ashtech Z-Xtreme Parts list manual

Z-XtremeTM GPS Receiver
SYSTEM GUIDE FOR RTK SURVEYING
Ashtech Precision Products
471 El Camino Real
Santa Clara, CA USA 95050-4300
Phone and Fax Numbers
•Main
• Voice: 408-615-5100
• Fax: [phone]
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• Fax: [phone]
• Europe
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• Fax: [phone]
• Support
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• International: 408-615-3980
• Fax: [phone]
• Internet
• [email protected]
• http://www.ashtech.com
• http://www.magellangps.com

ii
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Printed in the United States of America.
Part Number: 630844-01, Revision A
November, 2000
Trademarks
Z-XtremeTM, Instant-RTKTM, Z-TrackingTM,SSRadioTM, and the Ashtech logo are
trademarks of Magellan Corp. Ashtech®is a registered trademark of Magellan Corp.
All other products and brand names are trademarks or registered trademarks of their
respective holders.

iii
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iv
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95050-4300

v
Introduction to Real-Time Kinematic (RTK) Surveying ............. 1
The Global Positioning System (GPS) ............................................................. 2
Real-Time Kinematic (RTK) Surveying .............................................................2
Applications ...................................................................................................... 4
Limitations ........................................................................................................ 4
Ashtech ZX SuperStation ................................................................................. 5
System Components .................................................................... 7
Hardware .......................................................................................................... 7
GPS Receiver............................................................................................... 7
Geodetic IV Antenna ................................................................................ 9
Choke Ring Antenna ................................................................................ 9
Radio .......................................................................................................... 10
UHF/VHF ................................................................................................ 10
Spread Spectrum .................................................................................... 12
Radio Antenna ............................................................................................ 13
Handheld Computer ................................................................................... 15
TDS Ranger ............................................................................................ 15
Husky MP2500 ....................................................................................... 15
Power System ............................................................................................ 16
Internal Power ........................................................................................ 16
External Power ....................................................................................... 16
Software ......................................................................................................... 17
Field Application Software .......................................................................... 17
GPS FieldMate (Mine Surveyor II/Seismark II) ....................................... 17
Survey Pro with GPS .............................................................................. 18
Office Support Software ............................................................................. 18
Handheld Transfer/Mconvert .................................................................. 18
Survey Link ............................................................................................. 18
Post-Processing Software .......................................................................... 19
Ashtech Solutions ................................................................................... 19
Ashtech Office Suite ............................................................................... 19
Hardware Connectivity............................................................... 21
Base System .................................................................................................. 21
GPS Receiver - GPS Antenna.................................................................... 21
Radio - Radio Antenna ............................................................................... 22
GPS Receiver - Radio ................................................................................ 25
Handheld Computer - GPS Receiver ......................................................... 26
GPS Receiver - Receiver Power System ................................................... 28
Radio - Radio Power System ..................................................................... 30
Fully Connected Z-Xtreme Receiver .......................................................... 31
Contents

vi
Fully Connected Base Radio ...................................................................... 33
Fully Connected Handheld Computer ........................................................ 34
Backpack Rover System ................................................................................ 34
GPS Receiver - GPS Antenna.................................................................... 35
Radio - Radio Antenna ............................................................................... 35
GPS Receiver - Radio ................................................................................ 37
Handheld Computer - GPS Receiver ......................................................... 39
GPS Receiver - Receiver Power System ................................................... 40
Fully Connected Z-Xtreme Rover ............................................................... 41
Fully Connected Rover Radio..................................................................... 43
Fully Connected Handheld Computer ........................................................ 44
Pole-Mounted Rover System .......................................................................... 44
GPS Receiver - GPS Antenna.................................................................... 44
Internal Radio - Radio Antenna .................................................................. 45
Handheld Computer - GPS Receiver ......................................................... 46
Fully Connected Pole-Mounted Rover GPS Receiver................................ 47
Fully Connected Handheld Computer ........................................................ 48
RTK Survey Preparation............................................................. 49
Base System Setup ........................................................................................ 49
Select Appropriate Base System Site......................................................... 50
Position GPS Antenna Over Base Point..................................................... 51
Mount the Base Radio Antenna.................................................................. 52
Measure and Record Instrument Height (HI) of GPS Antenna................... 52
Connect System Components.................................................................... 53
Power Up Base System.............................................................................. 54
Configure Base GPS Receiver to Function as an RTK Base ..................... 54
Enter Base Point ID, Coordinates, and HI Into Base Receiver................... 55
Verify Function............................................................................................ 55
Rover System Setup ....................................................................................... 57
Mount Receiver Antenna ............................................................................ 58
Measure and Record Instrument Height (HI) of GPS Antenna................... 58
Mount Radio Antenna................................................................................. 58
Mount Handheld Computer ........................................................................ 60
Mount GPS Receiver (Pole-mount Only).................................................... 61
Connect System Components.................................................................... 62
Power-up Rover System............................................................................. 62
Configure Rover GPS Receiver to Function as an RTK Rover .................. 63
Verify Function ................................................................................................ 63
Executing an RTK Survey .................................................................................. 67
RTK Rover Initialization .................................................................................. 67
Base–Rover Separation (RTK Range of Operation) ...................................... 68
Communication........................................................................................... 68

