Abstract:
A current probe system includes a toroid made from a magnetic material and a wire made from an electrically-conducting material that forms at least one winding about a portion of the toroid. A current is induced in the winding(s) when a time-varying magnetic field is present in the toroid. A float coupled to the toroid floats the system at a water&#39;s surface. In use, a buoyant cable antenna is fed through the toroid and the system is moved along the antenna.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefore. 
    
    
     CROSS REFERENCE TO OTHER PATENT APPLICATIONS 
     None. 
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates generally to current sensors, and more particularly to an RF current probe system that can measure current flowing along a floating buoyant cable antenna. 
     (2) Description of the Prior Art 
     Currently, evaluating the azimuthal radiation pattern of a new or modified buoyant cable antenna requires that the antenna under test be located on water and manually rotated in azimuth during which time the antenna&#39;s signal is received/evaluated utilizing equipment located on land. This procedure requires that personnel be in the water to periodically and incrementally re-position the antenna (which can be as long as 150 feet). This can be risky and limited to periods not always practical for testing. The time required to perform this procedure also limits the number of position increments and thus impacts the resolution of the data. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a system for testing a floating buoyant antenna cable. 
     Another object of the present invention is to provide a system that simplifies evaluation of a buoyant antenna cable&#39;s azimuthal radiation pattern while the buoyant cable antenna is deployed at a water&#39;s surface. 
     Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings. 
     In accordance with the present invention, a current probe system includes a toroid made from a magnetic material that surrounds a spatial region. A wire made from an electrically-conducting material forms at least one winding about a portion of the toroid. A current is induced in the winding(s) when a time-varying magnetic field is present in the core&#39;s spatial region. A float coupled to the toroid floats the system at a water&#39;s surface. In use, a buoyant cable antenna is fed through the toroid and the system is moved along the antenna. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features and advantages of the present invention will become apparent upon reference to the following description of the preferred embodiments and to the drawings, wherein corresponding reference characters indicate corresponding parts throughout the several views of the drawings and wherein: 
         FIG. 1  is a schematic view of a current probe system for measuring current flowing along a floating buoyant cable antenna in accordance with an embodiment of the present invention; 
         FIG. 2  is a side view of a float and toroidal coil support thereby in accordance with another embodiment of the present invention; 
         FIG. 3  is a side view of a float supporting an alignment conduit and toroidal coil in accordance with another embodiment of the present invention; 
         FIG. 4  is a schematic view of a hard-wired data transmission arrangement in accordance with an embodiment of the present invention; 
         FIG. 5  is a schematic view of a wireless data transmission arrangement in accordance with another embodiment of the present invention; and 
         FIG. 6  is a schematic view of an on-board data recording arrangement in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and more particularly to  FIG. 1 , a current probe system in accordance with an embodiment of the present invention is shown and is referenced generally by numeral  10 . Current probe system  10  is used to measure the current flowing along a buoyant cable antenna deployed on a water surface where such current flow provides the necessary information to evaluate the buoyant cable antenna&#39;s azimuthal radiation pattern. The current is measured without any moving or manipulation of the buoyant cable antenna. 
     In general, current probe system  10  includes a toroidal coil  12  and a float  14  coupled to toroidal coil  12  such that toroidal coil  12  is maintained at the water&#39;s surface  100  or partially below the surface so that when the toroidal coil  12  is part of a buoyant antenna, it has a minimal effect on the buoyant antenna&#39;s attitude when system  10  is deployed on the water. More specifically, toroidal coil  12  has a toroidal core  12 A of magnetic material with a wire  12 B wound about core  12 A one or more times to define a coil winding. The number of windings is chosen such that the impedance resembles an inductor operated well below its self-resonant frequency. Toroidal coil  12  is held substantially perpendicular to the water&#39;s surface  100  such that its spatial region  12 C defined by core  12 A is substantially parallel to the water&#39;s surface  100 . 
