US2404012A - Radio direction finder - Google Patents

Description

juEy E6, 1946 R. H. WORRALL RADIO DIRECTION FINDER Filed Dec. 8, 1938 2 Sheets-Sheet 1 INVENTOR Haber? H. WorraZZ A TTORNE Y 2 Sheets-Sheet 2 R. H. WORRALL Filed Dec. 8, 1938 INVENTOR Roberi H. WorraZZ RADIO DIRECTION FINDER ATTORNEY Patented July 16, 1946 UNITED STATES PATENT OFFICE RADIO DIRECTION FINDER Robert H. Worrall, Honolulu, Territory of Hawaii Application December 8, 1938, Serial No. 244,710

(Granted under the act of March 3, 1883, as amended April 30, 19-28; 370 0. G. 757) 13 Claims.

My invention relates broadl to direction finding means, and more particularly to an improved type of radio direction finder.

An object of this invention is to provide an improved type of radio direction finder which can quickly and easily be disassembled for transportation, and readily reassembled, both mechanically and electrically.

Another object of this invention is to provide an improved type of radio direction finder especially suitable for use at high frequencies and useful over a wide frequency range.

Another object of this invention is to provide an improved type of radio direction finder constructed and shielded so as to obtain complete electrical balance between any two corresponding parts and ground.

.Another object of this invention is to provide an improved type of radio direction finder which minimizes polarization errors.

A further object of this invention is to provide an improved radio direction finder which is a separate yet complete unit in itself, and which may be used with any well shielded radio receiver.

It is well known to the art that the Adcock radio direction finder is less affected by polarization errors, i. e., so-called night effect and refraction, than other types of radio direction finders. The system of Adcock direction finding herein employed is known as a differential system of doublets, In such a system, good results depend upon electrical and mechanical symmetry in construction and upon proper shielding. How this and the above and other objects are accomplished is shown in the description below.

Referring to the drawings,

Fig. 1 is a view, partly in section, of the complete direction finder, except that the right half of the dipole collector assembly and supporting shielding tube, which is exactly like the left half illustrated, is omitted.

Fig. 2 is an end view, partly in section, of the dipole assembly showing the method of supporting and bracing the dipole rods.

Fig. 3 is a sectional view through the longitudinal center of the horizontal shielding tube .at 3-3, Fig. 1,

Fig. 4 is an electrical schematic diagram of the entire radio direction finder.

Fig. 5 is a cutaway view looking down on the top of the horizontal shielding tube at 3, Fig. 1, showing schematically how the conducting wires in the horizontal shielding tub have been rotated until they are in a horizontal plane.

This radio direction finder comprises the following major parts: the dipole collector assembly, the horizontal shielding tube iii, the vertical shielding tube 20, the tuning and balancing assembly. and shield, the coupling system and shield, 'the bearing assembly, and the interior connectors.

