Patent Publication Number: US-6670917-B1

Title: Balanced integrated position determination system and communication system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This patent application is a Continuation-in-Part of commonly owned U.S. patent application Ser. No. 09/388,035, filed on Sep. 1, 1999 now abandoned entitled “POSITION DETERMINATION SYSTEM AND RADIO IMPLEMENTED ON A POLE,” by Crothall et al., which is a Continuation of U.S. patent application Ser. No. 08/791,190, filed on Jan. 31, 1997, now U.S. Pat. No. 6,072,429 by Crothall et al., and entitled “INTEGRATED POSITION DETERMINATION SYSTEM AND RADIO TRANSCEIVER INCORPORATING COMMON COMPONENTS.” 
    
    
     TECHNICAL FIELD 
     The present claimed invention relates to the field of position determination systems. More specifically, the present claimed invention relates to an improved position determination device and radio relay device. 
     BACKGROUND ART 
     A typical differential global positioning system (DGPS) network includes a receiver which receives ephemerides data from satellites. Typically, such data is received from global positioning system (GPS) satellites which are a part of the GPS satellite network or satellites which are a part of the Global Navigation Satellite System(GLONASS). The ephemerides data is processed via an electronics package located within the GPS unit. The GPS unit receives differential correction data through a separate radio which is typically connected to the GPS unit by cable. The differential correction data is typically obtained from a radio coupled to a GPS unit which is located at a fixed site which is placed at a known location or it is obtained from other sources and is conveyed via radio. By processing the differential correction data together with the data received at the particular GPS receiver, the location of the GPS unit may be determined within a high degree of accuracy. This same method may be used to perform real time kinematic (RTK) surveys so as to accurately determine the relative position of the GPS system with sub centimeter accuracy. 
     Prior art GPS devices used in DGPS applications and RTK applications typically require numerous separate, distinct component units which are connected via cables. For example, the GPS receiver and processor would constitute one unit and the terrestrial radio would constitute a second unit which would be coupled to the GPS processor via cable. Typically, an input/output (I/O) unit which includes a display for data monitoring and a keypad for data input is also required. The I/O unit is coupled to the GPS receiver/processor unit and to the terrestrial radio via cable. Some systems also require the attachment of a separate battery via cable. Because multiple separate units are used in these prior art systems, the systems are bulky and they are difficult to move around. 
     For example, one type of prior art system which is typically referred to as “handheld” includes a GPS antenna, a GPS processor, a display processor, and a display in a single unit. A DGPS radio antenna and receiver are provided in a separate unit or units which are connected to the GPS processor. Another type of prior art system places the GPS antenna in an antenna unit and the display in a separate display unit. The GPS processor and the display processor may be contained in the GPS antenna unit, the display unit, or in a separate unit. A DGPS radio antenna and receiver are provided in a separate unit or units connected to the GPS processor. This format allows the user to separate the GPS antenna and the display units so that the GPS position and time information can be observed and operated upon in a protected environment. 
     The use of multiple units to house the various components required for prior art DGPS systems, and the requirement for cables and connectors to couple the units creates problems regarding reliability and durability. This is particularly true for DGPS systems which are mobile and which are jarred and shaken by use and movement. In addition, the systems are expensive to manufacture and assemble. Furthermore, the connections are often bulky, expensive and prone to breakage or malfunction. In addition, it is difficult to move the various boxes and cables around. 
     Typically, the GPS unit receivers are separated by long distances or by immobile structures; therefore, radio relay units are used to get the signal from one GPS unit to anther GPS unit. Prior art radio relay systems for relaying GPS signals typically include multiple separate components such as a transceiver operating at one frequency which is coupled via cable to a separate transceiver operating at a second frequency. These relay systems typically receive signals through an antenna which is cabled to a processor which is then cabled to a radio which rebroadcasts the signal through an antenna attached by cable to the radio. These relay systems are bulky and difficult to move around. Furthermore, these relay systems typically are expensive and are difficult to maintain and operate due to the fact that each of the components of the radio relay system is unique. In addition, most of the currently available systems are not durable and reliable enough for applications such as RTK surveying and operation in harsh environments such as construction sites. 
     Some recent prior art systems include GPS components that are attached to a range pole. However, in these recent prior art systems, much of the weight is located at or near the top of the range pole. This makes the system difficult to carry around and operate because the system tends to tip over. This can damage the system if it results in the operator dropping the system. At a minimum, this results in operator muscle fatigue because the operator has to constantly fight the system&#39;s tendency to tip over. 
     What is needed is a simple GPS network which is easy to move from place to place and which is durable, reliable, and inexpensive to manufacture and assemble. More specifically, a GPS network which includes a GPS unit, a radio and a radio relay which will reliably operate in difficult environments such as those presented by repeated movement and use in harsh environments such as construction sites is required. Also, a GPS network consisting of components which are easy to operate, use and maintain is required. Moreover, a system is needed that is mounted on a range pole and that does not easily tip over or produce operator muscle fatigue. 
     DISCLOSURE OF THE INVENTION 
     The present invention meets the above need with a position determination system which includes a position determination device which can be easily moved and which can be easily and cheaply manufactured and assembled. The above achievement has been accomplished by using a single integrated structure to house the position determination antenna the GPS receiver, a power conditioning system, the position determination processor, and the DGPS radio antenna and DGPS radio circuit board. The position determination device may be easily converted to a radio relay by altering the components located within the housing. The resulting position determination network includes an integrated position determination device and radio relay combination which will reliably operate in difficult environments and which is easy to operate, use and maintain. 
