Navstar Systems A190-001G1 User Manual 8

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Document Title	8

-_—-
_ NAVSTAR SYSTEMS LTD.
2 983 (d)(8) ID: LXQM 90 001G1
DRAFT I
DR5-96S-III
UHF Telemetry Radio
User Manual
NAVSTAR SYSTEMS Ltd.
Mansard Close, Weslgate, Northampton. Eng|and. NN5 5DL
DR5-96S-III
UHF Telemetry Radio
User Manual
Issue: 1.0
Including the operation of software Version 340
Document Number: 190-335 issue 1.0
Date: 23/03/98
Copyright © 1998 Navstar Systems Ltd, all rights reserved.
This document must not be reproduced in whole or part by any means physical or
electronic without the prior written consent of Navstar Systems Ltd.
Navslar Systems Ltd. reserve the right to make enhancements and modifications to
this manual and the equipment to which it refers without prior notice.
CONTENTS
1.0 INTRODUCTION 1
2.0 INSTALLATION
2.1 POWER SUPPLY
2.2 DATA CONNECTION
2.3 BASE STATION ANTENNA 4
2.3.1 UHF ANTENNA CONNECTION 4
2.3.2 GPS AND UHFANTENNA SPACING 5
2 3.3 DR5-96S-lll AND UHF ANTENNA SEPARATION 6
2.3.4 GPS RECEIVER AND DR5—965—Ill SEPARATION 6
3.0 OPERATION 8
3.1 BASIC USE 8
3.1.1 RTCM DISTRIBUTION, WITH STATUS RETURN 8
3.1.2 RTCM DISTRIBUTION WITH TDMA MULTIPLE STATUS RETURN 8
3.1.3 RTP OR DATA TRANSFER 8
3.1.4 GENERAL OPERATION 9
3.2 ADVANCED USE 9
3.2. I RADIO DESCRIPTION 9
3.2.2 CONNECTIONS 9
3.2.3 CONFIGURATION OF DR5-965-lll 10
3.3 MODEM PORTS AND CONTROL 15
3.3.1 THE RTCM DATA PORT 11
3.3.2 THE CONTROL PORT 1 1
3.3.5 THE RADIO INTERFACE PORT 1 1
3.4 THE CONTROL PORT COMMAND SET 14
3.4.1 SETTING THE RTCM DA TA PORTAND THE CONTROL PORT 15
3.4.2 SETTING THE RADIO INTERFACE PORT 16
3.5 USER CONFIGURABLE CONTROLS 17
4.0 FAULT FINDING GUIDE FOR DR5-965—III 18
DRS-QGS—III - Ooeratinu Manual ii
APPENDICES
___————
_—_—.————_——
A Standard Equipment and Options 20
B Radio Specification 21
C Application Notes 22
1. DRS - 963 - Ill Setup Parameters 23
24 TDMA + RTP Applications 28
3. Radio Range Estimating 35
D Global Positioning System (GPS) 53
DRS-QBS-III — Operating Manual iii
NavSymm® DRS-QGS-lll. Operating Manual Issue 1.0
1.0 INTRODUCTION
The primary function of the NavSymm® DRS—QGS-lll UHF Telemetry Radio is
to provide a radio frequency link for the distribution of GPS corrections in
differential solutions. It can therefore be used to supply standard RTCM
corrections when operated as part of a DGPS base station, or to supply raw
data in Real Time Positioning (RTP) systems. Additionally, it has timing
control features which the NavSymm® XRS/XRG range of GPS receivers
utilise to provide effective use of frequency allocations. The DRS-QGS—lll can
also be used with any GPS receiver which is able to provide an RSZSZ
data stream, and may also be employed for applications outside GPS.
Under normal joint operation with an XRS/XRS receiver, the DFtS-QGS-lll will
transmit RTCM 104 differential corrections (the Industry Standard) to a
number of mobile units. These mobiles will return corrected GPS position
and status information using the same datalink. The link is able to use
addressing and error checking to improve the reliability of the communication.
In an advanced system, the mobiles may also be configured as repeaters to
give extended coverage.
When the DRS-QGS-lll is used in an RTP system, raw measurements and
base station location data are passed over the datalink every second,
allowing the mobile unit to calculate a centimetric accuracy position.
The radio case is identical to the one used for XR5»M, and has been
designed to meet the same stringent environmental specification. interface to
the DRE-QGS-III is achieved using connectors again identical to those in the
XFlS-M. providing environmental and electrical sealing to the case.
The radio is supplied with an antenna suitable for short ranges, an antenna
lead. together with electrical leads for connection to both an XRS/XRG and a
power supply, NavSymm® can also supply antennas suitable for use over
longer ranges, and power amplifiers for use where by local regulations
permit.
In addition, NavSymm® can supply appropriate leads for connection to a
computer or other equipment.
NavSymmG’ DR5»968-Ill. Operating Manual Issue 1.0
2.0 INSTALLATION
Before installation, check the contents of the set of items supplied, by
referring to the shipping list and to Appendix A. Mount the radio as required,
using the mounting holes on the base of the unit. Make all necessary
connections before applying power. Figures 2.1, 2.2, and 2.3, show typical
installations.
Note:
DO NOT turn on the unit without an antenna or load connected.
Figure 2.1 Difi’erential GPS Configuration & RTP Base Station
Figure 2.2 Radio Modem Configuration
NavSymm‘W DFl5»968-Ill. Operating Manual Issue 1.0
Figure 2.3 RTP Mobile Configuration
2.1 POWER SUPPLY
The power lead as supplied by NavSymm® is terminated at one end with a
three pin DIN connector, and has bare ends of wire at the other. This is
identical to the cable used to power the XRS-M. The DFl5-96S-III will operate
from the same battery or power supply as the associated XRS—M, and
accepts the same range of input voltages, (eg. 11 - 32 Volts).
The correct lead must be used in order to maintain the power supply filtering,
and water-resistance, of the DRS-QGS-lll. Both the RED and WHITE leads
are connected to positive, and the BLACK lead to negative. The GREEN
lead is the eatth return for the unit, and must (in conjunction with the screen)
be connected to a good earth point, or to the negative terminal of the power
supply. Input power supply should be capable of providing 1.5A continuous,
and 2A peak, in addition to any other loads attached to it.
2.2 DATA CONNECTION
Connection between the RTCM port of the XRS/XRG and the DATA port of
the DRS-QBS-Ill is made via the 12-way to 12—way cable supplied, This cable
connects both data and transmit timing control. A table of connections is
given in Figure 3.1 (Section 3.2.2). The high quality cable supplied provides
a shielded and water resistant connection between the XR5/XR6 and DR5-
QSS-III. If a longer connection is required, a suitable cable can be supplied
by NavSymm®.
Connection to the 9-way serial port of a PC or RTP12 system (see Figures
2/3) is made via computer data cable supplied with the RTP system, or as a
special part as required (See appendix A for parts lists). This cable has a
RED cover on the D-Type connector cover.
Note: This cable is NOT the same as the XFi5/XR6 data cable and cannot
be used on the XR5/XR6, nor can the XR5/XR6 data cable be used
on the DRS-QGS-Ill.
NavSymm£7 DR5-965»III. Operating Manual Issue 1.0
2.3 BASE STA TION ANTENNA
2.3.1 UHF ANTENNA CONNECTION
The UHF antenna supplied will normally be a quarter wave whip antenna. A
mounting bracket system is provided, this should be assembled as shown in
Figure 2.4 For base station applications, a colinear antenna may be
supplied which will require diflerenl mounting arrangements.
Figure 2.4 UHF Antenna Connection
NavSymm‘” DFtS-QGS-III. Operating Manual issue 10
2.3.2 GPS and UHFANTENNA SPACING
Any UHF transmitting antenna should be mounted as high as possible. A
suggested minimum height being 8 metres, which will give a radio horizon of
12km (assuming there are no obstacles whatsoever). The UHF antenna and
the GPS antenna should be separated horizontally by a minimum of 5
metres, more if possible.
If this is not possible, the two antennas should not be at the same height,
The GPS antenna should be higher, and the UHF antenna must be mounted
at least 1.5metres from any adjacent metallic mast. In this situation,
reduction of radio range from some directions is to be expected.
The radio horizon can be calculated from the charts given in Figures 2.5 and
2.6. Any expected range of the radio will be reduced from this value by
environmental conditions or obstructions to the signal path. As a rule of
thumb, range will be reduced over land by about 30-50%, and by a further
20% because of buildings ortrees.
TX Antenna Radio HX Antenna
Height Horizon Height
(Feet) (Miles) (Feet)
Figure 2.5 Radio Horizon (Feet/Miles)
NavS mm” DR5»968-III. Operating Manual Issue 1.0
__V_____—_—————
TX Antenna Radio Rx Antenna
HMS!"t Horizon Height
(Metres) (Kilometres) (MEWS)
Figure 2.6 Radio Horizon (Metres/Kilometres)
Note:
A more detailed description of radio range is included in Application Note 3.
2.3.3 DR5-96S-III and UHF ANTENNA SEPARATION
The DRS-QSS-III should be mounted as close as possible to the Iransmifling
antenna, Maximum cable length is 10metres.
23.4 GPS RECEIVER and DR5-96S-III SEPARATION
The longest data cable between the XHS-M and the DR5-96S-III is 10metres.
Standard cable supplied is 0.5meires long.
NavS mmM DES-9684". Operating Manual issue 1,0
_Y__________—_————
2.4 REMOTE STATION ANTENNA
The DR5»965-III antenna and a GPS antenna should be separated as far as
is practical. If the system is being used to send back status (or other)
messages to the base station, this separation becomes more critical, since it
is undesirable for the radio transmitter power to be coupled into the GPS
receiver antenna. However, the XR5/XR6 GPS receiver features effective
filtering, and should not suffer degradation in performance when the
transmitting antenna is more than 1metres from the GPS antenna. The
Radio and GPS units can be mounted together inside (or outside) the host
platform, ensuring all connections to them are protected from mechanical
damage.
2.5 RFI
The DHS-QGS-III has been designed to meet all relevant specifications in
transmit mode, and will receive signals in a satisfactory manner provided
there are no other transmissions on the frequency chosen.
2.6 ENVIRONMENTAL
The DFtS-QGS-III meets sealing and temperature requirements provided each
connector is used with the correct cable, and has the dust and sealing caps
(supplied) properly fitted.
