US764093A - Wireless telegraphy. - Google Patents

Description

No. 764,093. PATENTED JULY 5, 1904.

L. D. WILDMAN.

WIRELESS TELEGRAPHY.

APPLICATION FILED JUNE 10, 1904.

N0 MODEL.

E I WL'ZaJJeJ: Zia/671167 UNITED STATES Patented July 5 1904.

PATENT OF I E.

WIRELESS TELEGRAPHY.

SPECIFICATION forming part of Letters Patent No. 764,093, dated July 5, 1904.

Application filed June 10, 1904:. Serial No. 211,884. (No model.)

To all w/tmn it may concern.-

Be it known that I, LEONARD D. IVILDuAN, a captain in the Signal Corps, United States Army, have invented certain new and useful Improvements in WVireless Telegraphy, of which the following is a specification, and which, if patented, may be used by the Government of the United States or any of its oflicers or employees in prosecution of the work for the Government, or by any other person in the United States,without the payment to him of any royalty thereon,in accordance with the Act of March 3, 1883, Chapter 143, United States Statutes, XXII, page 625.

My invention relates to wireless-telegraph systems which utilize in their operation electromagnetic or Hertzian waves; and it relates more particularly to a sending apparatus for generating or transmitting such waves.

In any system of wireless telegraphy it is now well recognized that the best form of sending apparatus is one which radiates a sustained or prolonged train of electromagnetic waves of'definite frequency. The sustained or prolonged train of waves is for the purpose of producing a building-up effect by means of resonance in the receiving-wire. The wave of definite frequency is for the purpose of enabling a receiving system to select waves of one frequency to the exclusion of waves of different frequencies at the receiving end.

One way of obtaining a sustained or prolonged train of waves of definite frequency is by using a closed undampened oscillating circuit to prolong the oscillations in conjunction with an open radiating-circuit to radiate the energy of the oscillations developed by the closed oscillating circuit, and one well-known way of efiiciently accomplishing this result consists in associating a multiple antenna with such closed oscillating circuit. I find it necessary, however, in order to radiate waves of definite wave length or frequency from such multiple antenna that each wire of the multiple-antenna radiating system be so designed as to radiate a wave of the same definite length.

One of the objects of my invention is, therefore, to'provide means for varying the inductance of each wire comprising the multipleantenna radiating system at such a point that the added inductance will alter the capacity as little as possible and which will provide a means whereby the length of the waves radiated from each wire of said antenna shall be the same as the length of. the waves radiated from every other wire, so that thereby all of said wires may be regulated so as to radiate waves of fixed and definite wave length.

As a general principle it may be stated that a closed oscillating circuit containing inductance, capacity, and resistance is under certain circumstances capable of producing prolonged oscillations of high frequency; but, as is well known, such closed oscillating circuit, being a persistent oscillator, is a poor radiator of electromagnetic waves. On the other hand, an open radiating-circuit such as is commonly used when an aerial wire is connected through a spark-gap to earth is a good radiating-circuit; but being a poor oscillator such circuit dampens the oscillations and produces only a feeble train of waves. However, when a closed oscillating circuit is -associated with an open radiating-circuit, each circuit will, generally speaking, have a natural period of oscillation of its own, dependent upon its inductance, capacity, and resistance unless some means are employed for harmonizing the natural periods of the two circuits. If the natural periods of oscillation of each of these circuits be brought into harmony, so that the period of the one is the same as the period of the other, We can sustain the supply of the rapidly-dampened oscillations of the antenna from the closed persistently-oscillating circuit. The open radiating-circuit will then take up the oscillations of the closed circuit to a greater degree than if the two circuits were not in harmony with each other. We have the best condition when'thc wave length is the same in each independent circuit--that is, when the'natural periods of vibration of the two circuits are identical. If in any installation, therefore, the capacity of each independent circuit is a practically fixed quantity, we may, by varying the inductance of either or both of said circuits, make the wave lengths of the two circuits equalthat is, bring their natural periods into harmony, as hereinafter more fully explained.

If the natural wave length of the antenna approximates the natural wave length of the closed oscillating circuit and we link the two together by a common helix-containing inductance, the length of the wave in said closed oscillating circuit is increased or decreased by this linking, according as the wave length of the said closed circuit is greater or less than the natural wave length of the antenna. As a means for connecting the circuits I employ what I call a linking-coil, which accomplishes the desired result of bringing the two circuits into harmony, in the manner hereinafter more fully explained.

