BIM1

EW N Radiometrix Hartcran House, 231 Kenton Lane, Harrow, HA3 8RP, England Tel: +44 (0) 20 8909 9595, Fax: +44 (0) 20 8909 2233 Issue 3, 14 September 2007 BiM1, TX1H VHF VHF Narrow Band FM transceiver The BiM1 transceiver modules offer a 100mW RF output VHF data link in Radiometrix transceiver standard pin-out and footprint. This makes the BiM1 ideally suited to those low power applications where existing wideband transceivers provide insufficient range. Features • • • • • • • • • • Conforms to EN 300 220-3 and EN 301 489-3 (10mW version only) Standard frequency 151.300MHz Other frequencies from 120MHz to 180MHz Available separately as BiM1T transmitter and BiM1R receiver TX1H is a BiM1T in TX1 pin-out Data rates up to 10kbps for standard module Usable range over 10km Fully screened Feature-rich interface (RSSI, analogue and digital baseband Low power requirements Figure 1: BiM1-151.300-10 The BiM1 is a half duplex radio transceiver module for use in long range bi-directional data transfer applications at ranges up to 10kilometres. The module operates on the UK licence exempt frequency of 173.225/173.250MHz with 10mW RF output and Australian frequency of 151.300MHz with 100mW RF output. The small footprint of 23 x 33mm and low profile of 10mm together with low power requirements of 60dBm range 10kbps, -120dBm sensitivity (for 12 dB SINAD) BiM1 transceiver, TX1H high power transmitter data sheet Page 1 Radiometrix Ltd., Figure 2: BiM1-151.300-10 BiM1 transceiver contains BiM1T transmitter circuit and BiM1R receiver circuit with their RF output and input connected to a common RF pin via an internal RF switch. TX1H transmitter circuit is the BiM1T transmitter circuit in the TX1 pin-out with slightly enlarged dimension to accommodate extra Power Amplifier circuit to produce 100mW RF output. Radiometrix Ltd., BiM1 transceiver, TX1H high power transmitter data sheet Page 2 Figure 3: TX1H block diagram Functional description The transmit section of the BiM1 consists of a frequency modulated Voltage Controlled Crystal Oscillator (VCXO) feeding a frequency doubler with two stage amplifier and RF filter. Final Power Amplifier stage is factory pre-set to appropriate band power level. Operation is controlled by a Tx Select line, the transmitter achieving full RF output typically within 5ms of this line being pulled low. The RF output is filtered to ensure compliance with the appropriate radio regulations and fed via a fast Tx/Rx changeover switch to the 50Ω antenna pin. The receive section is a double conversion FM superhet with IF at 21.4MHz and 455kHz fed by a Low Noise Amplifier (LNA) on the RF front-end. The receiver is controlled by RX Select line and will power up typically 0.1Vp-p). TX modulation requirements The module is factory-set to produce the specified FM deviation with a TXD input to pin 14 of 3V amplitude, i.e. 0V “low”, 3V “high If the data input level is greater than 3V, a resistor must be added in series with the TXD input to limit the modulating input voltage to a maximum of 3V on pin 7. TXD input resistance is 100kΩ to ground, giving typical required resistor values as follows: Vcc ≤3V 3.3V 5V 9V Series resistor 10 kΩ 68kΩ 220kΩ Reducing the output power of the BiM1 If the BiM1 is to be used for applications for which the regulatory Effective Radiated Power (ERP) limit is lower than 100mW its output power can be reduced to comply with relevant regulatory requirements. This is done by inserting a 10dB attenuator network between the module and the antenna or feed, as follows: To antenna 68R 1 2 3 RF Ground Antenna RF Ground 18 50 ohm microstrip lines 100R to antenna 100R 68R 100R from TX1 9 10 ground foil/ vias to ground plane Resistors are SMD (0603/0805) schematic diagram physical arrangement Figure 6: 10dB attenuator for BiM1 transceiver, BiM1T transmitter Keep all tracking around the attenuator network as short as possible, particularly ground paths, and use matched 50Ω microstrip lines for input and output connections (track width of 2.5mm if using 1.6mm thick FR4 PCB). However, this 10dB attenuator will also reduce the sensitivity of the BiM1 transceiver by 10dB. RF output can also be factory set from +5dBm (3mW) to +20dBm (100mW) depending on minimum order quantity. Radiometrix Ltd., BiM1 transceiver, TX1H high power transmitter data sheet Page 6 RX Received Signal Strength Indicator (RSSI) The BiM1 wide range RSSI which measures the strength of an incoming signal over a range of 60dB or more. This allows assessment of link quality and available margin and is useful when performing range tests. The output on pin 11 of the module has a standing DC bias of up to 0.5V with no signal, rising to 2.4V at maximum