However, as with all electronic equipment, it will function most reliably when
protected from environmental extremities. Ensure mounting is within
weather-proof housings, vehicles, or other enclosures.
NavSymm” DRS-QSS-lll. Operating Manual Issue 1.0
3.0 OPERATION
3.1 BASIC USE
The DRS-QGS-Ill will be configured for use in the system as described by the
customers order confirmation. It should only be necessary to connect the
system as shown in the diagrams, correct operation should then begin.
LED's are used to indicate correct operation. Power-on is shown by AMBER,
correct transmit by RED, and received signal by GREEN.
Reference to Application Note 2 will provide the user with more detailed
information on TDMA and RTP applications.
3.1.1 RTCM DISTRIBUTION, with STATUS RETURN
The serial interface of the DRS-QSS-Ill is pre-set during manufacture to
19200,N,B,1. As supplied, the DR5-QGS-lll will have the transmit control
handled by the XRS/XRG. A ‘Y‘-Iead is required at the base station to
separate the returning status messages from the outgoing data. This lead
should be ordered as an optional extra from NavSymm®.
3.1.2 RTCM DISTRIBUTION with TDMA MULTIPLE STATUS RETURN
A mobile DR5~96$—lll is supplied with the serial interface set to 19200,N,B,1
to allow connection to an XRS/XHG. Base station interfaces will be set to
19200,N,8,1 to allow most efficient transfer of data from the radio. The ‘Y’»
lead is used to split the outgoing RTCM messages from the returning status
messages. NavSymm® will supply any DRS-QGS-III which is intended for use
as a base station pre- marked with "BASE" on its label. Both the base station
and the mobiles are set—up to use binary compression, thereby providing
effective radio transmission and addressing, which ensures that a mobile will
ignore any data sent from another mobile.
See Appendix 0, Application Note 2 for details of the capabilities of the
TDMA system.
3.1.3 RTP or Data Transfer
AII DRS-QSS—Ill‘s are supplied set to 19200,N,8,1 with software transmission
control. The transmitter will send data when it is presented at the serial port,
even though it may be receiving data at the same time. This requires the
_——__——.__—_——
NavSymme DRE-QGS—III. Operating Manual Issue 1.0
communication programs to make their own allowances for ensuring there
are no conflicting transmissions For data transfer applications, it is
recommended that a half duplex transfer protocol such as “Kermit" is
employed.
3.1.4 General Operation
Assuming all connections to have been correctly made, and the XRS-M has
been configured for correct operation using the XRS-M programme, base
station and remote operation becomes totally automatic.
In a TDMA system the transmission periods will need to be set using the
XR5»M, paying special attention to ensure that the various mobiles will not
interfere with each other (Appendix 0, Application Note 2). An XRS-M
transmission can take place at pre-set times within any given second. With
other systems, transmission usually occurs as soon as data becomes
available.
3.2 ADVANCED USE
3.2‘ I Radio Description
The DRS-QBS-III Radio Modem transmits and receives half duplex serial data
at either 9600 bits/sec, or 4800 bits/sec, depending on the users setting. A
buffer RAM is provided enabling data to be passed asynchronously to the
host at Baud rates from 150 to 38400. Parity and stop bits are all adiustable
over the usual values. An error detecting algorithm can be selected to
maintain the integrity of the data transmission at high speed or over
interrupted paths.
It is possible to configure the DRS-QGS-III whereby it will automatically repeat
the data it receives, consequently extending the range of transmission, or as
an echo back configuration.
3.2.2 Connections
Power is supplied to the unit via a 3 way DIN connector as described in
section 2.1. The unit has a switching regulator which requires a 2A start-up
current, but once running, the DFl5-968—III uses only 1.4A to transmit, and
25mA to receive. The power supply does not need to be specially regulated
provided it meets the current requirements of the units.
All data port cables supplied will connect directly to an XR5/XR6, RTP12 unit,
or a PC. Cable specifically for use with an RTP12 system, or a PC, will have
a RED cover. The pins used are shown in Figure 3.1.
NavSymmg DRS-QGS-Ill. Operating Manual Issue 1.0
Normal connection will only use the data and retum connections, the
XR5/XR6 uses the transmit control line. All the other connections are used
for configuration purposes.
09543654” Cable Colour Data port _|_XFt5-M PC Control
Pin or RTP12 Port
A (1) GREEN +8v out - -
B (2) GRN / BLK Tx Control Radio - -
l_ Control
0 (9 ORANGE Spare - - -
D 4) -l_OR / BLK HSSI - RSSl out - _|
E (5) BLUE Erog Data Out — - Transmit
Data
F(6) BLUE / BLK Data In Transmit TxD -
Data
G (7) RED Frog Data In 1 — - Receive
Data
H (8) RED / BLK Data Out Receive RxD -
_4 Data
J @L WHITE CTS - CTS
KM) RED (WHITE RTS » RTS
L (11) WHITE / BLK BLACK Ov Ov _l_Sig Gnd Gnd
M (12) SCREEN & DRAIN Screen 3 Screen Screen — j
Figure 3.1 Data Port Connections DR5796S—III
3.2.3 Configuration afDR5-965-III
The DRS-QGS-Ill is delivered already configured for the application specified
by the customer. Changing this configuration involves opening the DRS-QGS-
Ill, making connection to the intemal control port, and utilising a terminal
programme to change the settings of the DRS-QGS-lll.
Users must ensure that they have read and understood all sections of the
manuals (for both the DRS—QGS-lll, and the XRS/XRG) before beginning to
make any changes. Once disturbed, the settings must be correctly reset
before the link will begin to work again (Section 3.4).
Appendix G contains several Application Notes describing the Setup
Parameters and use of the DRS-QGS-Ill in a range of systems. It is advised
that these are used as starting points for any attempts at re-configuration.
3.3 MODEM PORTS and CONTROL
This section describes the commands used to control the radio data ports.
The DRS-QSS-Ill has tour ports: the RTCM Data Port. Frequency
Programming Port, Control Port, and a Radio interface Port, Detailed
descriptions for use by applications engineers are given in Application Note 1.
______________——-———
10
NavSymm® DRS-QGS—lll. Operating Manual Issue 1.0
13.1 The RTCM Data I’ort
The RTCM Data Port is available at the 12-way connector on the outside of
the DRE-9684”. This port transmits and receives data from the XRS/XRG,
RTP12 unit, or a PC.
Any data presented at the port will be transmitted and received unchanged at
either end of a mobile link, provided that the data rate is matched to the port
setting.
3.3.2 The Control Part
The Control Port is also available via the 12 way connector marked ‘DATA’
on the DRS—QGS-III. it requires a special serial cable to connection to a PC
(BLUE 9-way D cover).
This Control Port allows the resetting of all the Data Port and Radio Interface
Port parameters. Normally, the DRS-QGS-Ill will have been supplied with the
two frequencies pre-set to the values requested by the purchaser. However,
it is possible to change these frequencies when required, using the Control
Port.
This feature is password protected. Contact NavSymm® for further details.
3.3.3 The Radio Interface Port
The Radio Interface Port controls the transmission and reception of the data
over the ainNaves, together with the hardware use of compression,
correction, addressing, data-rates and simple frequency switching.
Direct connection is not possible, the port is contained within the unit.
Configuration is via the Control Port.
11
NavSymm® DRS—QGS-III. Operating Manual Issue 1.0
Figure 3.2 Top PCB Layout (upper surface)
12
NavSymm“ DES-9684“. Operating Manual Issue 1.0
Figure 3.3 Top PCB Layout (lower surface)
NavSymmE DRS—QGS-III. Operating Manual Issue 1.0
3.4 THE CONTROL PORT COMMAND SET
To access the Control Port, connect the ‘Control Port Serial Cable' (BLUE 9-
way D cover) to the ‘DATA’ port.
The other end of the cable connects into the 9-way R8232 port of a PC.
Using a terminal program (such as Windows Terminal), set the
communication parameters to 9600 baud, 8 data bits, no parity, no
handshaking, and one stop bit. When power is applied to the radio, the
terminal should display:
DR5-965-III HDLC Modem Ver 1.0
Press return, the modem should reply something like, (but not exactly):
Command tailed
MODE COM1: 9600,N,8,1
MODE COM2: 9600,S,F,A,U,0
MODE COM3: 4800,N,8,1
MODE FR01: 456.9250,456.9250
MODE FRQZ: 462.0000,462.0000
This shows the present settings of the modem.
It is strongly suggested that careful note is made of the exact wording
of this reply, so that original settings may be restored should the
changes fail.
The parameters refer to:
COM1 - The Control Port
COM2 - Radio Interface Port
COM3 - RTCM Data Port
FRO1 - Frequency 1
FHOZ - Frequency 2
These ports may be re-configured by entering commands from the PC
terminal to the radio. It is important to follow the case and form of the
commands exactly. When commands have been executed correctly, the
radio will reply (thereby confirming the correct reception of the new
command) which will be implemented immediately.
The Data Port and Control Port are both asynchronous ports for R8232
communication and have identical command sets.
The Radio control Port is a synchronous port, controlling the data format over
the radio channel. This has a different command format.
Radio frequencies are pre-set, the data is displayed for information only.
14
NavSymm® DFlS-QGS-III. Operating Manual Issue 1.0
3.4.1 Setting the RTCM Data Port and the Control Port
Setting the data and control ports is a similar procedure to setting serial
communication ports on a PC.
The format of the command is as follows :-
MODE COMv:w,x,y,z 
where:-
v = the port number 1 or 3
w = the baud rate 150, 300, 600, 1200, 2400, 4800, 9600,
19200, 38400, 57600, 115200
x = parity O, E, O, 1, N for odd, even, zero, one or none parity
y = length 7 or 8 data bits
z = stop bit 1 or 2
 = carriage retum
The manufacturing defaults‘ are :-
MODE COM 1: 9600,N,8,1 
MODE COM 3: 4800,N,8,1 
All parameters have to be included and typed in upper case. No characters
can be shortened or omitted.
* NOTE:
These examples may not show the same settings as the radios supplied by
NavSymm@.
During manufacture, radios are individually adjusted to give best possible
performance for the application described in a customers purchase order.
15
NavSymmw DR5»958-Ill. Operating Manual Issue 1.0
3.4.2 Setting the Radio Interface Part
The radio interface port uses a similar basic format to the other ports, but
different parameters.
