RF DataTech ZRT470 ZRT470 Radio Modem User Manual

RF DataTech ZRT470 Radio Modem

User Manual

ZRT Manual Page 1 of 37 Rev. J – 11 September 2008ZRT SERIESRADIO MODEMSSETUP, INSTALLATION&OPERATING MANUAL
ZRT Manual Page 2 of 37 Rev. J – 11 September 2008
ZRT Manual Page 3 of 37 Rev. J – 11 September 2008CONTENTS1INTRODUCTION........................................................................................ 41.1 PRODUCTS COVERED...........................................................................................................41.2 IMPORTANT NOTICES..........................................................................................................42 PRODUCT OVERVIEW.............................................................................. 52.1 GENERAL ................................................................................................................................52.2 TRANSMITTER........................................................................................................................52.3 RECEIVER................................................................................................................................52.4 MPU CONTROL......................................................................................................................62.5 PROGRAMMING & CONFIGURATION...............................................................................62.6 SOFT MODEM: ........................................................................................................................62.7 MODES OF OPERATION .......................................................................................................62.8 HANDSHAKING.....................................................................................................................62.9 ADDITIONAL FEATURES......................................................................................................73SPECIFICATIONS ....................................................................................... 83.1 TECHNICAL SPECIFICATIONS............................................................................................83.2 APPROVALS AND LICENSING..........................................................................................104PRE-PROGRAMMED CHANNEL PLANS............................................ 124.1 UK MPT1411/VNS2111 CHANNELS .................................................................................124.2 UK MPT1329 CHANNELS....................................................................................................145SETUP & INTERFACING......................................................................... 155.1 INTERNAL CONSTRUCTION.............................................................................................155.2 INTERFACE PORT PIN CONNECTIONS ...........................................................................155.3 12VDC POWER......................................................................................................................175.4 ANTENNA PORT..................................................................................................................175.5 CHANNEL SWITCHES.........................................................................................................175.6 PROGRAMMING ..................................................................................................................175.7 RF POWER .............................................................................................................................175.8 TIME-OUT-TIMER.................................................................................................................185.9 INTERNAL MODEM.............................................................................................................185.10 RADIO DATA FORMATS.....................................................................................................195.11 FORWARD ERROR CORRECTOR.......................................................................................195.12 SQUELCH TAIL (DRIBBLE BITS) ELIMINATION .............................................................195.13 SERIAL INTERFACE & HANDSHAKING..........................................................................195.14 TRAFFIC PROTOCOL & ROUTING MODES......................................................................215.15 TRANSMIT & RECEIVE TIMING.........................................................................................225.16 POWER CONSUMPTION.....................................................................................................255.17 POWER SAVE MODE ........................................................................................................... 255.18 “RSSI” RECEIVE SIGNAL STRENGTH INDICATION.......................................................255.19 STATUS LEDS........................................................................................................................ 266STORE & FORWARD ............................................................................... 276.1 STORE & FORWARD BASED ON CLIENT PROTOCOL. .................................................. 276.2 MODBUS................................................................................................................................276.3 RFT ROUTING PROTOCOL.................................................................................................297 INSTALLATION........................................................................................ 327.1 INTRODUCTION ..................................................................................................................327.2 POWER SUPPLIES.................................................................................................................327.3 EFFECTIVE RADIATED POWER (ERP) .............................................................................. 327.4 ANTENNAS, COAX FEEDERS & PERIPHERALS..............................................................337.5 MOUNTING & INSTALLATION.........................................................................................357.6 FIXING DETAILS...................................................................................................................35
ZRT Manual Page 4 of 37 Rev. J – 11 September 20081INTRODUCTION1.1 PRODUCTS COVEREDThis manual covers the ZRT Series of low cost, high performance radio modems designed fordata applications in commercial and industrial systems.The ZRT is an advanced, simplex/half-duplex, data radio for transmission of serial data.Versions are available with three different serial port configurations:-A true RS232 interface full handshaking.As above but with 5V TTL voltage levels on the interface rather than RS232 levels.An RS232/RS422/RS485 interface with software selection of required mode. (RTS/CTSand DSR/DTR Handshaking lines looped back to each other in RS232 mode)Information is provided to assist with configuration, installation, and operation of the productsin point to point or point to multi-point applications. A separate programming manual coversthe use of the associated WinA4P software for programming and configuration of the radios.Component level servicing is not covered in this document; if the product fails its first linetesting it should be returned to a service centre.1.2 IMPORTANT NOTICES1.2.1 CopyrightAll rights to this manual are the sole property of R.F. Technologies Ltd. The copying of themanual in whole or in part by any method without written permission is strictly prohibited.1.2.2 Right To ChangeIn the interest of improvement, R.F. Technologies reserves the right to change the technicalspecifications or functions of its product without notice.1.2.3 SoftwareR.F. Technologies Ltd software is delivered “as is”. R.F. Technologies Ltd does not grant anykind of warranty or guarantees on its saleability or it’s suitability for use in specificapplications.Under no circumstances is R.F. Technologies liable for any damages arising from using thesoftware.The copyrights relating to all software is the sole property of R.F. Technologies Ltd.Any coping, editing, translating or modifying is strictly forbidden without prior written consentfrom R.F. Technologies Ltd1.2.4 Safety Critical ApplicationsThe ZRT has not been designed for, nor is it intended for, use in safety critical or life supportapplications. No functional warranty is given if the product is used in such applications.1.2.5 UseThe ZRT radio modems have been designed to work on various licensed and license-freefrequency bands in use around the world. In the license-free bands, the user must ensure thatthe radio modem is used under the terms & conditions applicable to the use of the bandsconcerned.In licensed bands, the user must obtain permission and the necessary licenses from the relevantauthorities.
ZRT Manual Page 5 of 37 Rev. J – 11 September 20082PRODUCT OVERVIEW2.1 GENERALThe ZRT Series has been designed as a range of high specification, low cost radio modems forstand alone applications or for integration into OEM products.Through the use of advanced DSP technology, the design has been optimised for reliability andlow current consumption, making the ZRT suitable for operation on remote sites without mainspower.Applications include security, command & control, data logging, SCADA, telemetry, remoteswitching or any similar applications where serial data needs to be transmitted.The ZRT is available with three different serial interfaces:-An RS232 interface with all signalling lines to allow full handshaking if required.A TTL version of the unit which uses 5V TTL voltage levels on the serial interfaceconnector rather than RS232 signalling levels, but is otherwise the same.A version with an RS232/RS422/RS485 interface. Required interface mode is selectedusing the configuration software. In RS232 mode, the RTS line is looped back to CTSand the DSR line is looped back to DSR. RS422/RS485 half-duplex (2-wire) or fullduplex (4-wire) modes are both supported.The data rate on the serial interface can set to a range of values from 150 baud to 38,400 baud,while the over-air data rate can be independently set to a range of values between 150 baud and9,600 baud. If high throughput speeds are not required, the modem can be set to a slower over-air rate to take advantage of the associated improvement in receiver threshold.The ZRT is available with two different transmit powers. The low power version meets thelicence-exempt ETS300-220 specification while the higher power 5W version meets the tougherETS300-113 and the USA and Canadian specifications.2.2 TRANSMITTERThe transmitter frequency can be user programmed anywhere within it’s pre-alignedbandwidth. There are two power versions available, 10mW to 750mW and 100mW to 5W. Thetransmit power of any particular hardware version can be set accurately within the relevantrange under software control.2.3 RECEIVERThe receiver is a very low current double conversion superheterodyne with an active balancedmixer for very good intermodulation performance. Careful attention to spurious response,adjacent channel and blocking performance, makes the product ideal for crowded telemetrychannels.To achieve high performance the programmable bandwidth of the receiver has been limited (forUHF it is 10MHz, + 5MHz from centre frequency), full details are in the technical specificationsection.Should re-alignment be required, the unit can be returned to our service centre.
ZRT Manual Page 6 of 37 Rev. J – 11 September 20082.4 MPU CONTROLThe Microprocessor (MPU) is the heart of the product and at the centre is a 128k flashmicroprocessor that controls all the interface circuits to the radio module and externalinput/outputs. As well as the control functions, the processor provides DSP functionality thatenables modem operation between 150 and 9,600bps. The processor has 128k of flash memoryfrom which the code is executed and internal EEPROM for storing programmed parameters.2.5 PROGRAMMING & CONFIGURATIONThe parameters of the ZRT are PC programmable via the serial port. Full details of all theprogrammable parameters are covered in the separate programming manual. Details of cablesand adaptors needed for the various interface versions are given in Section 5.6.2.6 SOFT MODEM:The ZRT has a “soft modem” which allows over-air transmission at rates between 150bps and9,600bps using a range of different modulation schemes. The over-air rate can be selected bythe operator to optimise link performance.2.7 MODES OF OPERATION2.7.1 Transparent OperationThe ZRT can operate transparently without packetising the data and without adding any otheroverheads, thereby maximising data throughput rates. It requires no knowledge of the data it istransmitting. Data is simply transmitted and received with minimal delay.2.7.2 Protocol specific modemThe radio recognises a complete frame and only transmits and receives data conforming to thatformat. No addressing of radios or routing of data is performed. Protocols such as MODBUS &DNP3 can be supported in this way.2.7.3 Routing modemThe radios recognise a protocol specific frame and the address to which the frame is to be sent.Routing information must be stored in each radio for each destination address that requires theuse of repeaters. Any radio in the system can operate as a repeater. The radio does not performany acknowledgement or retries. Any protocol using a fixed address field such as MODBUScan be supported.2.8 HANDSHAKINGOn the RS232 Full Handshaking and TTL versions, transmission control can either use RTScontrol signals or be configured for automatic initiation of transmission on receipt of serial dataat the traffic interface. In either case, the radio provides a CTS output which can optionally beused for flow control.On the RS232/RS422/RS485 version, transmission is automatic when transmit data is applied.The DSR line is internally looped back to DSR and, when configured for RS232 mode, the RTSline is also looped back to CTS.In all versions, the radio incorporates a 1,024 byte internal buffer to cope with situations wherethe interface data rate is higher than the over-air rate.