     A position determination network which includes all of the elements required for DGPS position determination and RTK is disclosed. The network includes a position determination device which holds all of the components necessary for position determination and RTK using DGPS techniques within a single housing. Though the position determination system may be operated using any of a number of different sources of telemetry signals such as GLONASS and the like, the positioning system will be herein described with reference to the use of GPS satellites for purposes of clarity. The GPS satellites include information on the ephemerides of each GPS satellite, parameters identifying the particular GPS satellite, and corrections for ionospheric signal propagation delays. A useful discussion of the GPS and techniques for obtaining position information from the satellite signals is found in Tom Logsdon,  The Navstar Global Positioning System , Van Nostrand Reinhold, 1992, pp. 17-90, incorporated by reference herein. Reference to a Global Positioning System or GPS herein refers to a Global Positioning System, to a GLONASS system, and to any other compatible satellite based system that provides information by which an observers position and/or the time of observation can be determined. Further information regarding GPS position determination is contained in U.S. Pat. No. 5,519,620 by Nicholas Talbot et al. entitled CENTIMETER ACCURATE GLOBAL POSITION SYSTEM RECEIVER FOR ON-THE-FLY REAL TIME KINEMATIC MEASUREMENT AND CONTROL which is incorporated herein by reference. 
     The term “DGPS” as used herein and “DGPS radiowave” signal as used herein includes electromagnetic signals containing GPS differential correction information transmitted by other GPS units and/or systems, by the Coast Guard DGPS network, by radio beacon signals, by FM subcarrier signals, by digital subcarrier on an analog two-way radio, by digital radio signals, by cellular telephone signals, by digital cellular telephone signals, by private and semi private network signals that use terrestrial and/or satellite apparatus for transmitting DGPS signals for correction of the GPS location and/or time information. 
     A first embodiment includes a GPS antenna, GPS/DGPS processing circuitry, a radio and a radio antenna. A power supply battery is placed into a cylindrical pole which is attached to the bottom of the housing so as to form a complete, portable, self-contained GPS system. A display panel includes an on/off switch and lighted indicators. A separate display unit is coupled to the GPS unit for display of position information. Communication between the display unit and the GPS unit may be by cable, communication link, or infrared methods. The separate display unit contains its own power source. However, in one embodiment, the display unit is powered by the GPS unit through the GPS unit&#39;s power supply. 
     A second embodiment is disclosed in which a tripod base instead of a pole is mounted to the housing. The tripod base includes a location mechanism which is used to precisely locate the GPS system with respect to a monument. The location mechanism may be a prismatic optical finder, a laser optical finder, a fixed height tripod, or a laser finder implemented in a tripod with a fourth leg. The tripod base includes a battery pack mounted on or within the tripod. This second embodiment may be used to precisely align a GPS system over a given reference point such as an United States Geological Survey (USGS) site. This allows for easy precise location of a GPS system. The housing and all of the components within the housing are the same as those disclosed in the first embodiment. Thus, the parts are interchangeable. This allows for economies of scale in manufacturing, easy assembly and maintenance, and allows for flexible use of the position determination network components in multiple applications. 
     In a third embodiment a radio relay unit is disclosed which uses many of the same components as do the first two embodiments. The radio relay unit includes a radio antenna, radio processing circuitry, and a power supply. A transceiver may be installed into the radio relay unit for transmitting and receiving DGPS correction information at the same frequency, or at a different frequency. DGPS correction information may be transmitted either from a second GPS unit or from other sources. This correction data may then be received directly by a GPS unit. Alternatively, the correction data may be received by a radio relay unit which then rebroadcasts the correction information. A GPS unit then receives the rebroadcast correction information on the radio contained within the GPS unit. Alternatively, multiple relay units may be used to transmit correction information over larger distances. Since the radio relay unit uses many of the same components used in the GPS unit, components between the first two embodiments and the third embodiment may be used interchangeably. In addition, the batteries, poles and tripods may be used interchangeably depending on the requirements of a particular project. 
     A position determination network which includes both the first, the second, and the third embodiments of the present invention is also disclosed. In this network a first GPS system consisting of a GPS unit mounted on a tripod is used as a base station and is located over a known location using the finder located in the tripod. A radio relay system composed of a radio relay unit mounted on a tripod is located within radio range from the first GPS system. A second radio relay system is placed near the site where locations are to be determined. Additional radio relays may be used to extend the range even further. A GPS system including a GPS unit mounted on a pole is then used to pinpoint the desired geographic location or locations. 
     Since the GPS antenna, GPS radio circuitry, GPS and DGPS processing circuitry, power conditioning system, radio, and radio antenna are integrated into a single housing, a GPS system which is easy to move, easy to use, and easy to assemble and disassemble is obtained. In addition, a more durable and reliable GPS unit results due to the shielding and protection of the various components resulting from the integration of the various components into a single housing. Since many of the components are common to both the GPS system and the radio relay system, the position determination network allows for inexpensive manufacturing of the required components. The GPS system and the radio relay system are easy to assemble and easy to repair due to the usage of a common assembly scheme and due to the use of common components. In addition, due to the design of the system and since a single housing is used, the GPS system and the radio relay system are more reliable and durable than the multiple cable connected units found in prior art systems. 