MODE COM2:a, b, c, d, e, f 
where:-
a = Baud Fiate
Set to 4800 or 9600 bits per second over the radio channel.
b = Transmit Initiation Control
S = Software - Idle gap of 10 characters, or more than 320
characters received.
H = Hardware - Pulse on RTS line or transmit control line
0 = Error checking
C = Clear - No error checking on received messages
F = Filtered - CRC, Overflow, Abort, Frame length and Non
Octet Aligned checking. A message which has
any errors will not be passed out of data port.
d = Message format
A = ASCII - No compression
8 = Binary - Packed standard status messages for
minimum transmit time
e = Network addressing
A = Addressed - Network addressing switched on
U = Unaddressed - No address checking, all messages
relayed
Ft: Repeating - received messages are immediately
re-transmitted
f = Frequency
0 = Select Frequency 1
1 = Select Frequency 2
 = carriage return
The manufacturing defaults’ are .'-
MODE COMZ: 4800, H, F, A, A, 0 
* NOTE:
These examples may not show the same settings as the radios supplied by
NavSymm®, During manufacture, radios are individually adjusted to give
best possible performance for the application described in a customers
purchase order.
16
NavSymm® DHS-BGS-IIL Operating Manual Issue 1.0
After  the radio modem replies
Command 0K MODE COM2: 4800, H, F, A, A, 0
This shows the new values of the control for the ports.
3.5 USER CONFIGURABLE CONTROLS
There are four DIP switches mounted on the radio modem board (See Figure
3.1), labelled as SW1 (1-4).
Switch 1 unconnected.
Swifch2 the reset switch for the processor, used only to download new
software. Both these switches should be left open (off).
Switch 3 connects the HTS line from the XFlS/XFlG to the RTS line of the
DFl5-QGS-III.
Switch 4 connects the Tx control line to the RTS line of the DRE-QGS-lll.
The default setting for both switches 3 and 4 is closed (on) and
provided NavSymm® cables are used this setting will work for all
applications. However, if different cables are used, these may
have to be changed to allow the DFlS-QSS—III to select
handshaking or hardware control of transmit.
The RV1 (Figure 3.1) potentiometer sets the level of the receiver detection
circuit. It should not be necessary to adjust this potentiometer.
If persistent data break up is occurring without an obvious cause, turn the
potentiometer one tenth turn clockwise, then turn it back again to its original
setting. If necessary, reset again by one further tenth turn anti-clockwise.
Do this whilst transmitting and monitoring the data. Leave the potentiometer
set to the position which gives best quality of reception.
If there is no change in the data break-up, return the potentiometer to its
original setting,
17
NavSymm‘R DRs-sss-m. Operating Manual Issue 1.0
4.0 FAULT FINDING GUIDE FOR DR5-96S-III
Fault-finding on the DRE-9684" radio is accomplished mainly by using the
LED’s on the top of the case.
This displays:
GREEN for quiescent (neither sending or receiving).
AMBEH for receiving.
RED for transmitting.
An XRS, SHARPE XRG, or a PC, which is connected correctly, will cause the
transmitter to function the moment data is ready for transmission, and to go
off the moment all available data has been sent. When incoming data is
received. it is passed immediately from the radio to the remote GPS unit or
computer. Refer to Figure 4.1 for the most obvious problems and their
solutions.
If you are still having problems, call the NavSymm® technical help line on
+44-1604—585588.
NavSymm‘l‘ DRS-SSS-III. Operating Manual issue 1.0
Symptom Occurs Solution
No LED: Check power leads, tuses, voltage supply.
Green LED: When expecting Check antenna connections on transmitter.
to transmit. Check data rate and port settings,
Green LED: When expecting Check antenna connections and receive
to receive. frequency.
Amber LED: When expecting Channel is in use or blocked by interference
to transmit. trom electrical equipment. Try re-Iocating
receiver and or antenna.
Amber LED: When expecting Channel is blocked by interference. Try moving
to receive. the receiver and or the antenna to get the LED
to blink in time with the transmitted signal.
Channel is in use by another user. Use a
monitor receiver to listen to the signals on the
trequency.
No Red LED: When expecting It the radio current is increasing and falling in
to transmit. time with the expected transmission, then the
antenna is incorrectly titted, or the cable is
taulty. If there is no increase in current when
transmission is expected. the baud-rate on the
GPS and radio do not match, or the radio is set
up to have transmission controlled by the GPS
and the transmit control line is not connected.
LED blinks Amber
in time
transmitted data but
only rubbish
received:
with
is
LED blinks Amber
in time
transmitted data but
there are occasional
errors in the data
stream:
LED blinks Amber
in time with Data on
transmit, but no data
is received:
with
Data rate over the air is sent differently at
transmitter and receiver. Set COM2 parameters
to match at receiver and transmitter. Parity or
data bits is set incorrectly at transmitter or
receiver.
Adjust Ftv1 +/- 1/10 turn to set detection
threshold. HV1 is tactory set tor best
performance with all radios. Making this
adjustment will set receiver to work only with
transmitter used to set up receiver.
Computer or modem is not set to the correct
baud rate. Some or all settings on COM2 do not
match between transmitter and receiver.
Figure 4.1 Fault Finding Checklist
19
NavSymm” DRS-QGS-III. Operating Manual Issue 10
APPENDIX A
PART NO.
DR5-9b‘S-III A1 90-00061
A complete product comprising:
2W UHF Transceiver A190-OO1 G1
5m Antenna Cable (FMSS) A141 -024G1
Antenna Mounting Bracket M35099/06
UHF Antenna Mounting Ring M141—205/02
Power Cable (2m) A110-024/A
Data Cable to XRS-M A141 -020G1
Frequency Programming Cable A141-03961
User Manual A190-032Ci1
Screw Pack A61—103G1
Warranty Card ??
OPTIONS
RTCM or TDMA Base station Y lead
10m Antenna Cable (R6213)
Data Cable to 9 way D-type (PC/RTP12
use - RED cover)
Data Cable to 9 way D-type (Kernel use)
25W Amplifier
ANTENNA OPTIONS
Whip / Colinear (6db)
Base Station Colinear a (Sdb)
Base Station Colinear b (6db)
Yagi (Reference Only)
20
141 ~303l01A ??
A141—042G1
A141-025G1
A141-027G1
A141-029G1
A141-035G1
A141-209
A141-210
A141-211
A141-213
NavSymm” DR5~QGS-Ili. Operating Manuai Issue 1.0
APPENDIX C
Radio Application Notes
22
NavSymmB DR5»968-Ill. Operating Manual issue 10
- Application Note 1 -
DR5—968-III SET-UP PARAMETERS
This application note covers the setup parameters for the DH5-968-lll in
greater detail. It discusses some of the implications of the available settings,
and how the radio is to be used to best effect in a system
PORT SETTINGS
The settings of the ports are changed using the programming adapter cable
supplied with the radio. Using a PC together with a standard terminal
program, all the facilities of the DRSJSJGS-III can be accessed and changed.
Parameters are stored in an EPROM and are saved When power is
disconnected from the DRS-QGS-lll.
Part I - Control Port
Command Form
MODE COM1: 9600,N,8,1
Port 1 is the loader and control port, accessed via the 10 way internal
connector (JB). Settings are variable, but under most circumstances there is
no need to change them from the default values of 9600,N,8,1. This setting
gives effective control of the DRS-QGS-Ill, without interfering with the
operation of the unit.
Part 2 - Radio Interface Port
Command Form
MODE COM2: 9600,H,F,A,U,O
Port 2 is the interface port for the radio. The parameters control the mode
and frequency of transmission. it is accessed via the 10 way internal
connector (JG).
Bits Per Second
MODE COM2: 9600,H,F,A,U,O
The BPS parameter is 9600 or 4800, the rate is expressed as bits per
second. Data is transmitted continuously within an HDLC packet, this means
23
NavSymmj’ DRs-SGS-Ill. Operating Manual Issue 1.0
that the rate of data and times occupied depend upon the data lengths. For
example, comparing data rates of R8232 defined as 9600 Baud and 9600
BPS there are some interesting effects.
Message H5232 Time Radio Fixed Total Saving
Length (Bits) (1115) Link (Bits) Time Time (ms)
(Bytes) (m3) (m5)
10.00 100.00 10.42 80.00 30.00 38.33 -27.92
100.00 1000.00 104.17 800.00 | 30.00 113.33 -9.17
256.00 2560.00 266.67 2048.00 l 30.00 243.33 23.33 1
320.00 3200.00 333.33 2560.00 30.00 | 269.67 36.67
Figure A], Message Length and Timings
The radio link requires a fixed time to switch from receive to transmit and to
set up the datalink. This means that for short packets, the radio takes longer
than the RSZSZ to transfer the data. For longer packets, the radio is more
effective at transferring data than the R8232. Therefore, most systems
should accumulate data into larger bursts, rather than sending a larger
number of smaller bursts.
Using a transmission data-rate of 4800 BPS results in a slightly more reliable
link for difficult paths (eg. from fixed station to fixed station). The increased
length of the transmission will also increase the likelihood of a mobile
experiencing signal fade. The lower data-rate changes the data shaping
value, whilst the occupied bandwidth on the radio channel remains constant.
Transmission Control
MODE COM2: 9600, H, F,A,U,0
The modem constantly monitors the data port, storing data as it is received.
Under software transmit control, where a pause of 10 characters length
occurs in the data, the stored data will be transmitted. Under hardware
control, the transmit control line causes all the characters stored in the buffer
to be transmitted at once. In both cases the transmitter is activated without
reference to the radio channel being clear. This is intended to prevent
external interference (from local sources) preventing operation of the system.
To ensure data is not lost (because of several stations in a TDMA system
transmitting at the same time) the GPS is programmed to cause transmission
only in the correct time-slot. (See Application Note 2 for more details).
With software control, either a one way link must be established, or a
software method employed which ensures data is being correctly transferred.
This is the basis of a packet system. The radios having been utilised as
dumb-modems in such a system.
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NavSymm“ DRS-QBS-lll. Operating Manual Issue 1.0
On some occasions it may be possible to make use of the data itself as a
handshaking control. For example: (1) in an FtTP mobile system which is
receiving a long base station message once per second, (2) by cross
connecting the received data into the handshaking lines of the mobile, (3) a
short status message can be returned, (4) and transmitted by the radio.