ZRT Manual Page 7 of 37 Rev. J – 11 September 20082.9 ADDITIONAL FEATURESThe ZRT incorporates the following additional features which enhance the usability of theproduct and assist with the operation and maintenance of systems using the product:-2.9.1 Status LEDs:The ZRT Radio Modems have a number of front panel LED’s to enable the operator to see at aglance the status of the product and the serial data port.2.9.2 Time-out TimerThe transmitter within the ZRT has a user programmable time-out timer which allows themaximum continuous transmission time to be set in order to prevent channel blocking due to afault.2.9.3 Power-Save ModesThe ZRT has both internally controlled and externally controlled power-save modes to reduceoverall power consumption to extremely low levels for operation on sites without mains power.2.9.4 Squelch Tail EliminationAs a user programmable option, the ZRT can also operate in a packetisation mode whereframing characters are added at the start and end of the user's message prior to transmissionand stripped off again at the receive end prior to passing the user data to the interfaceconnector. This can be useful in getting rid of any spurious characters which may otherwise begenerated at the end of messages by squelch noise as the receiver mutes and which can affectold or non-tolerant protocols.In a high interference environment, enabling packetisation will often help to block reception ofthe interfering signals.2.9.5 Forward Error CorrectionThe ZRT allows an optional forward error correction to be switched in when the over-air datarate is 9,600bps. This will improve error performance, but there is an associated datathroughput overhead of around 30% which therefore reduces the effective transmission rate forthe user data. The forward error corrector is not available at lower data rates as it offers nosignificant performance enhancement at these lower rates.
ZRT Manual Page 8 of 37 Rev. J – 11 September 20083SPECIFICATIONS3.1 TECHNICAL SPECIFICATIONS3.1.1 GeneralFrequency Range: ZRT169/170 138 - 175MHzZRT225 175 - 225MHzZRT450/470 406 - 512MHzZRT869 863 - 870MHz(50MHz – 950MHz to special order)Power Requirements: 12VDC (10V – 15.5DC)Standby: <75uAReceiver on & decoding: <70mATransmitting: 300mA to 2.1A dependent on Tx powerNumber of Channels: 80 sequential or 32 discrete user programmable channels.Min. ProgrammableChannel Step: 6.25kHz or 5kHzChannel Spacing: 12.5kHz, 20kHz or 25kHzOperating Temp.Stability: 2ppm –30 to +60ºCConstruction: Aluminium enclosure.Size: 75mm W x 130mm L x 30mm H (excluding brackets and connectors)Mounting: Screws to a flat surface.Weight: 250gConnectors: DC Power 2-way Klippon TypeSerial Data 9-way D-Type FemaleRF BNC (50 ohm)LED Indicators: TX, Busy, System, RXD, TXD3.1.2 Transmitter:RF Output Power: ZRT 169/450/869 10mW - 750mWZRT 170/225/470 50mW - 5WattsBandwidth: VHF 10MHz without re-alignmentUHF 12MHz without re-alignment869 30MHz without re-alignmentInternal Modulation: Programmable for FFSK, 2-Level FSK, GMSK or 4-Level FSK.Max. Deviation: ± 7.5kHz maxDuty Cycle up to 70%Adj. Channel Power: >65dB at 12.5kHzSpurious Emissions: As per ETS300-113Rise Time: < 9mS
ZRT Manual Page 9 of 37 Rev. J – 11 September 20083.1.3 ReceiverSensitivity: 0.25uV (-119dBm) for 12dB SINAD de-emphasised0.355uV (-117dBm) for 12dB SINAD flatBandwidth: VHF 5MHz without re-alignmentUHF 10MHz without re-alignment869 20MHz without re-alignmentSpurious Response: ZRT 169/450/869 >65dBZRT 170/225/470 >80dBBlocking: ZRT 169/450/869 >85dBuVZRT 170/225/470 >90dBuVIntermodulation: ZRT 169/450/869 >60dBZRT 170/225/470 >70dBAdjacent Channel: >65dB at 12.5kHzIF Frequencies: 45MHz and 455kHzSpurious Emissions: ZRT 169/450/869 <ETS 300-220ZRT 170/225/470 <ETS 300-113Mute Response Time: <2msec3.1.4 Internal ModemSerial Comms: Asynchronous (or Synchronous with custom software).Baud rate programmable between 150bps and 38,400bpsInterface: /232Full version :- RS.232 complete with signalling lines/TTL version:- 5V TTL levels rather than RS.232/232+485 version:- RS.422/RS.485 (2 or 4 wire) orRS232 with looped back signalling lines.Parity: Programmable as Odd, Even or NoneNRZI: On or OffStop bits: Programmable 1 or 2Data Bits: Programmable 7 or 8Signalling Formats: Programmable as V23, Bell202 or MPT1327, up to 1200 baud, coherentFFSK at 2400 baud, GMSK at 4800 baud, 4 Level FSK at 9600 baud.Synchronous/Async. Programmable as either up to 1200bps, synchronous above 1200bpsOver-air Baud Rate: 150 – 9600bps within 12.5kHzBit Error Rate: 150 - 2400 baud less than 1 x 10-3 at –120dBm4800 baud less than 1 x 10-3 at –117dBm9600 baud less than 1 x 10-3 at –115dBm (FEC on)9600 baud less than 1 x 10-3 at –112dBm (FEC off)Forward Error Corrector (FEC) is a programmable option at 9600bps.In the interest of improvement the above specifications are subject to change without notice.
ZRT Manual Page 10 of 37 Rev. J – 11 September 20083.2 APPROVALS AND LICENSINGThe ZRT has been designed to meet the relevant standards outlined below. Should others berequired, please contact the sales office.3.2.1 UK ApprovalsMPT1411/VNS2111: The 5W version of the ZRT has been tested to MPT1411 and thereplacement VNS2111 for licensed applications with a maximum datarate of 9600bps within a 12.5 kHz channel. A licence is required and thepermitted output power is normally stated on the licence.MPT1329: The radios meet the requirements of MPT1329BS2011: The unit complies with the Vibration specification BS2011.3.2.2 European ApprovalsETS 300-220 The unit meets the specification for European licensed exemptcommunications with a maximum RF power level of 500mW. Pleasenote the permitted power level may vary from country to country.ETS 300-113 The 5W version of the unit meets the specification for licensed dataradiosETS 301-489: The unit meets the required CE specification and carries a CE Mark.EN60950 The unit meets the relevant requirements of this Safety specification.3.2.3 European Declaration of ConformanceHereby, RF DataTech declares that the ZRT Series of Radio Modems is in compliance with theessential requirements and other relevant provisions of Directive 1999/5/EC.3.2.4 USA FCC Part 90 & 15 & Canadian RSS119This equipment has been tested and found to comply with the limits for a Class A digitaldevice, pursuant to Part 15 of the FCC Rules. These limits are designed to provided reasonableprotection against harmful interference when the equipment is operated in a commercialenvironment. This equipment generates, uses, and can radiate radio frequency energy and, ifnot installed and used in accordance with the instruction manual, may cause harmfulinterference to radio communications. Operation of this equipment in a residential area is likelyto cause harmful interference in which case the user will be required to correct the interferenceat his own expense. WARNING: Changes or modifications not expressly approved by RF DataTech could voidthe user’s authority to operate the equipment.This device complies with Part 15 of the FCC Rules. Operation is subject to the condition thatthis device does not cause harmful interference.
ZRT Manual Page 11 of 37 Rev. J – 11 September 2008RF EXPOSUREWARNING: To satisfy FCC/IC RF exposure requirements for mobile transmitting devices,a separation distance must be maintained between the antenna connected to this device andpersons during device operation. To ensure compliance, operations at closer than thesedistances are not recommended. The following table show the minimum distance for differentgain antennas:Antenna Gain Minimum Separation DistanceUnity or Less 0.5m3dB 0.7m6dB 1.0m8dB 1.3m10dB 1.6m12dB 2.0mThe antenna used for this transmitter must not be co-located in conjunction with any otherantenna or transmitterThis device has been designed to operate with external antennas having an impedance of 50ohms.To reduce potential radio interference to other users, the antenna type and its gain should be sochosen that the equivalent isotropically radiated power (EIRP) is not more than that requiredfor successful communication and is not higher than permitted levels.
