GE MDS TRANSNET900 Users Manual

MDS TransNET 900“

TransNET 900“

Spread Spectrum Data Transceiver

MDS 05-2708A01 Rev. A

September 2001

QUICK START GUIDE

Below are the basic steps for installing the transceiver. Detailed instructions are given in INSTALLATION on page 24 of this guide.

1. Install and connect the antenna system to the radio

¥ Use good quality, low-loss coaxial cable. Keep the feedline as short as possible. ¥ Preset directional antennas in the direction of desired transmission.

2. Connect the data equipment to the radio s INTERFACE connector

¥ Connection to the radio must be made with a DB-9 Male connector. Connections for typical systems

are shown below. ¥ Connect only the required pins. Do not use a straight-through RS-232 cable with all pins wired. ¥ Verify the data equipment is configured as DTE. (By default, the radio is configured as DCE.)

3. Apply DC power to the radio

¥ Observe proper polarity. The red wire is the positive lead; the black is negative.

4. Verify proper operation by observing the LED display

¥ Refer to Table 4 on page 32 for a description of the status LEDs. ¥ Refine directional antenna headings for maximum receive signal strength using the RSSI command.

TABLE OF CONTENTS

1.0 ABOUT THIS MANUAL ............................................................... 9

2.0 PRODUCT DESCRIPTION ......................................................... 9

Transceiver Features.................................................................... 10

Model Configuration Codes ..........................................................10

2.1 Spread Spectrum Radios How Are They Different? ....................10

2.2 Typical Applications ........................................................................ 11

Multiple Address Systems (MAS) ................................................. 11

Simplex Peer-to-Peer ................................................................. 11

Point-to-Point System................................................................... 12

Tail-End Link ( MAS Extension )................................................... 12

Repeater System Traditional......................................................13

2.3 Accessories .................................................................................... 14

3.0 GLOSSARY OF TERMS............................................................ 14

4.0 INSTALLATION PLANNING ...................................................... 17

4.1 General Requirements ................................................................... 17

4.2 Site Selection .................................................................................18

Terrain and Signal Strength .......................................................... 18

4.3 A Word About Radio Interference ................................................... 20

4.4 Antenna & Feedline Selection ........................................................ 21

Antennas ......................................................................................21

Feedlines ......................................................................................22

4.5 How Much Output Power Can be Used? .......................................23

For All MDS TransNET 900“ Systems........................................23

5.0 INSTALLATION.......................................................................... 24

5.1 Transceiver Installation ..................................................................25

5.2 Peer-to-Peer Systems .................................................................... 27

Simplex Peer-to-Peer ...................................................................27

5.3 Tail-End Links ................................................................................. 27

Interface Wiring ............................................................................27

5.4 Repeaters Traditional Method .....................................................28

Antennas ......................................................................................28

System Addresses........................................................................ 29

Interface Wiring ............................................................................29

Software Programming (TDD Command) ....................................30

Limitations of Single-Radio Repeaters ......................................... 30

5.5 Using the Radio s Sleep Mode ....................................................... 30

MDS 05-2708A01 Rev. A MDS TransNET 900 I/O Guide i

Sleep Mode Example ...................................................................31

6.0 OPERATION.............................................................................. 31

6.1 Initial Start-up ................................................................................. 31

6.2 Performance Optimization ..............................................................32

Antenna Aiming ............................................................................ 32

Antenna SWR Check.................................................................... 32

Data Buffer Setting ....................................................................... 33

Hoptime Setting ............................................................................33

Baud Rate Setting ........................................................................33

Radio Interference Checks ...........................................................33

7.0 TRANCEIVER PROGRAMMING............................................... 33

7.1 Programming Methods ................................................................... 34

7.2 Keyboard Commands ....................................................................34

Entering Commands..................................................................... 35

7.3 Detailed Command Descriptions ....................................................38

ADDR [1...65000] .........................................................................38

AMASK [0000 0000—FFFF FFFF] ................................................39

ASENSE [HI/LO]........................................................................... 39

BAUD [xxxxx abc]......................................................................... 39

BUFF [ON, OFF]........................................................................... 40

CTS [0—255] .................................................................................40

CTSHOLD [0-6000] ......................................................................41

DEVICE [DCE, CTS KEY] ...........................................................41

DMGAP [xx].................................................................................. 42

HOPTIME .....................................................................................42

MODE [M, R, R-M] .......................................................................43

OWM [xxxxx] ................................................................................43

