US1679095A - To wibeless - Google Patents

Description

July 31, 1928@ 1,679,095

G. w. PlcKARD v CLOSED-TUNED COIL OR LOOP AERIAL Filed June .'50, 1921 v s sheets-sheet 1 2e* Y 20 2 I9 2f L 7 z Hg, 2 f5 e 7 151 8 12 .5 2 J Je? July 31, 192s. 1,679,095

- G. W. PICKARD CLOSED TUNED COIL OR LOOP AERIAL Filed June 3o. 1921 s sheets-sheet 2 July 31, 1928. 1,679,095

G. w. PICKARD CLOSED TUNED COIL OR LOOP AERIAL Filed June 3o. 1921 3 Sheets-'sheet 5` Patented July 3l, 1928.

UNITED STATES PATENT OFFICE.

GREENLEAF WHITTIER PICKAR-D, OF NEWTON CENTER, MASSACHUSETTS, .ASSIGNORI TO WIRELESS SPECIALTY APPARATUS COMPANY, OF BOSTON, MASSACHUSETTS,

A CORPORATION OF NEW YORK.

Application iiled June 30, 1921. Serial No. 481,498.

i l5 are used extensively for direction finding, as

on ships and air planes, that is, for determining the location of a distant transmitter, and for the purpose of guiding and directing the ship or air plane. Such loops are also used for receiving signals and messages, because, by reason of their directional properties and sharp tuning, static and interference are in a large measure eliminated4 orreduced.

The theory of operation in receiving of such a .closed tuned circuit as disclosed in my patent above-mentioned and disclosed in .this application in an improved form` is briefly as follows. The electromagnetic Waves set up by the distant transmitter cut the closed tuned loop or receiving aerial in the same manner that the lines of force generated around a primary of a transformer cut the turns of the transformer secondary, setting up currents in the secondary circuit. In like manner, the electromagnetic Waves in cutting the loop aerial, Which is tuned to the frequency of the transmitted Waves, set up oscillations in the aerial. netic fiuxfwhich cuts the closed tuned aerial increases with its enclosed area or turn area. A loop or closed aerial operating according to the above principle must be positioned with its plane in line With the distant transmitter in order to receive maximum signal or energy. In a plane at right angles to the transmitter, the loop receives no energy from the transmitter nor is it affected by it. The voltage induced by the above flux in a closed radio loop of the above character depends upon the enclosed area or number of turns. However, it has been foundl that such a closed circuit has more sharply directional The electromagsiblefor optimum results in receiving or for direction finding. Finally, as the voltage generated in the loop circuit increases with the number of turns or inductance, While the current decreases inthe same proportion, I have found it advantageous to make the 'voltage low and the current high. A loop circuit closed through a condenser does not have all of its capacity localized in this condenser. By reason of the inevitable proximity of earth"A and other conducting objects, a certain amount of electrostatic capacity results from the conductor or 'conductors of the loop to its surroundings. If, as ina multiturn loop, 'the condenser is of small value (because of the large inductance of a multiturn loop), this external electrostatic field may be relatively large, and if the disposition of surrounding object.` is not symmetrical, the directional properties of the loop are impaired. If the loop be made of minimum inductance, that is, a single turn, the capacity of the condenser becomes large as compared with the external electrostatic field, and the disturbing effect of surrounding objects is minimized.

In using the radio compass or direction finder, it is an advantage, however, to have wthe loop aerial receiving set of minimum volume and extension. obtained in present-day radio Compasses and direction finders by providing multiple turns instead vof a single turn, whereby electromotive forces developed in each turn by the cutting of the magnetic waves are added together to produce an increased E. M.\F. in the loop for actuating the receiving apparatus or detector. Such a system, however, is inefiieient electrically, and it also is not possible `to obtain sharply directional properties on account of the Small capacity neces-I This compactness isy sitated by the high inductance of the multiturn loop, as above explained. Also, the increased resistance due both to the increased length of wire necessary for the multiple turns, and the increased high frequency resistance caused by the adjacent turns is wasteful of energy.