ZRT Manual Page 12 of 37 Rev. J – 11 September 20084PRE-PROGRAMMEDCHANNEL PLANSUsing the PC configuration software, the ZRT can be programmed with a number of userspecified or standard channel plans. Standard plans currently include all UK MPT1411 orMPT1329 channels. Further standard channel plans may become available in later releases ofthe configuration software. A mixture of channels from different channel plans can also beentered discretely using the software.The following tables show the channel numbers and associated frequencies for various channelplans:-4.1 UK MPT1411/VNS2111 CHANNELSCHANNEL SCANNER OUTSTATIONS1457.50625 463.006252 457.51875 463.018753 457.53125 463.031254 457.54375 463.043755 457.55625 463.056256 457.56875 463.068757 457.58125 463.081258 457.59375 463.093759 457.60625 463.1062510 457.61875 463.1187511 457.63125 463.1312512 457.64375 463.1437513 457.65625 463.1562514 457.66875 463.1687515 457.68125 463.1812516 457.69375 463.1937517 457.70625 463.2062518 457.71875 463.2187519 457.73125 463.2312520 457.74375 463.2437521 457.75625 463.2562522 457.76875 463.2687523 457.78125 463.2812524 457.79375 463.2937525 457.80625 463.3062526 457.81875 463.3187527 457.83125 463.3312528 457.84375 463.3437529 457.85625 463.3562530 457.86875 463.3687531 457.88125 463.3812532 457.89375 463.3937533 457.90625 463.4062534 457.91875 463.4187535 457.93125 463.4312536 457.94375 463.4437537 457.95625 463.4562538 457.96875 463.46875
ZRT Manual Page 13 of 37 Rev. J – 11 September 200839 457.98125 463.4812540 457.99375 463.4937541 458.00625 463.5062542 458.01875 463.5187543 458.03125 463.5312544 458.04375 463.5437545 458.05625 463.5562546 458.06875 463.5687547 458.08125 463.5812548 458.09375 463.5937549 458.10625 463.6062550 458.11875 463.6187551 458.13125 463.6312552 458.14375 463.6437553 458.15625 463.6562554 458.16875 463.6687555 458.18125 463.6812556 458.19375 463.6937557 458.20625 463.7062558 458.21875 463.7187559 458.23125 463.7312560 458.24375 463.7437561 458.25625 463.7562562 458.26875 463.7687563 458.28125 463.7812564 458.29375 463.7937565 458.30625 463.8062566 458.31875 463.8187567 458.33125 463.8312568 458.34375 463.8437569 458.35625 463.8562570 458.36875 463.8687571 458.38125 463.8812572 458.39375 463.8937573 458.40625 463.9062574 458.41875 463.9187575 458.43125 463.9312576 458.44375 463.9437577 458.45625 463.9562578 458.46875 463.9687579 458.48125 463.9812580 458.49375 463.99375
ZRT Manual Page 14 of 37 Rev. J – 11 September 20084.2 UK MPT1329 CHANNELSThe ZRT can be programmed to operate on the full MPT1329 band of channels with access tochannels 26, 27 & 32 denied, in line with MPT1329 band plan.The radio should be programmed for a maximum power level of 500mW.CHANNEL FREQUENCY1458.5000 Guard Ch.2 458.51253 458.52504 458.53755 458.55006 458.56257 458.57508 458.58759 458.600010 458.612511 458.625012 458.637513 458.650014 458.662515 458.675016 458.687517 458.700018 458.712519 458.725020 458.737521 458.750022 458.762523 458.775024 458.787525 458.800026 458.812527 458.8250 Not Used28 458.8375 Not Used29 458.850030 458.862531 458.875032 458.887533 458.9000 Not Used34 458.912535 458.925036 458.937537 458.9500 Guard Ch.
ZRT Manual Page 15 of 37 Rev. J – 11 September 20085SETUP & INTERFACING5.1 INTERNAL CONSTRUCTIONThe exploded view shows the main components of the radio modem. There are no useradjustments or settings which require removal of the covers.5.2 INTERFACE PORT PIN CONNECTIONSThe ZRT Series is equipped with a 9 way female D connector for the traffic interface. The pinsof this connector are allocated as follows:-5.2.1 RS232-Only (Full Handshaking) and 5V TTL versions 1. DCD: Data Carrier Detect - - - o 2. RXD: Receive Data - - - - - - - o- - - - - 6. DSR: Data Set Readyo o- - - - - 7. 3. o- - - - - 8. 4. DTR: Data Terminal Ready - - o o- - - - - 9. nc Not Connected 5.RTS: Request to SendTXD: Transmit Data - - - - - - - oCTS: Clear to SendGND: GROUND - - - - - - - - - - o
ZRT Manual Page 16 of 37 Rev. J – 11 September 20085.2.2 RS232/RS422/RS485 VersionsThe RS232/RS422/RS485 versions of the ZRT may be software programmed to have either anRS232 or an RS422/RS485 compatible interface.To allow programming without an interface adapter, a radio programmed for RS422/RS485operation will switch back to RS232 operation if the front panel rotary switches are set toposition 00 to select programming mode. Note that although the ZRT can withstand RS232voltages on its inputs in RS422/RS485 mode, this may not be the case for externally connecteddevices. To avoid any risk of damage to the externally connected equipment, care musttherefore be taken to ensure that programming mode is not selected while connected toRS422/RS485 terminal equipment.Pin allocation when set for RS232 operation:- o- - - - - 9. nc Not Connected 4. DTR: Data Terminal Ready - - - - - - - o(Internally connected to Pin 6) o- - - - - 8. CTS: Clear to Send (Internally connected to Pin 7) 3.: Transmit Data Input - - - - - - - -TXDo - - - - - 7. RTS: Request to Sendo (Internally connected to Pin 8) 2. : Receive Data Output - - - - - - - -RXD o o- - - - - 6. DSR: Data Set Ready (Internally connected to Pin 4) 5.GND: GROUND - - - - - - - - - - - - - - - o 1. Data Carrier Detect - - - - - - - - -DCD: oPin allocation when set for RS422/RS485 operation:- o- - - - - 9. nc Not Connected 4. DTR: Data Terminal Ready - - - - - - - o(Internally connected to Pin 6) o- - - - - 8. *****: Do Not Use(Internally connected to Pin 7) 3. : +ve Data In to Radio - - - - - - - -TXD +o - - - - - 7. : -ve Data In to RadiooTXD -(Internally connected to Pin 8) 2. : -ve Data Out from radio - - - - - -RXD - o o- - - - - 6. DSR: Data Set Ready (Internally connected to Pin 4) 5.GND: GROUND - - - - - - - - - - - - - - - o 1. : +ve Data Out from radio - - - - -RXD + oWhen half-duplex (2-wire) RS422/RS485 operation is programmed, the TXD- and TXD+ signalsare internally connected to the RXD- and RXD+ signals respectively. The 2-wire half-duplexbus only needs to be connected to the RXD- and RXD+ pins (Pins 1 and 2). Shorting links arenot required in the connector.When operating in 2-wire RS422/RS485 mode, the radio will output data on to a 2 wire circuitwhenever it is received, which could lead to a bus conflict in conditions of high interference andprevent a connected terminal from outputting transmit data. To avoid this condition it isrecommended that the message packeting option is turned on at both ends of the radio link.The DTR and DSR signals are looped back to each other internally in both configurations.When configured for RS232 operation, the RTS and CTS signals are also looped back to eachother. The radio should in most circumstances operate correctly in applications requiringRTS/CTS handshake although the it is unable to use CTS to prevent buffer overflow. Overflowsituations can easily be avoided by making the serial port baud rate the same as the radio signalbaud rate, or by ensuring that message sizes do not exceed the buffer size of 1024 bytes.
ZRT Manual Page 17 of 37 Rev. J – 11 September 2008The DTR input has a threshold of approximately +1.5V with respect to ground, it may be usedwith a standard RS232 level signal or a TTL level signal in either RS232 or RS485 mode, thesignal is active high in both cases.5.3 12VDC POWERA nominal 12VDC (9.6 – 15.5Vdc) is supplied to the unit via a 2 way pluggable terminal block,the polarity is marked on the front panel and the plug has a polarity key to prevent accidentalpolarity reversal. In the event of a polarity reversal the circuit board is protected by diodes andfuses.5.4 ANTENNA PORTThe antenna connection is a 50 ohm BNC connector. This should be connected to a suitableantenna or terminated in a 50 ohm load whenever the transmitter is activated. Transmissioninto an open circuit may cause excessive current to be drawn from the supply and damagecould occur.5.5 CHANNEL SWITCHESThe ZRT can be user programmed with up to 80 sequential or 32 discrete simplex or semi-duplex channels.The two front panel BCD switches select the required channels or, if both are set to zero,program mode is entered. In program mode, the radio interprets any signals on the serialinterface as programming commands rather than data for transmission.When viewing a ZRT with the aerial connector at the top, the left hand rotary switch is the"tens" switch and the right is the "units" switch, thus to set channel 37, set the left switch to 3and the right to 7.5.6 PROGRAMMINGThe parameters of the ZRT can be programmed via the serial port using either DOS orWindows based software. The individual configuration files can be stored on disc for futureuse or printed. Full details of all the programmable parameters are covered in the separateprogramming manual.The RS232 Only (Full Handshaking) version can be connected directly to the serial port on a PCusing a straight-through cable.The 5V TTL version needs an adaptor unit between the ZRT and the programming computer toconvert between RS232 and TTL voltage levels.The RS232/RS422/RS485 version does not need an adaptor because the serial port switches toRS232 mode automatically when the radio is put into program mode by setting both front panelswitches to zero. A standard straight-through cable with all pins connected may be used forconnection to the PC.5.7 RF POWERThe transmit power can be accurately set using a locally connected PC running the suppliedconfiguration software. This allows the RF power level to be programmed directly in Watts ormilliwatts with an accuracy of +/-1dB. There are no internal power adjustment points insidethe modem.There are two transmit power ranges available. The low power ZRT169, ZRT450 & ZRT869versions can be set between 10mW and 750mW, while the higher power ZRT170, ZRT225 &ZRT470 versions can be set between 50mW and 5W.