OWN [xxxxx]................................................................................. 43

PWR [xx—30]................................................................................. 43

RSSI .............................................................................................43

RTU [ON/OFF/0-80]......................................................................44

RX [xxxx] ......................................................................................44

RXTOT [NONE, 0—1440] ..............................................................45

SEND [n, -n, +n] ...........................................................................45

SETUP.......................................................................................... 46

SHOW [PORT, DC, PWR] ............................................................47

SKIP [NONE, 1...8] .......................................................................47

SSNR............................................................................................ 47

SREV............................................................................................ 48

STAT.............................................................................................48

TTEMP .........................................................................................48

TX [xxxx]....................................................................................... 48

UNIT [10000—65000] .................................................................... 49

8.0 TROUBLESHOOTING............................................................... 49

8.1 LED Indicators ................................................................................49

8.2 Alarm Codes ...................................................................................50

MDS 05-2708A01 Rev. A MDS TransNET 900 I/O Guide ii

Checking for Alarms STAT command ........................................50

Major Alarms vs. Minor Alarms ..................................................... 50

Alarm Code Definitions................................................................. 50

8.3 Troubleshooting Chart ....................................................................52

9.0 TECHNICAL REFERENCE ....................................................... 52

9.1 Technical Specifications ................................................................. 52

9.2 Data Interface Connections (DB-9) ................................................ 54

9.3 dBm-Watts-Volts Conversion Chart ...............................................57

IN CASE OF DIFFICULTY... ........................................................... 65

RF Exposure

Microwave Data Systems reserves its right to correct any errors and omissions in this manual.

Operational Safety Notices

The radio equipment described in this guide emits radio frequency energy. Although the power level is low, the concentrated energy from a directional antenna may pose a health hazard.

come closer than 2 meters (6 feet) to the antenna when the transmitter is operating.

This manual is intended to guide a professional installer in installing, operating and performing basic system maintenance on the described equipment.

Do not allow people to

ISO 9001 Registration

Microwave Data Systems adheres to the internationally-accepted ISO 9001 quality system standard.

MDS Quality Policy Statement

We, the employees of Microwave Data Systems, are committed to understanding and exceeding our customer s needs and expectations.

¥ We appreciate our customers patronage. They are our business.

¥ We promise to serve them and anticipate their needs.

¥ We are comitted to providing solutions that are cost effective,

innovative and reliable, with consistently high levels of quality.

MDS 05-2708A01 Rev. A MDS TransNET 900 I/O Guide iii

¥ We are committed to the continuous improvement of all of our

systems and processes, to improve product quality and increase customer satisfaction.

FM/UL/CSA Notice

MDS TransNET 900“ When Approved

This product is available for use in Class I, Division 2, Groups A, B, C & D Hazardous Locations. Such locations are defined in Article 500 of the National Fire Protection Association (NFPA) publication NFPA 70, otherwise known as the National Electrical Code.

The transceiver has been recognized for use in these hazardous locations by three independent agencies Underwriters Laboratories (UL), Factory Mutual Research Corporation (FMRC) and the Canadian Standards Association (CSA). The UL certification for the transceiver is as a Recognized Component for use in these hazardous locations, in accordance with UL Standard 1604. The FMRC Approval is in accordance with FMRC Standard 3611. The CSA Certification is in accordance with CSA STD C22.2 No. 213-M1987.

FM/UL/CSA Conditions of Approval:

The transceiver is not acceptable as a stand-alone unit for use in the hazardous locations described above. It must either be mounted within another piece of equipment which is certified for hazardous locations, or installed within guidelines, or conditions of approval, as set forth by the approving agencies. These conditions of approval are as follows:

1. The transceiver must be mounted within a separate enclosure which is suitable for the intended application.

2. The antenna feedline, DC power cable and interface cable must be routed through conduit in accordance with the National Electrical Code.

3. Installation, operation and maintenance of the transceiver should be in accordance with the transceiver’s installation manual, and the National Electrical Code.

4. Tampering or replacement with non-factory components may adversely affect the safe use of the transceiver in hazardous locations, and may void the approval.

5. When installed in a Class I, Div. 2, Groups A, B, C or D hazardous location, observe the following:

WARNING EXPLOSION HAZARD

ment unless power has been switched off or the area is know to be non-hazardous.