A second object of my invention is, therefore, to provide means whereby the wave length may be made the same in the closed and open oscillating circuit that is, whereby the radiating-condu-ctor may be attuned to the closed oscillating circuit.

Other objects of my invention will hereinafter appear.

My invention consists in the novel arrangement and proportionment of parts and the combinations thereof hereinafter set forth, and particularly pointed out in the claims.

Having thus stated the principles underlying my invention, my invention may best be explained by referring to the drawings which accompany and form a part of this specification, and which illustrate diagrammatically various arrangements of apparatus and circuits whereby the aforesaid objects may be carried into effect.

In the drawings, Figure 1 illustrates a transmitting system employing a multiple antenna and provided with means whereby each wire thereof is made to radiate a wave of the same definite wave length. Fig. 2 illustrates a transmitting system employing a single antenna associated with a closed oscillating circuit and provided with means for attuning the antenna to said closed oscillating circuit. Figs. 3 and 4 illustrate modifications in the forms of antennae that may be employed in the system illustrated in Fig. 2. Figs. 5 and 6 are diagrams employed in explaining the theory of electrical resonance.

In Fig. 1 the oscillating circuit, comprising the spark-gap /L and condenser g, is adjustably connected to the inductance-coil j by means of the sliding contacts f 2'. The wire 71; is connected to the earth at E and is adjustably connected to the coil 7' by the sliding contact k. The multiple antenna consists of a plurality of wires (0 I) 0 (Z c, and each said wire is adjustably connected to the coil by adjustable contacts a I) c d a.

In order to more fully explain the operation of the system shown in Fig. 1, it is necessary to consider the mathematical theory of the propagation of electrical waves along.

wires. Let 1) equal the velocity of light or of electric waves in plain wires or in air, a equal the frequency of electrical oscillations in the antenna, 7\ equal the wave length of the oscillations, T equal the period of one complete oscillation, L equal the inductance of one of the wires of the antenna, and C equal the capacity of one of the wires of the antenna. It is well known that in electricwave propagation o equals 71. from which it follows that 7\ equals 41/71. a equals'l/T For any particular antenna built up of a plurality of wires the wave length of waves natural to each wire is different if the lengths of the different wires forming the antenna are not exactly the same, if the diameters are not exactly the same, and if they are not made of the same material, becausethe capacity and inductance of said wires are partially dependent upon these factors. In any particular multiple antenna made up of a plurality of wires, as shown in Fig. 1, the capacity of each wire is practically a fixed quantity. One of the available ways of making the wave lengths natural to all of the wires equal is to vary the inductance of each wire.

The capacity C of the antenna may be con sidered a constant quantity for an elevated conductor of given height, because the pothe wave lengths of the waves radiated by each of the wires (6 Z) 0 (Z c of the multiple antenna (shown in Fig. 1) consists of a coil at or near the base of the antenna, with suitable means, such as the adjustable or sliding contacts a 7/ 0 (Z a, for connecting with it at definite points the wires forming the antenna. This coil may or may not be an integral part of the inductance placed in the closed oscillating circuit, and it may or may not bean integral part of the inductance placed in the circuit between the antenna and the ground, and it may or may not be an integral part of the inductance placed in the closed oscillating circuit and the ground, or both of them. In the form of this device shown in Fig. 1 the inductance which equalizes the wave lengths of the waves radiated by the wires forming the multiple antenna is an integral part of the coil 1', which contains the inductance placed in the closed oscillating circuit and that placed in the ground. This portion of the coil may be common to the closed circuit and the ground inductance, as would be the case if the sliding contact f were placed at f, or it may be extraneous to that part of ITO case it is an integral part of the same coil; but it is not necessary that it should be a part of this coil.

I am aware of the device for placing separate coils in each one of the wires forming a multiple antenna, in order to make the capacity and inductance of said wires equal, that was described by J. A. Fleming in a paper published in the Journal 0f the Society 0 f Arts on July 24, 1903. over, brings all of these inductance-points at the foot of the antenna, where the additional change in capacity is the least, and the inductance of several points being in common reduces the actual resistance in this circuit in addition to causing it to become a part of other circuits in the same transmitting apparatus. Actual experiments in which a hotwire ammeter was included in the antenna proved that the increase in current-flow at the current-antinode is quite marked when the system is constructed in accordance with the directions hereinbefore set forth, because the antenna is by the means herein described brought into harmony with the closed oscillating circuit as a whole, and in addition each wire is made to radiate a wave of the same wave length.