In such direction finders as are now in use, the energy or oscillations set up in the coil are detected by means of a detector circuit connected in shunt with the closed aerial and in shunt with the condenser in series with the aerial in the manner disclosed in Figure 2 of the above patent or occasionally by way of an inductive coupling such as a transformer having an inductance coil in series with the loop and inductance coils in series with the receiving circuit, as shown in Figure 3 of my patent. These two modes of connection, while completely operative, have involved certain disadvantages such as decreased signal reception through high resistance and a certain ioss in sharpness of directional characteristics by reason of the high loop inductance, as explained above,

this latter disadvantage bein(r uite serious' when the loop aerial is used as' a direction finder or radio compass.

en object of the invention is to provide a loop aerial in which the efficiency and directional properties are increased.

Another object of the invention is to provide a loop aerial and detector circuit in which the electrical connection between the two obviates the use of long leads or resistance-introducing coupling coils such as have heretofore been used.

Janother object of the invention is to provide a closed loop aerial and receiving detecting circuit in which electrostatic troubles between the loop, surrounding objects and the receiving circuit to the detriment of the directional properties and efficiency of the loop are obviated.

Another object of the invention is to provide a compact, simple construction of few parts which may be easily handled and operated.

In the accompanying drawings, I have illustrated embodiments of my invention in which j Figure 1 is an elevation with parts in section of one form of the invention;

Fig. 2 is a sectional plan view on the line 2 2 of Fig. 1, looking in the direction of the arrows and on an enlarged sca-le;

Fig. 3 is an elevation of a modiiied form of the invention;

Fig. 4 is a plan view thereof;

Fig. 5 is a detail sectional plan view on the line 5-5 of Fig. 3, looking in the direction of the arrows;

Fig. 6 is a sectional elevat-ion of another form of the invention, illustrated diagrammatically; and

Fig. 7 is an elevation, partly in section, of a further embodiment of the invention, illustrated diagrammatically.

\ Referring to Figs. l and 2, I have illus- `trated a closed aerial circuit 1 which is completed through a static condenser system 2. This condenser system, which is in series with the closed loop, is made (because of the low inductance of the loop of the present invention,) of two parts 2Ll and 2h'in parallel with each other and both connected or connectible in series with the loop 1. rl`he part 2 comprises a number of condensers, preferably mica condensers, each having different capacities and one and all being capable of being connected in series with loop 1. 'I he part I2" is a variable condenser, and after the approximate resonant capacity value of the condensers 2a is obtained, the iinal tuning adjustment may be secured by the variable condenser 2l.

'Ihe condenser system 2 comprises a metal casing C, supporting ithe aerial' 1, and provided at the bottom with a vertical tubular extension 3, rotatably supported yin frame 4, ball bearings 5 being provided for easy turning, whereby the entire apparatus, including the casing C, condensers 2 and the loop 1, may be rotated about a vertical axis for the purpose of properly positioning the same with reference to the distant transmitter. rIhe lower end of the tube or sleeve 3 is provided wit-h an adjusting wh-eel or handle 6. rIhe loop 1 is supported on casing C and insulated therefrom by bushings 7 of any suitable insulating material having good dielectric properties such as bakelite dileeto or quartz, the bushings being arranged at diametrically opposite points in easing 2. 'Ihe free ends ot the loop 1 are inserted within these bushings 7 and project inside of the casing C. One end of the loop is provided with a metal segment 8 to which are electrically connected adjacentjends of the condensers 2a and 2". 'lelescoping the tube 3 is a sleeve 9 provided at its lower end with an operating wheel or handle 10 and terminating at its upper end within casing2 in an insulating plate 110i suitable insulating and dielectric properties. Secured to the upper surface of the insulating plate 11 is a met-al plate or segment 12 adapt-ed to engage contact lingers 13 (Fig. 2) upon the condensers 2a at the ends thereof remote fromtheir points of connection to the segment 8. A contact finger 14 also engages the plate l2 and is electrically conlnectedthrough conductor 15 within casing C to the opposite end of the loop, whereby the circuit 1 is closed through one or niore of the condensers 2a. Extending vertically1 through the sleeve 9 is an actuating rod 16 provided at its lower end with an operating handle 17 for operating the variable condenser 2", The upper end 18 of the rod 16 l line with the distant transmitter receives'v has secured to it the relatively adjustable plates 19 of Ythe variable condenser 2", which are interposed between the relatively fixed plates-20 of the variable condenser. The plates 20 are electrically connected to segment 8, while the plates 19 are insulated from the rod 16 by suitable insulationr 21.

