System for tracking wild game

An assembly for tracking an animal which has been shot by an arrow. A shank portion of an arrow is received in a bushing which in turn receives a housing for a transmitter. The housing is retained on the bushing during arrow flight by an elastomeric ring. Upon impact of the arrow with the animal, the elastomeric ring is dislodged, releasing the housing from the bushing. Associated with the housing are members which penetrate the animal to attach the housing to the animal. A hand-held direction finding receiver receives signals from the transmitter so that direction to the animal is determined.

The present invention relates generally to the hunting, tracking, and tagging of deer or other wild game. More particularly, the present invention relates to a system for tracking deer or other wild game, including the tracking of wild game which has been wounded by an arrow or tagged with a dart. While the present invention will be described with respect to hunting wild game with an arrow, it should be understood that it is also applicable to the tagging of animals such as elephants. Thus, the term “arrow,” as used herein and in the claims, is meant to include darts or similar instruments for hunting, tagging, or tracking animals.

A deer or other wild game may travel a long distance after it has been shot with an arrow, and it may be difficult to track the wounded animal. The blood trail, a common means of tracking, may be difficult to follow due to, for example, rugged terrain, washing away of the blood by rain or the traveling of the animal through water, clotting of the blood, or the leaving of no blood trail at all due to only internal bleeding. As a result of the difficult tracking, the wounded animal is often lost and never retrieved.

Many attempts have been made to provide means such as transmitters attached to the arrows for tracking deer wounded by the arrows, including the devices disclosed in U.S. Pat. Nos. Re. 33,470 (reissue of U.S. Pat. No. 4,704,612); 3,790,948; 4,651,999; 4,675,683; 4,858,935; 4,976,442; 5,188,373; 5,446,467; 5,450,614; 6,055,761; 6,409,617; and 6,612,947. The transmitter sends signals, for the purpose of determining the location thereof, to a receiver held by the hunter. While the receiver in U.S. Pat. Re. 33,470 is described as being a radio-frequency receiver having a directional antenna and a magnitude indicator and earphone coupled thereto, in many receivers of the prior art, the receiver has no compass or display and essentially acts like a Geiger counter, i.e., it simply beeps louder and softer.

U.S. Pat. No. 5,188,373 to Ferguson et al discloses an arrow wherein a transmitter (for transmitting signals to a receiver) is releasably attached by tape, which is described as “having sufficient bonding or shear strength to maintain the transmitter affixed to the arrow in view of the forces applied to the transmitter when the arrow is shot, but not sufficient to withstand the impact of the transmitter against the hide of the target animal.” The transmitter is provided with barbs to secure the transmitter to the hide of the target animal. Such a device has an adverse impact on arrow balance and undesirably requires the application of the tape in order to prepare the arrow with the transmitter attached for use. Also disclosed is a transmitter device releasably secured within the arrow by an undesirably complex spring arrangement. This alternative device, in addition to having an adverse impact on arrow balance, undesirably requires that the arrow shaft be altered to receive the transmitter therein.

U.S. Pat. No. 5,446,467 to Willett discloses an arrow wherein a sender unit (for transmitting signals to a receiver) is mounted in a bracket which is secured to the arrow between the broadhead and the shaft, with a balancing weight provided on the other side. When the arrow hits, the sender unit, with a dart, snaps out of the bracket and into the game. This device, although it provides for a counterbalance of weight, does not allow for aerodynamic balancing. Wind resistance caused by the transmitter body may cause excessive drag on one side of the arrow, resulting in erratic arrow flight and rotation that will reduce accuracy and distance. In addition, the transmitter holder creates a problem with initial arrow penetration. Thus, if the arrow is fired at an angle and the transmitter is trapped between the body of the target and the arrow shaft, the transmitter may not release its holder. The failure of this release will stop the arrow from penetrating its intended target and bounce off, leaving a non-lethal flesh wound. Even when the transmitter deploys, the holder will still create a drag on the flesh as it enters the target, reducing the arrow's momentum and increasing the likelihood of a non-lethal wound. Moreover, the bracket is made of spring steel, which is disclosed as “designed to release the electronic sender device when it strikes the target.” However, it is not disclosed in Willett how the device is detachably attached to the spring steel bracket.

U.S. Pat. No. 4,976,442 to Treadway discloses an arrow having a notch or slot in which a transmitter (for transmitting signals to a receiver) fits, the transmitter provided with a curved hook which terminates in a sharp hook tip having a barb. The hook tip and barb are designed to project through the slot or notch in the arrow shaft and engage and remain in the animal when the arrow strikes the animal, wherein the force of the strike causes the transmitter to exit the notch in the arrow shaft and remain in the animal, regardless of the arrow location. This device, in addition to having an adverse impact on arrow balance, undesirably requires that the arrow shaft be altered by the placement of the notch therein.

Each of the above patents suffers from one or more infirmities. In many of these patents, the transmitter remains within a hollow shaft portion or otherwise attached to the arrow with the result that the deer cannot be tracked if the arrow passes entirely through the deer. The attachment of the transmitter device in many of the above patents has a detrimental impact on arrow balance or undesirably requires the arrow shaft to be altered by the forming of a notch or the like therein.

It is accordingly an object of the present invention to provide a system for tracking wild game wherein a transmitter device is attached to an arrow so that it detaches therefrom and attaches to the animal when the arrow strikes the animal, wherein the device is suitably balanced on the arrow and does not require altering of the arrow for attachment of the device.

It is another object of the present invention to provide such a transmitter device which is light in weight and compact.

It is a further object of the present invention to provide a compact receiver to act as a direction finder for the transmitter.

In order to provide such a system, in accordance with the present invention, there is provided an assembly comprising a transmitter to be carried by an arrow for effecting embedding of said transmitter into an animal struck by the arrow, said transmitter adapted to transmit signals to a receiver for tracking the animal, the assembly further comprising a bushing attachable to the arrow and having an outer surface and a groove in and circumscribing said outer surface, a housing for said transmitter, said housing having an inner surface adapted to circumscribe said bushing outer surface adjacent said groove, an elastomeric ring removably received in said groove and having a size and strength to hold said housing on said bushing during flight of the arrow and to dislodge from said groove and thereby release said housing from said bushing during impact of the arrow with the animal, the assembly further comprising at least one member for penetrating the animal for attaching the housing to the animal.

The above and other objects, features, and advantages of the present invention will be apparent in the following detailed description of the preferred embodiment thereof when read in conjunction with the accompanying drawings wherein the same reference numerals depict the same or similar parts throughout the several views.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIGS. 1 and 2, there is illustrated generally at30a typical arrow with which the present invention may be used. For a cross bow, the arrow is called a “bolt,” and the present invention is also applicable to bolts. Thus, the term “arrow,” as used herein and in the claims, is meant to include bolts as used in a cross bow as well as darts and the like, as previously discussed. The arrow30is typically used to hunt deer or other wild game. The arrow30includes a shaft32having a bow string notch34in one end and fins36(feather members or the like) adjacent thereto for guiding the arrow aerodynamically. The other end of the shaft32is attached to a broadhead36which has a number of, for example, 3 blades38emanating from a shaft portion40which terminates in a sharp point, illustrated at42, for piercing a target animal. The shaft portion40extends rearwardly beyond the rear ends of the blades38to define a shank portion44(having a length of, for example, about ¼ inch) which terminates in a threaded end portion46(having a length of, for example, about ⅜ inch). As used herein and in the claims, the term “forward” and variants thereof is meant to refer to a position ahead of another object with reference to a direction in which the arrow is aimed, and the term “rearward” and variants thereof is meant to refer to a position behind another object with reference to a direction in which the arrow is aimed. Thus, the arrow shaft32is rearward of the broadhead36. On the shank portion44adjacent the ends of the blades38is a collar48, which may be an enlarged part of the shank portion44or a separate piece. The arrow shaft32has an internally threaded bore50for threadedly receiving the threaded portion46and a counterbore52for receiving the shank portion44for attaching the broadhead36to the shaft32. The shank portion44and the counterbore52may each have a length of, for example, about ¼ inch, and the threaded portion46and threaded bore50may each have a length of, for example, about ⅜ inch, the bore50and counterbore52being slightly longer than the respective portions46and44to prevent bottoming out. Thus, for use of the arrow without the present invention, the broadhead36is screwed onto the shaft32and tightened with the collar bearing against the end of the shaft32.