The operation of the system is as follows: 'hen the potential difference developed at the terminals of the spark-gap h by a source of periodically-varying current (notv shown) becomes sufficient to break down the dielectric separating the spark-gap terminals, the condenser g discharges across said gap and high-frequency electrical oscillations are set up in the circuit g h a f. These electrical oscillations are conveyed to the multiple-antenna radiating system, and inasmuch as the natural periods of vibration of all the wires making up said system are equal each to the other electrical oscillations of identical periods and of identical wave lengths are developed in each of said wires, thereby causing each wire to radiate electromagnetic waves of corresponding and identical wave lengths.

As hcreinbefore stated, a sustained or prolonged train of electromagnetic waves is used for the purpose of producing a resonance effect, commonly called a building-up effect, at the receiving end of a wireless-telegraph station. This may be more clearly explained by means of the diagrams shown in Figs. 5 and 6. In these figures a c b is an aerial wire of length 2 in the wave-field of length The lines of force on the first wave-crest s striking the vertical part a c of a c 7) are converted into electric energy and rush as a current through 0, creating a tension at (Z. This rushes back again to a just in time to be augmented by the energy drained from the next wave-crest S and so on, building up an alternating potential in ac b, as shown by the successive hatched areas. If the coherer is con- My arrangement, how' nected at 6, this alternating potential when built up to the critical voltage 6 (Z of the coherer breaks it down, drains through the coherer to earth at E, the coherers resistance is restored by blow from decoherer, and is ready for the next train of waves.

In Fig. 2 I have illustrated one embodiment of my invention whereby the second object hereinbefore set forth may be realized in practice. In this figure 7L illustrates the secondary winding of a transformer. g is a spark-gap, and f is a condenser which when charged to the requisite potential discharges across said gap, thereby setting up high-frequency electrical oscillations in the circuit containing said gap and that portion of the coil 7' included between the points a and 0. oz, and 0 are sliding contacts for adjustably connecting the oscillating circuit with the inductance-coil j. m is a sliding contact for adjustably connecting one terminal of the secondary it to said coil 7' and a. represents sliding contacts for adjustably connecting the antenna a and the earth connection 70, respectively, to the coil 7'.

We may agaL make use of the formula equals 2 o O L, and inasmuch as the capacity of the closed and open oscillating circuit is practically fixed we may bring the natural periods of each of said circuits into harmony by varying the inductance L by suitably adjusting any of the sliding contacts m n 0 a It" until the hot-wire ammeter included in the antenna shows a maximum deflection. It is not necessary, however, that all these points should be connected to the coil 7' at the same time in order to utilize the herein-described apparatus for bringing the antenna into harmony with the closed oscillating circuit. For example, if the natural period of the circuit a 0 f g closely approximates that of the antenna a it may not be necessary to place the adjustable contact or upon the coil, provided the natural period of the transformer secondary h is in fairly close harmony. It may also be advisable with some lengths of antenna to remove the contact 0 from the coil. The contact in may also be placed upon the coil or connected at some point either upon the closed or open oscillating circuit, as may best be determined experimentally. By placing a hot-wire ammeter at the current-antinode in this system and locating the different terminals at difi'erent points upon the coil the maximum current may be indicated. WVith some lengths of antenna it has been found necessary to join all the points shown in Fig. 2 to the linking-coil j. of antenna it has been found advisable to connect some one or two of the terminals shown to points outside the closed oscillating circuit.

In Fig. 2 the open radiating-circuit may consist of a single antenna, as shown in said figure, or a multiple antenna, as shown in Fig. 1, or it may consist of a multiple antenna (0 brought to the linking-coil j as asingle wire,

With other lengths as shown in Fig. 4, if slight differences in the radiated waves are not undesirable. The antenna may also consist of a closed loop it brought to the linking-coil j as a single wire, as shown in Fig. 3.

I am aware of the devices known as tuningcoils, as now utilized by a number of systems of wireless telegraphy. Such systems generally aim to bring the antenna into harmony with the closed oscillating circuit and do not have a common inductance to both the closed and open circuit and do not have an adjustable connection, such as a in Figs. I and 2, from the radiating-conductor to the inductance-coil at a point intermediate the ends thereof, whereby the closed circuit can be a1- tered sothat its period can be brought into harmony with that of the open circuit. In the system disclosed in this application either circuit may be changed at will without materially altering the period of the other. The coily' also being common to all circuits aids in bringing the circuits into harmony by the well-known fact that if two circuits are nearly in harmony they will become closer in their natural periods and take up each others vibrations to a greater degree than if the coils which bring them into approximate harmony do not have a common inductance.