     In one embodiment, an integrated position determination system and communication system is described that includes a range pole and in which the various components are coupled to the range pole such that the system is both horizontally and vertically balanced. Because the system is both horizontally and vertically balanced, when a user grips the range pole, there is no tendency for the system to tip over. This prevents potential damage to the system from the system falling over and minimizes or eliminates muscle fatigue as typically occur with prior art systems. 
     These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the various drawing figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention: 
     FIG. 1 is a perspective view of an integrated GPS and radio relay system in accordance with the present invention. 
     FIG. 2 is a diagram of a integrated GPS and radio relay system in accordance with the present invention. 
     FIG. 3 is a cut away side-sectional view of the integrated GPS and radio relay system of FIG. 1 in accordance with the present invention. 
     FIG. 4 is an exploded view of a integrated GPS and radio relay system in accordance with the present invention. 
     FIG. 5 is a expanded view illustrating a magnesium housing and the components located within the magnesium housing in accordance with the present invention. 
     FIG. 6 is perspective view of a GPS unit mounted onto a tripod in accordance with a second embodiment of the present invention. 
     FIG. 7 is a perspective view of a radio unit mounted to a tripod in accordance with the present invention. 
     FIG. 8 is a diagram of a radio relay unit mounted to a tripod in accordance with a third embodiment of the present invention. 
     FIG. 9 is an exploded view of a radio relay unit mounted to a tripod in accordance with a third embodiment of the present invention. 
     FIG. 10 is a cut-away side-sectional view of the radio relay system of FIG. 7 in accordance with the present invention. 
     FIG. 11 is a schematic view of a network which incorporates the first embodiment and the second embodiment and the third embodiment in accordance with the present invention. 
     FIG. 12 is a flow chart illustrating a method for forming a balanced integrated position determination system and communication system in accordance with one embodiment of the present invention. 
     FIG. 13 is a upper right front perspective view of a balanced integrated position determination system and communication system in accordance with the present invention. 
     FIG. 14 is lower left rear perspective view of a balanced integrated position determination system and communication system in accordance with the present invention. 
     FIG. 15 is a right side elevational view of a balanced integrated position determination system and communication system in accordance with the present invention. 
     FIG. 16 is a front elevational view of a balanced integrated position determination system and communication system in accordance with the present invention. 
     FIG. 17 is a left side elevational view of a balanced integrated position determination system and communication system in accordance with the present invention. 
     FIG. 18 is a rear elevational view of a balanced integrated position determination system and communication system in accordance with the present invention. 
     FIG. 19 is a top plan view of a balanced integrated position determination system and communication system in accordance with the present invention. 
     FIG. 20 is a bottom plan view of a balanced integrated position determination system and communication system in accordance with the present invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention. 
     FIG. 1 shows GPS system which includes GPS unit  101  which is mounted onto pole  102 . GPS unit  101  includes housing  12  which mates with low noise amplifier housing  4 (not shown) and radome  1  to enclose the various internal components of GPS unit  101 . Bumper ring  18  and bumper  19  absorb shock from dropping or moving GPS unit  101 . Pole  102 , along with GPS unit  101  forms a single integral GPS system which can be easily moved from place to place. All of the electronics for location determination using DGPS correction information are located within the GPS unit  101  and pole  102 . Display panel  200  includes lighted indicator  202 , lighted indicator  203  and lighted indicator  204  and on/off switch  201 . Lighted indicators  202 - 204  indicate conditions such as, for example, “power on,” “radio operational,” and “receiving correction data.” Display panel  200  could include any of a number of other configurations and could include indications of signal strength, accuracy, communication quality, etc. In addition, display panel  200  may indicate satellite lock. A separate display unit  900  including display  901  is coupled to GPS unit  101  for display of location and correction data. 
     FIG. 2 shows GPS antenna  3  to receive ephemerides from satellite  110 , satellite  111  and satellite  112  as shown by arrows  113 - 115 . Antenna  3  receives ephemerides on two separate frequencies so as to obtain two sets of signals or “channels.” One set of signals is transmitted to low noise amplifier  5  as illustrated by arrow  117  and the other set of signals is transmitted to low noise amplifier  6  as shown by arrow  118 . Electrical signals are amplified by low noise amplifier  5  and the resulting signal is transmitted to GPS radio frequency circuit board  22  as shown by arrow  119 . Similarly, low noise amplifier  6  amplifies the incoming signals and transmits them to GPS radio frequency circuit board  22  as indicated by arrow  120 . GPS radio frequency circuit board  22  contains radio reception and transmission circuitry which then transmits the signals as shown by arrow  121  to digital circuit board  23 . Digital circuit board  23  contains logic for processing GPS ephemerides and correction information so as to determine the exact position of the GPS system. Radio antenna  10  receives radio broadcasts as illustrated by arrow  128  which contains DGPS error correction information from radio relay  700  which is transmitted to radio circuit board  25 , as shown by arrow  126 . However, error correction information may be received from any of a number of other sources. Radio circuit board  25  includes electronic circuits for broadcasting and receiving radio signals. Radio circuit board  25  processes the signal and transmits the signal to digital circuit board  23  as shown by arrow  131 . Using the error correction data in combination with the ephemerides received from satellites  110 - 112 , digital circuit board  23  calculates the position with greatly increased accuracy. In one embodiment, error correction data includes calculated pseudoranges. In a RTK system, error correction data includes carrier phase data and pseudoranges. The position may then be displayed on display unit  900 . 