MDS 05-2708A01 Rev. A MDS TransNET 900 I/O Guide iv

Do not disconnect equip-

Refer to Articles 500 through 502 of the National Electrical Code (NFPA 70) for further information on hazardous locations and approved Division 2 wiring methods.

FCC Part 15 Notice

The MDS TransNET 900“ transceivers comply with Part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) this device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation.

This device is specifically designed to be used under Section 15.247 of the FCC Rules and Regulations. Any unauthorized modification or changes to this device without the express approval of Microwave Data Systems may void the user s authority to operate this device.

Furthermore, this device is indented to be used only when installed in accordance with the instructions outlined in this manual. Failure to comply with these instructions may also void the user s authority to operate this device.

Revision Notice

While every reasonable effort has been made to ensure the accuracy of this manual, product improvements may result in minor differences between the manual and the product shipped to you. If you have additional questions or need an exacts specification for a product, please contact our Customer Service Team using the information at the back of this guide. In addition, manual updates can often be found on the MDS Web site at www.microwavedata.com.

Limited Modular Approval Notice

MDS TransNET radios are intended for use only inside an enclosure that is fully compliant to FCC Part 15 requirements. These enclosures have been tested with MDS radio products and meet the unintentional radiator requirements as set forth by the FCC. MDS certifies that any future enclosures offered with these products will meet the appropriate requirements and will not offer the products to end users as board-only solutions.

MDS 05-2708A01 Rev. A MDS TransNET 900 I/O Guide v

vi MDS TransNET 900 I/O Guide MDS 05-3301A01, Rev. A

1.0 ABOUT THIS MANUAL

This guide presents installation and operating instructions for the MDS TransNET 900™ keeping this guide near the equipment for future reference.

transceivers. Following installation, we suggest

2.0 PRODUCT DESCRIPTION

The transceiver, shown in Figure 1, is a spread spectrum radio designed for license-free operation in the 900 MHz frequency band. Employing microprocessor control and Digital Signal Processing (DSP) technology, they are highly reliable for long-distance communications, even in the presence of weak signals or interference.

DSP technology also makes it possible to obtain information about radio operation and troubleshoot problems, without going to the remote radio site. Using the appropriate software at the master station, diagnostic data can be obtained on any DSP radio in the system, even while payload data is being transmitted. The TransNET 900™ is housed in a compact and rugged die-cast aluminum case that need only be protected from direct exposure to the weather. It contains a single printed circuit board with all necessary components for radio operation. No jumper settings or adjustments are required to configure the radio for operation.

Figure 1. MDS TransNET 900 Transceiver

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Transceiver Features

Listed below are several key features of the MDS TransNET 900™ transceivers. These are designed to ease the installation and configuration of the radio, while retaining the ability to make changes in the future.

• 1,028 frequencies over 902–928 MHz, subdivided into eight frequency zones

• Configurable operating zones to omit frequencies with constant interference

• 65,000 available network addresses

MDS 05-2708A01, Rev. A MDS TransNET I/O Guide 1

THIS INFORMATION IS SUBJECT TO CHANGE.

DO NOT USE FOR PRODUCT ORDERING.

• Network-wide configuration from the master station; eliminates most trips to remote sites

• Data transparency–ensures compatibility with virtually all asynchronous SCADA system RTUs

• Peak-hold RSSI, averaged over eight hop cycles

• Operation at up to 115,200 bps continuous data flow

• Same hardware for master or remote configuration

• Data latency typically less than 10 ms

• Supports EIA-232 (formerly called RS-232) and RS-485 user

interface

• Low current consumption–5 mA or less average draw in “sleep” mode.

Model Configuration Codes

The radio model number is printed on the end of the radio enclosure, and provides key information about how the radio was configured when it left the factory. See Figure 2 for an explanation of the model number characters.

Graphic is pending.

Figure 2. MDS TransNET 900™ transceiver model configuration codes

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2.1 Spread Spectrum Radios—How Are They Different?

The main difference between a traditional (licensed) radio system and the MDS TransNET 900™ transceivers is that these units “hop” from channel to channel many times per second using a specific hop pattern applied to all radios in the network. A distinct hopping pattern is provided for each of the 65,000 available network addresses, thereby minimizing the chance of interference with other spread spectrum systems. In the USA, and certain other countries, no license is required to install and operate this type of radio system.