I am also aware of United States Letters Patent Nos. 710,121 and 726,413, in which are shown organizations somewhat similar to that shown in Fig. 2; but it is pointed out that in the former the antenna. is not adjustably connected to the inductance-coil at a point intermediate the ends thereof, but is fixedly connected at one of the terminals of said coil, and that in the latter the tuning of the radiatingconductor to the closed oscillating circuit is not contemplated.

Many formulas may be found in text-books whereby the inductance of a coil of the kind herein described may be calculated; but I find the following formula convenient and accurate for this purpose:

L 41K 1: [log a .08}

where R represents the radius of the coil and 0 represents the radius of the wire or tube of which the coil is formed.

I do not wish to be limited to the precise arrangement of apparatus and circuits herein shown and described, inasmuch as many modilications may be made by those skilled in the art without departing from the spirit of my invention; but

hat I claim as new, and desire to secure by Letters Patent, is

1. In a WIIQlGSS-tOlOglftPl] system, an oscillating circuit comprising a spark-gap and a condenser, a radiatirig-conductor attuned to said oscillating ei rcuit, an inductance-coil common to said oscillating circuit and to said radiating-conductor and an adjustable connection from said radiating conductor to said inductance-coil at a point intermediate the ends thereof, substantially as described.

2. In a wireless-telegraph system, an oscillating circuit comprising a spark-gap and a condenser, a radiating-conductor attuned to said oscillatingcircuit, an ind uctanee-eoil common to said oscillating circuit and to said radiating-conductor, an adjustable connection from said radiating-00nductor to said inductance-coil at a point intermediate the ends thereof and an adjustable connection from another point intermediate the ends of said inductance-coil to earth, substantially as described.

3. In a wireless-telegraph system, an oscillating circuit including a portion of an inductance-eoil, a radiating-conductor attuned to said oscillating circuit and an adjustable connection from said radiating-conductor to said inductance-coil at a point intermediate the ends thereof, substantially as described.

4. In a wireless-telegraph system, an oscillating circuit includingaportion of an inductance-coil, a radiating-co'nductor attuned to said oscillating circuit, an adjustable connection from said radiating-conductor to said inductance-coil at a point intermediate the ends thereof and an adjustable connection from another point interi'nediate the ends of said inductance-coil to earth, substantially as described.

5. In a wireless-telegraph system, a continuous inductancecoil, connections from points intermediate the ends of said inductance-coil to an oscillating circuit comprising a spark-gap and a condenser, and an adjustable connection from another point intermediate the ends of said coil to a radiating-conductor, the said radiatirig-conductor being attuned to the said. oscillating circuit, substantially as described.

6. In a wireless-telegraph system, a continuous inductance-coil, connections from points intermediate the ends of the said inductance-coil to an oscillating circuit comprising a spark-gap and a condenser, and adjustable connections from other points intermediate the ends of said inductance-coil to a radiating-eonductor and to earth,respectively, the said radiating-conductor being attuned to the said'oscillating circuit, substantially as described.

7. In a wireless-telegraph system a radiating system consisting of a plurality of elevated conductors, an inductance-coil, and connections from each of said elevated conductors to different points of said inductance-coil, whereby the natural periods of said elevated conductors are made equal each to the other, substantially as described.

8. In a wireless-telegraph system, a radiating system comprising a plurality of elevated conductors of unequal lengths and means for equalizing the natural period of said conductors, said means consisting of a continuous inductance-coil and means for adjustably con-,

necting each of said elevated conductors to different points of said coil, whereby the products of the capacity by the inductance of said elevated conductors are made equal each to,

the other, substantially as described.

9. In a wireless-telegraph system, an oscillating circuit comprising a spark-gap and a condenser, a radiating system consisting of a plurality of elevated conductors, an inductance-coil common to said oscillating circuit and to said radiating system, and adjustable connections from each of said elevated conductors to said inductance-coil whereby the natural periods of said conductors may be equalized and whereby the radiating system may be attuned to said oscillating circuit, sub- CHAS. A. CLEMENTS, M. H. DE LACY.

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