     Continuing with FIG. 2, when GPS unit  101  is used to determine error correction, digital circuit board  23  determines the correction information using known location information. The known location information may be input using display unit  900 . The correction information is then sent, as shown by arrow  132  to radio circuit board  25 (connectors attached to power and I/O circuit board  24  route the signal directly). Radio circuit board  25  then broadcasts the correction information through radio antenna  10  as shown by arrow  127 . Radio signals are sent and received at a frequency of 2.44 GigaHertz. However, any of a number of other frequencies could be used. 
     Continuing with FIG. 2, power I/O circuit board  24  contains electronic circuitry for power management and transfer functions and regulates power to other components. Power I/O circuit board  24  is coupled to battery  41  as shown by arrow  145  and provides power and power management functions for the electronic components GPS unit  101 . Power I/O circuit board is directly coupled to radio circuit board  25  and digital circuit board  23  as shown by arrows  124 . An on/off switch on display panel  200  is connected to power I/O circuit board as shown by arrow  129  such that, by engaging the on/off switch, the GPS unit may be turned on and off. Input and output to external devices is coupled through I/O ports  13 - 15  as shown by box  140  and arrows  141  and  142 . Display unit  900  is coupled to GPS unit  101  through I/O ports  13 - 15  as shown by arrows  143 - 144 . 
     FIG. 3 shows GPS antenna  3  to be mounted onto ground plane  2 . Ground plane  2  lies over low noise amplifier housing  4  and is enclosed by radome  1 . Low noise amplifier housing  4  fits into housing  12 . Upper magnesium housing  8  is secured by flexible bumper  7  to low noise amplifier housing  4 . Insulating ring  282  fills the space between bumper ring  18  and low noise amplifier housing  4  and absorbs shock from bumper ring  18 . Bumper  19  is molded to bumper ring  18  and is a soft plastic material for absorbing shock and vibration. GPS antenna  3  is coupled to low noise amplifier  5  by semi-rigid coaxial cable  16  which couples to connector  250 . Connector  250  couples to receptacle  216  which is attached to low noise amplifier  5 . Similarly, semi-rigid coaxial cable  17  extends from GPS antenna  3  to connector  251 . Connector  251  mates with receptacle  217  which is attached to low noise amplifier  6 . Low noise amplifier  5  and low noise amplifier  6  are small circuit boards which attached to low noise amplifier housing  4  and which amplify portions of the GPS signal separately. Low noise amplifier housing  4  is formed of plastic and the bottom side of low noise amplifier housing  4  is coated with copper to create an electromagnetic interference (EMI) and radio frequency interference(RFI) enclosure so as to shield EMI and RFI emissions from and to low noise amplifiers  5 - 6 . Connector  214  attaches to the bottom of low noise amplifier  5  and couples cable  212  to bulkhead connector  210 . Bulkhead connector  210  engages a connector receptacle on GPS radio frequency circuit board  22  so as to electrically connect low noise amplifier  5  to GPS radio frequency circuit board  22 . Connector  215  attaches to a connector receptacle attached to the bottom of low noise amplifier  6  and couples cable  213  to bulkhead connector  211 . Bulkhead connector  211  engages a connector receptacle on GPS radio frequency circuit board  22  so as to electrically connect low noise amplifier  5  to GPS radio frequency circuit board  22 . 
     Continuing with FIG. 3, antenna  10  includes a parallel feed network which feeds patch antennas  44 - 51  ( 46 - 51  are not shown). Flexible bumper  11  supports lower magnesium housing  9  which mates with upper magnesium housing  8  so as to enclose digital circuit board  23 , power I/O circuit board  24 , radio circuit board  25 , GPS radio frequency circuit board  22  and ring  21 . Lower magnesium housing  8  and upper magnesium housing  9  are made of a magnesium which shields RFI and EMI emissions. In order to decrease weight, lower magnesium housing  9  and upper magnesium housing  8  do not completely enclose the top and bottom of the enclosure which they form. Metallic cloth  272  is attached, using adhesive to lower magnesium housing  9  and metallic cloth  271  is attached, using adhesive strips to upper magnesium housing  8 . Metallic cloth strip  270  attaches to both lower magnesium housing  9  and upper magnesium housing  10  so as to form the sides of the enclosure. Metallic cloth  271  and metallic cloth  272  and metallic cloth strip  270  may be made of a metallic cloth such as a nickel plated polyester . Connector  26  which mates with a connector receptacle located on power I/O circuit board  24  connects the circuit boards  22 - 25  to I/O port  13  (not shown), I/O port  14 , and I/O port  15  (not shown), display panel  200  and power source coupling  55  through cable  40 . Antenna  10  includes a connector receptacle which directly couples to connector  280  which mates with a connector receptacle located on radio circuit board  25  so as to connect radio circuit board  25  with antenna  10 . Power source coupling  55  electrically connects with battery  41  to provide power to GPS unit  101 . Provision for connectivity of additional components and units is obtained by I/O ports  13 - 15  which allow for additional components to be coupled to the GPS system such as display and input units and alternate power sources. 