RADIO
CHANNEL
DR5
TO
MOBILE
Join “IN" data line to “CTS” on mobile to ensure “OUT" and “IN" occur together
Figure A2. Handshaking Control
When data is being passed from the DFtS»96$-III to the mobile RTP, the
radio channel must be inactive. At this time it is possible to return
transmission from the mobile to the base station (4). The hardware transmit
control In the PC based system may also be used to gather data on the DFt5-
QGS-III from a number of completely separated periods, and to transmit them
together under software control. This increases the efficiency of operation.
(See the previous section).
MODE COM2: 9600, H,F,A,U,0
This ensures that the data delivered to the XR5/XR6 (or PC) is completely
correct. However. there is no reason why software using the modem should
not use its own error correction routines. In this case, the modem can be set
to transfer all received data out of the data port. This is clear mode. In
addition this mode can be used to determine if data is being corrupted by
pulse interference. It has been noted that an apparently clear radio channel
can be blocked by very short bursts of noise, which cause single and double
character errors.
MODE COM2: 9600,H,F,A,u,0
ASCII is a generalised term for the data sent to the DRS-QGS-IIIA With ASCII
selected, all the data will be transmitted exactly as was received into the data
port. This is the most common mode of operation. The exception being
NavSymmi" DRS-QGS-III. Operating Manual Issue 1.0
TDMA, which uses Binary mode. In Binary mode, the modern examines the
incoming data. If the first received character is if (Hash or Pound), on
transmission the data is passed to a compression routine which compresses
Navstar status messages into a binary format. On receipt, the data is
decompressed and passed out of the data port. Currently, the compression
is specific to the XFtS/XRG status messages, and can be used in TDMA or
software controlled transmit code.
MODE COM2: 9600,H,F,A,U,0
In un-addressed mode the data will be passed out of the data port and
received by all radios. In addressed mode the radio examines the incoming
data on the data port from the XFtS/XRG to determine its address. if the first
four characters of the incoming data are #NNN (as they are with status
messages), where NNN can be any number from 0 to 254, the radio takes
that number as its address. If the first characters of the data are not ’#000‘
but an RTCM message from a base station, then the radio assumes an
address of 255.
Receiving of messages therefore depends on the message address received
over the radio channel, and the address of the receiving DRS-QGS-III.
Message Address Recelvlng Station Address
Figure A3. Addressing Truth Table
1 = Message passed out of data port
x = Message not passed out of data port
Station address 0 acts as a monitor for all messages fortest purposes.
Frequency Selection
MODE COM2: 9600,H,F,A,U,0
The frequency selection parameter can take the values 0 or 1 for the primary
and secondary frequencies. The radio has two frequencies pre-programmed
as requested by the customer. If new frequencies are later required, the
Frequency Programming Kit must also be supplied. More details are given in
Application Note 3.
9A
NavSymm“ DRS-SSS-III. Operating Manual Issue 1.0
Part 3 - DATA Port (RTCM)
Command Form
MODE coma: 9600,N,8,1
Port 3 is the data port, and is accessed via the 12 way connector marked
DATA on the DFts—QGS-III. This sets the parameters needed to communicate
with the terminal equipment, be it an XRS/XFtG, RTP 12, or PC.
The data rate and data size need to be considered in relation to the data rate
over the transmission. In general, the data rate can be anything the user
requires, provided that there are sufficient breaks in the data to allow
transmission.
For example, if the data rate overthe air is 9600 BPS, and the data port is set
to 19200, the data port may only transmit data to the DRS-QBS—III 50% of the
time. If this percentage is exceeded, the intemal memory of the DFts-QGS-Iil
will fill up and transmission will eventually stop.
The internal memory can store approximately 300mS of data at 9600 Baud.
Setting 9600,N,8,1 is suitable for RTP systems, but for use with a TDMA
system, the mobiles are set to 4800 Baud and the base station set to 19,200
baud.
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NavSymm“ DHS-QGS-III. Operating Manual Issue 1.0
— Application Note 2 -
DR5 - 968 - II TDMA and RTP APPLICATIONS
The DFt5—968—lll is designed to provide efficient, reliable transmission of GPS
data between base stations and mobile receivers. To achieve this, the DR5-
st-lll radio uses addressing, error detection, and data compression. This
application note describes the setup of a Time Division Multiple Access
(TDMA) vehicle tracking system with broadcast FlTCM distribution, together
with the Real Time Positioning (RTP) system.
RADIO SYSTEM CONFIGURATION
A thorough understanding of the operation of both the DRS-QGS-Ill and the
XRS/XRG is needed to configure a system. This is due to the flexibility of the
systems which permit a working system to be prepared under the most
adverse conditions. These application notes assume the user is familiar with
both the XRS/XRG and the DFtS-QSS-III product manuals.
These application notes seek to explain the logic behind each type of
operation, and to describe how to achieve the most efficient use of the radio
channel by using Time Division Multiple Access (TDMA) under the control of
an XFt5lXFl6.
Development of the DRS-QGS-Ill has specifically focused on the design of a
unit which will effectively track a large number of RTCM corrected mobiles,
ensuring that the XRS/XRG and DFl5-968-Ill will give optimum performance in
this mode.
There are a number of special features encapsulated within the DRS-QGS-lll
and XFt5/XFt6 which are specific to this requirement. A clear understanding
of these features will allow the capabilities of this system to be fully exploited.
TIME DIVISION MULTIPLE ACCESS APPLICATION
Radio systems communicate by transmitting data over a radio channel. The
DRSAQGS-Ill is a half-duplex radio, meaning that it can either transmit or
receive at any one instant. In fact, it takes a finite amount of time to change
from transmission to reception.
To make effective use of time. some external control of transmission is
required. The XRS/XRG provides this external control by allowing the user to
set the time and duration of the transmission control output from the FtTCM
port. This allows every second to be divided into small parts, each of which is
used to communicate data.
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NavSymm’“ DFtS-SGS-III. Operating Manual Issue 1.0
In a TDMA system, the base station transmits RTCM information in the first
part of the second, and the mobiles return their information in the subsequent
parts. An XFfS/XFtG will control transmissions to make sure that signals do
not interfere with each other.
In addition, the DRS-QSS-III is able to compress standard status messages
into a compact form which further reduces the amount of time required for
transmission. The DRE-QGS-III also uses addressing derived from the
XR5/XFt6 ID numbers, directing messages to the correct destinations. By
deriving this addressing from the attached XRS/XRG, the radios are dynamic
and do not need to be individually programmed.
The XR5 and SHARPE XR6 Setup
When programmed to operate as a base station, the XRS/XFte will provide
RTCM corrections to 50104, types 1, 2 and 9.
Type 1 provides a full set of corrections for all the satellites visible at the
base station.
Type 2 provides an overlap for satellites whose Ephemeris has changed at
the top of the hour, for a period of five minutes after the hour.
Type 9 messages only have data forthree of the visible satellites, and cycles
round all the visible satellites to send a full set of corrections. This occurs
over a longer period and is useful in a heavily occupied channel, or over a
slow data link.
Each of these corrections is prepared at the top of the second, and sent out
of the FtTCM port at the half-second mark. When in base station mode the
communication can take place at 19,200 baud which allows the data to be
communicated quickly and effectively from the XRS/XRS to the DFtS-QGS-Ill.
At the mobiles, the received FlTCM data is used to calculate position. A
status message is generated about half a second after the top of second, and
passed out of the GPS unit at the top of the following second. Status
messages contain information on the mobiles position, speed, heading, and
satellites used in the solution. Messages also have a unit identification
number which is used within the radio to prevent a mobile from receiving
other mobiles data.
Control of timing in a TDMA system is the key to achieving efficient data
transfer. It is essential to decide on the time allocations before beginning to
set up a system. The amount of time required for different messages is
detailed in Figure Bi. This assumes that the base station is set to 19,200
Baud, the mobiles are set to 4800 Baud, and the on air rate is set to 9600
BPS. These are the optimum settings for a TDMA system.
NavSymmIE DFt5-968-lll. Operating Manual Issue 10
Message Type ASCII Length Binary Length Radio Time '
Type 1 RTCM 120 Bytes 170 mS
Type 2 RTCM 70 Bytes 130 ms
__(50 + SOmS)
Type 9 RTCM 35 Bytes 80 ms
Standard 78 Bytes 40 Bytes 90 ms
Status
Reduced 63 Bytes 35 Bytes 85 mS
Status
Minimum 45 Bytes 17 Bytes 70 ms
Status
Figure B], Message Timing
‘ All radio times include SOmS setup time. This is not required twice it sending both
type 1 and type 2, thus type 1 and type 2 duration = 250ms.
The numbers of mobiles per second is determined by simple mathematics
Figure B2 shows the outline of a typical basic system.
Status Message RTCM Message Type
Type
Type 1 a. 2 Type 1 Type 9 None
Standard status 5 9 1° 11
B' 9“ 10'
Reduced Status
Minimum Status
Figure 82. Number of mobiles returned per second under diflerent
conditions
' Note these are minimum values. it is possible to increase these numbers by 1,
usrng fine adjustment of tx offset and duration.
The RTCM function selected depends on the trade-off of accuracy against
recovery of numbers of vehicles. If a full, accurate FtTCM solution is
required, then the initial 250 m8 of each second needs to be set aside for the
transmission of both type 1 and type 2 messages. For a marginal reduction
in accuracy at the top of the hour (5 - 20% for 5 minutes per hour), only type
1 messages can be sent, this allows one extra mobile to be returned each
second, by needing only 170 m8 tor RTCM distribution. it type 9 messages
30
NavSymm“ DR5»965-lll. Operating Manual Issue 1.0
are used, the accuracy is further reduced by 20 - 50%. but two additional
mobiles can retum their data each second.
