GPS Usage Guide
The following are general comments on dos and don'ts of using the
Trimble 4700 system.
- (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 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
- 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.
- 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
- 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.
- 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
- Keep one antenna with a receiver. This shouldn't matter, as the
antennas should be completely interchangeable. However, it can't
- 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
- Ground planes attach with the thumb screws on the bottom. These
are captive screws, so they should not come out of the ground plane.
- 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
- 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.
- 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
- 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
- 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.
- 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
- 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
- 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
- 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|
- 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.
- 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.
- 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
- 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.
- 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.
Written by Paul Gettings