The relatively movable plates 19 are electrically connected by a conductor 22 to conductor 15.

By the above construction, it will be seen that in tuning the closed loop l, oneormore of the condcnscrs 2a may bc successively thrown into series with the loop 1 by means ot' the actuating `handle 10 for securing rough adjustment and tuning of the circuit 1 and the inal ltuning and adjustment may be secured by rotating handle 17, thereby actuating and varying the variable condenser 2". By means of the handle 6, the entire apparatus may be properly positioned. A coill 23, which with aerial 1 as a whole constitutes a transformer and which may comprise a number of turns depending on given conditions, is secured by means ,of an adjustable collar 24 to the tube 3, this collar being adjustably clamped to tube `3 by any suitable clamping means 25. By rotating the collar 24 around the sleeve 3 and thereby rotating coil 23, the inductive coupling between coil 23 and loop 1 may be varied for optimum'eifect. The-leads 26 from coily .23 are electrically connected to any suitable detecting or transmitting circuit, such as, for instance, an audion circuit, crystal detector circuit or any standard transmitting circuit, whereby the oscillations set up in the loop l are inductively transferred to transformer secondary 23 and detected or whereby the reverse occurs on transmitting.

The coil aerial 1 in the present invention consists preferably of a single turn of low resistance conductor, or, if so desired, may consist of more than one turn.l If the loop be made of a single turn conductor, the most efficient form for this conductor is a circle of thin-walled copper tubing, as in Fig. 1, while for a loop of more than one turn a suitably stranded or braided cable should be used (Figs. 6 and 7) to keep the high fre quency resistance low. In all cases, the loop should enclose suilicient area to be operative under any given set of` conditions. By way of example only, such a ring or closed loop may have a diameter across the same of three feet, the diameter of the tubular part being about 2 inches, and the thickness of walls about 35 of an inch. Such. construction, when properly tuned by the condenser system 2, constitutes a closedtuned circuit.

enclosing an area whiclujvhen its plane is in maximum current, and when at right angles to the transmitter, has 'a null point. The copper tubing loop such as disclosed 1n Figs,

1 and 2 has minimum resistance, minimum inductance, maximum current and maximum capacity.

A single turn loop such as disclosed in Figs 1 and 2 provides a closed circuit havmg highr current and comparatively low voltage. This circuit 1 as a whole, by reason of the oscillations impressed uponl it by the electromagnetic waves, acts in receiving as a primary of a transformer which is in inductive` relation to the secondary of the transformer 23 secured to the tube 3 below it. Tlns secondary 23 is connected up to any suitable receiving and detecting circuit as described above. The secondary 23 is adjustably secured to sleeve 3, and can be adjusted around sleeve 3 as an axis to vary the coupling between it and coil 1. In the use of the apparatus, the coil 23 is adjusted until maximum response or optimum respense or signal is pbtained. Thereafter, by means of the clamping screw 25, the coil 2 3'is fixed relatively to the loop 1, and the whole, both coil 23 and loop 1, may be ro.- tated in accordance with direction-finding practice.

' An advantage of the type of coupling between the closed aerial 1 and the coil 23 resides in the fact that the coils l1 and 23 may be physically separated suiiicicntly so that there will be no electrostatic coupling or capacity eect between them which impairs the etliciency of/the apparatus as a direction finder. The optimum coupling between a receiving aerial circuit and' the 'detector or secondary circuit depends upon the `resistance or damping of these circuits, and where the resistance, as in my invention herein, is

very low, the optimum coupling is also very low, thereby permitting a considerable physical separation between the circuits, which in turn minimizes the electrostatic effect. In constructions now in use in which the receiving circuit is connected by means of an inductive coupling in series with the loop l or by leads such as above referred to, forming a detector shunt with the loop, the electrostatic effects are detrimental to the efficiency of the circuit, because of the close coupling necessitatedby the relatively high circuit resistance. y

As is well known, the coupling between two coils of a transformer can be adjusted either by increasing the parallel separation between the coils, or by moving the coils transversely ,to cach other, or by rotatingone coil around an axis, whereby the angular position between the coils is varied. lVhen the planes are parallel, we have maximum,l mutual inductance, and when the planes are at right angles, no mutual inductance. mum position or coupling between the coils which can be easily determined bythe o er- 'ator for obtaining the loudest signal.

his

However, there is always an ,opti-l optimum coupling under any condition can be obtained with the two coils 1 and 23 spaced sufficiently apart to avoid electrostatic coupling.