2.2 Typical Applications

Multiple Address Systems (MAS)

This is the most common application of the MDS TransNET 900™ transceivers. It consists of a central control station (master) and two or more associated remote units, as shown in Figure 3. An MAS network provides communications between a central host computer and remote terminal units (RTU’s) or other data collection devices. The operation of the radio system is transparent to the computer equipment. When used in this application, the transceiver provides an excellent alternative to traditional (licensed) MAS radio systems.

2 MDS TransNET I/O Guide MDS 05-2708A01, Rev. A

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RTU

MDS

P W R

S Y

D A

REMOTE RADIO

MDS 9810

D A

TRANS

EIVER

810

T X

A I N

T E R F

I D I

. 8 V

D C

–

N T

E N NA

–

REMOTE RADIO

MDS 9810

D A

T A

T RA

MDS 9810

P W

SCE

S Y

VER

IN T E R

I D IA

1 3

.8 V

D C

–

N T E N

N A

–

MASTER RADIO

MDS 9810

T RANSCEIVER

MDS 9810

P W R

S Y N C

IN T E

R F

I D I

. 8 V

D C

–

N T

E N N

–

RTU

P W R

9810

Y N C

A IN

T E R F

ID I

. 8 V

D C

–

MDS 9810

TA TRA

N SCEIVER

A NT E N

–

RTU

REMOTE RADIO

RTU

MDS 9810

P W R

S Y N C

IN T E

R F

REMOTE RADIO

MDS 9810

D A

T RANS

P W R

N C

810

T X

A IN

T E R F

I D I

. 8 V

D C

–

NT E

N NA

–

MDS 9810

DAT

T RA

N SC

EI VER

I D IA

1 3

. 8 V

D C

–

N T EN

N A

–

REMOTE RADIO

HOST SYSTEM

Figure 3. Typical MAS network

Simplex “Peer-to-Peer”

Peer-to-peer communication is possible using the transceiver’s simplex mode. With this arrangement (Figure 4), two or more remote units can share information by direct communication with each other in addition to communicating with a central master radio. This is possible because the transmit and receive frequencies for each hop channel are the same at each radio when simplex mode is enabled. If adequate transmission paths exist, each radio can communicate with all other units in the network. Additional details for peer-to-peer systems are provided in Section 5.2 (Page 16).

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RTU

MASTER RADIO

HOST SYSTEM

REMOTE RADIO

PEER-TO-PEER

RTU

REMOTE RADIO

PEER-TO-PEER

Figure 4. Typical simplex “peer-to-peer” network

RTU

REMOTE RADIO

PEER-T

O-PEER

REMOTE RADIO

Point-to-Point System

A point-to-point configuration (Figure 5) is a simple arrangement consisting of just two radios—a master and a remote. This provides a simplex or half-duplex communications link for the transfer of data between two locations.

MDS 05-2708A01, Rev. A MDS TransNET I/O Guide 3

HOST SYSTEM

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MASTER RADIO

RTU

REMOTE RADIO

Figure 5. Typical point-to-point link

Tail-End Link

( MAS Extension )

A tail-end link can be used to extend the range of a traditional (licensed) MAS system. This might be required if an outlying site is blocked from the MAS master station by a natural or man-made obstruction. In this arrangement, an MDS TransNET 900™ radio links the outlying remote site into the rest of a licensed MAS system by sending data from that site to an associated MDS TransNET 900™ installed at one of the licensed remote sites. (See Figure 6).

As the data from the outlying site is received at the licensed remote site, it is transferred to the licensed radio (via a local cable connection) and is then transmitted to the MAS master station in the usual manner. Additional details for tail-end links are given in Section 5.3 (Page 17).

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REPEATER

MASTER STATION

POINT

REMOTE

RADIO

Null-Modem

Cable

MDS 9810 / 9820

MASTER RADIO

SPREAD

LINK

-T O-POINT

SPECTRUM

RTU

REMOTE

RADIO

RTU

MDS 9810

/ 9820

REMOTE RADIO

REMOTE

RADIO

RTU

MAS SYSTEM (LICENSED OR UNLICENSED) MDS 9810/9820 LINK TO AN OUTLYING SITE

Figure 6. Typical tail-end link arrangement

Repeater System—Traditional

Although the range between MDS TransNET 900™ radios is typically 10 miles over average terrain, it is possible to extend the range considerably by connecting two units together at one site in a “back-to-back” fashion to form a repeater, as shown in Figure 7. Additional details for repeater systems are given in Section 5.4 (Page 17).