     In use, a buoyant cable antenna (not shown) in its axial orientation is passed through spatial region  12 C with the size of toroidal coil  12  being such that the antenna can be moved there through. As is known in the art of buoyant cable antennas, a circumference-oriented magnetic field is produced by a buoyant cable antenna as current flows there through. The buoyant cable antenna&#39;s magnetic field at the portion thereof in spatial region  12 C is concentrated by core  12 A that, in turn, induces an electric current in wire  12 B. The amount of current induced in wire  12 B is proportional to the amount of current flowing along the buoyant cable antenna. The induced current can be provided to a data interface  16  for onboard processing and/or transmission as will be explained further below. 
     Float  14  is any device or system that can keep toroidal coil  12  oriented at the water&#39;s surface  100  as described above. The material used for float  14  and its particular construction can be realized in a variety of ways without departing from the scope of the present invention. For example,  FIG. 2  illustrates one embodiment of float  14  that houses and supports toroidal coil  12  while also defining paths/conduits  14 A and  14 B extending from either side of spatial region  12 C of toroidal coil  12 . (For clarity of illustration, wire winding  12 B and data interface  16  are omitted from  FIG. 2 .) A buoyant cable antenna  200  floating on the water&#39;s surface  100  is led along path/conduit  14 A, through spatial region  12 C, and then along path/conduit  14 B. In this way, float  14  supports/orients toroidal coil  12  while also orienting buoyant cable antenna  200  relative to toroidal coil  12  at the buoyant antenna&#39;s natural waterline. 
     The relationship between paths/conduits  14 A/ 14 B and antenna  200  should allow for sliding movement there between so that the combination of toroidal coil  12  and float  14  can be moved along the length antenna  200 . Such movement can be made by pulling on a tether line  20  coupled to float  14 . The pulling force applied to tether line  20  can be a manual force (e.g., by hand, hand-cranked winch, etc.) or powered force (e.g., motor-driven winch under automatic control, etc.) without departing from the scope of the present invention. Another or additional option is to couple an underwater propulsor  22  to float  14  to generate or aid in the movement of toroidal coil  12 /float  14  along antenna  12 . 
     Another support and alignment embodiment of the present invention is illustrated in  FIG. 3  where float  14  includes two (or more) support arms  14 C extending out there from and over the water&#39;s surface  100 . Support arms  14 C are aligned with one another along a path that is substantially parallel to the water&#39;s surface  100  on which float  14  is floating. A hose or conduit  24  made from a non-magnetic material is coupled to and suspended by arms  14 C while passing through toroidal core  12 . Conduit  24  should have an internal diameter that permits buoyant cable antenna  200  to slide there through as float  14  is moved along antenna  200  as described above. 
     As mentioned above, the current induced in the toroidal coil&#39;s winding(s) (i.e., in wire  12 B illustrated in  FIG. 1 ) is indicative of the current flowing in the buoyant cable antenna passing through the toroidal coil. The transmission and/or recording of the induced current is handled by data interface  16  as wire  12 B is coupled thereto as illustrated in  FIG. 1 . Three non-limiting realizations of data interface  16  are presented in  FIGS. 4-6 . These realizations can be used alone or in combination with one another without departing from the scope of the present invention. In  FIG. 4 , a step-down transformer  30  receives the induced current from wire  12 B and an electric signal carrying cable  32  (e.g., a coaxial cable) carries the output of transformer  30  to some remotely-located data collection site (not shown). Transformer  30  isolates wire  12 B from cable  32  to reduce the likelihood of ground-loop related effects, reduces the impedance of wire  12 B in order to minimize the capacitance related effect created by seawater splash/washover. 
     In  FIG. 5 , data interface  16  is realized by a wireless transmitter  40  coupled to wire  12 B where a wireless signal  42  indicative of the induced current is transmitted over the airwaves. In  FIG. 6 , the induced current flowing in wire  12 B is provided to a processor  50  that assembles the current data for storage on a memory  52  for later processing or archival purposes. 
     The advantages of the present invention are numerous. The azimuthal radiation pattern of a floating buoyant cable antenna is readily evaluated in-sites by measuring the current flowing in the antenna. The cable antenna need not be rotated or otherwise manipulated. The current probe system can be readily moved and operated from a dry location such as a shore or the deck of a ship. 
     It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.