indication. ∆Vmin-max is typically 1V and is largely independent of standing bias variations. Output impedance is 56kΩ. Pin 11 can drive a 100µA meter directly, for simple monitoring. Typical RSSI characteristic is as shown below: 2.4 2.2 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 -140 -135 -130 -125 -120 -115 -110 -105 -100 -95 -90 -85 -80 -75 -70 -65 -60 -55 -50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 RF Level (dBm) Figure 7: RSSI level with respect to received RF level at BiM1 antenna pin Radiometrix Ltd., RSSI (V) BiM1 transceiver, TX1H high power transmitter data sheet Page 7 Packet data In general, data to be sent via a radio link is formed into a serial "packet" of the form :Preamble - Control - Address - Data - CRC Where: Preamble: This is mandatory for the adaptive data slicer in the receiver in the BiM1 to stabilise. The BiM1 will be stable after 10ms. Additional preamble time may be desired for decoder bit synchronisation, firmware carrier detection or receiver wake up. The minimum requirement is a single bit or unique bit pattern to indicate the start of message (frame sync.). Additionally, decoder information is often placed here such as: packet count, byte count, flow control bits (e.g. ACK, repeat count), repeater control, scrambler information etc. This information is used for identification purposes and would at least contain a 16/24 bit source address, additionally - destination address, site / system code , unit number and repeater address's may be placed here. User data , generally limited to 256 bytes or less (very long packets should be avoided to minimise repeat overheads on CRC failure and channel hogging). 16/24 Bit CRC or Checksum of control-address-data fields used by the decoder to verify the integrity of the packet. Control: Address: Data: CRC: The exact makeup of the packet depends upon the system requirements and may involve some complex air-traffic density statistics to optimise through-put in large networked systems. Networks BiM1’s may be used in many different configurations from simple pair's to multi-node random access networks. The BiM1 is a single frequency device thus in a multi node system the signalling protocol must use Time Division Multiple Access (TDMA). In a TDMA network only one transmitter may be on at a time, ‘clash’ occurs when two or more transmitters are on at the same time and will often cause data loss at the receivers. TDMA networks may be configured in several ways - Synchronous (time slots), Polling (master-slave) or Random access (async packet switching e.g. X25). Networked BiM1's allow several techniques for range / reliability enhancement: Store and forward Repeaters: If the operating protocol of the network is designed to allow data path control then data may be routed via intermediate nodes. The inclusion of a repeating function in the network protocol either via dedicated repeater/router nodes or simply utilising existing nodes allows limitless network expansion. Spatial Diversity: In buildings multi-path signals create null spots in the coverage pattern as a result of signal cancellation. In master-slave networks it is cost effective to provide 2 BiM1's with separate antenna at the master station. The null spot patterns will be different for the two BiM1's . This technique ‘fills in’ the null spots, i.e. a handshake failure on the first BiM1 due to a signal null is likely to succeed on the 2nd BiM1. Radiometrix Ltd., BiM1 transceiver, TX1H high power transmitter data sheet Page 8 "RS232" Serial data It is possible to transmit "RS232" serial data directly at 600 to 9600bps baud between a pair of BiM1 transceivers in half duplex mode. The data must be "packetised" with no gaps between bytes. i.e. The data must be preceded by >10ms of preamble (55h or AAh) to allow the data slicer in the BiM1 to settle, followed by one 00h and one FFh bytes to allow the receive UART to lock, followed by a unique start of message byte, (01h), then the data bytes and finally terminated by a CRC or check sum. The receiver data slicer provides the best bit error rate performance on codes with a 50:50 mark:space average over a 5ms period, a string of FFh or 00h is a very asymmetric code and will give poor error rates where reception is marginal. Only 50:50 codes may be used at data rates above 1kbps. We recommend 3 methods of improving mark:space ratio of serial codes, all 3 coding methods are suitable for transmission at 10kbps:• Method 1 - Bit coding Bit rate , Max 10kbps , Min 250bps Redundancy (per bit) 100% (Bi-phase) Each bit to be sent is divided in half, the first half is the bit to be sent and the second half, it's compliment. Thus each bit has a guaranteed transition