Referring toFIGS. 3 to 7, there is illustrated the arrow30with a transmitter assembly, illustrated generally at60, attached thereto, the transmitter assembly including a housing or support ring64releasably secured to a release bushing62, as described hereinafter. The bushing62is fixedly (securely) attached to the arrow30, as described hereinafter.

The bushing62has a cylindrical wall portion66open at one end thereby defining a passage or bore, illustrated at68, for receiving the forward end portion of the arrow shaft32. A wall portion70closes the other end of the bushing62, the wall portion70having a bore72there through for receiving the broadhead shank portion44. In order to fixedly attach the bushing to the arrow30, the shaft32is received in the bore68, the shank44is received through the bore42, and the threaded portion46is threadedly received in the threaded bore50and tightened to squeeze the bushing wall portion70between the collar48and the end of the arrow shaft32. The bushing wall portion70may have a thickness of, for example, about 1/16 inch. The portion44and counterbore52each may typically have a length of about ¼ inch. The threaded bore50(as well as threaded portion46) typically has a length of about ⅜ inch, and it is believed that a thread engagement over the resulting decreased length of about 5/16 inch (still being roughly about 1½ times the #832 thread diameter) is satisfactory. However, if necessary or desirable, the length of threaded bore50may be increased by, for example, about 1/16 inch. Various exemplary dimensions and materials and the like contained herein, unless recited in the claims, are for exemplary purposes only and not for purposes of limitation.

For the purposes of this specification and the claims, a “bushing” is defined as a member having a passage in which a shank portion of an arrow is receivable whereby the bushing is fixedly attached to the arrow. A bushing may have various shapes such as shown at62inFIG. 7and at202inFIG. 16.

The forward end portion (at or adjacent the wall portion70) of the bushing62has an increased diameter portion74, which is shaped to define, rearwardly thereof, a shoulder76, and has a short cylindrical portion78extending forwardly from the shoulder76. The forward end portion of the bushing62has a truncated conical surface extending forwardly from the short cylindrical portion78to the forward surface of wall portion70. Adjacent the rear end of the bushing62is a groove80in the outer bushing surface which groove circumscribes the bushing62. An elastomeric ring82, i.e., an o-ring or the like, is received in groove80. A transmitter circuit board86, described in greater detail hereinafter, is attached to the rear surface of the housing64by suitable means such as by bonding, an example of a suitable bonding agent being Permabond #2011 adhesive manufactured by Permabond LLC of Somerset, N.J. The housing or support ring64is generally cylindrical in shape and has a bore84extending axially there through and defining a radially inner surface the diameter of which is substantially equal to the diameter of the bushing radially outer surface but with some slack to allow the housing64to easily slide axially along and off of the bushing62. A similar bore88is provided in the circuit board86. As used herein and in the claims, the terms “housing” and “support ring” are meant to refer to structures used for support of articles such as the transmitter board86discussed hereinafter. As used herein and in the claims, the term “axially” and variants thereof is defined as referring to a direction along the longitudinal axis of the arrow shaft32, and the term “radially” and variants thereof is defined as referring to a direction normal to the longitudinal axis of the arrow shaft32. For example, the radially outer surface of the bushing62may have a diameter of about 0.468 inch, and the radially inner surface of the housing64may have a diameter of about 0.471 inch in order to leave just enough slack for the housing64to slide easily over the bushing62. The housing is received on the bushing to abut the shoulder76to restrain it from movement forwardly relative to the arrow30, and the elastomeric ring82, which is sized, as illustrated inFIG. 7, so that its radially outer portion protrudes from the groove80, is inserted in the groove80to restrain the housing from movement rearwardly relative to the arrow30during normal flight of the arrow30through the air.

It is important, in order to be able to track a wounded deer by receiving signals from the transmitter (described hereinafter) on the transmitter board86, that the transmitter and the housing64to which it is attached become embedded in the deer rather than perhaps passing through the deer with the arrow. In order to do so, in accordance with the present invention, the elastomeric ring82is sized and otherwise adapted to be removed from the groove80under the greatly increased force of the housing64acting there against during impact of the arrow30with a deer. For example, the elastomeric ring82may be composed of Buwa-N or other suitable material having a modulus of elasticity of about Durometer 70A (preferably between about 65 and75) and be sized to extend a distance, illustrated at90inFIG. 7, of about ½ inch (preferably between about 0.40 and 0.52 inch) from the bottom of the groove80, which may have a depth, for example, of about half that distance90. Thus, about half of the elastomeric ring82may desirably extend above the groove80to restrain the housing64during normal arrow flight. An elastomeric ring82which Applicants consider suitable is one manufactured by Parker-Hanifin Corp. of Salt Lake City, Utah and identified by number AS568A-012. The elastomeric ring82is thus sized and adapted to become removed from the groove80under the force of impact of the arrow30with a deer with the result that the housing slides relative to the arrow30rearwardly along and off the bushing62and becomes free of the arrow and free to become embedded in the deer, as described hereinafter with reference toFIGS. 11 to 13.

The housing or support ring64is composed of, for example, Delrin plastic material (acepal homopolymer), manufactured by E.I. duPont de Nemours and Company of Wilmington, Del., or other suitable material. In order to enhance the ease of sliding of the housing64over the bushing, the bushing62is composed of, for example, a different plastic material, desirably one which is a little harder and impregnated with a lubricant. For example, the bushing may be composed of 6/6 Nylatron plastic material, which is manufactured by AIN Plastics of Mount Vernon, N.Y., and which is impregnated with molybdenum disulfide lubricant.

The housing64is generally doughnut-shaped, having a radially outer surface87the rear portion89of which is cylindrical and the forward portion91of which is conically-shaped, i.e., it flares radially inwardly at a small angle of, for example, about 1 degree, the flared surface being provided to minimize weight added to the arrow30. Cut-outs93, for example, three, extend axially through the thickness of the housing64to also minimize weight added to the arrow30. A cut-out95is also provided in the circuit board86to minimize weight added to the arrow30.

Spaced circumferentially about the housing64are a plurality of, for example, three axially extending through bores92each having a forward counterbore94defining a forward facing shoulder96. Elongate casings98a,98b, and98care received in the counterbores94to rest on the shoulders96respectively and extend forwardly beyond the housing64. The inner diameter of each casing98is substantially equal to the diameter of the bore92. The casings98are attached to the housing64by threading or by other suitable means. The thickness of the housing64is selected to suitably hold the casings98in such a cantilever fashion sufficiently firmly. For example, the housing64may have a thickness of about 0.06 inch. This allows the thickness of the housing64to be minimized to again minimize weight added to the arrow30. The diameter of the housing64as well as the circuit board86is, for example, about 1.4 inch but is preferably about 1 inch or less. The length of each of the casings98is, for example, about 0.85 inch, and the length of each of the point heads104is, for example, about 0.47 inch.

A battery100(sized to last, for example, about 1 or 2 days) is received snugly but loosely in each of two of the casings98aand98band can extend into the respective bore92. A similarly sized container102is received loosely in the third casing98c. As desired, the container102may contain transmitter circuit components or have other purposes such as for carrying a spare battery or filler material for purposes which will be discussed hereinafter. The forward opening of each casing98is closed by a pointed head104having a rearward cylindrical portion106which slides into the forward end of the casing98with a close fit, i.e., the diameter of the cylindrical portion106may, for example, be about 0.160 inch, and the inner diameter of the casing98may, for example, be about 0.178 inch, thereby allowing some freedom of movement of the cylindrical portion106within the casing98. The point head104also has a conical portion105terminating in a forward sharp point107for penetrating the deer or other wild animal for attachment of the housing64and transmitter86to the deer. The rear end of the conical portion105has an increased diameter over the cylindrical portion106to provide a shoulder108which rests on the end of the casing98for thereby locating the head position and preventing its movement further into the casing. The casings98and the point heads104are composed of stainless steel or other suitable material. The relatively small diameter of the casings98(the outer diameter may, for example, be about 0.188 inch) allows them to easily penetrate a deer or other animal, but the relatively large surface area of the housing64acts as a stop to further penetration so that the transmitter assembly60does not pass through the deer but becomes attached thereto so that the deer can be located.