vii
Initialization................................................................................................. 69
Accuracy..................................................................................................... 69
Troubleshooting ............................................................................................... 71
Base System Troubleshooting ............................................................................ 72
GPS Receiver Does Not Track Satellites ....................................................... 72
Step 1. Is the GPS receiver powered up? ..................................................72
Step 2. Is the GPS Antenna Connected to the Receiver? .......................... 73
Step 3. A component may be malfunctioning. ............................................ 73
Base System Does Not Transmit Data ........................................................... 74
Step 1. Is the base radio powered up? ....................................................... 74
Step 2. Is the Base Radio Connected to the GPS Receiver? ..................... 75
Step 3. Is the Base GPS Receiver Set to Function as RTK Base? ........... 76
Step 4. Is Receiver Set to Output RTK Base Data on Port B? .................. 76
Step 5. Base coordinates entered correctly into base receiver? ...............76
Step 6. Is base receiver tracking satellites? ...............................................77
Step 7. You may have a component that is malfunctioning ........................ 77
Rover System Troubleshooting ..........................................................................78
GPS Receiver Does Not Track Satellites ....................................................... 78
Radio Not Receiving Data Transmitted By Base ............................................ 78
Step 1. Is the rover radio powered up? ..................................................... 78
Step 2. Is the rover radio antenna connected to the rover radio? .............. 79
Step 3. Is the base system transmitting data? ............................................ 80
Step 4. Is the base radio antenna connected to the base radio? ...............80
Step 5. Is the rover radio set to the same frequency as the base? ............80
Step 6. Is line-of-sight between base and rover antennae obstructed? ..... 81
Step 7. Are you within range specifications of your radio system? ........... 81
Step 8. Are you being jammed? ................................................................82
Step 9. You may have a malfunctioning component in your system .......... 83
Rover System Is Not Computing A Position ................................................... 83
Step 1. Is the radio receiving data transmitted by the base? ...................... 83
Step 2. Is the radio connected to the GPS receiver? ................................. 84
Step 3. Is the radio connected to the correct port? ..................................... 84
Step 4. Is the GPS receiver tracking satellites? ......................................... 85
Step 5. Are base and rover tracking at least 4 common satellites? ............ 85
Step 6. Your rover receiver may be malfunctioning ................................... 86
Rover Computing Position With High Uncertainties ....................................... 86
Step 1. Is the GPS receiver set to function as an RTK rover? .................. 86
Step 2. Are base and rover tracking at least 5 common satellites? ............ 86
Step 3. HDOP & VDOP Values Too High for Precision Requirements? ...87
Step 4. Precision requirements too stringent for RTK? .............................88
Step 5. Your rover receiver may be malfunctioning ................................... 88