Having chosen the RTCM format using the XFt5/XFt6 setup, (and selecting
19200,N.8,1 as the communications parameters) it is now possible to assign
the mobile IDs and message update rates. Take the total number of mobiles
required, divide by the number of mobiles per second possible (using the
data and RTOM formats chosen from Figure B2). This gives the number of
seconds required between updates.
lDNumber 31 30 29 28 27 26 25 24
3 3 2 2 2 2 2 2
Millisecond 320 250 580 810 740 670 600 53
Offset
Duration
ID Number
Second 2 2
Offset
Mllllsecond 460
Offset
460 39
Duration
ID Number
Second 1
Offset
Millisecand
Offset
Dura lion
Delay
Figure B3. Example TDMA configuration chart
n this examp e there are 36 mobiles, all receiving RTCM messages (1 and 2)
every second which takes up 250mS. Each XFts-M has been set to output
the minimum status message, having a length of 70mS each. Using table 2,
all the 35 mobiles can repon back in 4 seconds, and the time slice allocations
are given in Figure BS. Thus, for mobile number 21, the ID is set to 021, the
seconds interval is set to 4, the second offset is set to 2, millisecond offset is
set to 320, and the duration to 70. When all the mobile XR5/XR69 have been
programmed, they can be connected to DRS-QGS-Ill’s.
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NavSyme DRE-9654". Operating Manual Issue 1.0
The DR5-965-III Setup
Setting parameters for the DR5—968-III using mobiles is different to base
station applications. This is due to the fact that the XRS/XRG is unable to
receive data any faster than 4800 Baud.
Suggested settings are:
MOBILE BASE
MODE COM2: 9600,H,F,B,A,O MODE COM2: 9600,H,F,B,A,0
MODE COM3: 4800,N,B,1 MODE COM3: 19200,N,6,1
Figure B4. Comm port setting for TDMA application
For the mobiles, the hardware transmit control option is selected to ensure
the DRS-QGS—III controls the transmission. Filtering is turned on to prevent
corrupted data being delivered to the XRS/XRG, binary compression is
selected to get maximum efficiency on the radio channel, and addressing is
used to prevent mobiles from receiving other mobiles status messages.
In operation, the timings of the various signals are shown in Figure B5. The
HTCM messages and the mobile returns are all separated from one another
by 5—10 mS gaps which are caused by the turn-on delay of the transmitter. If
it is possible to examine the channel occupancy using a monitor receiver, it
may be possible to adjust the timings to give slight performance
improvements in signal timing.
22mg
M D RTCM T0 MOBILE
MOBILE
T, D STATUS
Fl D #001 #002 #003 #004 #005 ”006 #007 #008
3155 W
Time —>
Figure BS. Signal Timing
These data flows can all be checked using a storage oscilloscope and
monitor receiver, but the design of the DRS-QSS—III/XFtS/XRG combination is
such that this should not be necessary.
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NavSymm" DFlS-QGS-III. Operating Manual Issue 1.0
DR5-96S-III TDMA System Y-Lead
A ‘Y'-Iead can be supplied for the base station, this will enable outgoing
RTCM messages and returning status messages to be seperated. Details of
the pin connectors are given in Figure Be. The connections in brackets [ ] are
optional.
g-Way D-Type - to PC
12-Way Female - to DR5
12-Way Female - to XF15
DR5-965-III 12 Way D Type to PC (female) XR5/XR6 12 Way
9 Way
F (6) F (6)
L (11)
[M] (12) [M] (12)
Figure B6. TDMA ‘Y’ lead pin connection details
REAL TIME POSITIONING APPLICA TION
The NavSymm® RTP12 system requires data to be transferred from the base
station (a 12 channel XRS-M) to the RTP12 unit (which is a cased PC with
built-in XFtS-PC). This data consists of a burst of up to 320 Bytes, to be
repeated once or twice a second.
Configuration for the XR5/XR6 will be as for an FtTCM Base Station.
However, the RTP Base Station message is specified as per one of the RTP
output messages. These are stipulated in the XR5 RTP software (screen 5).
The DRS-QGS—Ill is configured for maximum data throughput rate (9600 Baud
N,8,1) to ensure most effective transfer of data. This HTP-DR5-968-III
combination is capable of transferring either 2 data bursts per second, or 1
data burst per second (as appropriate to the application).
33
NavSymm® DRE-9554". Operating Manual Issue 1.0
DR5-968—III settings for use with an RTP system, applicable to both base
station and mobile:
COM1.‘ 9600,N,8,1
COMZ: 9600,S,F,A,U,0
COMS: 9600,N ,8,1
Connection cables are supplied with the unit, and the system should operate
without any further modification. It is possible to increase the Port 3 rate to
19,200 Baud, which will give less occupied time on the R8232 link, but have
no real effect on the efficiency of data transfer.
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NavS mmE DRS-SGS-III. Operating Manual Issue 1.0
_V___________._———
- Application Note 3 -
RADIO RANGE ESTIMATING
Estimating radio path distances is often regarded as a black art. This section
is intended to familiarise NavSymm‘E7 customers with the basic principles of
DGPS data links and range.
RADIO WA VE PROPAGA TI ON
Radio waves travel (propagate) by various means:
Low frequency radio signals (such as the 150-350KHz beacon band) can
travel up to several hundred miles because they are able to pass between
the atmosphere and earth’s surface.
High frequency (HF) radio signals can travel long distances (possibly
several thousand miles) by reflecting between the upper atmosphere and the
earth’s surface. This may occur a number of times, until the signal is
attenuated beyond use.
Radio waves in VHF/UHF bands travel from point to point in straight lines.
The signals are not reflected by the atmosphere, nor are they propagated in
any way other than direct Iine-of—sight. Most DGPS links use VHF/UHF
frequencies.
The phrase “line-of-sight" must not be taken absolutely literally. It implies that
both the transmitting and receiving antennas must be in clear view of each
other. While this is a highly desirable situation (and essential when planning
long range links). it is not always essential to have a completely clear radio
path between the DGPS base station and the mobiles.
The majority of DGPS links will employ UHF signals. These perform very well
over water and open flat land, and adequately so in urban areas. In many
situations it is difficult to provide a continuously clear path between the DGPS
base station and mobiles. Provided that the range is not excessive. most
DGPS radio links at VHF, and UHF, will give good range coverage without
true Iine-of—sight conditions.
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NavS mm” DHS-QGS—III. Operating Manual Issue 1.0
_L______—__—__
DGPS RADIO LINK DISTANCE
The distance over which the DGPS radio signal carries is determined by
many factors, including:
- Transmitter power
- Height of transmitter antenna
. Gain of transmitter antenna
. Length and type of coaxial cable
. Height of receiving antenna
. Gain of receiving antenna
o Frequency
. Surrounding topography
a Weather
. Obstructions
From the above list, it will be apparent that DGPS radio link distance is not
easy to determine, particularly for long paths. The overall DGPS radio
system performance will be only as effective as the weakest link in the chain.
Some of the factors are beyond the users control, such as FCC restrictions,
weather, overall antenna height, and physical obstructions.
Generally, in planning a DGPS radio link, users must always strive for the
best possible operating signal strength. In the majority of situations, this is
best accomplished by:
. Paying special attention to the antennas being used.
a Position the antennas at both ends of the DGPS radio path as high as
possible.
0 Use good quality low loss cable and connectors.
. Ensure professional installation of the antenna, cable, and connectors.
. Remember that all cable has inherent losses, each additional length of
cable (beyond which is essential for the connection) will degrade the
overall performance.
Radio range should be the first calculation when planning a DGPS radio link,
even the most temporary one. The radio horizon (optical + 33%) has to be
checked in order to determine whether or not the link is generally possible.
Radio transmitter power, and heights of both the antennas (DGPS reference
and mobile), must be sufficient to ensure that the radio signal has the clearest
possible signal between them.
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NavS mm“iv DFlS-QGS-III. Operating Manual Issue 1.0
DGPS RANGE DETERMINATION
The design of the transmit and receive antenna system is very important, it
determines how well radio energy is transferred between antennas. Some of
the factors which require careful consideration are:—
- Gain
Direction
Polarisation
Height above Ground
ANTENNA HEIGHT VERSUS RANGE
Antenna height is simply a matter of the higher the better“. Increasing the
height extends the line of sight distance and reduces the blocking effects of
objects on the ground. View of the horizon is dependent on the antenna
height above the surface of the earth as shown below. It can be seen that
because of the curvature of the earth, the distance to the horizon is greater
when viewed from an elevated angle.
Line 01 sight
Radio waves are similar to light waves in that they tend to travel in straight
lines. However, radio waves also tend to retract (or bend) as they follow the
curvature of the earth. This extends the radio horizon beyond the optical
horizon. Bending of the wave is caused by the tendency of the radio wave to
travel slower as the density of the air increases. Since part of the radio wave
travels near the ground where the air is more dense, this bending will always
occur.
When studying the behaviour of radio waves in space, it is more convenient
to use a path that is a straight line instead of a curve. This requires that the
radius of earth curvature be simultaneously readjusted to preserve the correct
relationship.
For the standard atmosphere, this equivalent radius is 4/3 or 1.3 times the
actual radius of the earth as determined by experience. As previously stated,
the optical and radio wave paths differ.
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NavSymmF’ DRS-QBS—Ill. Operating Manual Issue 1.0
The distance in miles from an antenna to the optical and radio wave horizons
is determined as follows:
Optical Horizon Distance = Square root of 2h.
Radio Horizon Distance = 1.33 * Square root of 2h
(where ‘h' is dimension in feet)
The maximum possible distance at which direct—wave transmission is
possible between transmitting and receiving antennas, at given heights (the
line of sight distance), is equal to the sum of the horizontal distances
calculated separately for the individual antenna heights.
When the distance involved is less than line of sight, the path is sometimes
referred to as the optical path. The nomogram below shows the relationship.
Optical Radio
H on Horizon
Receiving- m Transmittmg-
Antenna height Antenna height
2000 2000
we
1 00
1500 Q ‘ ‘0 1500
1 GD
30
tooo 9° 1000
7 ED
700 700
50 70
500 500
50 so
5° 300
40 200
30 . {09.—
' ‘z‘d """ 50
I D 10
o n o
FEET MlLES FEET
As the distance between the transmitting and receiving antennas increases,
the energy concentration for a given area decreases. Therefore, the distance
from the transmitting antenna also determines how much energy an antenna
intercepts. This loss of signal strength due to increased distance is known as
path attenuation and is expressed in decibels (dB).
38
NavSymmg DR5v963~IIL Operating Manual Issue 1.0
The amount of power available at the receiving antenna is dependent on the
amount of energy it intercepts. An electrically large antenna will intercept
more energy than an electrically small one. The actual dimensions of the
antenna are related to wavelength. Because a smaller antenna intercepts
less energy, there is a decrease in useable range as frequency increases. It
is possible to increase the size (in terms of wavelength) of higher frequency
antennas so that they intercept more power. These antennas are referred to
as ‘gain' antennas.