     FIG. 4 shows housing  12  to include openings into which connector receptacles are disposed so as to form I/O ports  13 - 15 . Antenna  10  includes an omnidirectional parallel fed array of patch antennas  44 - 51 . It can be seen that lower magnesium housing  9  fits within bumper  11  and upper magnesium housing  8  fits within bumper  7  so as to shield the electronics within the enclosure formed by lower magnesium housing  9 , upper magnesium housing  8 , and magnetic cloth  270 - 272  from shock and vibration. Bumper ring  18  which is connected to bumper  19  dampens shock to GPS unit  101 . Bumper  19  and bumper ring  18  are particularly effective when GPS unit  101  is dropped as bumper  19  is likely to be the first part of GPS unit  101  to strike the ground. For example, vibrations resulting from such contact would be absorbed first by bumper  19  and any excess shock would be channeled through bumper ring  18  and absorbed by insulating ring  282 . Insulating ring  282  is made of a closed cell elastomeric foam such as Poron. 
     Continuing with FIG. 4, since lower magnesium housing  9 , upper magnesium housing  8 , and magnetic cloth  270 - 272  are made of material which reduces RFI and EMI emission, the enclosure which they form acts as a RFI and EMI shield. The use of bulkhead connectors  210 - 211  eliminates the need to have openings in upper magnesium housing  8  for cables to couple low noise amplifiers  5 - 6  to GPS radio frequency circuit board  22 ; thereby increasing the shielding effect. Bolts  19  extend through upper magnesium housing  8  and lower magnesium housing  9  and mate with nuts  25  so as to secure upper magnesium housing  8  to lower magnesium housing  9 . 
     FIG. 5 shows power I/O circuit board  24  and digital circuit board  23  and radio circuit board  25  and GPS radio frequency board  22  to be located between upper magnesium housing  8  and lower magnesium housing  9 . Connector  26  which is electrically coupled to cable  40  connects directly to a connector receptacle attached to power I/O circuit board  24 . Connector  283  mates with a corresponding connector receptacles so as to electrically connect GPS radio frequency circuit board  22  to digital circuit board  23 . Connector  284  mates with a corresponding connector receptacles so as to electrically connect power I/O circuit board  24  to digital circuit board  23 . Connector  285  mates with a corresponding connector receptacles so as to electrically connect radio circuit board  25  to power I/O circuit board  24 . Bolts  219  engage openings  291  in upper magnesium housing  8  and pass through openings in spacers  60  and through threaded openings in bottom magnesium housing so as to secure circuit boards  22 - 25  within upper magnesium housing  8  and lower magnesium housing  9 . Nuts  225  engage each of screws  219 . Ring  21  to which polyester sheet  20  is attached supports GPS radio frequency circuit board  22  on top of polyester sheet  20  so as to separate GPS radio frequency circuit board  22  from the other circuit boards  23 - 25  so as to limit interference from EMI from radio frequency circuit board  25  and power I/O circuit board  24 . Spacers  60  which may be stainless steel PEM spacers support and separate circuit boards  22 - 25 . 
     FIG. 6 shows a second embodiment which includes a tripod base  502 . GPS unit  101  is identical to GPS unit  101  shown in the first embodiment and illustrated in FIGS. 1-5. Tripod base  502  is interchangeable with pole  102  shown in the first embodiment and it attaches to housing  12  in the same manner as does pole  102  of the first embodiment. Tripod  502  includes top section  504  to which leg  505 , leg  506  and leg  507  are attached. Finder  510  allows GPS unit  101  to be precisely located over a landmark. Finder  510  may be a prismatic optical finder, a laser optical finder, a fixed height tripod, a laser finder with a fourth leg, or any of a number of other known location devices which are commonly used in construction and surveying equipment. Battery  41  is located within tripod  502 . Though battery  41  is shown to be located within top section  504  of tripod  502 , battery  41  could be located in or on any of legs  505 - 507 . In fact, it may be desirable to locate battery  41  in legs  505 - 507  depending on the type of location equipment used as finder  510 . Finder  510  could be used to precisely locate tripod  502  over a USGS marker such that the GPS unit would be able to function as a reference site such that the location of other GPS devices may be accurately determined by using DGPS techniques. The location and differential correction data may be monitored on display  901  of display unit  900 . Since display unit  900  is a separate unit it may be connected and disconnected as needed. 
     FIG. 7 shows a third embodiment which forms a radio relay. Radio relay system  700  incorporates many of the components disclosed in the first and second embodiments as shown in FIGS. 1-6. Radio relay system  700  includes radio relay unit  701  which is mounted on tripod  760 . Radio relay unit  701  includes housing top  704  which has a circular opening into which removable transceiver unit  702  fits. Removable transceiver antenna  703  attaches to removable transceiver unit  702 . Removable transceiver unit  702  can be easily removed from housing top  704 . When removable transceiver unit  702  is removed from housing top  704 , radio relay  701  operates at the 2.44 GigaHertz frequency. This allows for radio relay unit  701  to operate at any of a number of desired frequencies by simply inserting a removable transceiver unit  702  which operates at the desired frequency. Housing  12  and I/O ports  13 - 15  are identical to housing  12  and I/O ports  13 - 15  shown in the first and second embodiments. Though radio relay unit  701  is shown to be mounted onto tripod  760 , radio relay unit  701  could be either attached to a pole such as pole  102  shown in the first embodiment or attached to a tripod such as tripod  502  shown in the second embodiment. Alternatively, radio relay unit  701  may be set on top of some structure or set on the ground and a power source may be attached to one of I/O ports  13 - 15 . 