Horizontal shielding tube I9 supports the dipole collector assembly arranged as a pair of horizontall spaced vertical doublets, one doublet at each end. A saddle 23 is permanently secured to the horizontal shielding tube I9 and its lower portion is a smooth, sliding fit around the upper end of the vertical shielding tube 26, There is a locating slot in saddle 23 which engages with pin 22, screwed into tube 26. Set screw 2| locks saddle 23 to tube '20, Shielding enclosure 28, which contains the tuning, balancing and series condensers and the short-circuiting switches for the latter, is secured around tube 28. The lower end of tube 20 is supported in a ball bearing, the lower half 6 of which is secured to the top of shielding housing I3. At its lower end the exteriordiameter of shaft 20 is reduced, forming a shoulder 51, which rests upon the upper half 9 of the ball bearing. Set screws 26 secure vertical tube 20 to the upper half 9 of the ball bearing. The ball bearing is separable, the upper half 9 resting on balls I which, in turn, are supported by the lower half 6. The tube 20 and the upper half 9 of the bearing rotate about a vertical axis while the lower half 6 of the bearing and the shielding housing I3 remain fixed. Th dipoles or collectors I6, I1, horizontal tube I9 and the shielding enclosure 28 all rotate with tube 213, An azimuth scale 8 is secured to the upper half 9 of the bearing. An access door I l, hinged at 21, and l cked closed by thumb latch I5, provides access for changing the plug-in coupling coils 6i and I I. The supported end of each of the four dipole collector tubes I6 is fitted with a threaded insert 53 which screws on to terminal studs I8. These studs I8 are supported by and secured to insulating strips 50, which are attached by angle fittings to tube I9. An extension rod I1 screws into the unsupported end of each dipole collector tube I6. Insulating strips 41 and 52 form, with metal corner braces 48 (Fig. 2), a bracing frame for dipole collector tubes I6, and are held in position away from tube I9 by insulating pillars 49. The ends of the tube I9 are covered by tightl fitting metal covers 46. Conductor wires 24 are attached to studs I8 and connect the two sets of dipole collectors I6, I! together in such a manner that the upper dipole collector I6, I7 of each doublet connects with the lower dipole collector l6, I! of the doublet at the opposite end of the tube l9, Each wire 24 rotates through 180 degrees in traveling from one pair of dipole collectors I6, I! to the other. These wires 24 are supported and guided by a number of insulating spacers 42 which fit tightly inside tube l9. There is machined into the rim of each spacer 42 a spline slot into which longitudinal spline 43 engages when th spacers 42 are inserted inside the tube l9. Spline 43 is attached inside and at the top of tube l9 by screws 44. Each pair of spacers 42 is identical except that the slot is shifted along the circumference a definite number of degrees from the vertical varying from degrees to 90 degrees, depending on the position of the spacer or guide 42 along the tube It. The angular displacement of the slot on the spacers 42 nearest the longitudinal center of tube I9 is 0 degrees from the vertical, and this angle is increased gradually on each spacer 42 along the tube l9 until on the spacer 42 nearest each end of the tube l9, the angle is 90 degrees. Thus, by means of these spacers 42 the common plane of conductor wires 24 is uniformly rotated from the vertical at the ends of tube !9 to the horizontal half way between the ends. At the longitudinal midpoint of tube l9 a spring clip 25 engages the exact electrical center of each of the conductor wires 24. These clips are mounted on terminals 4|, which are supported by insulating disc 56. This disc 56 is a close fit inside the upper end of tube 20 and rests upon a shoulder 53. A terminal stud 45 screws into the bottom of each of the two terminals 4! and to these studs the upper ends of down lead wires 3| are connected. The tautness of wires 3! insid vertical shielding tube 20 can be adjusted b screwing terminal studs 45 in or out of terminals 4|. The electrical circuit of down lead wires 3| is interrupted by the insertion in each wire of a strain insulator 32. Wires 3! connect to terminal studs 54 which screw into each end of insulators 32. Each insulator 32 is fitted with connectors 33 by means of which the upper and lower portions of wires 3| are connected to the tuning and balancing assembly. The lowermost end of each wire 3| connects to a special terminal [0 which is drilled to receive plug-in coils 6| of standard manufacture, Terminals H] are supported by insulating disc which fits tightly inside the lower end of tube 20 and rests against shoulder 59. Each of the two series tuning condensers 34 is connected to a pair of terminals 33. A cam operated short-circuiting switch 39 is mounted on the frame of each condenser 34 and one terminal of each switch is connected to a separate group of stator plates of balancing condenser 35. The rotor plates of balancing condenser 35 are grounded to the shield. Knob 37 is mounted on the rotor shaft of balancing condenser 35. Tuning condenser 36 is connected across down lead wires 3!. iA. small variable condenser 38, shown only in Fig. 4, is connected between condenser 36 and the shield, An electrostatic shield 12 is mounted insid coil shield box 13 between coils BI and coil ll. Coil I I, also of standard manufacture, plugs into jacks mounted on insulatin support 30, which is secured to brackets 29 extending from shielding housing l3.

This radio direction finder is made readily transportable by its lightness and ease of assembly and disassembly. To disassemble, dipole collectors IS with their inserted extensions I! are unscrewed from terminal studs l8. Horizontal 4 shield tube I9, with saddl 23 secured thereto, lifts free from vertical tube 20 after set screw 2| is loosened, the locating pin 22 and shoulder 53 insuring that horizontal tub l9 will alway assume the same position on tube 20. Lifting, tube I9 straight up also frees wires 24 from spring clips 25. The vertical shielding tube 20, with shielding enclosure 28 and top half 9 of the ball bearing secured thereto, can then be lifted clear of the lower half 6 of the ball bearing. Assembly in the reverse order is also quickly and readily accomplished, For lightness, tubes l9 and 20 can be made of Duralumin.