viii

ix
Figure 1.1 RTK Setup for GPS Surveying.............................................................. 3
Figure 2.1 Ashtech Z-Xtreme GPS Receiver ......................................................... 8
Figure 2.2 Geodetic IV GPS Antenna - without and with Groundplane.................. 9
Figure 2.3 Choke Ring Antenna for Severe Multipath Environment..................... 10
Figure 2.4 Pacific Crest UHF/VHF Base Radio.................................................... 11
Figure 2.5 Pacific Crest UHF/VHF Rover Receiver.............................................. 12
Figure 2.6 Ashtech Spread-Spectrum Radio........................................................ 13
Figure 2.7 Spread Spectrum and UHF Radio Antennas ...................................... 14
Figure 2.8 Handheld Computers: TDS (left), Husky MP2500 (right) .................... 15
Figure 2.9 Power Sources: Internal (left) and External (right) .............................. 16
Figure 3.1 GPS Antenna Cable with TNC Connectors......................................... 21
Figure 3.2 Cable Connected to Z-Xtreme Receiver and Geodetic IV Antenna .... 22
Figure 3.3 Pacific Crest Base Radio Antenna Cable............................................ 23
Figure 3.4 Cable Connected to Pacific Crest Radio and Base Radio Antenna.... 24
Figure 3.5 Pacific Crest Base Radio Power/Communication Cable..................... 25
Figure 3.6 Cable Connecting Z-Xtreme Receiver and Pacific Crest Radio.......... 26
Figure 3.7 Computer Communication Cable ........................................................ 27
Figure 3.8 Communication Cable Connecting Z-Xtreme and Ranger Handheld . 28
Figure 3.9 Z-Xtreme Power Cable and Pouch for External Power....................... 29
Figure 3.10 Power Cable Connecting Z-Xtreme and External Battery................... 29
Figure 3.11 Pacific Crest Radio Power/Communication Cable .............................. 30
Figure 3.12 Cable Connecting Pacific Crest to External Battery............................ 31
Figure 3.13 Z-Xtreme Base Receiver with all Cable Connections ......................... 32
Figure 3.14 Pacific Crest Radio with all Cable Connections .................................. 33
Figure 3.15 Handheld Computer with all Cables Connected ................................. 34
Figure 3.16 Pacific Crest Rover Radio Antenna Cable .......................................... 35
Figure 3.17 Rover Antenna Connected to Internal Radio ...................................... 36
Figure 3.18 Pacific Crest PDL Rover Radio with Antenna ..................................... 37
Figure 3.19 Pacific Crest Rover Radio Power/Communication Cable ................... 38
Figure 3.20 Communication Cable Connecting Z-Xtreme and PDL Rover Radio.. 39
Figure 3.21 Computer Communication Cable ........................................................ 40
Figure 3.22 Cable Connections for Z-Xtreme Rover with External Radio .............. 41
Figure 3.23 Cable Connections for Z-Xtreme Rover with Internal Radio ............... 42
Figure 3.24 Pacific Crest Rover Radio with all Cable Connections........................ 43
Figure 3.25 Handheld Computer with all Cables Connected ................................. 44
Figure 3.26 Pacific Crest Rover Radio Antenna Cable .......................................... 45
Figure 3.27 Cable Connected to Internal Radio and Radio Antenna ..................... 45
Figure 3.28 Computer Communication Cable ........................................................ 46
Figure 3.29 Fully Connected Pole-mounted Rover GPS Receiver ........................ 47
Figure 3.30 Fully Connected Handheld Computer ................................................. 48
List Of Figures

x
Figure 4.1 Base Transport Case................................................................. 49
Figure 4.2 Base Transport Case, Kit Opened............................................. 50
Figure 4.3. Base Antennae Mounted on Conventional and GPS Tripods .. 51
Figure 4.4 Mounted Base Radio Antenna................................................... 52
Figure 4.5 Measuring HI (Height of Instrument) of Base GPS Antenna ..... 53
Figure 4.6 Base System Ready to Survey.................................................. 56
Figure 4.7 Rover Transport Case ............................................................... 57
Figure 4.8 Geodetic IV GPS Antenna on Rover Pole ................................. 58
Figure 4.9 Rover Antenna and Pacific Crest PDL Radios on Backpack.... 59
Figure 4.10 Radio Antenna Mounted On Pole and on Back of Receiver...... 59
Figure 4.11 Rubber Duck Antenna Mounted to Z-Xtreme ............................ 60
Figure 4.12 TDS Ranger Handheld Mounted on Rover Pole........................ 61
Figure 4.13 Receiver Mounted on Pole ........................................................ 62
Figure 4.14 Backpack Rover System Ready to Survey................................ 64
Figure 4.15 Pole-mounted Rover System Ready to Survey ......................... 65