Each battery100has an elongate negative terminal109which extends from the rear end thereof and is received in and electrically connected to electrically conductive contact or pin110which is received in an aperture112in the circuit board in contact electrically with an electrically conductive grounded metal pad which is printed onto the circuit board86. The cylindrical end wall111of the battery100constitutes a positive terminal which makes electrical contact with another electrically conductive metal pad which is printed onto the circuit board86by means of a small conductive spring114(having a diameter equal substantially to that of the battery100) which is received in each bore92between the respective terminal111of the battery100and the respective metal pad on the circuit board86(and a similar spring114is received in the respective bore92between the container and the circuit board86) to bias movement of the respective battery100or container102as well as the point head104in a forward direction as well as to provide electrical connections of the batteries100with the circuit115. The metal pads on the circuit board for contact with the negative and positive terminals109and111respectively of the respective battery100are suitably formed and electrically insulated from each other in accordance with conventional circuit board design and manufacturing principles. The connection of the batteries100to the transmitter circuit, illustrated at115inFIG. 23, is similar to that shown for connection of batteries244in the transmitter circuit222inFIG. 22, and such a connection is described and shown in greater detail hereinafter with reference toFIG. 38, with pins110being similar to and serving a similar function to pins254inFIGS. 22 and 38and with springs114being similar to and serving a similar function to springs249inFIGS. 22 and 38. The transmitter circuit115, which includes four or other suitable number of capacitors117for boosting voltage of batteries100for intermittent transmissions, is described hereinafter with reference toFIG. 23.

A barb or elongate member116is inserted in an opening118in each casing98and into a blind opening120in the respective point head104. The force of the spring89pinches the barb116to hold it tightly in the openings118and120to thereby securely hold the point head104to the casing98. The barbs116extend at an angle, illustrated at122, backwardly from the casing98of, for example, about 40 degrees and have sharp points124to act as fish hooks to keep the transmitter assembly60attached securely to the deer or other animal.

Referring toFIGS. 11 to 14, there is illustrated inFIG. 11the arrow30shot by a hunter110in flight toward a target, i.e., such as a deer113, with the transmitter assembly60carrying the transmitter86held in place on the arrow by the o-ring82set in the groove80. As seen inFIG. 12, the arrow30has pierced and is passing through the deer113, and the force of impact with the deer has dislodged the o-ring82from the groove80so that the transmitter assembly60separates from the arrow30. The release bushing62remains in place on the arrow30. The point heads104on the transmitter assembly60pierce the deer113to the depth of the housing64which, due to its large surface area, acts as a stop to further penetration. Thus, the housing64and transmitter86become attached to the surface of the deer and are secured thereto by the point heads104and casings98embedded in the deer. The barbs116, which are angled backwardly, as previously discussed, and have sharp points124on their ends, act as fish hooks to prevent the transmitter assembly60from falling out of the deer. As seen inFIG. 13, the arrow30continues to pass through the deer113, as is typical, leaving the transmitter assembly60on the deer113to transmit signals, illustrated at115. As seen inFIG. 14, these signals114are received by a hand-held portable indicator unit500carried by the hunter, thereby providing an indication to the hunter of the direction to the transmitter assembly60and thereby the deer or other prey animal after the deer has left the vicinity where it was shot so that the hunter can go to that location and retrieve the deer113.

It is important that the weight and size of the transmitter assembly60be minimized and that its weight be distributed in a balanced manner about the arrow30in order that the transmitter assembly60have minimal impact on arrow trajectory. Thus, as discussed in some instances heretofore, components where possible are made of light weight material such as plastics, and weight is removed such as by lightening holes93and95as much as possible from components without compromising integrity. Weight at a distance from the arrow shaft has a greater impact on arrow trajectory than weight closer to the shaft. Thus, the overall size radially is minimized, and the removal of weight by tapering housing portion91desirably reduces the impact on arrow trajectory more so than if the same weight were removed closer to the shaft. The transmitter weight is also minimized to keep the overall weight of the transmitter assembly60down. The weight of broadheads typically range from about 75 to 125 grams, the greater the weight the less the arrow speed but the greater the broadhead penetration. The overall weight of the transmitter assembly60and bushing62as described herein and as assembled by Applicants is less than 100 grams, and the overall weight of such an assembly is preferably less than 50 grams. It is considered that a combined weight of, for example, about 175 grams for the broadhead36, the transmitter assembly60, and the bushing62is suitable as long as symmetry is maintained, as discussed hereinafter.

It has been found that a transmitter assembly with two point heads104and two casings98may not engage the deer properly when the target is hit with the point heads and casings in vertical alignment. It is thus preferred that the transmitter assembly60have three point heads104and three casings98as described herein since this eliminates the above engagement problem and since this matches the three blades of a typical broadhead and thereby provides symmetry which minimizes balance problems. In order to maintain balance, the weight of the container102and its contents preferably equals the weight of one of the batteries100.

As described above, the components of the transmitter assembly60and the bushing62are distributed about the arrow shaft so as to maintain symmetry and balance, as best seen inFIG. 6. In order to achieve optimum balance, the transmitter assembly60is preferably dynamically balanced, i.e., spin balanced, similarly as done for automotive tires.

Referring toFIGS. 15 to 21, there is shown generally at200a transmitter assembly in accordance with an alternative embodiment of the present invention. The transmitter assembly200is releasably attached to arrow30by means of a bushing202. The release bushing202, which may be composed of 6/6 Nylatron plastic or polymeric material of the Polymer Corporation of Reading, Pa. or of other suitable material, has a flat circular (washer shaped) portion204having a central aperture, illustrated at208, and from the outer circumferential edge of which extend rearwardly three circumferentially evenly spaced elongate generally flat prongs206which are arcuate, as seen inFIG. 18, to conform with the circular curvature of the portion204. The arrow shank portion44is received in the washer-shaped portion aperture208as well as in a central aperture, illustrated at290, of a protective cap292so that the washer-shaped portion204(as well as the cap292, the aperture290of which is forward of the washer-shaped portion204) is secured between the collar48and the arrow shaft32when the arrow shaft is attached to the broadhead36as previously discussed. The prongs206extend rearwardly along and in generally surrounding relation to the arrow shaft32. The prongs206have axially aligned grooves, illustrated at210, in the outer surfaces211thereof adjacent the rear ends thereof for purposes which will be discussed hereinafter. For the purposes of this specification and the claims, the outer surfaces of the three prongs206are together defined as an outer surface of the bushing202, and the three aligned grooves210are together defined as a groove. The washer-shaped portion may, for example, have a thickness of about 1/16 inch, a diameter of about 7/16 inch, a diameter of aperture208of about 3/16 inch, and an overall length of about 1¼ inch. Each of the prongs206may, for example, have a thickness of about 1/16 inch, with the depth of each of the grooves210being about 1/32 inch.

The prongs206are received in a bore, illustrated at212, which extends entirely through a transmitter housing214. The housing214is composed of Delrin plastic material, a product provided by E.I. duPont de Nemours and Company of Wilmington, Del., or other suitable material. As seen inFIGS. 20 and 21, the housing214is generally triangular-shaped (with arcuate sides and rounded corners) along its length. A portion218protrudes from the forward end a distance of, for example, about 1/16 inch, and is circular with generally truncated corners corresponding to the rounded triangular corners of the housing214, for purposes which will be discussed hereinafter. The bore212is generally circular with a diameter, illustrated at216inFIG. 20, of, for example, about 5/16 inch, which is smaller than the diameter of the washer-shaped portion204so as to act as a stop for the washer-shaped portion204which accordingly abuts the forward end of the housing214to suitably position the bushing202. The bore212has three circumferentially evenly spaced cut-outs, illustrated at220, in its edge which are suitably shaped to receive the respective prongs206. A transmitter/antenna assembly/circuitry222has a generally flat antenna portion224(a thickness of, for example, about 1/32 inch) which has a central bore, illustrated at226, which is similarly shaped as bore212so as to be aligned therewith, the flat portion being suitably secured to the rear end of the housing214similarly as circuit board86is attached. The antenna portion224also serves as a circuit board. At228is a slightly undercut portion (depth of, for example, about 1/64 inch) in the radially outer surface of the housing214for a distance of, for example, about ⅛ inch from the rear end thereof. The prongs extend entirely through the bore212and through bore226so that the grooves210are outside but closely adjacent the rear side of the flat antenna portion224.