The operation of this radio direction finder is as follows: (refer to Fig. 4) Radio waves striking the collector induce currents in the dipole collectors l 5, H, in the shielding members I9 and 20, and also in the room screen 60 (Fig. 4), if used. The currents induced in the dipole collectors I6, I? are, of course, the desired currents. The currents induced in the shielding tubes I9 and 20 in turn induce currents into wires 24 and 3|, the coils and the other components within the shields i9, 20 and I3. These latter currents set up what is commonly called "antenna effect. The eifect of such currents is to induce a signal into the receiver at all times regardless of the position to which the collector is rotated. The antenna effect is eliminated in this radio direction finder by so designing and constructing the collector that, without any balancing condenser 35 in the circuit, there is complete electrical balance between any two corresponding parts of the circuit and ground. After this is achieved, the balancing condenser is inserted in the circuit to balance out the small currents which inevitably appear in actual operation. The design and construction of this radio direction finder has approached perfect electrical balance so closely in actual operation that the maximum capacity of the balancing condenser 35 used in this system is only 4.4 micromicrofarads on each side, while the average maximum balancing capacity necessary to use is less than plus or minus 0.2 micromicrofarad over the entire frequency range. The undesirable antenna effect thus eliminated, there remains the desired current induced in the four dipole collectors I6, H. The desired current travels along wires 24 and 3! to the tuning and balancing system and to coil 6|, inducing in coil l l a similar current which flows to the receiver input through suitable shielded leads. The system is tuned to the desired frequency by condenser 36 and is balanced by condenser 35 for the sharpest bearings. On one frequency band, because of the electrical constants of the system, it is necessary to insert series condensers 34 in the circuit. These condensers are short-circuited when not required by low capacitance, low-loss switches 39, both switches cam operated simultaneously by a single knob. Condenser 38 is adjusted until the capacity of the stator plates of tuning condenser 36 to ground is equal to the capacity of its rotor plates and shield to ground. While the output of the radio direction finder illustrated is magnetically coupled to the receiver input, other types of cou-- pling may be successfully employed. This radio direction finder is useful over a frequency range from 3,000 to 30,000 kcs. and its range may be extended in either direction. This frequency coverage is made possible by the use of plug-in coils.

The sequence of operation for taking bearings with this radio direction finder is as follows, assuming the approximate frequency is known,

the proper plug-in coils inserted and the equipment calibrated. First, set balancing condenser 35 at maximum position on either side. This introduces suificient unbalance to make the collector function as a good antenna. Second, set tuning condenser 36 for the approximate frequency. Third, tune the receiver around the-approximate frequency until a signal is heard. Fourth, tune condenser 36 for maximum signal. Fifth, adjust condenser 35 for minimum signal while rotating the loop. Sixth, make final adjustments of the receiver, condensers 35 and 3-6. Seventh, rotate loop to position of minimum signal.

It will be understood that the above description and accompanying drawings comprehend only the general and preferred embodiment of my invention and that various changes in construction, proportion and arrangement of the parts may be made within the scope of the appended claims without sacrificing any of the advantages of my invention.

The invention described herein may be manufactured and/or used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What I claim and desire to secure by Letters Patent, is as follows:

1. Direction finding means, comprising a shielding housing, a detachable vertical shielding tube rotatably mounted thereon, a horizontal shielding tube detachably mounted at its longitudinal center on said vertical tube, an upper and a lower vertical detachable collector secured at each end on said horizontal shielding tube and insulated therefrom and from each other, a conductor inside said horizontal shielding tube connecting each said upper collector to said lower collector at the opposite end of said horizontal shielding tube, insulating guide means to rotate the common plane of said conductors from the vertical at each end of said horizontal shielding tube to the horizontal at its center, two down leads extending through said vertical shielding tube, fixed clip means connected to said down leads so located as to engage said conductors in said horizontal shielding tube at the exact center of each, a series condenser connected in each said down lead, a low capacity switch to short circuit each said series condenser, a variable balancing condenser having a separate stator connected to each said down lead and a rotor connected to said vertical shielding tube, a variable tuning condenser connected across said down leads, a variable condenser connected between said tuning condenser and said vertical shielding tube to make the capacity of the stator of said tuning condenser to ground equal the capacity of its rotor and shield to ground, a shielding enclosure for said condensers and switches, arotatable coil disposed in said shielding housing connected to said down leads and rotating with said vertical shielding tube, a fixed coil mounted in said shielding housing below said rotatable coil and magnetically coupled thereto, an electrostatic shield disposed between said coils, and an azimuth scale attached to said vertical shielding tube.