ZRT Manual Page 18 of 37 Rev. J – 11 September 20085.8 TIME-OUT-TIMERThe transmitter within the ZRT has a time-out timer which allows the maximum continuoustransmission time to be set in order to prevent channel blocking due to a host fault. The timerworks in all modes (external/internal modem) and is programmable in one second stepsbetween 0 and 255 seconds. If not required the timer can be programmed off.If the timer is enabled and the selected time is exceeded, transmission will cease until the actionthat normally causes transmission is removed and then re-applied. More explicitly; withRTC/CTS handshake enabled RTS must be dropped and then raised again, or if handshake isnot enabled character transmission must be suspended for at least two character periods at theserial port baud rate. In all modes the modem’s SYS led is flashed at least twice when time-outoccurs, the flashing continues while lockout is in force. The lockout timer is disabled if thelockout time is set to 0. The lockout timer can be operated in “resettable” or “cumulative”mode, in resettable mode the timer restarts each time a transmission is made, in cumulativemode the timer counts up during transmit, and down during receive. If the timer counts up tothe lockout time during transmit, lockout occurs; this will eventually happen if the radio spendsmore than half of its time transmitting. Lockout in this mode is indefinite and can only be resetby powering the radio off.5.9 INTERNAL MODEMThe ZRT features an internal “soft modem” which offers unparalleled performance andflexibility over a wide range of speeds and formats. Data is presented to the modem via theRS232 (or TTL) serial connection at speeds between 150 and 38400 and then transmitted at theprogrammed radio baud rate. Buffering is provided when the data rate is higher than the radiotransmission rate.5.9.1 Modulation & Tone-setsWithin a 12.5kHz channel, the over-air transmission from the unit can be programmed for arange of speeds. For 150, 300, 600,1200, the modulation is FFSK with Bell 202 and V.23 (Mode 2)tone-sets both supported. At these lower speeds, it is also possible to select a protocol specificMPT1327 mode which uses a 1200/1800Hz tone-set to allow compatibility with number ofadditional modems from other manufacturers. At 2400bps the modulation is coherent FFSK, at4800bps it is GMSK and at 9600bps it is 4-Level FSK.If operating at speeds up to and including 1200bps and compatibility with other equipment isnot required, the use of the Bell 202 tone-set is recommended, as this will give the best linkperformance.5.9.2 Synchronous/Asynchronous Modem OperationThe radio modem can be programmed for asynchronous or synchronous operation at baudrates up to 1200. At baud rates of 2400 or more, modem operation may only be synchronous.This relates to the over-air signal and has no bearing on the format of the data presented at theserial interface portIn synchronous mode inverted NRZI encoding is used where a one is represented by atransition in the binary data, every transmitted bit fits into a time slot defined by the baud rate,this allows a phase locked loop to lock on to the data stream to give better performance in noisyconditions, the inverted NRZI encoding allows this to continue even when the signal is idlingsending stop bits. The inverted NRZI encoding gives a further advantage with GMSK signallingsince the polarity of the signal is unimportant.In asynchronous mode NRZ encoding is used where a “one” tone represents a binary one, anda “zero” tone a binary zero, whilst each character consists of bits of equal duration defined bythe baud rate, the time between the end of a stop bit and a following start bit may be arbitrary.This prevents the implementation of a phase locked loop to improve signal to noiseperformance but does allow use within older systems that do not implement synchronoustransmission or NRZI encoding.
ZRT Manual Page 19 of 37 Rev. J – 11 September 2008If compatibility with other radios is not required, the use of the synchronous mode isrecommended, as this will give best link performance.5.10 RADIO DATA FORMATSThe data rate over the air can be set up independently of the rate set for the serial interface, butthe over-air rate should be set either at the same speed or a lower speed than the serial interfacerate. The radio baud rate should be set at the minimum possible to maintain the requiredthroughput, lower speeds will give better results in poor signal conditionsThe radio signal can be set up to operate using 7 or 8 bit data, 1 or 2 stop bits, and odd, even orno parity. This setting is also independent of the serial port setup. This flexibility allowscompatibility with other radios.If the Forward Error Corrector is enabled (option only available at 9,600bps), the selected radiosignal format is over-ridden as detailed below.5.11 FORWARD ERROR CORRECTORAt 9600bps there is also a programmable option to switch in a forward error corrector. Whenswitched on, the over-air data format changes to a fixed format using 14 bit words. Thesecomprise 8 data bits, 5 CRC (Cyclic Redundancy Check) bits and a flag bit which is used todifferentiate control and data functions in messages. An additional 14 bit synchronisation wordis also sent after every 8 data words. The effect of this redundancy on a typical 9600bps linkconfiguration is to reduce the effective data transfer rate to around 6300bps.The error corrector is aimed at improving performance in weak signal conditions, rather thanrecovering data in deep fades or burst-error conditions. An error rate of 1x10-4 with the FECswitched off will typically improve by a factor of 2000 to around 5 in 10-7 when it is switched on,but an initial error rate of 1x10-3 with it off will only improve by a factor of around 250 tosomething like 4x10-5 when it is switched on.In terms of receiver sensitivity, the 1x10-6 threshold improves by around 0.4uV (or 6.4dB) whenthe FEC is switched on.5.12 SQUELCH TAIL (DRIBBLE BITS) ELIMINATIONThe ZRT has an optional packetisation mode which can be enabled using the configurationprogram. This adds framing characters at the start and end of the user’s message prior totransmission. The additional information is stripped off the messages at the receiver prior topassing the data to the interface connector. Packetisation can be useful in getting rid of anyspurious characters which may otherwise be generated at the end of messages by squelch noiseas the receiver mutes or by interference and which can affect old or non-tolerant protocols.It is important to note that packetisation must be set the same on all radios operating together.All radios must have it selected or all radios must have it de-selected.5.13 SERIAL INTERFACE & HANDSHAKING5.13.1 Handshaking on RS232/RS422/RS485 versionIn this version of the ZRT, transmission is automatic when transmit data is applied.When configured for RS232 mode, the RTS line is looped back to CTS and the DSR line islooped back to DSR. The radio should in most circumstances operate correctly in applicationsrequiring RTS/CTS handshake although the it is unable to use CTS to prevent buffer overflow.Overflow situations can easily be avoided by making the serial port baud rate the same as theradio signal baud rate, or by ensuring that message sizes do not exceed the buffer size of 1024bytes.
ZRT Manual Page 20 of 37 Rev. J – 11 September 20085.13.2 Handshaking on RS232-Only (Full Handshaking) and TTL versionsThe RS232 Only (Full Handshaking) and TTL versions can be programmed either to useRTS/CTS handshaking to initiate transmission, or to transmit automatically whenever data ispresent at the serial input. In the latter mode CTS is still operated to implement flow control butcan be ignored unless message sizes exceed 1k byte and the serial port baud rate is higher thanthe radio signal baud rate. These handshaking modes are compatible with modes A, C and D ofthe CMD400 manufactured by Pacscom Ltd.. Mode B (byte stuffing mode) is not supported.Transmission Using RTS/CTS Handshaking (RS232-Only and TTL Versions):-If handshaking is enabled, transmission is started by operating RTS. CTS can then be monitoredfor flow control purposes. In the idle state CTS is inactive, but when RTS is operated CTS willbecome active immediately and data may be input to the serial port. When all data has beenloaded to the serial port RTS should be dropped. Transmission will continue until all data inthe serial input buffer has been sent, then CTS will become inactive and transmission will cease.During transmission the amount of data in the serial buffer is checked by the radio, if the bufferbecomes ¾ full CTS is dropped to request the host to stop loading data, CTS is activated againwhen the buffer is reduced to ¼ full. To prevent timing problems data will still be accepted intothe buffer when CTS is de-activated due to buffer filling during transmit, however any datareceived once CTS has dropped at the end of a transmission will be discarded, this preventssuch data from being prefixed to the beginning of the next message.Transmission Without Hardware Handshaking (RS232-Only and TTL Versions):-If RTS/CTS handshaking is disabled the radio will start transmission as soon as data is receivedat the serial port, transmission ceases as soon as the serial buffer has been emptied and a periodequivalent to two characters at the radio signal baud rate has elapsed. It is important to notethat since transmission ceases as soon as a two character delay in the incoming data stream isseen, data characters in a message must be presented in a continuous back to back stream.In this mode CTS is still used to indicate the serial buffer fill level in the same way as describedin the section on transmission using handshake, the difference is that in the idle state CTS isalways active indicating readiness to accept data. In most applications CTS can be ignored asmessages are likely to be smaller than the serial input buffer (1k byte), bear in mind also that ifthe radio baud rate and data format is the same as that configured for the serial port the bufferis being emptied as fast as it is being filled and so buffer overrun is unlikely.5.13.3 Data ReceptionAny data received by the radio is simply output to the serial port, and in RS232 configurationsthe DCD line can be programmed to operate in three different modes to assist the host. Firstlyby indicating that a carrier is detected on the radio channel, this is useful if a busy lockoutfunction is required (although this can be dangerous if the channel is susceptible to interferenceas well as wanted signals), secondly DCD can indicate presence of a carrier and a valid datasignal, data will normally be output under this circumstance, the third mode behaves in thesame way as the second except that DCD remains active until all data has been output to theserial port after the signal has gone, this allows DCD to be used as a wake up signal.In RS422 and RS485 2-wire configurations, the radio will output data on to the 2 wire circuitwhenever it is received, which could lead to a bus conflict in conditions of high interference,preventing any connected terminal from transmitting data when it wants to. To avoid thiscondition it is recommended that the message packeting option is turned on at both ends of theradio link in this mode.