In order to releasably secure the housing214to the release bushing202, an elastomeric o-ring230is received in the aligned grooves210of the prongs206. The position radially of the grooves210is such that the o-ring230bears against the rear side of the antenna portion224whereby, in accordance with the present invention, the bushing202is secured within the housing214to hold the housing on the arrow30during flight thereof, but the strength of the o-ring230is such as to be removed from the grooves210to allow the housing214to detach from the bushing202and the arrow under the force of impact of the housing214with a deer113or the like. Thus, the o-ring230may have a diameter, illustrated at232of, for example, about 1/16 inch (or about twice the depth of the grooves210) so as to protrude from the grooves210. For example, the elastomeric ring230may be composed of a similar material as elastomeric ring82is composed. The elastomeric ring230is thus sized and adapted to become removed from the grooves210under the force of impact of the arrow30with a deer with the result that the housing214slides, relative to the arrow30, rearwardly along and off the bushing202and becomes free of the arrow and free to become embedded in the deer113.

Two of the three apex portions of the triangular housing214have bores, illustrated at240, extending therethrough in which are received snugly but loosely suitable cylindrical batteries or dry cells244, for example, Panasonic BR435 (sized to last, for example, about an hour). The batteries244are held in place to the rear by the antenna portion224and forwardly thereof by suitable battery retainers or caps248(secured in counterbores illustrated at246) or by other suitable means. The retainers248are shown to be generally washer-shaped.

Referring toFIG. 38as well asFIG. 22, the batteries244are connected in parallel with each other and with three or another suitable number of capacitors300(in parallel with each other) whose function is to store up power between transmissions for use during transmissions. Each battery244has an elongate negative terminal250which extends through but does not contact spring249and is received in an electrically conductive female pin254which in turn is received in an aperture, illustrated at252, in and soldered (to secure it in place) to an electrically conductive grounded ring223printed on the circuit board224, with the head221of the pin overlying and in electrical contact with the printed-on ring223. Thus, the negative terminal250is electrically connected to the grounded ring223. An outer concentric ring225, insulated (electrically isolated) from inner ring223, is also printed onto the circuit board. The two rings223and225are part of the circuit board copper (conductive) pattern and are thus formed in accordance with conventional circuit board design and manufacturing principles. The cylindrical end wall227of each battery244constitutes a positive terminal of the battery244and is therefore suitably insulated from the negative terminal250. The small conductive spring249electrically connects the positive terminal227to the outer ring225. Battery244is thus suitably shaped for the intended purpose while providing suitable means for both positive and negative terminals connecting suitably to the circuit board while offering long life with small size.

The other of the three apex portions of the triangular housing214has a bore, illustrated at260, extending therethrough in which is received the transmitter circuit board262, which is welded or otherwise suitably attached to the antenna board224, the opening264in the antenna board224corresponding to (is in alignment with) the bore260. Similarly as described for the embodiment ofFIGS. 1 to 13, the components of the assembly200are desirably distributed about the arrow shaft so as to maintain symmetry and balance. This would include providing components of equal weight in each of the three apex portions, i.e., the transmitter circuit board262in one apex portion having substantially the same weight as that of the battery, retainer, and casing in each of the other apex portions. As previously discussed, in order to achieve optimum balance, the assembly200is preferably dynamically balanced.

The truncated portions of the circular portion218allow access to the three apex portion bores240and260. Although such access may not be needed to the bore260, the truncation about bore260at least provides symmetry.

Illustrated at270is a hook assembly providing three hooks272for penetrating the deer113or other animal for attaching the housing214thereto as the arrow, with the bushing202released from the housing214, passes further into or through the animal. The hook assembly, which is composed of stainless steel or other suitable material, comprises a circular ring274from which three equally circumferentially spaced elongate shanks276extend axially of the ring274. The ring274is received about the circular forward housing portion218thereby protectively covering the three apex portion bores240and260. The shanks276extend rearwardly from the ring274and are received (press-fitted) in slots, illustrated at278, which are centrally located in each of the three walls of the generally triangular-shaped housing214over the lengths thereof. The slots278may, for example, have a depth of about 1/16 inch and a width of about 1/32 inch. The shank end portions280(which terminate in the hooks272) are curved so as to extend radially from the slots278and then forwardly thereby orienting the flesh-piercing hooks272to face forwardly for penetrating the deer as it is shot by the arrow.

In addition to the aperture290, the protective cap292, which may be composed of Delrin or other suitable material, has first, second, and third counterbores294,296, and298respectively, each being of a greater diameter than the previous. The diameter of the aperture290may be the same as the diameter of the washer-shaped portion204for receiving the arrow shank portion44. The first counterbore294is sized to snugly receive the washer-shaped portion204. The second and third counterbores296and298are provided to nest the transmitter housing214and the hook assembly270respectively.

The provision of the hook assembly270advantageously brings the mass closer to the center so that it has a lesser effect on arrow trajectory. The transmitter assembly200provides a narrower body which advantageously allows less resistance to penetration, less air resistance, less unbalanced effect due to torque, is desirably less noticeable (appearance-wise), and may weigh less (for example, the hook assembly270may weigh less than 6 grams vs. 45 grams for the point heads104).

Referring toFIG. 22, the circuit222is activated by a suitable switch, for example, a magnetic reed switch304operable by a hand-carried magnet, illustrated at306, which is briefly held near the switch304when the arrow is loaded for a shot. The transmitter is therefore operating prior to the shot so that proper operation of the transmitter can be confirmed prior to the shot. The switch304is desirably fully enclosed in a glass envelope (not shown) to eliminate contamination and corrosion and thus yield increased reliability. Other types of switches may be used, for example, an inertial switch.

The switch304is connected via line310to a suitable microcomputer308which serves to detect closures of the switch304and which also serves to extend the battery life by “pulsing” the transmitter (when energized) at a rate of, for example, about 5 percent (extending battery life by a factor of 20 from, for example, 2.4 to 48 hours of battery life). This allows the batteries244to be much smaller (miniature) than would otherwise be practical, given the desired maximum range and life span of the transmitter. Thus, each of the miniature batteries244may, for example, have a voltage of about 3 volts and a size of about 0.16 inch diameter and about 1 inch long. The microcomputer308desirably is also equipped, using principles commonly known to those of ordinary skill in the art to which this invention pertains, to detect low battery conditions and shut down the transmitter to prevent harmful interference caused by an under-powered transmitter chip (hereinafter described) and to monitor battery condition and remaining life span and report (by telemetry) this information to the user so that an arrow is not selected and employed which has weak batteries. These functions of the microcomputer308are discussed in more detail hereinafter with reference toFIG. 35. The microcomputer308may, for example, be one sold by Digikey Corp. of Thief River Falls, Minn. and identified by part number 12F675-USN-ND.

The microcomputer308is electrically connected via lines312to a suitable integrated circuit UHF transmitter chip314. The frequency of the chip314(radio frequency) is set by use of a quartz crystal316at, for example, 950 Mhz, and capacitor318in series therewith stabilizes the crystal316to the desired frequency. If needed, a variable capacitor may be provided in parallel with capacitor318to compensate for variances in frequency due to tolerances of the crystal316. Power is supplied to the chip314via line320, and two (or other suitable quantity) capacitors322in parallel with each other and between power line320and ground are provided to eliminate RF (radio frequency) interference to the microcomputer308. The transmitter chip314may, for example, be one sold by Atmel Corp. of San Jose, Calif. and identified by part number T5750.