2. Direction finding means, comprising a shielding housing, a detachable vertical shielding tube rotatably mounted thereon, a horizontal shielding tube detachably mounted at its longitudinal center on said vertical tube, an upper and a lower vertical detachable collector secured at each :end on said horizontal shielding tube and insulated'therefrom and from each other, a-conductor inside said horizontal-shielding tube connecting each said upper collector to said lower collector :at the opposite end of said horizontal shielding tube, insulating guide means to rotate the common plane of said conductors from the vertical at each end of said horizontal shielding tube to the horizontal at its center, two down leads extending through said vertical shielding tube, fixed c1ip meansconnected to said down leads so located as 'to engage said conductors in said horizontal shielding tube at the exact center of each, a series condenser connected in each said down lead, a low capacity switch to short circuit each said series condenser, a variable balancing condenser having a separate stator connected to each said down lead :and a rotor connected to said vertical shiel-ding'tube, a variable tuning condenser connected across said down leads, a variable condenser connected between said tuning condenser and said vertical shielding tube to make the capacity of the stator of said tuning condenser to ground equal the capacity of its rotor and shield to ground, a shielding enclosure for said condensers and switches, a rotatable plug-in coil disposed in said shielding housing connected to said down leads and rotating with said vertical shielding tube, a fixed plug-in -coil mounted in said shielding :housing below said rotatable plug-in coil and magnetically coupled thereto, an electrostatic shield disposed between said plug-in coils, an access opening in said shielding housing with a closure :therefor,and an azimuth scale attached to said vertical shielding tube.

3. Direction finding means, comprising .a shielding housing, a detachable vertical shielding tube rotatably mounted thereon, a horizontal shielding tube detachably mounted (at its longitudinalcenter on said vertical tube an upper and a lower vertical detachable collector secured at each end on said horizontal shielding tube and insulated therefrom and from each other, :a-conductor inside said horizontal shielding tubeconnecting each said upper collector to-said lower collector at the opposite end of said horizontal shielding tube, insulating guide means to rotate the common plane of said conductors from the vertical :at "each end of :said horizontal shielding tube .to the horizontal at its center, two down leads extending through said verticalshielding tube, fixed clip means connected to said down leads so located as to engage said conductors-in said horizontal shielding tube at the exact center of each, a series condenser connected in -ea'ch said down lead, a low capacity switch to short circuit each said series condenser, a variable balancing condenser having a separate stator con-,

nected to each said down lead and a rotor connected to said vertical shielding tube, a variable tuning condenser connected across said down leads, a variable condenser connected between said tuning condenser and said vertical shielding tube to make the capacity of the stator of said tuning condenser to ground equal the capacity of its rotor and shield to ground, a shielding-enclosure for said condensers and switches, and an azimuth scale fixed on said vertical shielding ube.

4. Direction finding means, 1 comprising a shielding housing, an access opening therein and closure therefor, a vertical shielding tube rotatably mounted on said housing in a separable bearing, the lower .half of said bearing secured to .said.'.housing,.the :upper half secured .to said vertical tube, said vertical tube and upper half of said bearing detachable by lifting, a saddle means slidingly fitted n the upper end of said vertical tube and detachably secured thereto, a horizontalshielding tube fixedly secured at its longitudinal center to said saddle means and supported thereby, an upper and a lower vertical detachable collector supported at each end of said horizontal shielding tube and insulated therefrom and from each other, a conductor inside said horizontal shielding tube connecting each said upper collector to said lower collector at the opposite end of said horizontal shielding tube, in-

- sulating guide means to rotate the common plane of said conductors from the vertical at each end of said horizontal shielding tube to the horizontal at its center, two down leads extending through said vertical shielding tube, fixed clip means connected to said down leads so located as to engag said conductors in said horizontal shielding tube at the exact -electricalcenter of each, a series condenser connected in each said down lead, a low capacity switch to short circuit for said condensers and switches, a rotatable insulated coil mounting fixed in the lower end of said vertical shielding tube and connected to said down leads, a rotatable coil disposed in said shielding housing and plugging in to said rotatable coil mounting, a fixed coil mounting and plug-in coil secured in said shielding housing below said rotatable coil, said fixed and said rotatable coils coupled magnetically, an electrostatic shield disposed between said coils, and an azimuth scale attached to said vertical shielding tube.