ZRT Manual Page 21 of 37 Rev. J – 11 September 20085.14 TRAFFIC PROTOCOL & ROUTING MODES5.14.1 Transparent ModeIn this mode, the radio has no knowledge of the data it is transmitting, data is simplytransmitted and received under hardware control with the option of RTS control or initiation oftransmit after receiving serial data, with CTS providing an optional flow control. Thisconfiguration is useful when expanding older systems where the radios must be compatiblewith other manufacturers equipment.5.14.2 Protocol Specific ModeThe radio recognises a complete frame and only transmits and receives data conforming to thatformat. No addressing of radios or routing of data is performed. Protocols such as MODBUScan be supported in this way.5.14.3 Routing ModeThe radios recognise a protocol specific frame and the address to which the frame is to be sent.Routing information must be stored in each radio for each destination address that requires theuse of repeaters or store & forward nodes. Any radio in the system can operate as arepeater/store & forward node. The radio does not perform any acknowledgement or retries.Any protocol using a fixed address field such as MODBUS or RFT ROUTING can be supported.5.14.4 STORE & FORWARD OPERATIONThe ZRT can support “Store & Forward” repeater operation to cope with situations where thedirect communication between sites is not possible due to range or terrain. The ZRT seriessupports up to six repeaters within one link, although the more repeaters used, the greater thesignal strength has to be at each receiver, as there will be some accumulative degradation overthe whole link.The forwarding is carried out based on the Protocol Routing Mode and is based on the addressfields within the data to be transmitted. At a repeater site, the incoming message is stored andthen re-transmitted if it is for a protocol address further down that chain of radios.
ZRT Manual Page 22 of 37 Rev. J – 11 September 20085.15 TRANSMIT & RECEIVE TIMINGThe ZRT only operates in a simplex or semi-duplex mode. In simplex mode the receive andtransmit frequencies are the same, whereas in the semi-duplex mode they are different.In either mode data is only sent in one direction at a time as the radios do not have separatesynthesisers for transmit and receive. If full duplex mode is required (transmit & receive at thesame time) the ART product should be considered.In simplex/semi-duplex mode, the radio synthesiser must be reloaded each time Receive orTransmit is selected. Although relatively short, the synthesiser loading time must be taken intoaccount when looking at data transfer times.In order to reduce adjacent channel interference in line with ETS300-113, the power output fromthe transmitter has finite rise and fall times, a distant receiving radio will therefore see anincoming signal later than a nearby one. The receiving radio also requires time for the carrierdetect circuit to operate and for the modem to lock on to the incoming audio signal.When using the ZRT, there are a few timing considerations to be taken into account. The mainone is the programmable “lead in delay”, which is required for the modem to lock on to theincoming data stream and is dependant on the radio signal baud rate. Minimum timings aregiven below:Baud Rate Lead in Delay(Minimum)150 80ms300 60ms600 40ms1200 40ms2400 40ms4800 20ms9600 30msFor simplex/semi-duplex operation, time is required for the transmit and receiver synthesiserto be loaded and locked prior to transmission/reception. This timing constraint is importantwhen deciding how soon after receiving a message a reply may be sent. For simplex/semi-duplex operation the ZRT is ready to receive data approximately 25ms after transmissionceases. It is therefore necessary to either wait this length of time after receiving a message beforesending a reply or to extend the lead in delay by the same amount to hold off transmission ofthe data.For applications where power save is in use the lead in delay should be extended to allow thereceiving device to wake up. The time required can be calculated by adding the save on time tothe save off time and adding 10 percent, e.g. for a save on time setting of 800ms and a save offtime of 200ms the lead in delay should be 1100ms.Care must be taken when replying to a previously transmitting ZRT when RTS/CTS handshakeis not being used, in this mode the transmitting device will wait for two character times beforeturning off its carrier and may therefore miss the beginning of a reply if it comes too soon, thismay be overcome either by imposing an additional two character delay in the controlling deviceor by extending the lead in delay by that amount.The ZRT also has a facility for imposing a lead out delay, which is the time that the carrierremains on after transmission of the message is complete. This delay can normally be left atzero as it is only of use where a controller makes use of the DCD signal to suppress dataprocessing but suffers some delay in processing received data, or where there is a need to delayany spurious squelch tail characters generated sufficiently that connected equipment does notconfuse them with part of the message.
ZRT Manual Page 23 of 37 Rev. J – 11 September 20085.15.1 Receive To Transmit Switching TimeWhen using the internal modem the action that initiates transmission can be either receipt of acharacter at the serial port or the operation of RTS. These examples use the first mode. The radiodoes nothing until the stop bit of the first character for transmission has been received, thetransmitter is then started:The time delay between receipt of the stop bit for the first character to be transmitted at thetransmitting radio and output of the start bit of that character at the receiving radio is the sumof the values ttxon, tlid, trbyte, and tmdel shown in the diagram above. Values for theseparameters are indicated below:TABLE A: Timing values for duplex and simplex modes are as follows:symbol Description Semi-duplexsimplexttxon Time from external action to commencing transmission 9ms 9mstlid Duration of synchronisation transmission (lead in delay) Table B Table Btrbyte Duration of 1 byte at radio signal baud rate Table C Table Ctmdel Modem decode latency Table D Table DTABLE B: The lead in delay is a programmable parameter but minimum values dependant onbaud rate must be adhered to. However, in a scanning system with the base station oncontinuous transmit the base station lead in delay can be set for Zero (thereby saving valuabletime) as the internal outstation modems will always be synchronised.Baud 150 300 600 1200 2400 4800 9600Min tlid 80ms 60ms 40ms 40ms 40ms 20ms 30msTABLE C: The duration of a byte at the radio baud rate is dependant upon the data formatemployed, the table below assumes a format of one start bit, 8 data bits, no parity and 1 stop bit,i.e. a total of 10 bits per character. If another format is used the appropriate correction must bemade.Baud 150 300 600 1200 2400 4800 9600trbyte 66.7ms 33.3ms 16.7ms 8.3ms 4.17ms 2.08ms 1.04msTABLE D: The modem decode latency takes into account delays introduced by hardware andsoftware filters. The total delay is baud rate dependant:Baud 150 300 600 1200 2400 4800 9600tmdel 6.9ms 3.5ms 1.7ms 1.3ms 1ms 1ms 1ms
ZRT Manual Page 24 of 37 Rev. J – 11 September 20085.15.2 Message DurationThe time taken to transmit a message can be simply derived by multiplying the number ofcharacters in a message by the values given in table C making any appropriate corrections fordata format. The exception is 9600 baud where extra synchronisation sent during the messagemust be taken into account, 8 synchronisation bits lasting a total of 0.833ms are sent afterevery eighth message character.5.15.3 Transmit To Receive Switching TimeIn full or semi-duplex operation transmit to receive switching time does not need to beconsidered as the receive path is maintained during a transmission, in simplex operation sometime must be allowed to reload the transmitter synthesiser to stop it from interfering with thereceiver. The diagram below indicates the minimum time in which the radio is able to receive asignal after completing a transmission.symbol Description valuethold Period for which carrier is held up after sending last databyte2.5ms + LODtrxrdy Time to reload transmit synthesiser in simplex mode 6msDuring the time thold the radio transmits some padding bits to allow for propagation delays inthe receiving device before shutting off the carrier, this prevents possible chopping of themessage tail. The time thold is composed of a fixed 2.5ms period plus the programmable valueLOD (lead out delay). LOD is normally set to zero. After the time trxrdy has expired the radiois ready to receive a new signal.N.B. If RTS/CTS handshaking is not used the transmitter is turned on whenever data is received at theserial port, the transmitter is left on until all buffered data has been transmitted and no data has beeninput for a time equivalent to the length of two characters at the radio baud rate (refer to table C). Ingeneral data transmitted by the radio is delayed with respect to its receipt at the serial port by the receiveto transmit switching time, if the radio baud rate and serial port baud rate and both data formats are thesame this delay remains constant throughout the transmission. At the higher baud rates this delay isgenerally greater than the length of two characters and so the procedure to stop transmission is started assoon as the last character has been sent, at the lower baud rates however it is possible that the time tholdis extended while the radio waits for the two character timeout to expire, this can also happen if datacharacters are not loaded back to back into the serial port.