in the centre and a mark:space of 50:50 . This is Bi-phase or Manchester coding and gives good results, however the 100% redundancy will give a true throughput of 5kbps. Another variation of this code is to encode a ‘1’ as a long bit with one transition and ‘0’ as a short bit with two transition or vice versa. Each encoded bit starts with a guaranteed transition to reverse the voltage level even if stream of 00h/FFh is encoded. This is called Differential Manchester Encoding. This encoding method is easier to decode as the decoder has to sample encoded bit several times and if the sample value is more than 75% of a long bit period, then it is decoded as ‘1’ and if there was transition then it is decoded as ‘0’ or vice versa. • Method 2 - FEC coding Bit rate , Max 10kbps, Min 2.4kbps Redundancy (per byte) 100% Each byte is sent twice; true then it's logical compliment. e.g. even bytes are true and odd bytes are inverted. This preserves a 50:50 balance. A refinement of this simple balancing method is to increase the stagger between the true and the inverted data streams and add parity to each byte. Thus the decoder may determine the integrity of each even byte received and on a parity failure select the subsequent inverted odd byte. The greater the stagger the higher the immunity to isolated burst errors. Digitised analogue data Linear operation of BiM1 transceivers will allow direct transfer of analogue data, however in many applications the distortion and low frequency roll off are too high (e.g. bio-medical data such as ECG). The use of delta modulation is an excellent solution for analogue data in the range 1Hz up to 4kHz with less than 1% distortion. A number of propitiatory IC's such as Motorola's MC3517/8 provide CVSD Delta mod/demod on a single chip. Where the signal bandwidth extends down to DC , such as strain gauges, level sensing, load cells etc. then Voltage to Frequency / Frequency to Voltage chips (such as Nat Semi LM331) provide a simple means of digitising. Radiometrix Ltd., BiM1 transceiver, TX1H high power transmitter data sheet Page 9 Expected range Predicting the range obtainable in any given situation is notoriously difficult since there are many factors involved. The main ones to consider are as follows: • • • • • Type and location of antennas in use Type of terrain and degree of obstruction of the link path Sources of interference affecting the receiver “Dead” spots caused by signal reflections from nearby conductive objects Data rate and degree of filtering employed The following are typical examples – but range tests should always be performed before assuming that a particular range can be achieved in a given situation: Data rate 1.2kbps 10kbps 10kbps 10kbps Note: Tx antenna half-wave half-wave helical helical Rx antenna half-wave half-wave half-wave helical Environment rural/open rural/open urban/obstructed in-building Range 10-15km 3-4km 500m-1km 100-200m The figure for 1.2kbps assumes that the receiver bandwidth has been suitably reduced by utilising an outboard sallen-key active audio filter and data slicer or similar arrangement. The BiM1 TXD input is normally driven directly by logic levels but will also accept analogue drive (e.g. 2-tone signalling). In this case it is recommended that TXD (pin 14) be DC-biased to 1.2V approx. with the modulation ac-coupled and limited to a maximum of 2Vp-p to minimise distortion over the link. The varactor modulator in the BiM1 introduces some 2nd harmonic distortion which may be reduced if necessary by predistortion of the analogue waveform. At the other end of the link the BiM1 RXD output is used to drive an external decoder directly. Although the modulation bandwidth of the BiM1 extends down to DC it is not advisable to use data containing a DC component. This is because frequency errors and drifts between the transmitter and receiver occur in normal operation, resulting in DC offset errors on the BiM1 audio output. The BiM1 in standard form incorporates a low pass filter with a 5kHz nominal bandwidth. This is suitable for transmission of data at raw bit rates up to 10kbps. In applications such as long range fixed links where data speed is not of prime concern, a considerable increase in range can be obtained by using the slowest possible data rate together with filtering to reduce the receiver bandwidth to the minimum necessary. Antennas The choice and positioning of transmitter and receiver antennas is of the utmost importance and is the single most significant factor in determining system range. The following notes are intended to assist the user in choosing the most effective antenna type for any given application. Integral antennas These are relatively inefficient