Such an arrangementas 'above described,'

in which the closed aerial 1 as a whole constitutes a primary of an oscillation transformer and the coil 23 constituteswthe secondary 'of the transformer,l materially -lowers the losses in the complete apparatus and ensures better tuning and efficiency. The decreasing of the resistance and inductance in the coil 1 ensures increased current and obviates the necessity for a large number of turns in coil`1. The number of secondary turns of the transformer 23 is large compared to the number of turns of the closed aerial whereby the necessary voltage is developed for operating the detector. In other words, in receiving, the coil 1 and the secondary23 constitute a step-up transformer.

This being the case, there is no necessity for a large number of turns in the loop -1 to generate the necessary voltage to operate the detector, this increased voltage being secured in the secondary 23 by the present invention. An advantage of the construction shown lin lFig. 1 is that the receiving circuit is of V`very low resistance because no coupling coil is used, nor are there any long leads. This permits the use of a single turn receiving coil, hence giving maximum efficiency. Again, the directional properties of the system are extremely sharp, because the closed loop circuit 1 has no long leads or connections to any more or less grounded circuit,

as isthe case in the ordinary modes of communication. Furthermore, the system is extremely simple because it is not necessary, as in the case of inductive couplings, to insert an inductance in series with the loop, nor is it necessary to provide long leads to the detector circuit. j

As illustrated in Fig. 1, both the closed aerial or primary and the secondary coil 23 are mounted on the same frame, and if the apparatus is used on a singlewave-length, .the coupling may be made non-adjustable and fixed by the constructor at the best value. Of course, if used on wide wave-length ranges, the coupling between the coils 1 and 23 should be made variable in any suitable manner such as those enumerated above.

In Figs. 3, 4 and 5, I have illustrated a modified embodiment of lthe invention in which the number of movable and adjustable parts is reduced to a minimum and i which is especially adapted for larger aerials which cannot be conveniently rotated. In this form, I have illustrated a closed loop or circuit 30 having in series therewith an adjustable tuning condenser 31 and a second closed loop or circuit 32 having in seriesy therewith an adjustable tuning condenser 3 3. These two loops 30 and 32 may be secured 1n Vlustrated, the loops being substantially circular and ofthe same size, havino' similar electrical characteristics, insulated fiom each other, and arranged-symmetrically relative to each other. The closed aerials 30 and 32 may comprise anv suitable conductive material or any number of turns, but, for purposes of illustration, I have shown the same as being composed of my tubular constructions such as disclosed in Fig. 1'. Extending vertically along the line of intersection ofthe two loops 30 and 32 is a rod 35, journaled at 36 in the support 34 and having a wheel or handle 37 at its lower end. Secured to rod 35 at its upper end is a coil 38 comprising any suitable or sufficient number of turns for the purposes of this invention. This coil 38 is arranged with its axis on a line coinciding with the line of intersection of the planes of the two loops 30 and 32 and is arranged centrally and symmetrically of the two loops. Leads 39 from the coil 38 may be connected to any suitable receiving or de- .,tector circuit as above-described or a transmitting circuit. Secured to rod 35 above the handle 37 is a pointer 40 adapted to play over a dial 41 whereby the direction may be determined.

Electrical oscillations set up from a transj above construction, I am enabled to obtain direction without necessitating the rotation of the aerial or aerials. At the same time, the necessity for varying the inductive coupling between lthe loop and the coil and at the same time rotating both the loop aerial vand secondary coil is obviated. The principle of the invention disclosed in Figs.v 3 to 5 is the same as that disclosed in Fig. 1, that is to say, the aerials 30 and 32 as a whole upon receiving constitute the primary of a transformer, while the coil 38 constitutes the secondary of said transformer.