1
Introduction to
Real-Time Kinematic (RTK) Surveying
In the early days of surveying with GPS, data collection time on a point was measured
in hours, few was the appropriate adjective to describe the number of points estab-
lished in a day, and completion of a large project could take weeks. The results of a
days work was not known until days later when the data was finally processed at the
main office. The equipment required to perform this seemingly magical task filled the
back of a Chevy Blazer and came at a price tag of approximately $150,000 each.
And, by the way, two sets of equipment were needed.
Imagine the scepticism if a user of that system were told that some day, data collec-
tion times would be measured in seconds, hundreds would describe the number of
points established in a day, and large projects could be completed in hours. Results
would be known immediately, in real time. The equipment required to perform this
truly magical task would be carried by one person all day, and the price of the entire
system would be under $40,000 (including both sets of equipment).
What you’ve just read is the difference between GPS surveying in the early 1980s and
GPS surveying today. Early GPS surveying was static in nature. A user sat on a point
for an extended period of time, 1-3 hours or more. If time permitted, this user would
move to another point after collection was completed. Data was then sent off to the
main office for post-processing. Only after the data was processed were the results of
the survey obtained. Since then, GPS surveying has become more dynamic in
nature. Equipment has become small enough to be portable. With the incorporation
of a radio link between sets of GPS equipment, data can be processed in real-time, as
it is being collected. New techniques in data processing has resulted in the ability to
establish precise positions in seconds. These advances allow for a user to move
around a project site, quickly establishing the position of objects of interest and seeing
immediately the fruits of his/her labor. This is RTK Surveying.

2 Real-Time Kinematic Surveying
The Global Positioning System (GPS)
Let’s take a quick look at what makes this all possible, the Global Positioning System
(GPS). GPS consists of three primary components: satellites, ground-based control
and monitoring stations, and receivers.
The control and monitoring stations’ main purpose is to monitor and maintain the sat-
ellites. As a user, these stations are invisible to you. You need know nothing else
about them except that they exist to ensure the satellites are functioning properly.
Satellites make up the second primary component of GPS. A full constellation is
defined as 24 satellites, although at the time of this writing 27 are currently opera-
tional. Each satellite is positioned approximately 20,000 km above the earth’s surface
and has an orbital period of slightly less than 12 hours. On board each satellite,
among other things, is a radio transceiver. The transceiver receives information and
instructions from the control station and transmits information about its identity, loca-
tion, time, etc. Each satellite is capable of transmissions on two separate frequen-
cies, L1 at 1575.42 MHz and L2 at 1227.60 MHz. Unlike control and monitoring
stations, you are required to have knowledge regarding the location, geometry, and
number of satellites available during data collection periods. These important factors
will dictate the reliability and accuracy of a GPS survey.
GPS receivers function exactly as the name implies, they receive and store transmis-
sions from the GPS satellites. This is their primary function, and for some receivers,
this is their only function. In addition to reception and storage of satellite transmis-
sions, some receivers perform additional functions such as compute and display
receiver position in various datums and grid systems, output raw data and computed
position through serial ports, display satellite availability information, etc. The more
sophisticated receivers are capable of receiving raw data from a second GPS receiver
collecting data simultaneously, and combining this data with its own to compute a very
accurate position of its location in real-time. This is how an RTK receiver functions.
Real-Time Kinematic (RTK) Surveying
RTK mode of GPS surveying requires the use of at least two GPS receiver systems
functioning simultaneously, as shown in Figure 1.1. In fact, this is true for any mode
of GPS use where better than 100 meters of positional accuracy is required. In a two-
receiver GPS RTK system, one receiver subsystem is designated as the base, and
the other is designated the rover. The base receiver system is usually located on a
known position, i.e. known latitude, longitude, height or easting, northing, height.
Once operational, the base system collects raw data from all available satellites. This
raw data is packaged and sent out the serial port to an awaiting radio transmitter. The
transmitter broadcasts the packaged raw data to anyone who wants to listen. This is

3
Introduction
the basic function of a base receiver in an RTK system.
The RTK rover is the business end of the system. The rover system is man-portable,
usually situated in a backpack. You interface with the system through a handheld
computer/data collector. Once operational, the radio portion of the rover system
receives the transmissions from the base system containing the base GPS receiver
raw data. The radio passes the received base raw data to the rover receiver via the
serial port. Simultaneously, the rover GPS receiver collects its own raw data at its cur-
rent position. The raw data from the base GPS receiver and the raw data from the
rover GPS receiver are processed by the rover receiver and the centimeter-level vec-
tor (horizontal angle, vertical angle, and distance) between the base and rover receiv-
ers is computed. Finally, the rover receiver computes the rover position using the
known base position and the computed vector. This is the basic function of the rover
receiver in an RTK system.
With the base and rover functioning as described above, a user carrying the rover
system can move about a project site and position features of interest quickly and
accurately. Positions are computed immediately, giving the user confidence that all is
functioning properly. And since the base system does not discriminate to whom it
transmits its raw data, there is no limit to the number of rover systems that can oper-
ate off of one base station.
Figure 1.1 RTK Setup for GPS Surveying