compared to the larger externally-mounted types and hence tend to be effective only over limited ranges. They do however result in physically compact equipment and for this reason are often preferred for portable applications. Particular care is required with this type of antenna to achieve optimum results and the following should be taken into account: 1. Nearby conducting objects such as a PCB or battery can cause detuning or screening of the antenna which severely reduces efficiency. Ideally the antenna should stick out from the top of the product and be entirely in the clear, however this is often not desirable for practical/ergonomic reasons and a compromise may need to be reached. If an internal antenna must be used try to keep it away from other metal components and pay particular attention to the “hot” end (i.e. the far end) as this is generally the most susceptible to detuning. The space around the antenna is as important as the antenna itself. Radiometrix Ltd., BiM1 transceiver, TX1H high power transmitter data sheet Page 10 2. Microprocessors and microcontrollers tend to radiate significant amounts of radio frequency hash which can cause desensitisation of the receiver if its antenna is in close proximity. The problem becomes worse as logic speeds increase, because fast logic edges generate harmonics across the VHF range which are then radiated effectively by the PCB tracking. In extreme cases system range may be reduced by a factor of 5 or more. To minimise any adverse effects situate antenna and module as far as possible from any such circuitry and keep PCB track lengths to the minimum possible. A ground plane can be highly effective in cutting radiated interference and its use is strongly recommended. A simple test for interference is to monitor the receiver RSSI output voltage, which should be the same regardless of whether the microcontroller or other logic circuitry is running or in reset. The following types of integral antenna are in common use: Quarter-wave whip. This consists simply of a piece of wire or rod connected to the module at one end. At 151MHz the total length should be 471mm from module pin to antenna tip including any interconnecting wire or tracking. Because of the length of this antenna it is almost always external to the product casing. Helical. This is a more compact but slightly less effective antenna formed from a coil of wire. It is very efficient for its size, but because of its high Q it suffers badly from detuning caused by proximity to nearby conductive objects and needs to be carefully trimmed for best performance in a given situation. The size shown is about the maximum commonly used at 151MHz and appropriate scaling of length, diameter and number of turns can make individual designs much smaller. Loop. A loop of PCB track having an inside area as large as possible (minimum about 5cm2), tuned and matched with 2 capacitors. Loops are relatively inefficient but have good immunity to proximity detuning, so may be preferred in shorter range applications where high component packing density is necessary. Integral antenna summary: whip *** *** * ** helical ** ** *** * loop * * ** *** Ultimate performance Ease of design set-up Size Immunity to proximity effects 471mm @ 151MHz RF Whip antenna wire, rod, PCB track or a combination of these length(mm) = 71250 / freq(MHz) RF Helical antenna 35-40 turns wire spring length 120mm, dia 10mm trim wire length or expand coil for best results RF Ctune C match RF GND track width = 1mm 2 min. area 500mm capacitors may be variable or fixed (values depend on loop dimensions) Loop antenna Figure 8: integral antenna configurations Radiometrix Ltd., BiM1 transceiver, TX1H high power transmitter data sheet Page 11 External antennas These have several advantages if portability is not an issue, and are essential for long range links. External antennas can be optimised for individual circumstances and may be mounted in relatively good RF locations away from sources of interference, being connected to the equipment by coax feeder. Helical. Of similar dimensions and performance to the integral type mentioned above, commerciallyavailable helical antennas normally have the coil element protected by a plastic moulding or sleeve and incorporate a coax connector at one end (usually a straight or right-angle BNC type). These are compact and simple to use as they come pre-tuned for a given application, but are relatively inefficient and are best suited to shorter ranges. Quarter-wave whip. Again similar to the integral type, the element usually consists of a stainless steel rod or a wire contained within a semi-flexible moulded plastic jacket. Various mounting options are