A signal at the desired frequency is transmitted from chip314along line324to antenna326which is an integrated loop antenna, which comprises a closed loop of metal printed directly onto the surface of transmitter board222. The transmitter circuitry includes an X64 phase-locked-loop frequency synthesizer driving a low power antenna amplifier circuit (RF amplifier), which are integral with the transmitter chip314(not external thereto). An inductor328is electrically connected between the power line330and line324to provide DC power to the RF amplifier. Capacitor332, which is electrically connected between line324and ground, and three (or other suitable number) capacitors334, which are connected in series in line324, are provided to achieve an “impedance match” between the antenna326and the transmitter chip314to increase the efficiency of the antenna326, using principles commonly known to those of ordinary skill in the art to which this invention pertains.

If desired in order to allow careful tuning of the antenna, if necessary, after the transmitter is assembled, an adjustable capacitor may be provided in parallel with the capacitors334. In the event that there is insufficient room on the circuit board for an adjustable capacitor, a trimcap, illustrated at336, may, if needed, be provided in parallel with the capacitors334. The trimcap336, which is part of the copper pattern that is printed onto the circuit board, behaves electrically like a very small capacitor and serves the same purpose. The trimcap336comprises an oblong copper strip having a length of, for example, about 0.5 inch long, printed onto the circuit board and which can be “trimmed” with a sharp knife, such as, for example, an X-acto knife, to a length to achieve the desired precise tuning. Once the proper length is determined, subsequent transmitters can be provided with trimcaps which are trimmed to the same length.

Referring toFIG. 25, the quartz crystal316, magnetic switch304, microcomputer integrated circuit308, and transmitter integrated circuit314are all installed on printed circuit board222. The second printed circuit board224provides the connections for the batteries244(as previously discussed) and also holds the antenna326. The two boards222and224are permanently connected together such as by direct solder connections which join adjacent metal areas that are printed onto both boards222and224.

Referring toFIG. 35, the microcomputer308has installed therein a program, illustrated generally at350. The magnetic switch304is periodically examined, as illustrated at352, to determine if the user wishes to switch the transmitter on or off. If the magnetic switch304is open, the battery status is updated, as indicated at368, and sleep mode is entered, as indicated at360. If the magnetic switch304is closed, opening thereof is awaited, as indicated at358, after which there is a change of transmitter status354, as indicated at356. Each opening and closing of the magnetic switch304is treated as a single event (i.e., open+close=one event), and the reaction356of the microcomputer308to this event, a change in transmitter status354, is determined by the condition of the transmitter prior to the event. If the transmitter was “on” prior to the event, the transmitter is switched “off” and remains “off” when the magnet306is removed. If the transmitter was “off” prior to the event, the transmitter is switched “on” and remains “on” when the magnet306is removed. The switch304is spring-loaded so that it normally is an “open circuit”, and it only “closes” when a magnet306is held nearby. Removing the magnet306will restore the switch304to its “normally open” condition.

The microcomputer308is programmed to spend most of its time in a low-power operating mode called “sleep”, as indicated at360, during which the microcomputer308cannot execute any instructions, but it also advantageously draws very little current from the batteries244during this mode. An internal low-power timer, called “watchdog”, indicated at362, is used to interrupt the “sleep” mode, as indicated at364, for example, approximately 50 times per second. Once “sleep” is interrupted, the execution of the program350proceeds. After the necessary tasks are completed, the microcomputer re-enters “sleep” mode, as indicated at360, to conserve battery power.

Whenever the “sleep” mode is interrupted by the “watchdog” timer362, the current status of the transmitter314is tested, as indicated at366, to determine if the transmitter status is on or off. The current status of the transmitter is stored in the program350as a variable quantity, which can be changed by the program350, as indicated at356, as previously discussed. If the transmitter status is currently off, then no output pulse from the transmitter is required. The magnetic switch304is then tested, as indicated at352and as previously discussed. If the switch304is not closed (indicating that no magnet is nearby), the program350, after updating the battery status, as indicated at368, re-enters the “sleep” mode, as indicated at360, to conserve battery power.

If the tested transmitter status is “on”, the microcomputer integrated circuit enables the transmitter chip314, as indicated at370, for a period of, for example, 1 millisecond, but does not enable the transmitter output. This waiting period, indicated at372, allows the quartz crystal316and the internal circuits of the transmitter chip314to “stabilize” prior to switching on the output of the transmitter integrated circuit. After the delay, the transmitter output is enabled, as indicated at374, for a period of, for example, 1 millisecond, as indicated at376. Following the 1 millisecond radio transmission, the microcomputer integrated circuit disables the transmitter integrated circuit314, as indicated at380, to conserve battery power, and the battery status is updated, as indicated at368. If desired, the program350may include steps to transmit data about remaining battery life.

After the transmitter314is disabled, the program proceeds to the previously discussed testing of the magnetic switch304, as indicated at352. If the switch304is closed (indicating that a magnet306is near it), the program350waits until the switch304opens, as indicated at358, then reverses the current status of the transmitter314(either on or off), as indicated at356, then updates battery status and re-enters “sleep” mode, as indicated at368and360respectively. Thereafter, the “watchdog” timer362causes the program350to “wake up”, as indicated at364, and the cycle begins again.

The duration of the transmitter pulse in this embodiment is 1 millisecond. Only one pulse is generated during each program execution “loop”. Execution of the program350is repeated in this embodiment approximately 50 times per second, because the internal “watchdog” timer362interrupts the “sleep” mode 50 times per second. This translates into a time interval (between “watchdog” interruptions) of approximately 20 milliseconds. The transmitter314is therefore turned on (when enabled) for only 5 percent of the time (1 millisecond divided by 20 milliseconds) to advantageously conserve and prolong battery life. Of course, programs in other embodiments may have different pulse durations and time intervals.

Battery power is applied to the microcomputer308and transmitter314at all times while the batteries244are installed. When the transmitter314is off, the transmitter integrated circuits are disabled by the microcomputer308, and the microcomputer integrated circuit308is in the “sleep” mode for more than 99.9 percent of the time. The total load on the batteries244is therefore extremely low, so periodic battery replacement may not be required for several months. Whenever the transmitter314is turned on, battery load increases significantly, but the pulsed nature of the transmissions advantageously allows reliable operation for a period of 24 to 48 hours.

Referring toFIG. 23, there is shown a schematic of transmitter circuit115(loop) for the embodiment ofFIGS. 1 to 13. Circuit115includes a magnetic switch400, a microcomputer402, a transmitter chip404with a quartz crystal406(for a radio frequency of 916 Mhz), stabilizing capacitor408, and capacitor410, all of which are similar to magnetic switch304, microcomputer308, transmitter chip314with quartz crystal316, stabilizing capacitor318, and pair of parallel capacitors322of the circuit222ofFIG. 22. At412is a capacitor in parallel with the crystal406to fine-tune the crystal406to the desired frequency thereby compensating for crystal tolerance. The transmitter chip404outputs along line414to antenna416, which is a grounded loop which may, for example, 1 inch in diameter and 0.05 inch in width. In series with the antenna416are a capacitor418and inductor420, and an inductor422and capacitor424are each in parallel with the antenna416to achieve “impedance matching” to increase antenna efficiency in accordance with principles commonly known to those of ordinary skill in the art to which this invention pertains.

Referring toFIGS. 26 and 27, the portable indicator unit500, which is usable for either of the transmitter embodiments described hereinbefore, includes a directional antenna502, an antenna connector504, a direction finding (DF) unit506, a display computer508which includes an LCD display and touch-sensitive screen510, a display connector512, and a pair of latch mechanisms514(both shown inFIG. 28).

Referring toFIG. 28, the direction finder506includes a radio receiver516, a microcomputer524, a North-South compass sensor520, and an East-West compass sensor522.

Referring toFIG. 30, the microcomputer chip524receives and processes signals from the radio receiver516and the compass sensors520and522and outputs signals (raw data) to the display computer508which are indicative of the direction to the transmitter60and thus the deer or other prey113and outputs such direction when operated in the manner hereinafter described.