4 MDS TransNET I/O Guide MDS 05-2708A01, Rev. A

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POINT-TO-POINT LINK

REMOTE RADIO

HOST COMPUTER

MASTER

RADIO

REPEATER LINK

Null-Modem Cable

RTU

MASTER

RADIO

REMOTE RADIO

RTU

REMOTE RADIO

RTU

Figure 7. Typical repeater system configuration

2.3 Accessories

The MDS TransNET 900  transceivers can be used with one or more of the accessories listed in Table 1. Contact the factory for ordering details.

Table 1. Accessories

Accessory Description MDS P/N

RTU Simulator Test unit that simulates data from a remote

EIA-232 to EIA-422 Converter

terminal unit. Comes with polling software that runs on a PC. Useful for testing radio operation.

External adapter that converts the radio’s DATA INTERFACE connector to EIA-422 compatible signaling. May be required for long cable runs (over 50 feet/15 meters).

03-2512A01

03-2358A01

3.0 GLOSSARY OF TERMS

If you are new to spread spectrum radio, some of the terms used in this guide may be unfamiliar. The following glossary explains many of these terms and will prove helpful in understanding the operation of the transceiver.

Antenna System Gain—A figure, normally expressed in dB, representing the power increase resulting from the use of a gain-type antenna. System losses (from the feedline and coaxial connectors, for example) are subtracted from this figure to calculate the total antenna system gain.

Bit—The smallest unit of digital data, often represented by a one or a zero. Eight bits (plus start, stop, and parity bits) usually comprise a byte.

Bits-per-second—See BPS. BPS—Bits-per-second. A measure of the information transfer rate of digital

data across a communication channel. Byte—A string of digital data usually made up of eight data bits and start, stop,

and parity bits. Decibel (dB)—A measure of the ratio between two signal levels. Frequently

used to express the gain (or loss) of a system.

MDS 05-2708A01, Rev. A MDS TransNET I/O Guide 5

Data Circuit-terminating Equipment—See DCE. Data Communications Equipment—See DCE. Data Terminal Equipment—See DTE. dBi—Decibels referenced to an “ideal” isotropic radiator in free space.

Frequently used to express antenna gain. dBm—Decibels referenced to one milliwatt. An absolute unit used to measure

signal power, as in transmitter power output, or received signal strength. DCE—Data Circuit-terminating Equipment (or Data Communications

Equipment). In data communications terminology, this is the “modem” side of a computer-to-modem connection. By default, MDS TransNET 900™ transceivers are set as DCE devices.

Digital Signal Processing—See DSP. DSP—Digital Signal Processing. In the MDS TransNET 900™ transceivers,

the DSP circuitry is responsible for the most critical real-time tasks; primarily modulation, demodulation, and servicing of the data port.

DTE—Data Terminal Equipment. A device that provides data in the form of digital signals at its output. Connects to the DCE device.

Equalization—The process of reducing the effects of amplitude, frequency or phase distortion with compensating networks.

Fade Margin—The greatest tolerable reduction in average received signal strength that will be anticipated under most conditions. Provides an allowance for reduced signal strength due to multipath, slight antenna movement or changing atmospheric losses. A fade margin of 20 to 30 dB is usually sufficient in most systems.

Frame—A segment of data that adheres to a specific data protocol and contains definite start and end points. It provides a method of synchronizing transmissions.

Frequency Hopping—The spread spectrum technique used by the MDS TransNET 900™ transceivers, where two or more associated radios change their operating frequencies several times per second using a set pattern. Since the pattern appears to jump around, it is said to “hop” from one frequency to another.

Frequency Zone—The transceivers use up to 1,028 discrete channels in the 902 to 928 MHz spectrums. A group of 16 channels is referred to as a zone. The transceivers use five to eight frequency zones.

Hardware Flow Control—A transceiver feature used to prevent data buffer overruns when handling high-speed data from the RTU or PLC. When the buffer approaches overflow, the radio drops the clear-to-send (CTS) line, which instructs the RTU or PLC to delay further transmission until CTS again returns to the high state.

Host Computer—The computer installed at the master station site, which controls the collection of data from one or more remote sites.

Latency—The delay (usually expressed in milliseconds) between when data is applied to TXD (Pin 2) at one radio, until it appears at RXD (Pin 3) at the other radio.

MAS—Multiple Address System. A radio system where a central master station communicates with several remote stations for the purpose of gathering telemetry data. Figure 3 on page 3 shows an example of an MAS system.