4 Real-Time Kinematic Surveying
Applications
The two primary survey tasks for which RTK systems are used are feature location
and feature stakeout.
Using GPS RTK for feature location was briefly discussed above. With the base and
rover systems operational, a user, carrying the rover system, moves around the
project area positioning features of interest. Features of any type can be positioned,
centerline of a road, perimeter of a pond, light poles, corners of buildings, etc. Fea-
tures can include existing boundary monuments or new monuments needing to be
positioned for the first time. This capability makes GPS RTK a great tool for mapping
applications, such as topographic and planimetric surveys, and as-built surveys. RTK
systems are also very efficient for mapping stockpiles and gravel pits for volume com-
putations.
Feature stakeout is a task that can only be accomplished with GPS operating in RTK
mode. Stakeout of a feature involves stakeout of a point or series of points that define
the location of the feature. Given the coordinates of a point, you must be able to find
the exact location on the ground that corresponds to those coordinates. Convention-
ally, this is done by the total station operator directing the rod person to the correct
location through observing the rod person’s current location and directing the amount
of movement to the correct location. With RTK, the rover operator can determine his/
her current location by observing the handheld computer screen. The coordinates of
the point of interest are also known by the handheld computer. With the RTK system
knowing its current location and the location of the point to be staked, the system can
direct the user to the correct location. This capability makes RTK a very effective
stakeout tool. Any object can be staked out with GPS RTK including roads, pipelines,
DTM’s, grids, etc.
In most cases, an RTK system will be vastly more productive in these types of sur-
veys than a conventional total station with the added benefit that an RTK system can
be operated by only one person.
Limitations
GPS RTK does have limitations that affect its ability to perform some of the survey
tasks discussed above. Being aware of these limitations will ensure successful
results from your RTK surveys.
The main limitation is not limited to RTK but is a limitation of the GPS system in gen-
eral. As discussed earlier, GPS depends on reception of radio signals transmitted by
satellites approximately 20,000 km from earth. Being of relatively high frequency and
low power, these signals are not very effective at penetrating through objects that may
obstruct the line of sight between the satellites and the GPS receiver. Virtually any

5
Introduction
object that lies in the path between the GPS receiver and the satellites will be detri-
mental to the operation of the system. Some objects, such as buildings, will com-
pletely block out the satellites signals. Therefore, GPS can not be used indoors. For
the same reason, GPS cannot be used in tunnels or under water. Other objects will
partially obstruct or reflect/refract the signal, such as trees. Reception of GPS signals
is very difficult in a heavily forested area. In some cases, enough signal can be
observed to compute a rough position. But in virtually every case, the signal is not
clean enough to produce centimeter-level positions. Therefore, RTK is not effective in
the forest.
This is not to say that GPS RTK can only be used in areas with wide-open view of the
sky. RTK can be use effectively and accurately in partially obstructed areas. The trick
is to be able to observe, at any given time, enough satellites to accurately and reliably
compute a position. At any given time and location, 7-10 GPS satellites may be visi-
ble and available for use in RTK surveying. The RTK system does not require this
many satellites to function. Accurate and reliable positions can be determined with 5
satellites properly distributed throughout the sky. Therefore, an obstructed location
can be surveyed if at least 5 satellites can be observed. This makes RTK use possi-
ble along a tree line or against the face of a building but only if that location leaves
enough of the sky open to allow the system to observe at least 5 satellites.
Ashtech ZX SuperStation
The Ashtech solution for RTK surveying is the ZX SuperStation. The ZX SuperStation
includes all required components to perform post-processed and real-time GPS sur-
veys. The ZX SuperStation is powered by the Ashtech Z-Xtreme dual-frequency GPS
receiver. Being a dual-frequency receiver (utilizes satellite signals on both L1 and L2
frequencies), the Z-Xtreme makes your GPS system versatile. When performing
post-processed surveys such as control establishment and densification, the Z-
Xtreme will allow for long separation between base and rover receivers while main-
taining the highest level of accuracy. For RTK surveys, system initialization times are
short and the solution reliable, resulting in high productivity.

