Abstract:
A portable system for measuring and positioning a football on the playfield is revealed. The system measures ultrasonic sound wave propagation delay and relates it to yardage. It corrects for wind errors by sending ultrasonic waves in both directions on the playfield and measures the difference.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Methods for determining the location of a football on the playfield are out of date and can be advanced by the introduction of modern technology. The use of chains to determine the distance left for a first down, and the use of eyeball judgment when centering the ball, can be modernized.  
         [0002]     Some attempts at modernizing have been made but fall short because of their bulky arrangement, long cables, expensive apparatus, or fixed base requirements. A completely portable, quickly deployable system using inexpensive technology would be a great addition to the game. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0003]     The system uses ultrasonic sound wave propagation delay as a means of measuring distance. It is composed of a portable unit carried by the official during the game, a group of Repeater Beacons placed around the perimeter of the playfield, and a base station located on the sideline.  
         [0004]     After being set up as described above, the system is calibrated by taking the portable unit to a corner of the playfield at the end zone. It is triggered and an RF pulse and an ultrasonic pulse are emitted. The RF pulse alerts the Repeater Beacons and Base Unit that a measurement is under way. As each Repeater Beacon detects the ultrasonic wave, it retransmits an RF pulse, each on a separate frequency. When the Base Unit receives the initial RF pulse from portable unit, it starts a high speed counter. As the RF pulse from each of the Repeater Beacons is received, the count is recorded.  
         [0005]     This is repeated at the other three corners of the playfield. The maximum and minimum delay time is now known as the portable unit is at its farthest and nearest point on the playfield from each of the Repeater Beacons. This data is converted into a mathematical algorithm by the Base Unit which relates these counts to playfield yardage.  
         [0006]     When the game begins, the official can determine the location of the ball simply by placing the portable unit next to the nose of the ball and triggering it. The exact location of the ball is known and other measurements can be extracted, such as, the distance to go for a first down, total yardage, etc.  
         [0007]     The system can be placed in a constant measurement mode that aids the official in centering the ball when a play ends out of bounds.  
         [0008]     To compensate for errors entered into the system by wind, each of the Repeater Beacons can send out an ultrasonic burst of their own, each on a separate frequency, and be detected by the beacon on the other end of the playfield. The difference between the two propagation delays will be caused by the wind and is extracted from the measurement by factoring it into the algorithm.  
         [0009]     The system does not require the playfield to be 100 yards long, 50 yards wide, or proportional to a regulation football field. It simple converts whatever distance is used during calibrated as the limits of the playfield and divides it up as if it were of regulation size (center of the field is called the 50 yard line, i.e.).  
       PRIOR ART  
       [0010]     U.S. Pat. No. 5,446,701 (Utke) describes a similar system but uses a reference receiver as an integral part of the measurement apparatus, not required in the system revealed here. The system revealed in this document eliminates the need for a reference receiver by adding the calibration step referred to in Claim  6 . U.S. Pat. No. 5,446,701 also lacks the ability to accurately detect and compensate for errors created by wind as described in Claim  10  of this document, by measuring its effects in the long axis of the field where accuracy is needed. U.S. Pat. No. 5,446,701 also defines the location of the object being located in cylindrical and elliptical cylindrical coordinates, as opposed to simple Cartesian coordinates better suited to the use of trigonometric and algebraic principles for deriving ball position. The system revealed in this document also provides for measurement redundancy by making measurements from both end zone corners to both opposite end zone corners.  
         [0011]     U.S. Pat. No. 5,346,210 (Utke) describes another similar system which relies on a calibration source or reference receiver, not needed in the system reveal in this document because of the information gained in the calibration step described in Claim  6 . U.S. Pat. No. 5,346,210 Claim 1 describes a system requiring sensors to pick up ultrasonic signals as opposed to cordless repeater beacons as described in this document, which are more easily deployed. U.S. Pat. No. 5,346,210 Claims 21 and 31 describe different configurations using delay circuits, not required in the system revealed in this document.  
         [0012]     U.S. Pat. No. 4,675,816 uses an RF radio beacon and triangulation from rotating antennas. It does not use ultrasonic sound.  
         [0013]     U.S. Pat. No. 6,851,198 uses a laser for measurement instead of ultrasonic wave delay time.  
         [0014]     U.S. Pat. No. 6,778,283 describes an optical system not related to this concept.  
         [0015]     U.S. Pat. No. 4,989,341 describes a mechanical system with a chain and optical window, also not related to this concept.