GPS Usage Guide

1. (DIS-)ASSEMBLY & PACKING
   • THERE IS NOTHING, NOTHING, IN THE SYSTEM THAT REQUIRES TOOLS TO ASSEMBLE OR DISASSEMBLE! If you find yourself breaking out tools to disassemble the system, you are doing it very, very wrong.
   • The 2m range pole breaks down into 3 pieces of pole: a top half with quick-connect, padded handle, and level bubble; a lower half with screw connector and spike; and a bipod attachment with 2 quick-adjust legs. Returning the range pole in more than 3 pieces, or with loose bolts/etc. is considered damage which must be fixed by the user!
   • The radio mast comes in 3 pieces, no more.
   • Do not disassemble cables or connectors.
   • Do not disassemble receivers.
   • Do not disassemble antennas.
   • Do not disassemble tribrachs.
   • Do not disassemble tripods.
   • Do not disassemble the range pole into more than the 3 major pieces.
   • All items have a defined storage location. This is listed in the checklist. Follow the checklist when returning equipment.
   • Do not accept equipment for checkout without putting items in their place according to the checklist.
2. CABLES & CONNECTORS
   • Do not kink cables! Any sharp bend in the cable can quickly become a break in the conductor, making the cable worthless. Repairing such a break is difficult and time-consuming.
   • Always coil cables in a loose bundle, being careful not to introduce twists; twisted cables tend to become tangled, and then a tug on one end can kink the cable.
   • Be sure to use the dust/dirt caps on all connectors; water can short the pins of a cable, and dirt can prevent contact between the pin and socket. More importantly, these caps help prevent damage to the connector itself from rocks, feet, etc. Each connector is ~$80 to replace.
3. BATTERIES
   • The batteries used in the GPS are sealed lead-acid (SLA) cells, which are weatherproof.
   • SLA batteries should only be charged by a SLA battery charger; other types may well ruin the battery, or cause it to explode.
   • Battery contacts should be kept clean; dirty contacts can be nicely cleaned with a pencil eraser.
   • The chargers provided with the GPS cannot overcharge the batteries; they can be left plugged into the chargers indefinitely.
   • One camcorder battery (2.3 Ah) will run the receiver and TSC1 for 4 hours. The receiver can be connected to 2 batteries, allowing 8 hours of use before a battery change. The base station (without TSC1) uses ~40% for 8 hours; run time is ~24 hours on the 6 Ah battery.
   • The display on the TSC1 is only valid for the current battery being used by the receiver; this means that for the rover, with 2 camcorder batteries, the power level will drop to 0 twice before the receiver is truly out of power.
   • Receivers will automatically switch between power ports; when one battery is drained, the receiver will switch on its own.
4. ANTENNAS
   • Antennas are delicate; don't hit them against rocks, etc.
   • If high accuracy (better than 10 cm) is needed, use ground planes on the base and rover antennas.
   • Tripods should be used for any static survey, as holding the antenna stable for the 10+ minutes required is not feasible.
   • Antennas are weather proof, so long as the square core is not broken or disassembled.
   • Historically, the North arrow should be aligned to True or Magnetic North (choose one and be consistent). These antennas are "micro-centered", with phase centers guaranteed to be within 5 mm between antennas.
   • Keep one antenna with a receiver. This shouldn't matter, as the antennas should be completely interchangeable. However, it can't hurt.
     • The rover antenna is marked with red tape.
     • The base antenna has no tape marking.
   • The base station antenna should always have the ground plane attached.
   • Ground planes attach with the thumb screws on the bottom. These are captive screws, so they should not come out of the ground plane.
5. TRIPODS & TRIBRACHS
   • The level bubble on a tribrach is very sensitive. Always try to get the bubble within the circle before using the tribrach's adjusting screws.
   • Do not leave the brass tribrach adapter on the antenna when transporting the antenna; there is less chance of damage if the adapter is in the tribrach.
   • The tribrach is actually 2 pieces, held together by a clamp. There is normally no reason to disassemble the tribrach. The tribrach pieces are rotationally symmetric, so assembly is easy.
   • Tripods should be transported with the cover on the top. This way, the screw and face are less likely to be damaged.
   • When positioning the tribrach, make sure that all 3 pads are on the tripod face. If they are not, move the tripod until the pads are on the face and the tribrach is positioned.
   • The eyepiece of the tribrach has 2 focus rings; one focuses the image (outer), and the other the crosshairs (inner).
   • Due to the use of the optical plummet (the eyepiece), it is not necessary to use a plumb bob. This can be done to check the optical plummet, if desired.
6. RECEIVERS & HAND CONTROLLER
   • The 4700 receivers are quite robust, but the connectors are relatively fragile. Never force a cable into a connector!
   • The receiver housing and front panel is weatherproof.
   • Be sure to use the rubber plug covers to prevent damage or shorting of the connector pins.
   • There are 3 identical connectors on the back of the receivers; one is for the hand controller (#1), one is for a battery or PC connection (#2), and one is for the radio or battery (#3). Look at the icons, and the connectors should be obvious.
   • A receiver can have 1 or 2 batteries plugged in at once; it will automatically switch from one port to the other. Only ports 2 & 3 can handle batteries.
   • Our rover receiver has an internal radio modem; this is the coax connector on the back. The base receiver has a plastic plug in this location; don't remove it!
   • The front panel lights are useful, but only if the hand controller is not attached. See the manual for the meaning of the lights.
   • The hand controller can turn receivers on and off remotely, so there is no need to directly handle the receivers if the hand controller is available. The hand controller provides a much more intuitive interface anyway.
   • The hand controller has an internal battery than can be recharged by an OSM-IV (use the attached Lemo-ended cable). It will also draw power from the receiver or OSM-IV, if attached. The icon in the lower left corner of the screen indicates the power source.
   • Log rover data to the hand controller; the receivers can only hold 42 files, and have less memory. This is not an option with the base receiver.
   • The hand controller has 2 Lemo plugs; they are basically identical. Use whichever minimizes cable bends.
   • The hand controller is weatherproof, but not proof against immersion in water.
   • Downloading the hand controller requires the Trimble Data Transfer program. This is included with Survey Office and on the Survey Controller CD. GPLoad will not talk to the hand controller.
   • The hand controller cannot properly function if all the memory is used for data storage. When the hand controller drops below ~40kB free, it may refuse to load a job or take data. A warning is displayed on the status line, stating that "main memory almost full." The only fix is to free memory by clearing files. Preferably download the files before deleting. Files can also be moved to the PC card to free space in the main memory.
7. RADIO MODEMS
   • The base station uses the large Trimmark II radio modem to broadcast. The rover uses an internal radio modem to receive only.
   • The rover and base station must be set to the same channel and code settings. The rover radio is set via the Configuration->Survey Styles->RTK->Rover radio menu of the hand controller; it cannot be set from the receiver panel.
   • The base radio channel is set by the knob behind the weatherproof panel. Radio codes are set by the Trimble Trimmark radio program on a PC. Base codes are set by the hand controller when connected to the base station GPS receiver.
   • The callsign for the FCC license is WPSH818.
   • Radio antenna height is critical to getting the greatest range. Doubling the height can quadruple the effective range of the radio. For this reason, always put the base radio antenna as high as possible.
   • The base radio antenna should be put on the second tripod, using the tribrach and adapter as if for a GPS antenna. Attach the radio mast to the tribrach, and the antenna cable to the top of the mast.
   • Radio antennas should be kept from bending, as this could potentially break the antenna over time.
   • The position of the bulge on the 5dB tips is critical; do not move it.
   • Due to problems with FCC licensing, of the 16 channels available, we are only legally allowed to use 4 of them:

     Legally Usable Frequencies

     Frequency (MHz)	Radio Channel
     464.500	7
     464.550	8
     469.500	15
     469.550	16

   • Certain frequencies are typically used for voice communication (the primary purpose of the channels), and hence should be avoided for data use. It is possible to use the channels, but not recommended; definitely use Carrier Detect on these frequencies. The frequencies cited by the FCC as being of particular concern [base radio channel numbers in ()]:
     • 469.500 (15)
     • 469.550 (16)
   • We have two antenna tips for the RTK radios: a short 0dB gain tip, and a long 5dB gain tip. The 5dB gain tip has a radiation pattern shaped like a horizontal disk, with approximately 4 times the range of the 0dB gain tip. However, the radiation pattern has a maximum slope of 12° from horizontal, requiring the two radio antennas to be close in elevation. The 0dB gain tip has a nearly spherical radiation pattern, with much less horizontal range. The maximum slope approaches 90° from horizontal. Hence, the 0dB tip should be used in areas of steep topography and short horizontal distance; the 5dB everywhere else. Neither tip improves the effectiveness through obstacles. If using the 0dB tip, antenna height becomes very important; use as many sections of the radio mast as possible.
8. FASTSTATIC/RAPID STATIC SURVEYS
   • Each station is a single "survey" inside a job. This allows power down of the receiver and data logger between stations. Also note that doing this means that every station is a separate data file. If storing in the receiver, only 42 files may be stored at a time! This restriction is avoided by logging to the data collector (TSC1), but it has less memory built-in than the receivers. Ideally, store to the TSC1 with a memory card.
   • Do not set "Auto Store" in the Survey Style. If set, a point is stored as soon as enough data has been collected, and further logging is stopped. If not set, the system will log data until told to stop and store the point.
   • Default PDOP requirement is <= 6.0. Considering that gravity survey technique uses 30 minutes or more of data, this can be relaxed a bit.
   • Data recorded is always stored, even if the point is not "stored" in the Job database. The data is available as a GPS file, although records of the point name, etc. are lost from the Job file.
   • Cannot set the file names used to log GPS data - always conforms to the Trimble default (SN-JD-Session). Can rename using the data in the Job file from the data collector.
   • Can put multiple stations in a single data file; not sure how to break apart the resulting data file into separate ones for processing.
9. PC CARDS
   • The Survey Controller can use PCMCIA ATA flash cards to store data. We currently own a single 32MB card for data storage.
   • PCMCIA cards have a top and bottom side - the card should have the logo towards the front of the controller.
   • Inserting the card upside down will prevent it from working, and requires enormous force to insert. Once inserted, however, it is VERY HARD TO REMOVE!
   • To remove the card, press the small black button towards the top of the controller. This should eject the card enough to easily pull out.
   • When the card is installed and recognized, a small icon will appear in the lower left corner of the TSC1 when it is turned on. The icon is a small box surrounding the letters "PC".
   • Data can be stored in the controller's memory or on the card; preferably use the card, as it has 16x the memory of the controller.
   • 32MB should be more than enough space for even large projects with long-duration occupations. It will take longer to download, however. Downloading of the PCMCIA card can be done directly by inserting the card in a computer with a PCMCIA slot.
10. DATA ARCHIVAL
    There is an archive for GPS data maintained by the Thermal Group; it is under /data/thermal/archive/GPS_data on the CMES Sun machines. Anyone using the GPS system may add their data to the archive; it may be compressed to minimize disk usage. Talk to the Thermal Group to add your data to the archive. The advantage of adding the data to the archive is that the Thermal Group maintains their own backups, which is yet another copy in the event of catastrophic events. This archive is not guaranteed (it is free, though), and additional copies should be used for processing.