6 Real-Time Kinematic Surveying

7
System Components
An RTK system is made up of a number of components that, at first glance, may seem
a bit overwhelming. On the contrary, setup of an RTK system is not a complicated
task. The trick is understanding the purpose of each component in the system and
how they relate to each other. With this understanding, connecting the hardware
components and using the software components becomes logical and straightfor-
ward.
Hardware
An RTK system includes a number of hardware components, each with a specific
function. The ZX SuperStation offers options for many of the components, each with
specific advantages. Choosing the right component will depend on the requirements
and environment in which the system is to be used. In this section, each of the major
components of the ZX SuperStation is presented. If options exist for a specific com-
ponent, each option is discussed.
GPS Receiver
The GPS receiver, Figure 2.1, processes and stores the satellite signals. An RTK
system requires at least two GPS receivers, a base and a rover.

8 Real-Time Kinematic Surveying
The ZX SuperStation is built around the Z-Xtreme dual-frequency GPS receiver. The
Z-Xtreme supports an integral battery, removable PC card memory, and optional inter-
nal radio. It is capable of functioning as the base or rover in RTK and post-processed
surveys. The integrated display and control panel supports the ability to perform
some survey tasks without a handheld computer. Environmentally, the receiver meets
MIL-STD-810E specifications for wind-driven rain and dust.
In order for the GPS receiver to receive satellite signals, it must utilize an antenna.
The GPS receiver antenna is the actual collection point of the satellite signals. It is
also the point for which the position of the rover system is computed. Therefore, to
determine the location of a feature, the GPS receiver antenna must be placed over
this feature. The horizontal position of the feature is determined by the location of the
center of the antenna. The vertical position of the feature is determined by the loca-
tion of the center of the antenna minus the known height of the antenna above the
feature. Each GPS receiver in the system has one GPS receiver antenna. The ZX
SuperStation offers a choice between two different GPS receiver antennae for the
base system: the Geodetic IV antenna and the Choke Ring antenna. Obstruction con-
ditions at the base position will dictate which antenna is appropriate.
Figure 2.1 Ashtech Z-Xtreme GPS Receiver

9
Components
Geodetic IV Antenna
The Geodetic IV antenna, Figure 2.2, is the standard antenna used by the base and
rover RTK systems. It is small, lightweight, and meets the needs of most users. This
is the only antenna available for use with the rover system. The other antenna option
is too large and heavy for practical use on the rover.
The Geodetic IV antenna is available with an optional groundplane attachment, which
is effective in reducing noise created by satellite signals reflecting off nearby obstruc-
tions. The technical name for this noise is multipath. The groundplane attachment
reduces the effects of multipath on the data collected. In order to be effective at
reducing the effects of multipath, the groundplane attachment significantly increases
the size and weight of the antenna. For this reason, the groundplane attachment is
only recommended for use at the base station. If the base system is to be located in
an area where obstructions, such as metal buildings, may cause multipath, the
groundplane attachment is a good option.
Choke Ring Antenna
The choke ring antenna, Figure 2.3, is the ultimate antenna for multipath rejection. If
the base system is to be located in a harsh multipath environment, the choke ring
antenna is advisable. An example of a harsh multipath environment would be the top
of a building which houses large metal compressors and air conditioning units. These
structures will reflect satellite signals which the antenna may pick up. The choke ring
Figure 2.2 Geodetic IV GPS Antenna - without and with Groundplane

10 Real-Time Kinematic Surveying
antenna is designed to function in the most demanding multipath environments.
Radio
The radio is the mechanism through which the base and rover GPS receivers commu-
nicate in the RTK system. Therefore, a radio is a component of both the base and
rover systems. As explained earlier, the base GPS receiver must transmit its raw data
to the rover GPS receiver in order for the rover GPS receiver to compute the vector
between the base and rover systems. The base system transmits the data and the
rover system receives the data using radios. The base radio is usually the larger of
the two since it must have transmit capabilities. It also consumes much more power.
The rover receiver needs only to receive the transmission. This requires much less
capability and power consumption. In some RTK systems, the rover radio is so small
that it is embedded inside the rover GPS receiver. Two distinctly different radio types
are available with the ZX SuperStation, one working in the UHF/VHF frequency
range, and another in the spread-spectrum frequency range. Distance requirements
between the base and rover systems will primary dictate which radio system to
choose.
UHF/VHF
If the intent is to perform RTK surveys with distances between the base and rover in
excess of 2 km, then a radio functioning in the UHF or VHF frequency range is recom-
Figure 2.3 Choke Ring Antenna for Severe Multipath Environment