5. Direction finding means, comprising a shielding housing, a vertical shielding tube rotatably mounted on said housing in a separable bearing, the lower half of said bearing secured to said housing, the upper half secured to said vertical tube, said vertical tube and upper half of said bearing detachable by lifting, a saddle means slidingly fitted on the upper end of said vertical tube and detachably secured thereto, a horizontal shielding tube fixedly secured at its longitudinal center to said saddle means and supported thereby, an upper and a lower vertical detachable collector supported at each end of said horizontal shielding tube and insulated therefrom and from each other, a conductor inside said horizontal shielding tube connecting each said upper collector to said lower collector at the opposite end of said horizontal shielding tube, insulating guide means to rotate the common plane of said conductors from thevertical at each end of saidhorizontal shielding tube to the horizontal at its center, two down leads extending through said vertical shielding tube, fixed clip means connected to said down leads so located as to engage said conductors in said horizontal shieldingv tube at theexact electrical center of each, a series condenser connected in each said down lead, a low capacity switch to short circuit each said series condenser, a variable balancing condenser hav, ing a separate stator connected to each said down lead and a rotor connected to saidvertical shielding tube, a variable tuning condenser connected across said down leads, a variable condenser connectedbetween said tuning condenser and said vertical shielding tube to make the capacity of the stator of said tuning condenser to ground equal the capacity of its rotor and shield to ground, a shielding enclosure for said condensers and switches, and an azimuth scale attached to said vertical shielding tube,

6. Direction finding means, comprising a collector system of dipoles arranged as two horizontally spaced vertical doublets, a rotatable T- shaped support formed by a horizontal and a vertical tubular shielding member, a balanced horizontal transmission line connecting the upper dipole collector of each doublet with the lower dipole collector of the other, a balanced vertical transmission line detachably connected by clip means to the exact electrical center of said horizontal transmission line, said transmission lines contained inside said shielding tubular members, tuning and balancing means connected to said vertical transmission line with a shielding enclosure therefor, a shielding housing, coupling means for said vertical transmission line disposed within said shielding housing, said dipole collectors, tubular shielding members, shielding enclosure and shielding housing symmetrically disposed about a vertical plane through said dipole collectors, said dipole collectors, tubular shielding members and shielding housing symmetrically disposed about a vertical plane through the axis of said vertical tubular shielding member perpendicular t0 the axis, of said horizontal shielding tubular member, said dipole collectors and horizontal shielding tubular member symmetrically disposed about a horizontal plane through the axis of said horizontal shielding tubular member, said dipole collectors, tubular shielding members and shielding housing being detachable.

'7. Direction finding means, comprising a collector system of dipoles arranged as two horizontally spaced vertical doublets, a rotatable T- shaped support formed by a horizontal and a vertical tubular shielding member, a balanced horizontal transmission line connecting the upper dipole collector of each doublet with the lower dipole collector of the other, a balanced vertical transmission line detachably connected byclip means to the exact electrical center of said horizontal transmission line, said transmission lines contained inside said shieldingtubularmembers, tuning and balancing means connected to said vertical transmission line with a shielding enclosure therefor, a shielding housing, coupling means for said vertical transmission line disposed within said shielding housing, said dipole collectors, tubular shielding members and shielding housing being detachable.

8. Direction finding means, comprising a collector system of dipoles arranged as two horizontally spaced vertical doublets, a rotatable T,- shaped support formed by a horizontal and a vertical tubular shielding member, a balanced horizontal transmission line connecting the upper dipole collector of each doublet with the lower dipole collector of the other, a balanced vertical transmission line detachably connected by clip means to the exact electrical center of said horizontal transmission line, said transmission lines contained inside said shielding tubular members, tuning and balancing means connected to said vertical transmission line with a shielding enclosure therefor, a shielding housing, coupling means for said vertical transmission linedisposed within said shielding housing, and an azimuth scale attached to said vertical shielding tubular member, said dipole collectors, tubular shielding members and shielding housing being detachable.