Referring toFIG. 24, there is illustrated generally at530the circuitry for the direction finding unit506.

A suitable receiver516is, for example, one identified by number ATR5A-914, sold by Abacom Technologies of Etobicoke, Ontario, Canada, and which is modified in accordance with the following discussion. The receiver516includes a signal channel width circuit532. In order that the transmitter batteries may be small and light, the circuitry532is provided to provide a very narrow channel width, for example, a channel width of 916.335 to 916.365 Mhz for a frequency of 916.35 Mhz. The circuit532has an intermediate frequency signal input line534to receiver516, with an inductor536and a variable capacitor538and a mixer output signal line540also with an inductor542and a variable capacitor544, and a filter in parallel therewith, the relationship between the capacitances of the variable capacitors538and544determining the channel width in accordance with principles commonly known to those of ordinary skill in the art to which this invention pertains.

The radio receiver516is tuned to the same frequency as the that of the transmitter86in the assembly60or transmitter262in the assembly200. The tuning circuit548for the receiver516includes a capacitor550for selecting the channel and a variable capacitor552in parallel therewith for fine tuning, in accordance with principles commonly known to those of ordinary skill in the art to which this invention pertains.

The receiver516produces an output voltage that is proportional to the strength of the signal of the signal detected by the directional antenna502, i.e., the signal received from the transmitter86or262. This voltage is called RSSI or received signal strength indicator. Thus, a circuit556inputs a signal (analog voltage of, for example, 0.5 to 2.5 volts) which is representative of the received signal strength to the microcomputer524via line558, which translates this signal into a numeric value that is stored in the microcomputer, using an analog-to-digital converter or ADC, in accordance with principles commonly known to those of ordinary skill in the art to which this invention pertains. The circuit556includes a stabilizing filter including a resistor560and a capacitor562. The capacitor562charges to the maximum value level of the receiver RSSI signal level (ranging from 0.5 to 2.5 volts) during a pulse so that it is unnecessary to synchronize the microcomputer measurement of the signal strength with the transmitter pulse rate. Line564is provided to discharge the capacitor562to reset it for a new measurement of the received signal strength, each time a new RSSI measurement is performed.

The microcomputer524(grounded as illustrated at760and having a timing or “clock” circuit as illustrated at770, having a quartz crystal772, to provide a timing signal for running thereof) constantly performs measurements of the RSSI signal produced by the receiver516and also constantly performs measurements (vector components) of the Earth's magnetic field as observed by the two sensors520and522. The resulting measurements are compiled into a message that is sent from microcomputer terminal or pin654via circuit650(FIG. 24), described in greater detail hereinafter, over line606to the display computer508at display connector512(FIG. 27). This message is constantly updated and re-transmitted to the display computer508, for example, approximately 20 times per second. This message contains the RSSI measurement, the North-South compass sensor measurement, and the East-West compass sensor measurement. A suitable microcomputer524is, for example, one identified by number PIC16LC773-201/SO, sold by Digikey Corporation of Thief River Falls, Minn.

Each compass520and522has a magnetic sensor coil566whose electrical characteristics are influenced by the Earth's magnetic field, the coils566being oriented 90 degrees relative to each other so that one sensor is aligned to detect the North-South vector component of the Earth's magnetic field and the other sensor is aligned to detect the East-West vector component of the Earth's magnetic field, as observed by the direction finding unit506. The maximum output of the coil566for the North-South compass occurs when facing North or South, and, similarly, the maximum output of the coil566for the East-West compass occurs when facing East or West. The compass circuit568includes a pair of gates570and572for the respective ends (such as North end and South end) of the respective coil566. Each gate is normally on by virtue of voltage passing through power supply line576from microcomputer524. Each gate is also connected to a line576from the microcomputer524, which sends a signal through respective line576to turn the respective gate off. When a gate is turned off, the respective coil end is grounded by the output signal from the gate so that the directional component of the other end of the coil can be measured. Thus, when South gate572for North-South compass520is turned off, the opposite or North end of the North-South coil566is free to oscillate. The respective switch578for the oscillating coil end is also turned on by a corresponding signal through respective line580from microcomputer524. This allows current to flow through a circuit including the corresponding line582, corresponding resistor584, the corresponding normally on gate (in our example, gate570), corresponding line574, line586which connects to the outlet pin of the differential amplifier588, and line594which connects to one of two inlet pins of the differential amplifier588. A circuit592containing parallel resistors596,598, and600connect to the other inlet pin of the differential amplifier588. Resistors596and600are connected to ground and +5 volts DC respectively. Resistor598is connected to power supply line574which includes resistor602. The ratios of resistors596,598, and600are selected so that the voltage at each of the inlet pins of differential amplifier588is equal to the set oscillation point thereof, which causes the respective coil566to oscillate. The purpose of line590from line586to the microcomputer is to allow measurement of the oscillation frequency by the computer. There is also a self-induced magnetic field due to direct current in the coil566. Depending on which gate is on, the direct current will add to or subtract from the earth's magnetic field, and the direction can be suitably calculated therefrom by microcomputer524. Such a compass sensor may, for example, be of the type marketed by PNI Corporation of Santa Rosa, Calif. and described in U.S. Pat. Nos. 4,851,775 and 5,239,264, which are incorporated herein by reference.

A data output circuit604is connected to microcomputer524for use, if desired, for telemetry about battery life. Thus, receiver data line554is provided to receive telemetry data which has been received from the transmitter by the receiver516and to send the data to the microcomputer524. Transistor601in the line554between the receiver516and the microcomputer524, resister603in series therewith, and resisters605and607in parallel therewith are suitably arranged, using principles commonly known to those of ordinary skill in the art to which this invention pertains, to adapt the data from the receiver516into a form acceptable to the microcomputer524.

Circuit650is connected to the microcomputer524via line652at pins654and655and to the PDA or display computer508via lines606and607to feed data to and from the direction finding (DF) unit506for providing compass and RSSI data to DF unit506via line606, as previously described, and for other purposes as more specifically described hereinafter. Line652includes transistor660(provided to achieve electrical compatibility with the input requirements of display computer508), resister662in series therewith between transistor660and pin654, and a pair of resisters664and666in series with and between transistor660and pin655. A resister668in parallel is connected to line652between transistor660and resister662. Line606is connected to the line652at a point between the transistor660and resister664, and line607is connected to the line652at a point between the resisters664and666. These circuit elements are suitably selected and connected, in accordance with principles commonly known to those of ordinary skill in the art to which this invention pertains, to achieve the objectives described hereinafter.

Microcomputer terminal or pin655feeds data to the direction finding (DF) unit506for “stimulating” the DF unit506. The DF unit506has no “power on/off” switch and normally “sleeps” to conserve battery power. When the display computer508turns on, it is programmed, as previously discussed, to send a message (any message will work) to pin655to “wake up” the DF unit506to energize all internal circuits required for normal (non-sleep) operation. The message is periodically re-transmitted by the display computer508to maintain the “on” condition of the DF circuits. If no message is detected by the DF unit for a period of approximately 5 seconds, the DF unit506“assumes” that the display computer508is turned “off,” and it therefore turns off all internal DF circuits and returns to “sleep” mode to conserve battery life.

The signal produced by the display computer508at pin655normally consists of a negative voltage that periodically pulses to a positive voltage to indicate that the display computer508is turned on. The message from the DF unit506to the display computer508must also contain a negative voltage since this is required by the circuits inside the display computer508. No source of negative voltage is provided by the DF unit506since such would increase the design complexity and reduce the battery life of the DF unit506. Alternatively, the negative voltage that is generated by the display computer508on pin655is “robbed” or provided for use by resister664to provide the negative voltage for the DF output message.