Communication range is calculated by determining the path attenuation and
relating it to the power output of the transmitting antenna. Path attenuation
places a practical limit on maximum useable range because a point is
reached where it is impractical to radiate sufficient power to overcome path
loss. While antenna height establishes the maximum possible range, the
radiated power determines the practical limit, since that determines the signal
level at the receiving antenna Even though base station power could be
increased to several thousand watts, the system ‘talk back’ range would still
be limited by the power output capability of the remote units.
CALCULATING RADIO RANGE
Determination of radio range is a complex matter which has many variables,
some of which were described in the preceding section. Here, it is not
intended to cover all the variables, but an outline is given covering the basic
approach. This can be used to determine the distance over which a
telemetry link will operate whilst providing reliable communication. The
following steps may be taken:
Determine the line of sight transmission distance
1. Select the antenna height above the terrain.
2. Calculate the transmitter and receiver transmission line losses at the
operating frequency.
3. Determine transmitter power output and receiver sensitivity in dBm.
4. Determine transmitter and receiver antenna gain.
5. Calculate path loss at the operating frequency.
Once these parameters have been determined, an estimate of the RF link
range can be determined over smooth terrain. Obviously, if there are major
obstacles in the signal path, designing a useable radio link may be difficult.
For example:
if there is a 10,000 foot high mountain between the base station and a remote
site, whose antenna are only 100 feet above the average terrain.
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NavSymm® DRE-QGS-III. Operating Manual Issue 1.0
The following information describes how these parameters may be
calculated.
Line Of Sight Distance
The line of sight distance can be determined by the following equation:
D(optical) = «lzh,+ 2h,
D1 (radio) = 1.3 " D
Where
D = Distance in miles to optical horizon
D1 = Distance in miles to radio horizon
h, = Transmitter antenna height
h, = Receiver antenna height
For example:
assume that the antenna heights about the spherical earth are 25 feet for the
receiver, and 100 feet for the transmitter. Line of sight distance would then
be
D = 1l2(25) + 02000 = 21.2 miles
D1 = 1.3 * 21.2 = 27.5 miles
Path Loss
Determining (by calculation) the line of sight distance, does not guarantee
that same range in reality. The transmitter power, receiver sensitivity,
transmission line loss, antenna gain or loss, and operating frequency must
also be considered. The line of sight distance only means that the curvature
of the earth does not block the signal. To determine path loss with these
factors, assume that the HF system has the following fixed parameters:
. Transmitter RF Power Output - 2.0 Watts (33dBm)
. Operating Frequency = 450MHz
. Total Tx Transmission Line Loss (heliax, 100ft) = 0.85dB
- Total Fix Transmission Line Loss (RG/U, 25h) = 1.25dB
- Receiver 12dB SlNADE Sensitivity = 116dB
. Transmit and receive antennas (7 element Yagi) = 10dB
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NavSymm” DHS-SGS-III. Operating Manual Issue 1.0
Determine the path loss (PL) at radio line of sight of 27.5 miles using 100 and
25 foot antennas at 450MHz by using the following general equation:
PL = 117 + 20 Iogmf MHz - 20 log N, h,h, + 40 logm D
Where:
PL = Path loss in dBm
1 17 is a constant
f = Operating frequency
ht = Transmitter antenna height in feet
hr = Receiver antenna height in feet
D = Distance between antennas in miles
PL = 117 + 20 logm 450 - 20 log m (100’)(25') + 40 Iogm 27.5
PL = 117 + 53.06 - 67.9 + 57.5 =159.6dB
Therefore, the path loss at radio line of sight is 159.6dB at 450 MHz, with a
receiver antenna height of 25 feet and a transmitting antenna height of 100
feet. The figure below shows the relationship between path loss and radio
range over smooth earth with the above listed conditions.
PATH LOSS W (15
DisTANCE IN MILES
I 2 3
. 900 MHZ too/50h . QDOMHZ 100/Est! ‘A 450MHZ 100/25h
PATH LOSS CHART
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NavSymm® DRE-QBS-Ill. Operating Manual Issue 10
Path Margin
Path margin is the effective amount of transmitted power available before
path loss is subtracted. If path margin is greater than path loss,
communication is possible across the radio system. The formula for path
margin is as follows:
Path Margin = Power Out - Rx Sensitivity - Cable loss + Antenna gain
Assume the following conditions exist:
Transmitter Power = +33dBm (2 Watts)
Receiver Sensitivity = -116dB (12dB SINAD)
Cable Loss = 0.85dB (Tx) 1.25dB (Rx)
Antenna Gain = 10dB (each antenna)
Path Margin = 33 -(-116) - 0.85 - 1.25 +10 +10
= 166.9dB
Therefore, from this example:
with a path margin of 166.9dB, minus a path loss of 159.6dB, equals 7.3dB
of margin at the receiver.
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NavSymmw DRE-SGS-Ill. Operating Manual Issue 1.0
ALTERNATIVE TYPES of DGPS RADIO LINK ANTENNAS
The subject of selecting antennas for communication purposes is complex.
This section attempts to simplify this process, and to assist users in
identifying the correct antenna for specific applications.
Antennas for DGPS radio links will fall into one of two categories:- either
Omni-Directional, or Directional.
Omni—Directional antennas can both transmit and receive radio signals in a
horizontal circular plane all around the antenna (i.e. 360 degrees).
Directional antennas (as the term implies) are designed to transmit (radiate)
or receive signals, only in the direction in which the antenna is pointing.
Directionality is accomplished by focusing the radio signal within the antenna,
a process which effectively amplifies the signal. The analogy here is similar
to a flashlight, where a reflector placed around the bulb intensifies the light
beam by focusing the light rays from the bulb. Due to this phenomenon, a
directional antenna (eg. Yagi type) has gain, due to the increase in signal
focusing. Omni-Direction antennas can also be designed to focus signals
(include gain) in a circular pattern.
The choice of antenna, together with its physical location, will greatly effect
the overall operation of the DGPS radio link. Any improvements (i.e. using an
antenna with higher gain) made at one end of a DGPS radio link, will
enhance the overall performance of the entire link.
There are many manufacturers and suppliers of radio antennas, with the
differences between them being in type, gain, and mechanical factors.
Mechanical factors include material, construction, and quality of finish. Users
are reminded that the old saying “you get what you pay for” is particularly
true with antennas. Antennas are a vital component part of the DGPS
system, and are constantly exposed to adverse conditions. Purchase only
the best quality.
The following is intended to assist in deciding which type of antenna will best
suit the users DGPS radio link requirements.
Omni-Directional Antennas (Omni ’s)
This type has a 360 degree radiation pattern. Is it a good choice for DGPS
links where the base station has to communicate with mobile receivers which
keep changing their azimuth position, or where the base station is
transmitting to a number of mobiles in different directions.
Omni’s can vary from a couple of inches in height up to several feet,
depending on frequency and gain. Unless the omni is a gain type, it will
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NavSymm@ DRS-SBS—III. Operating Manual Issue 1.0
normally have unity gain (i.e. OdB or no gain). In other words, the antenna
will neither increase, nor decrease, the signals passing through it. For many
DGPS applications the unity gain antenna is quite acceptable, being a low
cost, compact, and strong antenna, which is simple to mount.
Signal Radialion Signal Radiation
1-\ /t
1— —>
4—/ N
Side View
Plan View
Figure C6. 0mni~Directional Antenna
Half- Wave Dipole Antennas
This is a significant and fundamental type of antenna, providing the basis for
a large number of other omni and directional antenna designs.
A very simple hall-wave dipole antenna could be made from two pieces of
stiff wire, placed one above the other in a vertical plane. The RF signal
connection is made to the inner ends of each piece of wire at the centre of
the antenna. One feed to the upper wire, and one to the lower. It the length
of each piece of wire is then cut to be exactly one quarter of the radio signal
wavelength (eg. the wave length is 70cm for a typical UHF signal), the whole
assembly will function as a half-wave dipole antenna.
Antenna length is directly related to the frequency of operation. The higher
the frequency, the shorterthe antenna becomes.
A half-wave dipole is said to be balanced, its two component parts (the upper
and lower sections) are equal in all respects. Not all antennas are balanced,
as will be explained later.
When a half-wave dipole is mounted in the vertical position, the signal
radiated from it is also vertical. The antenna is then described as being
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NavSymm'E” DHS-SBS-lll. Operating Manual Issue 1.0
vertically polarised, or a “Vertical Antenna". Horizontal polarisation is also
possible.
Antenna manufacturers product data leaflets will probably show a graph that
gives the pattern of radiation for the specific antenna. In the case of the half-
wave dipole, the electrical radiation pattern will be the shape of a circle
around a centre point, There will be no, or little, radiation directly above or
directly below the half-wave vertical antenna. The radiation will be a
continuous circle around the antenna. This gives rise to the designation of
“Omni—Directions", and unity gain can be expected.
Signal Radiation Signal Radiation
\ /¥
/ \
Antenna
Mast
Side View Plan View
Figure C7. Half—Wave Dipole Antenna
Quarter-Wave Whip Antennas
Derivatives of the half-wave dipole antenna have been developed to meet
specific requirements. For example, the quarter-wave whip antenna is
designed to meet applications calling for a physically small antenna. This
antenna having been made smaller by removing the lower section (used on
the vertical half-wave dipole). This leaving only a shorter single element,
measuring a quarter of a wave length. The quarter-wave radiating element is
often constructed from small diameter stiff wire, hence the name "whip“.
How does the quarter-we ve whip operate with only a single element ?
This is achieved by using the ground plane around and below the quarter-
wave element. For example, a ground plane can be formed by mounting the
quarter-wave whip on the metal roof of a vehicle. Radio signals see this
metal surface as being the second (lower) element of the half-wave vertical
dipole. A ground plane can also be created by mounting the antenna to a
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NavSymm" DFl5-963-III. Operating Manual issue 10
metal enclosure, hereby achieving the same effect as the vehicle roof. In
theory, any ground plane should have a radius of at least a quarter
wavelength in order for the antenna to operate at maximum efficiency. Some
designs incorporate 3, 4, or more, horizontal rods at the base of the antenna
to establish the ground plane where none exists. (eg. when the antenna is
mounted to a pole clear of the ground). Such an antenna is called a Ground
Plane.