     FIG. 8 shows radio relay system  700  to include radio antenna  10  which receives radio broadcasts from sources broadcasting at its frequency and transmits on the same frequency. Radio antenna  10  may receive signals from a GPS unit such as GPS unit  780  which may be located over a landmark having a known location. Signals received by radio antenna  10  such as signals from GPS unit  780 , shown by arrow  793 , are transmitted to radio circuit board  25  as shown by arrow  781 . Radio circuit board  25  demodulates the signals and transmits the signals to power I/O and digital circuit board  800  as shown by arrow  799 . When a removable transceiver unit  702  is plugged into radio relay system  700 , the signals are transmitted to removable transceiver unit  702  as shown by arrow  782 . Removable transceiver unit  702  broadcasts the signals at a higher frequency through removable transceiver unit antenna  703  as shown by arrow  783 . This high frequency signal may be received by other radio relay systems such as radio relay system  790 , as shown by arrow  788 . When removable transceiver unit  702  is not plugged into radio relay system  700 , radio relay system  700  operates as a relay at the frequency at which radio circuit board  25  and antenna  10  broadcast and receive. Display panel  200  includes an on/off switch which is coupled to power I/O and digital circuit board  800  as shown by arrows  785  and  786 . Display panel  200  includes a number of lighted indicators which indicate the status and operation of relay system  700 . Power is provided to radio relay system  700  by power source  801  as indicated by arrow  787 . Power I/O and digital circuit board  800  also connects to I/O ports  13 - 15 , as illustrated by arrows  794 - 795  and box  797 , to which separate display units and input devices may be attached. 
     Continuing with FIG. 8, radio relay system  700  also operates by receiving signals at the frequency at which removable transceiver unit  702  operates. Thus signals may originate from other radio relay systems such as radio relay system  790  as shown by arrow  784 . These signals are received by removable transceiver unit antenna  703  and are transmitted to removable transceiver unit  702  as shown by arrow  789 . Removable transceiver unit  702  transmits the signals to power I/O and digital circuit board  800  as shown by arrow  791  which transmits the signals to radio circuit board  25  as shown by arrow  798  which broadcasts the signals through radio antenna  10  as shown by arrow  796 . The resulting radio broadcast may be received by GPS unit  780  as shown by arrow  792 . 
     FIG. 9 shows removable transceiver unit  702  to fit within receptacle opening  711  of housing top  704 . Flexible bumper  7  is mounted above upper magnesium housing  8  and flexible bumper  11  is mounted below lower magnesium housing  9  so as to securely hold upper magnesium housing  8  and lower magnesium housing  9  within housing  12 . Flexible bumper  7  and flexible bumper  11  absorb shock and vibration so as to protect the electronics located within upper magnesium housing  8  and lower magnesium housing  9 . Flexible bumper  7 , flexible bumper  11 , lower magnesium housing  9  and upper magnesium housing  8  are identical to flexible bumper  7 , flexible bumper  11 , lower magnesium housing  9  and upper magnesium housing  8  shown in the first and second embodiments. In addition, housing  12  identical to housing  12  shown in the first two embodiments. Furthermore, metallic cloth  271 - 272  and metallic cloth strip  270  are identical to metallic cloth strip  270  and metallic cloth  271 - 272  shown in the first two embodiments. Power source  41  is identical to power source  41  shown in the first two embodiments and display panel  200  is identical to display panel  200  shown in the first two embodiments. In addition, I/O ports  13 - 15  are identical to I/O ports  13 - 15  shown in the first two embodiments of the present invention and they allow for coupling input and output between radio relay system  700  and other devices. Radio relay unit  701  is supported by tripod  760  which connects to radio relay unit  701  via screw threads  761 . Power source  41  fits within tripod  760 . 
     FIG. 10 shows removable radio transceiver unit  702  to fit within opening  711  in housing top  704 . Removable radio transceiver unit  702  includes connector  740  which mates with connector receptacle  730 . Connector receptacle  730  is coupled to power I/O and digital circuit board  800  by cable  751 . Power I/O and digital circuit board  800  is coupled to connector receptacles in I/O ports  13 - 15  (connector receptacles for I/O ports  13 , 15  are not shown), to display/control panel  200 , and to power source coupling  55 . Power I/O and digital circuit board  800  couples to radio circuit board  25  via connector  810 . Radio circuit board  25  is coupled to antenna  10  which includes a parallel feed network and antennas  44 - 51  ( 46 - 51  are not shown) via receptacle  80  which is secured to antenna  10 . Power source coupling  55  is identical to power source coupling  55  shown in the first and second embodiments and allows power to be coupled from battery  41  to power I/O and digital circuit board  800 . Battery  41  is contained within tripod  760 . Tripod  760  is identical to tripod  502  shown in the second embodiment of the present invention except that tripod  760  does not include finder  510 . Cable  40  connects power source coupling  55 , display board  200 , and I/O ports  13 - 15  to power I/O and digital circuit board  800 . Radio transceiver  702  operates at 900 MegaHertz. However, any of a number of different frequencies may be used. Different frequencies may be easily obtained by using removable transceiver units operating at various different frequencies and inserting removable transceiver units operating at the desired frequency as dictated by the situation. Thus, a repeater operating at a different frequency may be easily obtained by replacing transceiver  800  with a transceiver operating at the desired frequency. Signals to and from antenna  10  are broadcast at 2.44 GigaHertz, however any of a number of other frequencies could also be used. 