ZRT Manual Page 25 of 37 Rev. J – 11 September 20085.16 POWER CONSUMPTIONThe ZRT is a very low power product and is ideal for operation from batteries with solar powerbackup. The information below is intended to help the user decide on the best battery and solarcell size for operation at non powered sites.5.16.1 Transmitter RF power verses currentTX Power 5W 4W 3W 2W 1W 500mW 200mW 100mW 50mWMax. Current 2.1A 1.8A 1.6A 1.3A 950mA 675mA 500mA 390mA 300mA5.17 POWER SAVE MODEThe ZRT is equipped with an internal and external power save mode. These are outlined below:5.17.1 Internal Power SaveIn this mode the microprocessor switches the transceiver off and after a pre-programmed time(Save on time) switches the unit back on (Save off time). If a carrier is not detected then thetransceiver again switches off. If during the time the transceiver is awake a carrier is received,the unit will stay on. After the carrier drops out the receiver will stay on until the programmedresume time elapses. Once the resume time has elapsed the unit will return to its power savemode. The Save On/Off and Resume time are all programmable via the PC program. Obviouslythe amount of power saved increases with the programmed save on/off ratio, however withpower save enabled long lead times must be programmed to wake up the unit beforecommunication can take place. Therefore it may not be possible to run all applications underthe power save mode due to the turn around times required by the host system. In somecircumstances it is possible to achieve power save and fast polling: If polling of all outstations iscarried out in cycles with a reasonable gap between each cycle, a long initial poll can be used towake up all stations, the resume timer will then restart each time an outstation is polledallowing fast access, when the cycle is complete all stations will return to power save after theresume time has expired.5.17.2 External Power SaveUnder this mode the on/off ratio is controlled externally via the DTR line (DTR shut downmust first be enabled using the set up program). In this mode more of the modem's circuits areshutdown (including the microprocessor), this saves more power but care must be taken toensure that the modem is enabled when a transmission is to take place. Note that there is ahardware link option to allow the serial port to shut off when DTR is not active; this allows theradio current to be reduced to its bare minimum. In applications where DTR is not connectedthis link option must of course be disabled.5.18 “RSSI” RECEIVE SIGNAL STRENGTH INDICATIONThe ZRT produces an internal DC signal which is proportional to the received signal strength.The DC signal is passed to the internal MPU where it accurately measures its value by aninternal A-D converter. The radios are individually calibrated during production so that signalstrength can then be read in dB micro volts on a PC connected to the serial port.
ZRT Manual Page 26 of 37 Rev. J – 11 September 20085.19 STATUS LEDSThe ZRT has a number of LEDs to enable the operator to see at a glance the status of theproduct and the serial port:-RX RF Carrier Detect/BusyTX TransmitSYS SystemRXD Receive DataTXD Transmit Data5.19.1 System LEDWith the Exception of the System LED the remainder are self explanatory. The System LEDlights when the radio is being programmed and is also used as a quick check as to the status ofthe unit. If any alarms are detected it will flash out an Error number.5.19.2 Error NumberThe modem reports errors in two ways, firstly the BUSY led will come on and the SYS led willflash a number of times, the BUSY led will then go out again and if the fault persists theprocedure will be repeated. An error number can be determined by counting the number oftimes the SYS led flashes while the BUSY led is on.ERROR No FAULT1Position of the channel switches has changed.2A channel has been loaded that has no RX frequency programmed.3Transmission has been attempted on a channel that has no TX frequencyprogrammed.4The receiver synthesiser phase locked loop has failed to lock due to badchannel data or programming of an out range frequency.5The transmitter synthesiser phase locked loop has failed to lock due tobad channel data or programming of an out of range frequency.6The contents of the microprocessor's EEPROM are corrupted (failedchecksum) in the general program area.7Internal comms with a high power amplifier have failed.8The contents of the microprocessor's EEPROM are corrupted (failedchecksum) in the calibration area.9The contents of the microprocessor's EEPROM are corrupted (failedchecksum) in the factory program area.10 No POCSAG message stored for repeat test.11 Rotary channel switch position overridden by software.12 Tx power setting out of range.13 Packet Mode cycle pointer invalid.14 Bad routing table area EEPROM checksum.15 I2C Bus initialisation error.
ZRT Manual Page 27 of 37 Rev. J – 11 September 20086STORE & FORWARD6.1 STORE & FORWARD BASED ON CLIENT PROTOCOL.To conserve valuable air time and avoid the possibility of collisions due to coverage overlapswith other repeaters transmitting at the same time, only messages that require forwarding byspecific repeaters are re-transmitted when the ZRT is used in “Store & Forward” mode.This is achieved by stripping out the addresses of incoming serial messages, comparing theaddress with the list of outstation addresses stored in the unit and routing the messagesaccordingly. This requires knowledge of the client’s message structure and, specifically, wherethe address can be found in the message.There is normally local communication at the store and forward site, via the RS232 port.We have written various store & forward drivers to cope with a number of client specificmessage formats and are always happy to write new drivers as and when required. Furtherinformation is available from the sales office.6.2 MODBUS6.2.1 Setting Up MODBUS OperationThe ZRT can be programmed to transport “MODBUS ASCII” or “MODBUS RTU” formatmessages in single master systems. These options are selected as the “INTERFACEPROTOCOL” in the “EDIT MODE/INTERFACE” menu. It is not necessary for all radios to runthe same Modbus interface, “MODBUS ASCII” and “MODBUS RTU” modes can be mixedwithin a system.When Modbus modes are enabled the “NETWORK ID” and “RADIO ADDRESS” fields must befilled out such that every radio in a system has the same network ID, but a different radioaddress. Notes should be kept detailing the installation of radios and their addresses.When transporting Modbus messages the master station radio must be programmed with arouting table. This is accessed in the “EDIT MODEM/INTERFACE” menu by setting“ROUTING TABLE” to “ON” and selecting “EDIT ROUTING TABLE”. This selection leads toseveral pages of Modbus addresses and the route by which every Modbus address is reachedmust then be entered, for example if the Modbus device with address 37 is physically connectedto the radio with radio address 23, and radio 23 is accessed from the base station via relayradios 4 and 19, then the field entitled “MBUS 37” should be loaded with the route “4,19,23”. Ifthe Modbus devices with Modbus addresses 65 and 93 are physically connected to radio 45 andno relays are required then the fields entitled “MBUS 65” and “MBUS 93” should both beloaded with “45”.6.2.2 MODBUS OperationOperation in Modbus modes relies on the master/slave poll/reply nature of Modbus. The setup of the radios does not differentiate between a master and slave, the only difference inpractice would be that the master station radio will be loaded with a routing table. There is norestriction on the number of masters in a system, but they should all be loaded with routingtables.When a poll is initiated at a master station radio the destination Modbus address in the Modbusmessage is looked up in the routing table to determine the addresses of the radio(s) required tocomplete the link, the message is then sent and all the radios expect to send a reply back thesame way. Once this reply has been sent the radios are all ready to start another poll/replysequence.
ZRT Manual Page 28 of 37 Rev. J – 11 September 2008If a radio is specified as a relay in a link, any locally connected Modbus devices will not beaware of communications that take place as no activity occurs on the serial port in this state.This may cause problems however if more than one master exists in a system as a radio that isbeing used as a link in a relay is not available to transmit messages.6.2.3 Power-Save Operation With MODBUSWhen Modbus modes are enabled in the configuration programme two further fields appearentitled “MIN PWR SAVE ADDRESS” and “MAX PWR SAVE ADDRESS”. If power saveoperation is not required set both these fields to zero.If power save operation is required it is enabled by setting the “RADIO ADDRESS” to a valuegreater or equal to “MIN PWR SAVE ADDRESS” and less than or equal to “MAX PWR SAVEADDRESS”. The radio will then enter low power standby mode for the time programmed in the“PSAVE ON TIME” field in the main edit menu, it will then wake up and check for an incomingsignal, if none is present it will return to sleep and repeat the cycle. If a signal is detected theradio will stay awake until a reply to the outward bound message has been returned.When the master station or relay radios send an outward bound message, the address of theradio to which the message is being sent is checked against the min and max power saveaddresses, if a power saved radio is indicated a cyclic wake up message is sent for the periodindicated by the programmed power save on time before the actual data message is sent, if apower saved radio is not indicated the data message is sent immediately. These parametersalong with some others are also used to calculate a timeout time in the event that no reply isreceived. It is therefore essential that all radios in a system are programmed with the sameparameters even if not power saved, otherwise communications will fail.Note that if “DTR SHUTDOWN” is enabled a radio remains completely shut down while DTRis inactive, it will not wake up according to the power save timer to see if any incomingmessages are present. This mode should therefore only be used in conjunction with real timemessage scheduling.6.2.4 Serial Port Handshaking With MODBUSWhen Modbus modes are enabled the DTR and DSR signalling lines can be used to assist inpower saving the host Modbus device. The RTS and CTS lines are not used and the “RTS/CTSHANDSHAKE” option in the “EDIT MODEM/INTERFACE” menu of the WinA4P programmeshould be set to “OFF” in RS232 versions. When the Modbus slave is ready to accept data itshould assert DTR, DSR will be asserted in response and the received message will be output tothe Modbus device. The “HOST INACTIVITY TIME” field in the set up programme defines atime limit for the Modbus device to assert DTR in response an incoming message and if thistime limit is exceeded the radio sends back a reply indicating the destination device failed torespond and the link is cancelled. After sending a response, the Modbus slave may then releaseDTR and return to power save mode. Note that as long as DTR is asserted the radio will notreturn to its power save mode (if enabled in the setup programme). DSR will remain asserted inthis case.The master station can also control the power saving of its radio using DTR, the radio will operate in power save mode as long as DTR is not active, asserting DTR wakes the radio, DSRis asserted in return to indicate that the radio is awake and ready to accept data.If use of the handshake lines is not required DTR should be connected to a voltage of +3.5 to+15V such that sleep mode is never allowed.