9. Direction finding means, comprising a shielding housing, a detachable vertical shielding tube rotatably mounted thereon, a horizontal shielding tube detachably mounted at its longitudinal center on said vertical tube, an upper and a lower vertical detachable collector secured at each end on said horizontal shielding tube and insulated therefrom and from each other, a conductor inside said horizontal shielding tube connecting each said upper collector to said lower collector at the opposite end of said horizontal shielding tube, insulating guide means to rotate the common plane of said conductors from the vertical at each end of said horizontal shielding tube to the horizontal at its center, two down leads extending through said vertical shielding tube, fixed clip means connected to said down leads so located as to engage said conductors in said horizontal shielding tube at the exact center of each, a series condenser connected in each saiddown lead, a low capacity switch to short circuit each said series condenser, a variable balancing condenser having a separate stator connected to each said down lead and a rotor connected to said vertical shielding tube, a variable tuning condenser connected across said down leads, a variable condenser connected between said tuning condenser and said vertical shielding tube to make the capacity of the stator of said tuning condenser to ground equal the capacity of its rotor and shield to ground, a shielding enclosure for said condensers and switches, a rotatable coil disposed in said shielding housing connected to said down leads and rotating with said vertical shielding tube, a fixed coil mounted in said shielding housing below said rotatable coil and magnetically coupled thereto, an electro static shield disposed between said coils, and an azimuth scale attached to said vertical shielding tube, said collectors, shielding tubes, shielding enclosure and shielding housing symmetrically disposed about a vertical plane through said collectors, said collectors, shielding tubes and shielding housing symmetrically disposed about a vertical plane through the axis of said vertical shielding tube perpendicular to the axis of said horizontal shielding tube, said collectors and horizontal shielding tube symmetrically disposed about a horizontal plane through the axis of said horizontal shielding tube.

10. Direction finding means, comprising a shielding housing, a detachable vertical shielding tube rotatably mounted thereon, a horizontal shielding tube detachably mounted at its longitudinal center on said vertical tube, an upper and a lower vertical detachable collector secured at each end on said horizontal shielding tube and insulated therefrom and from each other, a conductor inside said horizontal shielding tube connecting each said upper collector to said lower collector at the opposite end of said horizontal shielding tube, insulating guide means to rotate the common plane of said conductors from the vertical at each end of said horizontal shielding tube to the horizontal at its center, two down leads extending through said vertical shielding tube, fixed clip means connected to said down leads so located as to engage said conductors in 4 said horizontal shielding tube at the exact center of each, a series condenser connected in each said down lead, a low capacity switch to short circuit each said series condenser, a variablebalancingcondenser having a separate stator connected to each said down lead and a rotor con:- nected to said vertical shielding tube, a variable tuning condenser connected across said down leads, a variable condenser connected between said tuning condenser and said vertical shielding tube to make the capacity of the stator of said tuning condenser to ground equal the capacity of its rotor and shield to ground, a shielding enclosure for said condensers and switches, a rotatable plug-in coil disposed in said shielding housing connected to said down leads and rotat-f a vertical plane through the axis of said vertical shielding tube perpendicular to the axis of said horizontal shielding tube, said collectors and horizontal' shielding tube symmetrically disposed about a horizontal plane through the axis of said horizontal shielding tube;

l'l. Direction finding means, comprising a shielding housing, a detachable vertical shielding tube rotatably mounted thereon, a horizontal shielding tube d'etachably mounted at its longitudinal center on said vertical tube, an upper and a lower vertical detachable collector secured at each end on said horizontal shielding tube and insulated therefrom and from, each other, a conductor inside said horizontalshielding tube connecting each said upper collector to said lower collector at the opposite end of said horizontalshield-ing tube, insulating guide means to rotate the common plane of said conductors from the vertical at each end of said horizontal shielding tube to the horizontal at its center, two downleads extending through said vertical shielding tube, fixed clip means connected to said down leads so located as to engage said conductors in said horizontal shielding tube at the exact center of each, a series condenser connected inea ch said down lead, a low capacity switch to short circuit each said series condenser, a variable balancing condenser having a separate stator connected to eachsai'd down lead and a rotor connected-to said vertical shielding tube, a variable tuning condenser connected across said down leads, a variable condenser connected between said tuning condenser and said vertical shielding tube to make the capacity of stator of said tuning condenser to ground equal the capacity of its rotor and shield to ground, a shielding enclosure for said condensers and switches, and an azimuth scale fixed on said vertical shielding tube, said collectors, shielding, tubes, shielding enclosure and shielding housing symmetrically disposed about a vertical plane through said collectors, said collectors, shielding tubes and shielding housing symmetrically disposed about a vertical plane through the axis of said vertical shielding tube perpendicular to the axis of said ho-rizontal shielding tube, said collectors and horizontal shielding tube symmetrically disposed about 11 a horizontal plane through the axis of said horizontal shielding tube.