     There are many different combinations of the various components shown in the present invention. FIG. 11 shows an example of one of those combinations. GPS system  1050  which includes GPS unit  101  is located over a known location  1010  such as a USGS survey site. Tripod  502  includes an optical location finder which is used to precisely locate GPS system  1050  over the known location  1010 . Correction information are broadcast from GPS system  1050 , as shown by arrow  1051  are received by radio relay  1040  at a frequency of 2.44 GigaHertz. Radio relay  1040  relays the signals to radio relay  1030  at 900 MegaHertz as shown by arrow  1041 . The signals received by relay  1030  are then transmitted at 2.44 GigaHertz to GPS system  1020  as shown by arrow  1031 . GPS system  1020  includes GPS unit  101  and pole  102 . Using the correction information and telemetry data obtained from satellites, the location of GPS system  1020  may be accurately determined. Connected to GPS unit  101  of GPS system  1020  is display unit  900  which can be used to monitor the position of GPS system  1020  in order to exactly locate a desired position. Since radio relay  1020  and radio relay  1030  may also operate at 2.44 GigaHertz, a single radio relay, or both radio relay  1030  and radio relay  1040  could be used and operated at the 2.44 GigaHertz frequency, depending on the requirements of the particular location. 
     Though the GPS system of the present invention is described with reference to dual frequency operation, the present invention is also well suited for operation in a single frequency operating system. In addition, though the present invention is described with reference to the use of transceivers, transmitters, receivers, or transceivers could also be used depending on the requirements of the particular situation. For example, GPS unit  1050  of FIG. 11 could be receive only. In such an embodiment, a smaller, more simply designed radio antenna may be used and simplified radio processing circuitry could be used. For example a simple dipole antenna may be used in place of the complex structure of antenna  10 . Alternatively, separate radio antennas may be used for transmitting and receiving, depending on the needs of the particular location. Radios may transmit and/or receive at any of a number of frequencies. In one embodiment, radios operate at frequencies allowed by, and under the requirements of Federal Communication Commission Part 9 and Part 2 regulations. 
     In one embodiment, one or more of I/O ports  13 - 15  are adapted for connection to an external radio such as external radios  1201 - 1204  of FIG.  12 . The operating characteristics of external radios  1201 - 1204  are selected to fit the needs of the particular operating situation. For example, in different countries and in different regions of the US, communication is at different power levels and at different frequencies. Thus, a radio transmitting at, receiving at, or transmitting and receiving at a desired frequency and at a desired power level may be used as required by the particular situation. When dual frequency operation is required, multiple external radios may be coupled to I/O ports of the GPS unit which operate at different frequencies as required by the location. For example, one radio may be used to receive signals and a second radio may be used for transmission. 
     FIG. 12 shows a method for forming an integrated position determination system and radio system that is easy to carry. First, as shown by step  1201  a carrying point is defined along a range pole. In the present embodiment, the carrying point is defined within a gripping region of the pole. This gripping region is the location where the user grips the pole. In the present embodiment, the gripping region is positioned such that an average height user can comfortably grip the pole. 
     In the embodiment shown in FIG. 13, a 6 foot range pole is used and carrying point  1301  is located three feet from the top of the pole. It can be seen that carrying point  1301  is within gripping region  1302 . In the present embodiment, components  1313  and  1314  are positioned so as to form a natural and relatively narrow gripping region  1302  therebetween. Alternatively, a gripping region could be indicated by a handgrip (not shown) that fits over the range pole or other indicia visible to a user that indicates where the pole is to be grasped. 
     Continuing with FIG. 12, as shown by step  1202 , the components of the integrated position determination system and communication system are positioned along the range pole such that the integrated position determination system and communication system is horizontally and vertically balanced. In the present embodiment, horizontal balance is obtained by positioning the components of the integrated position determination system and communication system such that the components are balanced about the centerline of the range pole. Vertical balance is obtained by balancing the components vertically about the carrying point. 
     Continuing with step  1202 , by vertically balancing the components about the carrying point, an integrated position determination system and communication system is obtained that does not tend to tip in any given direction when held. This facilitates holding the pole while moving into position to make a measurement and facilitates carrying the range pole. In one embodiment of the present invention, all of the components are balanced about the carrying point such that there is a zero vertical moment at the carrying point. Alternatively, the components are balanced so as to minimize the vertical moment at the carrying point. By vertically balancing the components about the carrying point, the tendency of the system to tip over is reduced, thereby reducing muscle fatigue and potential damage due to tipping over as commonly occurs with prior art systems. 
     Vertical balance is obtained by balancing the components of the integrated position determination system and communication system about the carrying point. Any of a number of different methods can be used to balance the components of an integrated position determination system and communication system about a carrying point. In one embodiment, some of the components of the integrated position determination system and communication system are placed within separate housings which are separately coupled to the range pole. In the present embodiment, only those components that are required to be positioned at or near the top of the pole are kept at or near the top of the pole. All other components are located lower along the pole to give the required balance. 