ZRT Manual Page 29 of 37 Rev. J – 11 September 20086.2.5 Timeouts in MODBUS ModesWhen a transmission from a master station radio is made in Modbus mode the radio willcalculate a timeout for a reply, this calculation is based on many configuration parametersincluding the radio baud rate, lead in delay, host inactivity time, maximum message length,power save timing etc. If power saving is enabled and the baud rate is low this time can be large(the calculation limits the result to a maximum of 4.25 minutes. To reduce the possibility of“hung” radios the destination radio will send a link closing message if the destination Modbusslave does not reply. This link closing message is only used by the radios to close the link, it isnot passed to the Modbus master.If the Modbus master itself times out before the radio link does, it can send another poll, radiosalong the link will cancel the previous route and set up the new one. The exception to this is theprevious destination radio if it is still trying to wake up its Modbus slave, it will ignore the newmessage and try to download its original message when the slave awakes, a conflict will thenarise if a reply is sent. To avoid this situation the Modbus master timeout time should allow themaximum “HOST INACTIVITY TIME” to expire plus the time required to get a message and itsreply through the link.6.3 RFT ROUTING PROTOCOL6.3.1 Setting Up RFT Routing OperationThe ZRT can be programmed to route non-specific protocol messages in single master systemsusing “RFT ROUTING” mode. This mode supports relay messaging. This option is selected asthe “INTERFACE PROTOCOL” in the “EDIT MODEM/INTERFACE” menu.In describing operation the address contained in the host system message will be referred to asthe “protocol address” and address programmed in the radio under the “RADIO ADDRESS”field in the setup program will be referred to as the “radio address”.RFT Routing mode is controlled at the master station by picking out an 8 bit protocol addressfield in the message to be sent, this address is then looked up in the routing table stored in themaster station radio. The routing table can contain the radio address (as programmed in theRADIO ADDRESS field in the setup program) of a single radio connected to the requireddestination device or a list of relay radio addresses plus the destination radio address. Themessage is then transmitted from the base station radio as a packet with the routing informationprefixed to it. The message is then relayed through any relay radios specified until it reaches thedestination radio where it is output from the serial port in its original form with the packetinformation removed. During this process each radio considers itself to be part of an establishedlink. A reply is then expected, however the outstation radios are not programmed with routingtables, a reply issued is assumed to be destined to the master station. The address in theprotocol message is therefore not checked and the reply is simply sent back down theestablished link to the master station radio where it is output from the serial port. As the replyis passed back the link members no longer consider themselves to be part of an established linkand return to idle.Note that there is no differentiation in operating mode between a relay radio and an outstationradio, if an outstation radio is specified as a relay in a link any device connected to the localserial port will be unaware of relay communications taking place.The packet used to transfer protocol messages specifies the route to be taken and also thecurrent stage in the route, it is therefore of no concern if radios further down a relay link “hear”the message before they are expected to repeat it, they will ignore the message until specificallyrequested to repeat it.
ZRT Manual Page 30 of 37 Rev. J – 11 September 2008The position of the address in the protocol field is specified using the “ADDRESS OFFSET”parameter in the setup programme. A setting of 0 specifies zero offset, i.e. the address is the firstbyte in the message, an offset of 6 specifies the 7th message byte and so on. 16 bit addressing ormore is not supported as a maximum of only 256 destinations can be supported by the routingtable. If the protocol message format does use 16 bit addressing specify the offset for the leastsignificant byte and try to ensure that no two devices use the same l.s.b. in their address.In order to determine the position of the address in a protocol message the radio has to knowwhere the message starts and ends, this can be done in one of two ways: If the RTS/CTSHANDSHAKE option is turned on (option only available in RS232 Full Handshaking and 5VTTL radio versions), RTS should be activated before commencing a message, CTS will beactivated in response and the message may be loaded. The first character received after CTSbecomes active is considered to be the start of the message. Transmission will start as soon asenough characters have been loaded for the protocol address to be extracted and the routedetermined from the routing table. Transmission continues until RTS is de-activated, CTS willdrop when transmission is complete. CTS may also drop if the serial input buffer becomes morethan ¾ full to implement flow control, if this happens RTS should be kept active until CTS is re-activated, more characters may then be loaded or RTS may be dropped.If the RTS/CTS HANDSHAKE option is turned off or is not an available option, the radio relieson gaps in the serial data to determine the start and end of messages. A gap equivalent to twocharacter periods at the serial port baud rate is treated as a message end. The first characterreceived after such a gap is treated as the first character of the next message.When RFT ROUTING mode is enabled the “NETWORK ID” and “RADIO ADDRESS” fieldsmust be filled out such that every radio in a system has the same network id, but a differentradio address. Notes should be kept detailing the installation of radios and their addresses.The master station radio must be programmed with a routing table, this is accessed in the“EDIT MODEM/INTERFACE” menu by setting “ROUTING TABLE” to “ON” and selecting“EDIT ROUTING TABLE”. This selection leads to several pages of protocol addresses, the routeby which every protocol address is reached must then be entered, for example if the device withprotocol address 37 is physically connected to the radio with radio address 23, and radio 23 isaccessed from the base station via relay radios 4 and 19, then the field entitled “ADDR 37”should be loaded with the route “4,19,23”. If the devices with protocol addresses 65 and 93 arephysically connected to radio 45 and no relays are required then the fields entitled “ADDR 65”and “ADDR 93” should both be loaded with “45”.6.3.2 Power-Save Operation With RFT RoutingWhen RFT ROUTING mode is enabled in the configuration programme two further fieldsappear entitled “MIN PWR SAVE ADDRESS” and “MAX PWR SAVE ADDRESS”, if powersave operation is not required set both these fields to zero.If power save operation is required it is enabled by setting the “RADIO ADDRESS” to a valuegreater or equal to “MIN PWR SAVE ADDRESS” and less than or equal to “MAX PWR SAVEADDRESS”. The radio will then enter low power standby mode for the time programmed in the“PSAVE ON TIME” field in the main edit menu, it will then wake up and check for an incomingsignal, if none is present it will return to sleep and repeat the cycle. If a signal is detected theradio will stay awake until a reply to the outward bound message has been returned.When the master station or relay radios send an outward bound message, the address of theradio to which the message is being sent is checked against the min and max power saveaddresses, if a power saved radio is indicated a cyclic wake up message is sent for the periodindicated by the programmed power save on time before the actual data message is sent, if apower saved radio is not indicated the data message is sent immediately. These parametersalong with some others are also used to calculate a timeout time in the event that no reply isreceived. It is therefore essential that all radios in a system are programmed with the sameparameters even if not power saved, otherwise communications will fail.
ZRT Manual Page 31 of 37 Rev. J – 11 September 2008Note that if “DTR SHUTDOWN” is enabled a radio remains completely shut down while DTRis inactive, it will not wake up according to the power save timer to see if any incomingmessages are present. This mode should therefore only be used in conjunction with real timemessage scheduling.6.3.3 Serial Port Handshaking With RFT RoutingWhen RFT ROUTING mode is enabled the RS232 port lines DTR and DSR, can be used to assistin power saving. The RTS and CTS lines are optionally used according to the “RTS/CTSHANDSHAKE” option in the “EDIT MODEM/INTERFACE” menu for flow control. When theslave is ready to accept data it should assert DTR, DSR will be asserted in response and thereceived message will be output to the device. The “HOST INACTIVITY TIME” field in the setup programme defines a time limit for the device to assert DTR. If this time limit is exceededthe radio sends back a reply indicating the destination device failed to respond and the link iscancelled (this message is not output to the device connected to the master station serial port).After sending a response, the slave may then release DTR and return to power save mode. Notethat as long as DTR is asserted the radio will not return to its power save mode (if enabled inthe setup programme). DSR will remain asserted in this case.The master station can also control the power saving of its radio using DTR, the radio willoperate in power save mode as long as DTR is not active, asserting DTR wakes the radio, DSR isasserted in return to indicate that the radio is awake and ready to accept data.If use of the handshake lines is not required DTR should be connected either to a voltage of +3.5to +15V such that sleep mode is never allowed.6.3.4 Timeouts in RFT Routing ModeWhen a transmission from a master station radio is made in RFT ROUTING mode the radio willcalculate a timeout for a reply, this calculation is based on many configuration parametersincluding the radio baud rate, lead in delay, host inactivity time, maximum message length,power save timing etc. If power saving is enabled and the baud rate is low this time can be large(the calculation limits the result to a maximum of 4.25 minutes. To reduce the possibility of“hung” radios the destination radio will send a link closing message if the destination slavedoes not reply. This link closing message is only used by the radios to close the link, it is notpassed to the device connected to the master station radio.If the device connected to the master station radio itself times out before the radio link does, itcan send another poll, radios along the link will cancel the previous route and set up the newone. The exception to this is the previous destination radio if it is still trying to wake up itsslave, it will ignore the new message and try to download its original message when the slaveawakes, a conflict will then arise if a reply is sent. To avoid this situation the master timeouttime should allow the maximum “HOST INACTIVITY TIME” to expire plus the time requiredto get a message and its reply through the link.