Circuit700provides the power supply, comprising a 3.0 volt, nominal battery701(two AAA cells) and a 5 volt power supply integrated circuit (IC)702for the direction finder (DF) unit506, the positive terminal of the battery701being connected to the IC pin705via line703, and a capacitor707being in parallel with the battery701. IC702is enabled or disabled by the microcomputer524via line708connecting IC terminal or pin710to microcomputer pin712. A power supply switch includes diodes704and706. A line714, which contains diode704, connects line703(hence connects IC pin705and battery701) to microcomputer pin716. A line718, which contains diode706, connects IC pins720to line714(hence to microcomputer pin716). Grounded fixed and variable capacitors722and724respectively are disposed along line718between the IC702and the diode706. Grounded fixed and variable capacitors726and728respectively are disposed along line714between the microcomputer524and the diodes704and706. A line730, which contains a resistor732and which has grounded fixed and variable capacitors734and736, connects line718at a point between the capacitors722and724(hence connects IC pins720) with microcomputer pin738.

The power supply IC702accepts an input voltage at pin705from battery701along line703which is as low as 1.8 volts DC and boosts the voltage by a factor of 3. The resulting voltage is then regulated down to about 5 volts DC, for use by the various circuits in the direction finding unit506.

In order to allow continuous operation of the microcomputer524while the IC702is turned off (disabled via line708), an alternative power source is provided by the diodes704and706. When IC702is turned off, power to the microcomputer524is provided by diode704directly from the battery701along line714to microcomputer pin716. When the microcomputer524is then turned on as a result of a stimulus from the display computer508detected on microcomputer pin655, the microcomputer524enables the power supply IC702by driving microcomputer pin712to a positive voltage for delivery along line708to IC pin710. Once the IC702is thus turned on, power for the microcomputer524is provided by IC pins720along line718containing diode706and to microcomputer pin716.

The microcomputer524desirably will run down to a supply voltage as low as about 2 volts and as high as about 5 volts. While in “sleep” mode, the supply voltage is desirably about 2.5 volts from the battery701via line714to microcomputer pin716. When IC702is enabled, the supply voltage therefrom at pins720along line718to microcomputer pin716is desirably about 4.5 volts. These voltages can be suitably designed into the power supply circuit700using principles commonly known to those of ordinary skill in the art to which this invention pertains. A second power supply input at microcomputer pin738from line730and IC pins720, whose purpose is to provide separate power for the internal circuits of the microcomputer524that are only required to measure the RSSI signal, is only required when the direction finding unit is turned on, so it does not require any “sleep” power source. A suitable power supply IC702is one identified as TPS60140, sold by Texas Instruments of Dallas, Tex.

An RC circuit750(comprising a grounded resistor752and a grounded capacitor754in parallel and providing an input at microcomputer pin756along line758) is provided as a power-on reset circuit, i.e., the circuit750provides a slight time delay between installation of the battery701and computer start-up.

The latch mechanism514and the connector504, which is of a quick-disconnect type, allow the display computer508and the directional antenna502of the indicator or display assembly500to be easily detached from the direction finder unit506when the assembly500is not being used, thereby to facilitate storage and transportation. These connectors504and514are conventional items, a suitable connector504being, for example, a BNC connector marketed by Digikey Corporation of Thief River Falls, Minn., and a suitable connector514being, for example, part number 300-0187, marketed by Northstar Systems, Inc. of Rancho Cucamonga, Calif.

The sensitivity of the directional antenna502has various values depending on the direction of the transmitted signal in relation to the direction of the antenna502. Maximum sensitivity occurs when the directional antenna502faces directly towards the radio transmitter60. Minimum sensitivity occurs when the directional antenna502faces directly away from the radio transmitter60. Intermediate directions will exhibit intermediate values of antenna sensitivity. Such a directional antenna may be one provided by Hygain Corporation of Starkville, Miss.

The display computer508is a conventional item of consumer electronics typically called a PDA (personal digital assistant). The PDA508is modified by the present invention by the installation of a software program, illustrated at700A and700B inFIGS. 32 and 33respectively, that enables its use as a display computer. Such a PDA may, for example, be one identified by no. M505 and marketed by Palm Corporation of Santa Clara, Calif.

The display program700(includes700A and700B) that is installed in the display computer508accepts the message produced by the direction finder506and transmitted over line606and uses the data to generate a polar plot graphical display, illustrated at702inFIG. 34E. The display program700has two modes of operation, i.e., acquire mode, illustrated at700A inFIG. 32, and display mode, illustrated at700B inFIG. 33. The display program700uses the touch-sensitive screen510in the PDA508to switch between these two modes of operation.

In the acquire mode700A, the display program stores data about signal strength and signal direction at various directional orientations of the antenna502until enough information is obtained to generate the complete polar plot display702. During the acquire mode700A, the user must slowly rotate the display unit500through a 360-degree circle to allow acquisition of this data.FIGS. 34A,34B,34C, and34D illustrate generally at704A,704B,704C, and704D respectively acquire displays at various stages (start, ⅓ complete, ⅔ complete, and completed) in the progress of performing the 360-degree rotation.

In the display mode700B, the data obtained during the acquire mode700A is analyzed and used to generate the complete 360-degree polar plot graphical display702(FIG. 34E). After receipt of the data message606from the direction finder506, as illustrated at706, the message606is broken down to extract the North-South compass sensor data708, the East-West compass sensor data710, and the RSSI data712, as indicated at714,716, and718respectively. In order to correct for errors caused by the proximity of magnetic materials that may be used in the display computer508and the direction finder506, numerical correction factors, illustrated at720and722, are applied to the North-South compass sensor data708and the East-West compass sensor data710respectively to obtain corrected North-South compass sensor data724and the East-West compass sensor data726, as illustrated at728and730respectively. The corrected North-South compass sensor data724is then divided by the East-West compass sensor data726, as illustrated at732, to yield a numeric value equal to the tangent of the compass heading, illustrated at734. The arctangent is then calculated, as illustrated at736, to obtain the actual compass heading, illustrated at738, expressed in degrees. The compass heading738is then rounded off to the nearest 10 degree increment, as illustrated at740. The resulting rounded off compass heading742is then divided by 10, as illustrated at744, to yield a table pointer746, i.e., a number ranging from 0 to 35.

In the acquire mode, the RSSI data712is stored in a numeric array of dimension 1×36. The compass number746(0 to 35) is now used to identify which element in the array should receive the RSSI data712contained in the message. Once the element is identified, the RSSI data712is moved to that array element, as illustrated at748, thereby providing table entry750.

The starting point for X and Y values for a vector, illustrated at752inFIGS. 34B,34C, and34D, representing the data contained in the message606, are selected for the center, illustrated at754inFIG. 34B, of the screen510. The North-South compass sensor data708and the East-West compass sensor data710are now each multiplied by the RSSI data712to re-scale the length of the vector752to be drawn and are further multiplied by a constant numeric value selected to ensure that the resulting vector length does not exceed the limits of the display screen510on the PDA508. The values for the X and Y co-ordinates for the center of the screen510are then added to the resulting (re-scaled and magnitude corrected) North-South and East-West compass sensor values, and the resulting values are then used to define the end point, illustrated at756inFIGS. 34B,34C, and34D, for the vector752to be drawn on the screen510. Now that the X and Y values for the starting and ending points754and756respectively of the vector are identified, the individual vector752for the individual message606is drawn by the program700A on the graphical LCD display510, as illustrated at758, and this indicates to the user that readings have already been obtained for the particular compass bearing.

The acquire program700A then checks to see if the touch-sensitive screen510has been activated, as illustrated at760, which would indicate that the user wishes to switch to the display mode700B. If no such activity has occurred, the acquire program700A loops to the beginning, as illustrated at762, and repeats the process for the next message606coming from the direction finder506. If the screen510has been activated, the acquire program700A exits to the display program700B, as illustrated at764inFIGS. 32 and 33.

Referring toFIG. 33, the data previously stored in the 1×36 numeric array is now used to generate a complete polar plot graphical display, illustrated at766inFIG. 34E, of signal strength versus signal direction. This is achieved by drawing36individual line segments (one such line segment illustrated at768inFIG. 34D) each segment joining the tips756of two adjacent vectors752.

The X and Y values for the starting and ending points (which are points756for two adjacent vectors752) must be identified before each line segment768can be drawn on the screen510of the display computer508. Once these points are identified, the line segment768can be drawn, and the display program700B proceeds to the next line segment768. This process is repeated for a total of 36 times, yielding 36 line segments768joining 37 vector points756, resulting in the display line766.