In Fig. 6, I have illustrated another embodiment of the invention comprising a closed aerial or loop 45, which may consist of several turns of stranded wire wound upon a suitable insulating frame 46 and in series with which is an adjustable tuning condenser 47. Located within loop 45 is a secondary coil 49 consisting of suitable nurnber of turns of wire, preferably exceeding the number of turns in aerial 45, being the I or loo -with coil 49 constitutes a transformer functioning according to the principles of the invention described above. v

In Fig. 7, I have illustrated a form of my However, in the present embodi- The coil 49 may be connected,

aerial circuit, coupled inductively to a coil of a detecting or transmitting circuit, the

two constituting the primary of an oscillation transformer.

A form of the presentv invention which I have used consisted of33 turns of 378 inch Belden highl frequency cable wouhd as a single layer solenoid on asquare frme 44 inches on a side. This loop aerial i'th its associated tuning condenser, and when cou-y pled to'a detector circuit for maximum signal, had the extremely low resistance of 1.2 ohms at avwave length of 12,500 meters. Good signals were received from European stations, and, owing to the low resistance of and secondary invent`on slightly modified from that of Fig. st he .loop aerial, very sharp tuning was POS- 6, which comprises the closed tuned primary aerial 51 comprising several turns tuned y a' variable condenser 52 in series with it. Cupled with this loop aerial'is a secondary coil 53y f a sufficient numberl of turns. Any desire variation of coupling may be obtained by either moving the coil 53 axially away or towards the coil 51, or, as indicated by the double-headed vertical arrow, coil 53 may be either moved laterally across, the face of coil 51 or rotated around an axis parallel with the -double-headed ar row, to vary the coupling. o y

The secondary circuit of Fig. 7 including coil 53 is tuned by a variable condenser 54, and theradio frequency amplifier 55 is connected between this secondary circuit and the indicator 56. In the form of Fig. 7, the diameter of the secondary 53 approximates or is of the order of magnitude of that of the coil aerial 51, and such secondary 53, inasmuch as it is tuned to the frequency ofthe primary 51, acts as a closed tuned coil aerial to a certain extent, the current set up in coil 53 by the transmitted electromagnetic waves being added in quadrature to the currents transferred by induction from aerial 51 to coil 53.

The main features of the above-described constructions reside in the fact that the inductance and resistance of the closed aerial circuit is reduced to a minimum by reason of the omission of conductive leads and inductances inserted inseries or in shunt in the circuit. The secondary coil with which the primary or closed loop aerial co-operates as a whole is suiiiciently spaced to prevent electrostatic couplings, but at the same time is so adjustably coupled to the closed aerial as to receive maximum or optimum signal. This arrangement increases the sliarpness'of directivity by an appreciable amount. By the above construction, increasedicurrent is secured in the coil aerial, which current is transferred directly from the coil aerial to a sible.

.It is to be understood that the invention is not limited-to the embodiments and features specifically shownand described herein, but that such embodiments and features are subject to changes' and modifications' denser connectibly in series therewith,-

means for rotating said aerial, local operating apparatus, means extending alonoF the axis of rotation of said aerial for a justing said condenser, and a circuit inductively associated with the loop as a transformer secondary to the loop as a primary; the loop beingl insulated from the local uapparatus and the secondary being electrically connected to the local apparatus.

2. In a radio apparatus of the character described, a closed loop of tubular metal having a condenser in series therewith, and having sufficient area to act as an aerial, said loop constituting the primary 'of a transformer, a rotatable metal tube on lwhich said loop is mounted, and from which its ends are insulated, said condenser also being carried by said rotatable tube, leads controlling said condenser and extending` through said rotatable tube; and the coil when in line with the distant transmitter,

and means for detecting the oscillations set up in said loop by the electromagnetic waves set up by said distant transmitter, which comprises a secondarycoil in inductive relation to said loop, .and mounted upon the pivot of said loop, said secondary coil being adjustably mounted on said pivot as an axis independent of said loop, and' both vcoil and loop being rotatable together around said loop axis for direction finding 5 purposes.

4. In radio apparatus ofthe character described, a single turn closed aerial of tubular metal having a, plurality of oondensers connectible in series therewith, means for rotating said aerial around a Vertical axis, a plu- 10 rality of condenser adjusting devices arranged along the axis of said aerial, and a multiturn' coil adjustable on the said axis, coupled t'said aerial and connected in a circuit, said coil and aerial constituting a trans 15 former.

`GREI'INLEAF WHlTTlER PICK'ARD.

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