12. Direction finding means, comprising a shielding housing, an access opening therein and closure therefor, a vertical shielding tube rotatably mounted on said housing in a separable bearing, the lower half of said bearing secured to said housing, the upper half secured to said vertical tube, said vertical tube and. upper half of said bearing detachable by lifting, a saddle means slidingly fitted on th upper end of said vertical tube and detachably secured thereto, a horizontal shielding tube fixedly secured at its longitudinal center to said saddle means and supported thereby, an upper and a lower vertical detachable collector supported at each end of said horizontal shielding tube and insulated therefrom and from each other, a conductor inside said horizontal shielding tube connecting each said upper collector to said lower collector at the opposite end of said horizontal shielding tube, insulating guide means to rotate the common plane of said conductors from the vertical at each end of said horizontal shielding tube to the horizontal at its center, two down leads extending through said vertical shielding tube, fixed clip means connected to said down leads so located as to engage said conductors in said horizontal shielding tube at the exact electrical center of each, a series condenser connected in each said down lead, a low capacity switch to short circuit each said series condenser, a variable balancing condenser having a separate stator connected to each said down lead and a rotor connected to said vertical shielding tube, a variable tuning condenser connected across said down leads, a variable condenser connected between said tuning condenser and said vertical shielding tube to make the capacity of the stator of said tuning condenser to ground equal the capacity of its rotor and shield to ground, a shielding enclosure for said condensers and switches, a rotatable insulated coil mounting fixed in the lower end of said vertical shielding tube and connected to said down leads, a rotatable coil disposed in said shielding housing and plugging in to said rotatable coil mounting, a fixed coil mounting and plug-in coil secured in said shielding housing below said rotatable coil, said fixed and said rotatable coil coupled magnetically, an electrostatic shield disposed between said coils, and an azimuth scale attached to said vertical shielding tube, said collectors, shielding tubes, shielding enclosure and shielding housing symmetrically disposed about a vertical plane through said collectors, said collectors, shielding tubes and shielding housing symmetrically disposed about a vertical plane through the axis of 12 said vertical shielding tube perpendicular to the axis of said horizontal shielding tube, said collectors and horizontal shielding tube symmetrically disposed about a horizontal plane through the axis of said horizontal shielding tube.

13. Direction finding means, comprising a shielding housing, a vertical shielding tube rotatably mounted on said housing in a separable bearing, the lower half of said bearing secured to said housing, the upper half secured to said vertical tube, said vertical tube and upper half of said bearing detachable by lifting, a saddle means slidingly fitted on the upper end of said vertical tube and detachably secured thereto, a horizontal shielding tube fixedly secured at its longitudinal center to said saddle means and supported thereby, an upper and a lower vertical detachable collector supported at each end of said horizontal shielding tube and insulated therefrom and from each other, a conductor inside said horizontal shielding tube connecting each said upper collector to said lower collector at the opposite end of said horizontal shielding tube, insulating guide means to rotate the common plane of said conductors from the vertical at each end of said horizontal shielding tube to the horizontal at its center, two down leads extending through said vertical shielding tube, fixed clip means connected to said down leads so located as to engage said conductors in said horizontal shielding tube at the exact electrical center of each, a series condenser connected in each said down lead, a low capacity switch to short circuit each said series condenser, a variable balancing condenser having a separate stator connected to each said down lead and a rotor connected to said vertical shielding tube, a variable tuning condenser connected across said down leads, a variable condenser connected between said tuning condenser and said vertical shielding tube to make the capacity of the stator of said tuning condenser to ground equal the capacity of its rotor and shield to ground, a shielding enclosure for said condensers and switches, and an azimuth scale attached to said vertical shielding tube, said 001- lectors, shielding tubes, shielding enclosure and shielding housing symmetrically disposed about a vertical plane through said collectors, said collectors, shielding tubes and shielding housing symmetrically disposed about a vertical plane through the axis of said vertical shielding tube perpendicular to the axis of said horizontal shielding tube, said collectors and horizontal shielding tube symmetrically disposed about a horizontal plane through theaxis of said horizontal shielding tube.

ROBERT H. WORRALL.

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