6 MDS TransNET I/O Guide MDS 05-2708A01, Rev. A

Master (Station)—The one radio transceiver in a spread spectrum network that automatically provides synchronization information to one or more associated remote transceivers. A radio may be programmed for either master or remote mode using software commands. See Section 7.0, TRANCEIVER

PROGRAMMING (beginning on page 22).

MCU—Microcontroller Unit. This is the processor responsible for controlling system start-up, synthesizer loading, hop timing, and key-up control.

Microcontroller Unit—See MCU. Mode—This refers to the programmed function of an MDS spread spectrum

radio—master or remote. (See also Remote Station and Master Station.) Multiple Address System (MAS)—See Point-Multipoint System. Network Address—User-selectable number between 1 and 65000 that is used

to identify a group of transceivers that form a communications network. The master and all remotes within a given system must have the same network address.

Point-Multipoint System—A radio communications network or system designed with a central control station that exchanges data with a number of remote locations equipped with terminal equipment.

Poll—A request for data issued from the host computer (or master PLC) to a remote radio.

PLC—Programmable Logic Controller. A dedicated microprocessor configured for a specific application with discrete inputs and outputs. It can serve as a host or as an RTU.

Remote Radio—A radio in a spread spectrum network that communicates with an associated master station. A radio may be programmed for either master or remote mode using software commands. See Section 7.0,

PROGRAMMING

Remote Terminal Unit—See RTU. RTU—Remote Terminal Unit. A data collection device installed at a remote

radio site. SCADA—Supervisory Control And Data Acquisition. An overall term for the

functions commonly provided through an MAS radio system. Standing Wave Ratio—See SWR. SWR—Standing Wave Ratio. A parameter related to the ratio between

forward transmitter power and the reflected power from the antenna system. As a general guideline, reflected power should not exceed 10% of the forward power (≈ 2:1 SWR).

(beginning on page 22).

TRANCEIVER

Zone—See Frequency Zone.

4.0 INSTALLATION PLANNING

The installation of the radio is not difficult, but it does require some planning to ensure station reliability and efficiency. This section provides tips for selecting an appropriate site, choosing an antenna system, and reducing the chance of harmful interference.

MDS 05-2708A01, Rev. A MDS TransNET I/O Guide 7

4.1 General Requirements

There are three main requirements for installing the radio—adequate and stable primary power, a good antenna system, and the correct interface between the transceiver and the data device.

Figure 8 shows a typical remote station arrangement. At a remote station, a

directional antenna is normally used, and a Remote Terminal Unit (RTU) or other telemetry equipment replaces the host computer normally used in a master station.

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REMOTE TERMINAL UNIT

REMOTE RADIO

ANTENNA SYSTEM (Directional Type Normally Used)

13.8 VDC POWER

CABLE

13.8 VDC POWER SUPPLY

Figure 8. Typical remote station arrangement

LOW-LOSS FEEDLINE

4.2 Site Selection

For a successful installation, careful thought must be given to selecting proper sites for the master and remote stations. Suitable sites should provide:

• Protection from direct weather exposure

• A source of adequate and stable primary power

• Suitable entrances for antenna, interface or other required cabling

• Antenna location that provides an unobstructed transmission path in

the direction of the associated station

These requirements can be quickly determined in most cases. A possible exception is the last item—verifying that an unobstructed transmission path exists. Radio signals travel primarily by line-of-sight, and obstructions between the sending and receiving stations will affect system performance. If you are not familiar with the effects of terrain and other obstructions on radio transmission, the discussion below will provide helpful background.

(

)

Terrain and Signal Strength

While the 900 MHz band offers many advantages over VHF and lower UHF frequencies for data transmission, it is also more prone to signal attenuation from obstructions such as terrain, foliage or buildings in the transmission path.

8 MDS TransNET I/O Guide MDS 05-2708A01, Rev. A

A line-of-sight transmission path between the master station and its associated remote site(s) is highly desirable and provides the most reliable communications link. A line-of-sight path can often be achieved by mounting the station antenna on a tower or other elevated structure that raises it to a level sufficient to clear surrounding terrain and other obstructions.

The importance of a clear transmission path relates closely to the distance to be covered by the system. If the system is to cover only a limited geographic area, say up to 3 miles (4.8 km) for the MDS TransNET 900™, then some obstructions in the transmission path can usually be tolerated with minimal impact. For longer range systems, any substantial obstruction in the transmission path could compromise the performance of the system, or block transmission entirely.