Zero, or negative gain, is a feature of quarter-wave whip antennas.
Helical Antennas
With the introduction of the hand-held walkie-talkie radio, a refinement of the
quarter-wave vertical antenna came into being. This development is referred
to as the Helical Antenna. As the name implies, the radiating element is
wound is a helical path around a vertical former. The result is an antenna
significantly shorter in length compared to the quarter-wave vertical.
The advantages of the helical include low cost and small physical size. It is
mainly used for short range (up to a few hundred feet) links. Gain is much
less than unity.
Helical Element
Contained
Typical Antenna 4—1”, Within Antenna
Length —
3.5 - 8 inches
(9 - 21 cm)
Mounting Surface
Figure C8. Helical Antenna
Co-Linear Dipole Antennas
This antenna is a good choice for DGPS base stations, and also for high
mobility units such as vehicles or ships.
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NavSymm") DRS-BGS—Ill. Operating Manual Issue 1.0
Such antennas is made up of interconnected half-wave dipoles stacked
vertically. This configuration provides ‘antenna gain’ over a single half-wave
vertical dipole antenna, and can be used to cover long distance DGPS links.
The increase in gain is derived from the stacking of vertical dipole elements,
whereby the electrical signals are compressed in the vertical plane. This
forces the signals to extend in the horizontal plane, effectively creating an
increase in the gain of the antenna
Another way to explain this increase in gain is to imagine an inflated balloon
lying on a flat surface If you apply downward pressure, the balloon expands
sideways. The volume of the air inside the balloon still remains the same. it
has simply been forced into a different direction.
Gain is usually from about 3 to 10dB. This is equivalent to a Yagi antenna,
but retaining the 360 degree omni pattern.
Signal Radiation Signal Radiation
Li
\ii/
'__LJ__—'
/ ii \'
Antenna Antenna may be
contained within a
Mast Fibreglass Tube
Side View Plan View
Figure C9. Co-Linenr Dipole
Directional Yagi Antennas
This is the best choice of antenna for use in long range DGPS links (named
after its inventor). It is also commonly used as a TV antenna, with the
familiar long horizontal boom and small perpendicular elements. As a
general rule, the more elements on the boom, the more gain the Yagi
antenna will produce.
Any antenna having gain (co-linear or Yagi) will increase the output power of
any transmitter connected to it. in other words, a transmitter giving an RF
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NavSyme” DRS-‘aes-Ill. Operating Manual Issue 1.0
output of 2 watts coupled to a Yagi antenna rated at 3dB gain, would have its
effective (or actual) radiated RF power doubled to 4 watts. The effective
radiated power (ERP) is the important factor. Use of a Yagi antenna can also
reduce DC current consumption of the transmitter. This could be an
important advantage to users of battery powered DGPS links. In practice,
this is achieved by reducing the transmitter power (and consequently, the DC
current), whilst increasing the antenna gain to meet the required EFlP level.
As the Yagi is directional, it will also reject/reduce unwanted radio signals
from other users on the same radio frequency, (eg. where the other stations
are in a different azimuth direction from the DGPS base statiommobiles).
When installing the Yagi antenna, care must be taken to ensure that it faces
in the correct direction, and that the elements are correctly polarised. Note
that the Yagi elements become progressively shorter towards the front of the
antenna. The installed must point towards the appropriate DGPS station,
although it can be mounted with its elements either horizontally or vertically
polarised. It is essential to ensure that all of the radio links DGPS
station(s) Yagi antennas have the same orientation.
Typically, the Yagi antenna is used at fixed base stations when directing
signals in a particular direction. For example. on a shore mounted base
station transmitting signals directed towards mobile receivers at sea. The
width of the beam decreases with the increase in gain (as the antenna
becomes more focused). Referring back to the torch analogy, this is
equivalent to the difference between a floodlight and a spotlight. For high
gain, the beam width can reduce to just a few degrees.
NavSymm'“ DRS-QGS-III. Operating Manual Issue 1.0
MIXED ANTENNA WORKING
It is perfectly acceptable to mix different types of antennas in order to
engineer the best possible link. Where communication is needed between a
Yagi antenna and any of the vertically polarised types (such as a whip), the
user must mount the Yagi with the elements vertically aligned to correspond
with the venical orientation of the whip. A significant signal loss will result if
this basic precaution is not followed.
Base Station
(Yagi Type Antenna)
Mobiles
(eg. Using Omnl-directional Antenna)
Figure C10. Transmitter and Receiver
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NavSymm® DRS-QGS-III. Operating Manual Issue 1.0
THE DECIBEL (dB)
The dB is not a unit of measurement such as the volt or amp. It is the ratio
between two distinct values and is commonly used in RF engineering. Users
should have a basic understanding of this term.
Example 1:
if 2 watts of RF power is applied to an amplifier having an output of 4 watts,
it would have a gain of +3dB, that is, a doubling of the original power level.
Conversely, if a 1 watt RF signal was connected into a filter network, and
the measured output is 0.5 watts, it would have experienced a loss of —3dB
in the filter.
The dB is a logarithmic function, which means that it is possible to directly
add (or subtract) dB values as whole numbers when calculating problems
associated with radio engineering.
Example 2:
a 3dB increase in transmitter power, when coupled into a 10dB gain
antenna, will yield a 13dB overall increase in effective radiated power (951.
an increase of 20 times).
ANTENNA GAIN and THE dB
As previously mentioned, the amount of gain provided by a Yagi antenna is
basically dependent on the number of elements used in the design.
Therefore, a 12 element Yagi antenna will have greater gain than an 8
element design. When discussing dB and antenna gain, it is usual to express
the gain of an individual antenna in dBd, relative to a half-wave dipole. This
is taken as the unity (OdB) reference point. Some antenna manufacturers will
quote their gain levels in dB isotropic (dBi), in which case, simply deduct 2.16
to convert to dBd.
Common reference points in radio engineering are +3dB and -3dB. These
represent double and half power respectively. Note also that 1dB loss is
equivalent to a factor of 20% power reduction.
Users remember the ratios for MB, 3dB and 10dB, it becomes very easy to
calculate most dB relationships.
Number Of Elements
Length Of Boom
18 | + 14dB | 4.3m
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NavSymmé‘ OHS-9684“. Operating Manual Issue 10
CONNECTING THE ANTENNA
Great care must be taken to minimise signal losses when antennas are
connected to DGPS radio link transmitters and receivers.
A coaxial feeder cable is required to connect a radio transmitter or receiver to
an antenna. Whenever a radio signal is passed down any cable, there will be
losses in signal strength due to the attenuating effect of the cable. The
degree of attenuation will vary depending on the type of cable employed, and
the frequency of the signal. At higher frequencies, a cable will have a greater
effect on the signal passing through it.
A comparison test between a 10 metre, and a 25 metre length, of medium
quality RG-SB cable (a standard, widely used type of coaxial feeder cable)
demonstrates just how much signal strength can be lost at UHF.
The 10 meter cable: will show that a 450MHz signal passing through it
will have a loss of 1dB. In practice, this would mean that the output of a
0.5 watt transmitted signal is reduced to 0.4 watts before it reaches the
antenna.
The 25 meter cable: transmitting a 0.5 watt signal will have a loss of (MB
overall, which would leave less than 0.2 watts at the input to the antenna.
Figure C11. Cable Losses (see cable Mfr.)
IT IS VITAL TO KEEP CABLE LENGTHS AS SHORT AS POSSIBLE.
Use only the highest quality cable and connectors.
Cable and connector joints are the most common cause of excessively
high signal losses.
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LICENSING INFORMATION
All users of DGPS radio link equipment operating within the USA or Canada
must obtain a radio license from either the FCC, orthe DOC, respectively.
Additionally, all DGPS radio link equipment (either made, imported to, or
used) in the United States and Canada must meet the approval of
appropriate legislation
Similar regulations apply internationally.
Customers requiring assistance to obtain a license should contact
NavSymm® at the address found at the back of this manual.
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NavSymm“ DRS-QSS-lll. Operating Manual Issue 1.0
APPENDIX D
1.1 GLOBAL POSITIONING SYSTEM (GPS)
The Global Positioning System (GPS) is a military satellite based navigation
system developed by the US. Department of Defence, which is also made
freely available to civil users.
Civilian use of GPS is made available at the users own risk, subject to the
prevailing DOD policy or limitations, and to individuals understanding of how
to use the GPS.
ln today’s satellite constellation there are a minimum of 24 operational
satellites (plus several operational spares) in 6 orbital planes, at an altitude of
about 22,000 km. The GPS system can give accurate 3-D position, velocity,
time, and frequency, 24 hours a day, anywhere around the world.
GPS satellites transmit a code for timing purposes, and also a ‘Navigation
message” which includes their exact orbital location and system integrity data.
Receivers use this information, together with data from their internal
almanacs, to precisely establish the satellite location. The receiver
determines position by measuring the time taken for these signals to arrive.
At least three satellites are required to determine latitude and longitude if your
altitude is known (eg. a ship at sea), and at least a fourth to obtain a 3-D fix.
However, the US. Department of Defence deliberately degrades signals from
the constellation of GPS satellites by applying errors in the form of Selective
Availability (SA), thereby reducing the accuracy obtainable by civilian GPS
receivers. DoD policy is to set the level of SA degradation to give a
horizontal accuracy of 100 metres (95% of the time). Most of the effects of
SA can be eliminated by utilising Differential GPS (DGPS) techniques.
1.2 GPS POSITIONING and NA VIGA TI ON
The NavSymm® XFl5 or SHARPE XRG GPS Receivers need to be able to
see at least 4 satellite vehicles (SV's) to obtain an accurate 3—D position fix.
When travelling in a valley or built-up area, or under heavy tree cover, users
will experience difficulty acquiring and maintaining a coherent satellite lock.
Complete satellite lock may be lost, or only enough satellites (3) tracked to be
able to compute a 2-D position fix, or even a poor 3D fix due to insufficient
satellite geometry (is. poor DOP). Note also, that inside a building or beneath
a bridge, it probably will not be possible to update a position fix. The
Receiver can operate in 2-D mode if it goes down to seeing only 3 satellites
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NavSymmw DR5—QGS—III. Operating Manual Issue 1.0
by assuming its height remains constant. But this assumption can lead to
very large errors, especially when a change in height does occur. A 2-D
position fix is not to be considered a good or accurate fix, it is simply “better
than nothing".
