Navstar Systems A190-001G1 User Manual 8
Navstar Systems Ltd 8
Contents
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-_—- _ 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,zwhere:- 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. 24 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. 27 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. 28 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. 31 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. 32 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. 34 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. 35 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. 36 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. 37 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. 39 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 40 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 41 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. 42 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 43 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 44 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 45 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. 46 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 47 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 49 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 50 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. 51 NavSymm® DRs-ess-nt Operating Manual Issue 1.0 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. 52 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 53 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 <4 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 55 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. 56 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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