Much depends on the minimum signal strength that can be tolerated in a given system. Although the exact figure will differ from one system to another, a Received Signal Strength Indication (RSSI) of –90 dBm or stronger will provide acceptable performance in many systems. While the equipment will work at lower signal strengths, this provides a “fade margin” to account for variations in signal strength which may occur from time-to-time.

Conducting a Site Survey

If you are in doubt about the suitability of the radio sites in your system, it is best to evaluate them before a permanent installation is begun. This can be done with an on-the-air test (preferred method); or indirectly, using path-study software.

An on-the-air test is preferred because it allows you to see firsthand the factors involved at an installation site and to directly observe the quality of system operation. Even if a computer path study was conducted earlier, this test should be done to verify the predicted results.

The test can be performed by first installing a radio and antenna at the proposed master station site and then visiting each remote site with a transceiver and a hand-held antenna. (An RTU simulator—MDS Part No. 03-2512A01—can be connected to each radio in the network to simulate data during this test.)

With the hand-held antenna positioned near the proposed mounting spot, a technician can check for synchronization with the master station (shown by a

SYNC

lit

lamp on the front panel) and measure the reported RSSI value. If adequate signal strength cannot be obtained, it may be necessary to mount the station antennas higher, use higher gain antennas, or select a different site. To prepare the equipment for an on-the-air test, follow the general installation procedures given in this guide and become familiar with the operating instructions given in Section 6.0, beginning on Page 20.

If time is short, and a site survey is impractical, a computer path study is a good alternative. Factors such as terrain, distance, transmitter power, receiver sensitivity, and other conditions are taken into account to predict the performance of a proposed system. Contact MDS for more information on path study services.

MDS 05-2708A01, Rev. A MDS TransNET I/O Guide 9

4.3 A Word About Radio Interference

The MDS TransNET 900™ transceivers share frequency spectrums with other services and other Part 15 (unlicensed) devices in the USA. As such, near 100% error free communications may not be achieved in a given location, and some level of interference should be expected. However, the radio’s flexible design and hopping techniques should allow adequate performance as long as care is taken in choosing station location, configuration of radio parameters and software/protocol techniques.

In general, keep the following points in mind when setting up your communications network:

1. Systems installed in rural areas are least likely to encounter interference;

those in suburban and urban environments are more likely to be affected by other devices operating in the license-free frequency band and by adjacent licensed services.

2. If possible, use a directional antenna at remote sites. Although these antennas

may be more costly than omnidirectional types, they conﬁne the transmission and reception pattern to a comparatively narrow lobe, which minimizes interference to (and from) stations located outside the pattern. (The use of a directional antenna may not be possible in a simplex peer-to-peer network, where all remotes are designed to communicate with one another.)

3. If interference is suspected from a nearby licensed system (such as a paging

transmitter), it may be helpful to use horizontal polarization of all antennas in the network. Because most other services use vertical polarization in this band, an additional 20 dB of attenuation to interference can be achieved by using horizontal polarization.

4. Multiple MDS TransNET 900™ systems can co-exist in proximity to each

other with only very minor interference as long as they are each assigned a unique network address. Each network address has a different hop pattern.

5. If constant interference is present in a particular frequency zone, it may be

necessary to “lock out” that zone from the radio’s hopping pattern. The radio includes built-in software to help users remove blocked frequency zones from its hopping pattern. Refer to the discussion of the command for more information.

6. If interference problems persist even after removing blocked zones, try

reducing the length of data streams. Groups of short data streams have a better chance of getting through in the presence of interference than do long streams.

7. The power output of all radios in a system should be set for the lowest level

necessary for reliable communications. This lessens the chance of causing unnecessary interference to nearby systems.

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4.4 Antenna & Feedline Selection

Antennas

The equipment can be used with a number of antennas. The exact style used depends on the physical size and layout of a system. Contact your MDS representative for specific recommendations on antenna types and hardware sources.

In general, an omnidirectional antenna (Figure 9 and Figure 10) is used at the master station site in an MAS system. This provides equal coverage to all of the remote sites.

10 MDS TransNET I/O Guide MDS 05-2708A01, Rev. A

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GE MDS TRANSNET900 Users Manual

Specifications and Main Features

Frequently Asked Questions

User Manual