The display program700B begins by resetting an index pointer770, as illustrated at772, to a value of zero, which then points to the RSSI value712(stored in the 1×36 array) for a compass heading of zero degrees. This is only performed once when the display program700B begins.

The index value770is used to calculate the sine and cosine of 0 degrees, as illustrated at774, and these resulting values are stored in the values for starting X and starting Y, illustrated at776and778respectively, for the line segment yet to be drawn. These X and Y values are then multiplied by the RSSI value for 0 degrees (found in the 1×36 array) to adjust the radial distance from the center754of the screen510to the starting point756of the line segment768. The starting point X and Y values776and778respectively are further multiplied by a constant numeric value selected to ensure the resulting vector length does not exceed the limits for the display screen510on the PDA508. Then the X and Y co-ordinates for the center754of the screen510are added to the X and Y values for the starting point to translate them to their proper positions on the display screen510, resulting in adjusted starting point X and Y co-ordinates782and784respectively for the particular line segment768now being identified.

The index value770, which was 1, is now incremented, as illustrated at786, to point to the next entry788in the 1×36 data array, i.e., a value of 2, with a compass heading of 10 degrees.

The incremented index value788is used to calculate the sine and cosine of the new compass heading (10 degrees), as illustrated at790, and these values are stored as the values for ending X and ending Y, illustrated at792and794respectively, for the line segment768still to be drawn. These X and Y values792and794respectively are then multiplied by the RSSI value for the new index value788(in this case, 10 degrees) (found in the 1×36 array) to adjust the radial distance from the center754of the screen510to the ending point of the line segment768. The ending point X and Y values792and794respectively are further multiplied by a constant numeric value selected to ensure that the resulting vector length does not exceed the limits of the display screen510on the PDA508. Then the X and Y co-ordinates for the center754of the screen510are added to the X and Y values for the ending point to translate them to their proper positions on the display screen510, as illustrated at800, resulting in adjusted ending point X and Y co-ordinates796and798respectively for the particular line segment768now being identified.

Since the adjusted start and ending point X and Y co-ordinates have now been identified, the program700B now draws the corresponding single line segment768connecting the tips756of the vectors752for, in this case, 0 and 10 degrees, as illustrated at802.

The index pointer770is now tested to see if all 36 segments have been drawn, as illustrated at805. If not, the program700B loops to the beginning and repeats the process described above to draw the next line segment768. This time (and during subsequent times) the index770is not re-set to zero and the process is repeated with a starting point of 10 degrees (20 degrees next time, etc.) instead of 0 degrees. The next iteration of the program loop therefore draws a line segment connecting the tips of the vectors for 10 and 20 degrees. This process is repeated 35 more times until the index value770equals a value of 36, indicating that all 36 line segments768have been drawn and the polar plot graphical display766is finished.

Once completion of the display766is completed, the display program700B checks to see if the touch-sensitive screen510has been activated, as illustrated at806, which would indicate that the user wishes to switch to the acquire mode700A. If no such activity has occurred, the display program700B loops endlessly, as illustrated at808, waiting for an input to the touch-sensitive screen510. There is no reason to repeat the drawing process since the hardware in the display computer508will retain the image766previously drawn indefinitely. If the screen510has been activated, the display program700B exits to the acquire program700A, as illustrated at810inFIGS. 32 and 33.

As seen inFIG. 34E, the pattern766of joined line segments768will indicate a direction in which the signal is the strongest. InFIG. 34E, the direction of greatest signal strength is indicated to be North, as illustrated at812. The hunter110can then head in that direction looking for the deer113and, if need be, use the display unit500again until the deer is found.

Referring toFIG. 37, there is shown generally at900an alternative embodiment of the circuitry for the direction finding unit506, which includes an alternative receiver902which employs a fully integrated 916 MHz receiver integrated circuit or chip904, which may, for example, be one identified as part no. TDA5212, sold by Infineon Corp. of San Jose, Calif. By “fully integrated” is meant that a single silicon chip comprises the entire receiver, without the need for additional chips or semiconductors to achieve a working receiver, although additional chips or semiconductors may be employed to enhance its performance. This receiver902is a single conversion superhetrodyne type with a 10.7 MHz intermediate frequency and high-side injection of a crystal controlled local oscillator. The local oscillator employs a phase-locked-loop which multiplies the crystal frequency of 14.484375 MHz by a factor of 64 to achieve a final local oscillator frequency of 927.00 MHz. This local oscillator signal is then mixed with the transmitter signal (after amplification, as discussed hereinafter) which operates at a transmitter frequency of 916.300 MHz. The result of the “mixing” yields the intermediate frequency signal of 10.7 MHz (927.00-916.30). The intermediate frequency signal is then passed through a 10.7 MHz quartz crystal filter, illustrated at908, with a bandwidth of approximately 30 KHz to reduce the amount of noise present in the signal and thereby increase the receiver sensitivity. The 10.7 MHz intermediate frequency signal is then amplified by several amplifier stages inside the Infineon chip904to achieve an overall maximum signal sensitivity (measured at the antenna) of somewhere between −110 and −120 dbm (0.2 to 0.7 microvolts). The amplifier stages inside the Infineon chip904automatically generate the RSSI signal that is employed to drive the rest of the direction finding unit506. The crystal controlled local oscillator, phase-locked-loop, mixer, intermediate frequency amplifier, and RSSI circuits are all contained inside the Infineon chip904. The quartz crystal906(that determines the radio channel frequency) and the quartz crystal filter908(that determines the channel width) are external to the Infineon chip. Preferably, the receiver902includes a preamplifier integrated circuit or “low noise amplifier,” illustrated at910, between the antenna504and the input to the infineon IC904to increase the operating range for the direction finding unit900(possibly as great as a mile or more) or provide increased reliability under adverse circumstances (such as a prey animal lying on top of the transmitter). A suitable chip for preamplifier IC910is part no. UPC8211TK, marketed by California Eastern Laboratories of Santa Clara, Calif. (North American sales and marketing partner of NEC Corporation. The preamplifier IC910utilizes a 3 volt power supply, which is provided by a 3 volt DC regulator integrated circuit912. A suitable chip for IC912is part no. TPS76030, marketed by Digikey Corporation of Thief River Falls, Minn. The receiver516(FIG. 24) may also be provided with such a preamplifier IC. The direction finding unit900as described above and as illustrated inFIG. 37may be made and used by one of ordinary skill in the art to which this invention pertains using principles commonly known to those of ordinary skill in the art to which this invention pertains.

Appended hereto and incorporated herein by reference are copies of the source code for certain programs as follows. The code for the program for the “loop” transmitter microcomputer402(FIG. 23) is labeled “G2A_LP.asm” and comprises 3 sheets. The code for the program for the “fishhook” transmitter microcomputer308(FIG. 22) is labeled “Arrow Transmitter Program” and comprises 2 sheets. By inspection thereof, it can be seen that the code for this program is written to be identical (or substantially identical) to the aforementioned “loop” transmitter program labeled “G2A_LP.asm”, i.e., the same code is provided for both the “loop” and “fishhook” transmitters. The code for the program for the direction-finder microcomputer524is labeled “PF—50A.asm” and comprises 17 sheets. The above programs are written in PIC Assembly language. A suitable IBM program to employ the above programs is the PIC IDE (integrated Development Environment) and PIC ASM assembler, available at the website: http://www.microchip.com/. The code for the PDA display program700A and700B (FIGS. 32 and 33respectively) is labeled “Pda” and comprises 32 sheets. This program is written in NSBasic for Palm. A suitable IBM program to employ it is the NSBasic for Palm IDE which is available at http://www.nsbasic.com/palm/.

It should be understood that, while the present invention has been described in detail herein, the invention can be embodied otherwise without departing from the principles thereof. For example, while the preferred embodiment of the present invention refers to 3 hooks or 3 point heads, it is envisioned that another number thereof may also be provided suitably symmetrically about the housing or that another number may be provided and symmetry and balance achieved in a different way. Such other embodiments are meant to come within the scope of the present invention as defined by the appended claims.