ZRT Manual Page 32 of 37 Rev. J – 11 September 20087INSTALLATION7.1 INTRODUCTIONCorrect installation of the ZRT radios should ensure reliable data communications for manyyears. The most important installation points to remember are:-Suitable antenna system mounted at the correct height & polarisation to achieve therequired distance.Reliable power supply capable of supplying the correct voltage and current.Correct installation for the environment.Correct interface and set-up.Assuming the unit has been correctly installed and tested at the correct data speed, other factorsthat may affect the performance include the RF power (normally specified by the regulatingauthority), the local topography and the weather.7.2 POWER SUPPLIESThe ZRT can be powered from any power source provided that the voltage is between 9.6VDC& 16VDC with a –ve GND. If a +ve GND system is in use, an isolated converter will berequired.The ZRT requires a supply capable of providing between 300mA and 2.5A depending on themaximum transmit power required.Under no circumstances should the output of the supply rise above 16VDC.For 240/110VAC, 50VDC or 24VDC, a range of uninterruptible power supply units areavailable with a in-built charger and power fail indication. A range of suitable Gel type batteriesis available should a back-up supply be required during power failures.7.3 EFFECTIVE RADIATED POWER (ERP)The Radio Frequency (RF) Power allowed can be specified in two ways:The “Terminated power into 50 ohms”, which in the case of the ZRT would be amaximum of 5W.The “ERP”, which is the actual radiated power, taking into account the gain/loss ofthe antenna and loss in the feeder. Hence, if we use an aerial with a gain of 3dB (x2)and assume no loss in the cable, the ERP with an input of 5W would be 10W.The gain of an antenna is very useful as it enables lower power transmitters to be used in manycases in place of high power transmitters, with the advantage of a much lower currentconsumption.For example if the ERP allowed for a link is 5W, then a ZRT operating at 5W into a unity gainantenna, would require a supply current of 2.1Amps to provide an ERP of 5W.If however, we use an 8 element directional Yagi with a Gain of 10dB, we would only need500mW of RF Power for the same performance.With a ZRT operating at 500mW, the current consumption would only be 600mA. If the site isbattery or solar powered then the saving is very significant.Care must be taken when setting the power as permitted RF power is often specified as amaximum ERP.
ZRT Manual Page 33 of 37 Rev. J – 11 September 20087.4 ANTENNAS, COAX FEEDERS & PERIPHERALS7.4.1 AntennasApart from the radio modem, the antenna is probably the most important part of the system.The wrong choice or a bad installation will almost certainly impede the product’s performance.Depending on the application either an omni-directional or directional antenna will berequired.7.4.2 Types of AntennasWe can offer a complete range of antennas to suit all applications; details of some of the morepopular ones are outlined below:-Antenna Types TypicalGain Polarisation UseVertical Whip 0dB VerticalHelical - 3dB Vertical In-house testing and local useEnd Fed Dipole 0dB VerticalFolded Dipole 0dB Vertical/Horizontal Local Scanner or Multi-point system6dB Co-linear +6dB Vertical3dB Co-linear +3dB Vertical Wide area Scanner12 Element Yagi +12dB Vertical/Horizontal 4 Element Yagi +8dB Vertical/Horizontal Outstation or point to point linkCorner Reflector +10dB Vertical/HorizontalOutstations in areas of badInterference or where radiation mustbe kept to a minimumPatch Antenna 0dB Vertical/Horizontal Kiosk or Wall mounting7.4.3 Directional AntennasFor point to point communications, a directional Yagi or corner reflector is probably the besttype of antenna to use, as directional antennas provide relatively high gain in the forwarddirection within a limited beamwidth and very good rejection of unwanted signals at the rear.The number of elements and hence the size, will depend on the gain and beam width required.Yagi antennas can be used in the vertically polarised or horizontally polarised, butcommunicating products should be fitted with antennas of the same polarisation. If not a lossof signal strength will occur. Use of both vertical and horizontal propagation can be very usefulon single or repeater sites where isolation is required between communication paths. Usingdifferently polarised antennas for each path will increase the isolation which will reducepossible interference between the paths.7.4.4 Omni-Directional AntennasWith approximately 360 degree radiation pattern, this type of antenna is ideal for the centralsite of a scanning station or where communication to a group of widely dispersed outstations isrequired.7.4.5 Patch or Plate AntennasThe patch or plate antennas are normally rectangular or round, with a back plate of aluminiumor stainless steel. A polycarbonate or ABS cover is fitted to protect the antenna from theenvironment. This type of antenna can be produced in different sizes with various radiationpatterns to suit the application. Depending on the construction and radiation pattern, the gain isusually between -3dB to + 3dB. Their use is very popular on road side kiosks, buses, trains,aircraft, or where covert communication is required.
ZRT Manual Page 34 of 37 Rev. J – 11 September 20087.4.6 Antenna MountingLocation: The antenna should be mounted in a clear area, as far away as possible fromobstructions such as metal constructions, buildings and foliage.Height: The ZRT operates in the UHF band, which requires near line of sightcommunication. Hence, for extended ranges the height of the antenna isimportant.7.4.7 PolarisationA Yagi or corner reflector antenna can be mounted for vertical or horizontal polarisation.Scanning systems employing a vertically polarised antenna will necessitate the outstationantennas to be of the same orientation. In vertical polarisation the elements are perpendicular tothe ground. By mixing polarisation within systems, unwanted signals can be reduced by asmuch as 18dB. However, such systems require detailed planning.7.4.8 AlignmentIf a directional antenna is to be used, it will need alignment with the scanner or communicatingstation. A map and compass can be used, but the final adjustment should be performed bymeasuring the receive signal strength (RSSI) from the scanner, as outlined in the operationssection.7.4.9 Antenna Coax Feeder:As with the antenna, the use of the wrong coax feeder can seriously affect the performance ofthe system. Hence, the coax cable should be selected to give a low loss over the distancerequired. For outstations in the local vicinity of the scanner/ base station, the loss is not veryimportant but for distant stations the loss is very important. As a rule of thumb, never operate asystem with a loss of more than 3dB.To illustrate the point, a 3dB loss in the feeder will result in a 50% loss in transmitted RF powerand a 50% reduction in the received signal strength. Therefore, double the received signalstrength will be required for the same bit error rate. Although increasing the RF power willcompensate for the loss in transmitted power, there is no effective way to improve the receivedsignal strength.Coax cable should be installed in accordance with the manufacturers’ instructions, with cableruns kept as short as possible. Sharp bends, kinks and cable strain must be avoided at all costs.If long term reliability is required, the cable must be securely mounted to avoid excessivemovement and longitudinal strain, due to high winds, rain and snow.7.4.10 Signal Loss v. Cable Length at 500MHzCable TypeAttenuation per 100ft Attenuation per 100mRG58 13.0dB 37.0dBRG213 6.0dB 17.5dBLDF2-50 3/8inch Foam Heliax 2.44dB 8.0dBLDF4-50 1/2inch Foam Heliax 1.60dB 5.26dBLDF5-50 7/8inch Foam Heliax 0.883dB 2.9dBLDF6-50 1-1/4inch Foam Heliax 0.654dB 2.15dBLDF7-50 1-5/8inch Foam Heliax 0.547dB 1.79dB
ZRT Manual Page 35 of 37 Rev. J – 11 September 20087.4.11 Coax & Connectors:50 Ohm coax connectors of a good quality should be used, termination must be in accordancewith the manufacturer's specification, any special tools required to terminate the connectorsmust be used. Connectors exposed to the environment should be sealed to prevent the ingressof moisture. If the cable is penetrated by water a high loss will occur and the cable will need tobe replaced. Once assembled it is advisable to test the cable and connectors for open and shortcircuits.7.4.12 VSWR Measurement:Voltage standing wave ratio (VSWR) is the ratio of detected volts from the forward RF power,to the detected volts from the reflected (returned) RF power. This ratio is used to measure thecombined coax cable and antenna match. A good match will ensure that most of the RF Poweris radiated, whereas a bad match will result in the reflection of a large amount of the power,thereby reducing the transmitter's range. A perfect match will give a 1:1 ratio and bad matchwill give 2:1 or higher. For guidance, a good system will measure between 1.2:1 and 1.5:1.7.4.13 Lightning ArrestersAt high or exposed sites, the use of a lightning arrester is recommended. This in-line device fitsbetween the antenna and the product with an earth strap connected to ground. Should alightning strike occur, most of the energy should be diverted to ground leaving the equipmentwith little or no damage.7.5 MOUNTING & INSTALLATIONThe ZRT is built into tough durable aluminium enclosure that can be mounted in any plane, butshould not be exposed to rain etc. as the enclosure and connectors do not meet the relevant IPratings.If IP65, 67 or 68 is required then an additional enclosure will be required. A number of suitableenclosures are available as options.7.6 FIXING DETAILSZRT Series.ANTENNABU SYSYSTXProg/ChannelSwi tchZRT Series.TXDRXDINP UT -12V+
ZRT Manual Page 36 of 37 Rev. J – 11 September 2008
ZRT Manual Page 37 of 37 Rev. J – 11 September 2008RF DataTechis a trading division of:-R.F. Technologies Ltd27 – 29 New RoadHextableKent BR8 7LSTel: +44 (0) 1322 614 313Fax: +44 (0) 1322 614 289E-Mail: info@rfdatatech.co.ukADDITIONAL PRODUCT DATAwww.rfdatatech.co.uk

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