The receivers antenna must have a clear view of the sky to acquire satellite
lock. Remember always, it is the location of the antenna which will be given
as the position fix. If the antenna is mounted on a vehicle, survey pole, or
backpack, allowance for this must be made when using the solution.
To measure the range from the satellite to the receiver, two criteria are
required: signal transmission time, and signal reception time. All GPS
satellites have several atomic clocks which keep precise time and these are
used to time-tag the message (is. code the transmission time onto the signal)
and to control the transmission sequence of the coded signal. The receiver
has an internal clock to precisely identify the arrival time of the signal. Transit
speed of the signal is a known constant (the speed of light), therefore: time x
speed of light = distance.
Once the receiver calculates the range to a satellite, it knows that it lies
somewhere on an imaginary sphere whose radius is equal to this range. If a
second satellite is then found, a second sphere can again be calculated from
this range information. The receiver will now know that it lies somewhere on
the circle of points produced where these two spheres intersect.
When a third satellite is detected and a range determined, a third sphere
would intersect the area formed by the other two. This intersection occurs at
just two points. The correct point is apparent to the user, who will at least
have a very rough idea of position. A fourth satellite is then used to
synchronise the receiver clock to the satellite clocks.
In practice, just 4 satellite measurements are sufficient for the receiver to
determine a position, as one of the two points will be totally unreasonable
(possibly many kilometres out into space).
This assumes the satellite and receiver timing to be identical. In reality, when
the NavSymm® GPS Receiver compares the incoming signal with its own
internal copy of the code and clock, the two will no longer be synchronised.
Timing error in the satellite clocks, the Receiver, and other anomalies, mean
that the measurement of the signals transit time is in error. This effectively, is
a constant for all satellites, since each measurement is made simultaneously
on parallel tracking channels. Because of this, the resultant ranges
calculated are known as “pseudo-ranges".
To overcome these errors, the NavSymm® GPS Receiver then matches or
“skews" its own code to become synchronous with the satellite signal. This is
repeated for all satellites in turn, thus measuring the relative transit times of
individual signals. By accurately knowing all satellite positions, and
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NavSymmw BBS-9684“. Operating Manual Issue 1.0
measuring the signal transit times, the user’s position can be accurately
determined.
Utilising its considerable processing power, the NavSymm® GPS Receiver
rapidly updates these calculations from satellite data to provide a real time
position tix. Memory options allow storage of navigation and position data for
subsequent post-processing or post-mission analysis, all within a single unit.
1.3 STANDARD POSITIONING SERVICE (SPS)
Civil users world-wide are able to use the SPS without restriction or charge.
Accuracy of the system is intentionally degraded by the DoD through the
application of Selective Availability (SA). This degradation is achieved by the
system deliberately broadcasting extra errors into the satellite orbit
information, and by ‘dithering’ the satellite clocks.
A predicted accuracy for the SPS has been published in the 1994 Federal
Radionavigation Plan as:-
. 100 metre horizontal accuracy
. 156 metre vertical accuracy
- 340 nanosecond time accuracy
The figures refer to 95% position fix accuracies, expressing the value of two
standard deviations of radial error from the actual antenna position, this
position being an estimate made under specified satellite elevation angle and
PDOP conditions.
Dilution Of Precision (DOP) is a measure of the satellite geometry, and is an
indicator of the potential quality of the solutions. The lower the numerical
value, the better the potential accuracy (for example, a PDOP below 3
indicates good satellite geometry). For 3-D positioning, fluctuations in DOP
can be harmful to the solution, especially in Kinematic/Dynamic modes.
For example, the following DOP terms are computed by the SHARPE XFtG:
HDOP Horizontal Dilution of Precision (Latitude, Longitude)
VDOP Vertical Dilution of Precision (Height)
TDOP Time Dilution of Precision (Timing errors)
PDOP Position Dilution of Precision (3-D positioning)
GDOP Geometric Dilution of Precision (3-D position & Time)
Estimated accuracy = DOP x measurement accuracy
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NavSymm” DRE-SSS-Ill. Operating Manual Issue 1.0
While each of these terms can be individually computed, they are formed
from co-variances, and are not independent of each other. For example, a
high TDOP will cause receiver clock errors which will eventually result in
increased position errors.
Horizontal accuracy figure of 95% is the equivalent to 2RMS (twice root-
mean-square), or twice the standard deviation radial error.
Similarly, for vertical and time errors, a figure of 95% is the value of 2
standard-deviations of vertical or time error.
. Root-mean-square (HMS) error is the value of one standard deviation
(67%) of error.
. Circular Error Probability (CEP) is the value of the radius of a circle,
centred at a position containing 50% of the position estimates.
- Spherical Error Probability (SEP) is the spherical equivalent of CEP, which
is centred at a position containing 50% of the position estimates.
CEP and SEP are not affected by large errors which could make the values
an overly optimistic measurement. These probability statistics are not
suitable for use in a high accuracy positioning system. The SHAHPE XRG
reports all accuracy’s in the form of a standard deviation (HMS) value.
1.4 PRECISE POSITIONING SERVICE (PPS)
This service is only available to authorised users with cryptographic
equipment and special receivers. Access is limited to the U.S. and Allied
military, U.S. Government agencies, and selected civil users specifically
approved by the US. Government.
1.5 DIFFERENTIAL GPS
Differential GPS (or DGPS) is a method of removing errors common to
several nearby receivers (eg. satellite orbit, clocks, SA, and also those
caused by atmospheric distortion of the satellite signal).
The basis of the system is to position a GPS receiver at a known location,
and to tell this receiver where it is. Once this fixed GPS receiver (or Base
Station) is operating. it is then able to calculate the expected ranges from the
satellites using its known location, and make a comparison with data received
directly from each of the satellites in view. Any errors (differential) in the
measurements are calculated, and transmitted to the mobile receivers.
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NavSymmE DR5-SBS-III. Operating Manual Issue 1.0
A mobile receiver operates in the same manner as the Base Station, by
taking data from all satellites in view. However, before calculating its own
position, the mobile receiver adjusts its own measurements using the
corrections supplied from the Base Station.
Utilising this DGPS technique in survey operation, the NavSymm® SHARPE
XFiG GPS Receiver will output real time positions to an accuracy ranging from
3 metres down to 2 centimetres, depending on the DGPS mode of operation.
1.6 REAL- TIME KINEMA TIC (RTK) POSITIONING
RTK GPS is a differential technique which makes use of both pseudcrange
and carrier phase measurements to compute the position of the mobile
receiver, relative to that of the base station. This highest accuracy mode
relies on having differentially corrected carrier phase measurements at the
millimetre level, which can in turn, lead to positioning accuracies down to
20m.
There are many operational considerations associated with FlTK positioning,
which can determine the accuracy obtained. These are covered in more
detail in the advanced section of the SHARPE XR6 manual.
1.7 GEODETIC DATUMS
The default geodetic datum of the NavSymm® XR5 and SHARPE XFl6 is
WGS 84 (World Geodetic System 1984). To establish a position based on a
local land map, it is necessary to select the corresponding local map datum.
For example: in the UK the mapping datum is OSGB 36.
A full list of datum’s supported is given in the SHARPE XRG manual.
Note:
1) it is vitally important to use the correct geodetic datum as there may
be differences of several hundreds of metres between datum‘s. This is
probably the largest cause of error and problems to users of precise
GPS equipment.
2) the Base Station position must be set to the same datum co-ordinate
value in which the end solution is required.
3) ensure the same datum transformation parameters are used at both
ends in the DGPS operations. Although the same name may be used
by different equipment or software suppliers, different values may have
been used by the different sources.
57
USER NOTES
Navstav Systems Ltd.
USER NOTES
Navslar Systems Ltd.
NavSymm® CONTACT DETAILS
For further details and hot—line support please contact:
Sales, International Customer Support, and Service
Navstar Systems Ltd
Mansard Close
Westgate
Northamptonshire NN5 5DL
England
Telephone: +44 1604 585588
Facsimile: +44 1604 585599
E-Mail: navstar@telecom.com
Web Site: http://www.telecom.com/navstar
Sales office in the USA
NavSymm®
2300 Orchard Parkway
San Jose
California 95131—1017
USA
Telephone: 1 -888-367-7966
Facsimilie: 1 408-428-7998
E-Mail: navsymm @ telecom.com
Dias-963 Mk'" first
NAVSTAR
Freguency Programming User Interface SYSTEMS
The frequency programming user interface allows the user to change the operating
frequency of the transceiver through a series of ASCII Commands. The frequency
programming user interface is entered by sending a control sequence from an attached
terminal e.g. Prooomm or Windows Terminal. This will prevent general users from
changing the frequency.
Connect the PC to the data port using the Control Serial Cable (Blue Marker). The
interface defaults to 9600 baud NO parity.
Enter the password ( Hold CTHL and type navstar) followed by . Note if
using Windows Terminal it is necessary to set the Control Keys to be used by the
Program not by Windows, this is done under Settings, Terminal Preferences.
When the correct authorisation word has been sent to the radio an acknowledgement is
returned ( Access 0K ). This will add two extra controls to the user interface. The user
will enter a command to set the frequency. The microprocessor will calculate the
relevant synthesiser values and set the synthesiser accordingly. An acknowledgement
is sent to the user reporting the new frequency.. Once the transceiver has been
authorised using the password it will remain authorised until the unit is switched off.
The command structure to change the frequency is as follows:
MODE FRQ1:456.5000,456.5000
where FR01 is the frequency to change i.e. FRQ1 or FRQZ. The frequencies are in
MHz and must be entered to 4 decimal places (to give enough resolution for 12.5kHz
channel spacing) They are the transmit and receive frequencies respectively. If the
user enters an invalid frequency an error message is returned. Note the radio checks
that the frequencies entered are within the transmit band of the radio and will return an
error message if either frequency is out of range.
If the radio has not been authorised by using the above password sequence ‘ACCESS
DENIED’ will be returned from the radio when trying to set a new frequency. The new
frequency settings are remembered at power down and only need to be set once.
NOTE: When setting the transceiver to new frequencies that have not been used
before it is advisable to check that no one else is using the frequency before
transmitting data.

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