     Referring now to FIGS. 13-20, an integrated position determination system and communication system  1300  is shown that includes a GPS antenna  1310  and a radio antenna  1311  that are located in separate housings. GPS antenna  1310  and radio antenna  1311  are positioned near the top of the pole. All other components are moved down the pole to balance the system about the carrying point. In the present embodiment, the integrated position determination system and communication system  1300  includes receiver  1314  that includes a housing that contains position determination system processing circuitry including a GPS receiver and a GPS processor. Additionally, radio signal processing circuitry and a power supply (e.g., a battery) is contained within receiver  1314 . 
     Continuing with FIGS. 13-20, in the present embodiment, the radio signal processing circuitry contained within receiver  1314  includes a radio data transmitter (also referred to as a radio modem) that transmits data in serial form digitally at a frequency of 450 MegaHertz. In an alternate embodiment, the radio signal processing circuitry contained within receiver  1314  operates at a frequency of 900 MegaHertz. However, other frequencies could also be used. 
     Continuing with FIGS. 13-20, system  1300  also includes data logger  1313 . In the present embodiment, data logger  1313  is coupled via cable (not shown) to receiver  1314 . Data logger  1313  includes an alphanumeric keypad and a display for coupling information to and from a user. That is a user provides input via data logger  1313  and receives output that is displayed on the display of data logger  1313 . 
     In the present embodiment, cables (not shown) couple GPS antenna  1310  to receiver  1314  and couple communications antenna  1311  to receiver  1314 . Similarly, a cable (not shown) is used to couple data logger  1313  to receiver  1314 . 
     In one embodiment, the integrated position determination system and communication system  1300  of FIGS. 13-20 is vertically balanced by locating a GPS antenna  1310  that weighs 1 pound at the top of range pole  1315  (three feet above carrying point  1301 ) and locating communications antenna  1311  that weighs 1 pound such that the center of gravity of the communications antenna is at a distance of 2.5 feet above carrying point  1301 . In this embodiment, data logger  1313  that weighs one pound is located 0.5 feet above carrying point  1301  and receiver  1314  which weighs 3.5 pounds is located 1.857 feet below carrying point  1301 . In the present embodiment, level  1312  has minimal weight and does not contribute significantly to the vertical moment. This gives a total vertical moment about carrying point  1301  of zero. That is, GPS antenna  1310  contributes 3 foot-pounds (1 pound * 3 feet), communications antenna  1311  contributes 2.5 foot-pounds (1 pound * 2.5 feet), data logger  1313  contributes 1 foot-pound (2 pounds * 0.5 feet) for a total of 6.5 foot-pounds. This is balanced out by locating receiver  1314  at a distance 1.857 feet below carrying point  1301  to produce a vertical moment of zero footpounds (6.5-3.5 * 1.857). Because the vertical moment of integrated position determination system and communication system  1300  of FIGS. 13-20 is zero foot-pounds at carrying point  1301 , good handling characteristics are obtained, thereby reducing muscle fatigue and potential damage due to tipping over as commonly occurs with prior art systems. 
     Referring back to step  1202  of FIG. 12, by horizontally balancing the components about the centerline of the range pole, an integrated position determination system and communication system is obtained that does not tend to tip in any given direction when held upright. This facilitates holding the pole in position to make a measurement. In one embodiment of the present invention, all of the components are balanced about the centerline such that there is a zero horizontal moment at the centerline. Alternatively, the components are balanced so as to minimize the horizontal moment at the centerline. Preferably, the moment at the centerline is held to less than or equal to 3 inch-pounds. In one embodiment, the components are balanced to obtain a horizontal moment of 2.25 inch-pounds or less about the centerline. It has been found that a moment of 2.25 inch-pounds or less gives good handling characteristics, thereby reducing muscle fatigue and potential damage due to tipping over as commonly occurs with prior art systems. 
     In the embodiment shown in FIGS. 13-20, horizontal balance is obtained by locating each of components  1310 - 1314  as close to the centerline of range pole  1315  as possible. In this embodiment, components  1310 - 1311  are centered about the centerline of the range pole  1315 . Each of components  1312 - 1314  have centers of gravity that are located at a distance from centerline A—A of range pole  1315 . Therefore, components  1312 - 1314  must be positioned relative to centerline A—A so as to balance-out. 
     In one embodiment, data logger  1313  of FIGS. 13-20 has a weight of 2 pounds centered 3.75 inches from centerline A—A. Receiver  1314  has a weight of 3.5 pounds centered 1.5 inches from centerline A—A. In the present embodiment, level  1312  has minimal weight and does not contribute significantly to the horizontal moment. Because data logger  1313  is positioned opposite component  1314 , a total horizontal moment of 2.25 inch-pounds is obtained (2 pounds * 3.75 inches−3.5 pounds * 1.5 inches). Because the horizontal moment of integrated position determination system and communication system  1300  of FIGS. 13-20 is 2.25 inch-pounds relative to centerline A—A, good handling characteristics are obtained, thereby reducing muscle fatigue and potential damage due to tipping over as commonly occurs with prior art systems. 
     The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.