or less conventional form. A high frequency current is impressed upon the antenna 1 by the power source 2 which in this case is an oscillating vacuum tube. The circuit of the grid 3 includes the secondary winding 4 of a transformer. The transformer has a primary coil or winding 5.

For convenience of description, the circuit 6 is known as the talking circuit, and it is in this circuit that the improvement exists. The circuit includes the telephone transmitter 7 which is regarded as having the well known arrangement of vibratory diaphragm and compressible carbon granules, the function of which is to vary the current in the talking circuit originating from the battery 8. The circuit includes a filament 9 and a rheostat 10. A given setting of the rheostat will permit a given. current flow in the talking circuit, supposing the telephone diaphragm to be at rest, but vibration of the diaphragm will increase or decrease the current flow above the initially given value so that the heat or light of the filament 9 will vary to correspond.

Interposed between the foregoing talking circuit 6 and the primary coil 5 is a pair of tubes 11 and 12 in concentric relationship (Fig. 2). The latter is larger than the former, permitting the intervening space to be filled with a substance 13 such as carborundum, selenium, magnetite, etc. which varies in electrical conductivity under the application of varying heat. The substance is subjected to the heat of the filament 9 which is inserted in the tube 11 but in spaced relationship thereto. The filament maytake any desired form. The substance 13 is held in place between the tubes by any suitable end closure.

Suitable binding posts 14 and 15 serve as connectors for the primary coil 5. A battery 16 and rheostat 17 are connected in this circuit which, although it contains the primary coil 5 of the transformer is secondary in rela tionship to the talking circuit 6.

The battery 16 acts as a booster t0 the secondary talking circuit. The rheostat 17 will permit any desired current flow through the coil 5 and substance 13. But inasmuch as this substance is still subject to the heating effect of the filament 9 it follows that varia tions in the heat will vary the conductivity of the substance so that the current of the battery 16 may flow with more or less facility. It is thus apparent that the activity in the secondary talking circuit is dependent upon the activity in the primary portion 6 of the talking circuit.

In Figure 3 the substance which varies in electrical conductivity under the action of heat or light now takes the form of a tube 18. The filament 9, which may be regarded as the same (Figs. 1 and 2) is inserted in this tube. The second concentric tube 12 and the filling 13 are dispensed with, the secondary talking circuit, including the coil 5 and bat tery 16, is now connected directly with the tube 18.

The operation As has been stated, the use of the invention is described as in connection with a talking circuit. It will obviously operate with equal facility when used in a circuit which is subject to vibrations other than those of the voice. For example, the telephone transmitter 7 may be replaced by a telegraph key. The principle of the modulator remains the same regardless of what the origin of the means that produdes the changes of current value in the primary portion of the talking circuit 6.

Assume first that the diaphragm of the telephone 7 is idle. The oscillator 2 is regarded as being in operation and the amplitude of the current impressed upon the an tenna 1 is therefore constant. Both the rheostats 10 and 17 are adjusted to a given set-- ting. The current value in the primary talking circuit will therefore be constant so that the heat given off by the filament 9 will be constant. Similarly, the current value in the secondary talking circuit (including the pri mary coil 5 of the transformer) will be constant.

Assume that the telephone transmitter 7 is spoken into. There is an immediate change in both the primary and secondary portions of the talking circuit 6 resulting in the production of an E. M. F. across the terminals of the secondary transformer coil 12. The grid of the oscillator 2 will therefore be impressed not only with the high frequency current due to the interaction of the coils 19 and 20 of the oscillator circuit but also the low frequency E. M. F. in the talking circuit due to the speech.

It is plain that the low-frequency E. M. F. of the talking circuit will result in an increase or decrease of the grid potential above or below normal, and inasmuch as the grid potential reacts upon the antenna circuit by means of the oscillator 2 itself and the coils 21 and 19, it is evident that the amplitude of the antenna current will be changed in accordance with the varying M. F. of the coil 4, or getting back to the origin, of the talking circuit 6. The foregoing constant values of the primary and secondary portions of the talking circuit undergo a change when the telephone diaphragm is vibrated. The immediate result of such vibrations is an increase or decrease of current flow from the battery 8 and an increase or decrease of heat at the filament 9. The next result is an increase or decrease of conductivity of the substance 13 so that the flow of current from the battery 16 in the secondary talking circuit is either facilitated or restricted. The next result is the production of a variable E. M. F. across the terminals of the secondary transformer coil 4 with the effect previously described.

Similarity of principle prevails in Figure 3. The substance of the tube 18 is affected by the heat of the filament 9, and as the heat varies, the conductivity of the tube 18 varies in turn so that a regulation of the current from the battery 16 is accomplished in the manner clearly understood.

l'Vhile the construction and arrangement of the improved modulator is that of a generally preferred form, obviously modifications and changes may be made without departing from the spirit of the invention or the scope of the claims.

I claim 1. In a system of radio communication, an oscillator including a grid circuit, said oscillator having an associated antenna, and a modulator for varying the amplitude of the oscillator current impressed upon the antenna, comprising a transformer having one side connected in the grid circuit of said oscillator, a microphone circuit including a filament, and means connected with the other side of the transformer being variable in electrical conductivity by variations in the light emitted by the filament.

2. In a system of radio communication, an oscillator including a grid circuit, said 0scillator having an associated antenna, and a modulator for varying the amplitude of the oscillator current impressed upon the antenna comprising a transformer having one side connected in the grid circuit of said 0scillator, an electrically energized primary microphone circuit including a filament, an electrically energized secondary circuit connected with the other side of the transformer, and a resistor included in the secondary circuit being associated with the filament and variable in its conductivity by current fluctuations in the filament.

HENRY H. C. DUNVVOODY.

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