available, from a simple BNC connector to wall brackets, through-panel fixings and magnetic mounts for temporary attachment to steel surfaces. A significant improvement in performance is obtainable if the whip is used in conjunction with a metal ground plane. For best results this should extend all round the base of the whip out to a radius of 300mm or more (under these conditions performance approaches that of a half-wave dipole) but even relatively small metal areas will produce a worthwhile improvement over the whip alone. The ground plane should be electrically connected to the coax outer at the base of the whip. Magnetic mounts are slightly different in that they rely on capacitance between the mount and the metal surface to achieve the same result. A ground plane can also be simulated by using 3 or 4 quarter-wave radials equally spaced around the base of the whip, connected at their inner ends to the outer of the coax feed. A better match to a 50Ω coax feed can be achieved if the elements are angled downwards at approximately 30-40° to the horizontal. (471mm long @ 151MHz) 1/4-wave whip 1/4-wave whip Metal ground plane 1/ (3-4 4w , eq av u e all ra y di s p al a el ce em d) en ts 30 -40 de g. 50 Ω coax feed 50 Ω coax feed Fig.9: Quarter wave antenna / ground plane configurations Half-wave. There are two main variants of this antenna, both of which are very effective and are recommended where long range and all-round coverage are required: 1. The half-wave dipole consists of two quarter-wave whips mounted in line vertically and fed in the centre with coaxial cable. The bottom whip takes the place of the ground plane described previously. A variant is available using a helical instead of a whip for the lower element, giving similar performance with reduced overall length. This antenna is suitable for mounting on walls etc. but for best results should be kept well clear of surrounding conductive objects and structures (ideally >1m separation). 2. The end-fed half wave is the same length as the dipole but consists of a single rod or whip fed at the bottom via a matching network. Mounting options are similar to those for the quarter-wave whip. A ground plane is sometimes used but is not essential. The end-fed arrangement is often preferred over the centre-fed dipole because it is easier to mount in the clear and above surrounding obstructions. Radiometrix Ltd., BiM1 transceiver, TX1H high power transmitter data sheet Page 12 Yagi. This antenna consists of two or more elements mounted parallel to each other on a central boom. It is directional and exhibits gain but tends to be large and unwieldy – for these reasons the yagi is the ideal choice for links over fixed paths where maximum range is desired. Please note: Using a Yagi or other gain antenna with the BiM1 will exceed the maximum radiated power permitted by UK type approval regulations. It can be used in the UK only in conjunction with the BiM1R receiver. For best range in UK fixed link applications use a half-wave antenna on BiM1T transmitter and a halfwave or Yagi on BiM1R receiver, both mounted as high as possible and clear of obstructions. Module mounting considerations Good RF layout practice should be observed. If the connection between module and antenna is more than about 20mm long use 50Ω microstrip line or coax or a combination of both. It is desirable (but not essential) to fill all unused PCB area around the module with ground plane. Variants and ordering information The BiM1 transceiver is manufactured in the following variants as standard: For Australian general applications on 151.300MHz TX1H-151.300-10 Transmitter BiM1T-151.300-10 Transmitter BiM1R-151.300-10 Receiver BiM1-151.300-10 Transceiver For UK alarm applications on 173.225MHz: BiM1-173.225-10 Transmitter BiM1-173.225-10 Receiver BiM1-173.225-10 Transceiver For UK general applications on 173.250MHz: BiM1-173.250-10 Transmitter BiM1-173.250-10 Receiver BiM1-173.250-10 Transceiver Other variants can be supplied to individual customer requirements at frequencies from 151.300MHz to 173.250MHz and/or optimised for specific data speeds and formats. However these are subject to minimum order quantity (MOQ) and long lead time. Please consult the Sales Department for further information. Some of the non-standard frequencies readily available. i.e. no MOQ or long lead time, are as follows: Part number: BiM1-xxx.xxx-10 (where xxx.xxx is the operating frequency) Frequency (MHz) 138.125 149.170 151.275 151.300 151.775 152.175 152.500 152.575 152.650 152.850 153.8125 153.9125 153.925 154.463 155.475 155.715 Radiometrix Ltd., Type approval Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Note 1, 2, 3 1, 2, 3 1, 2, 3 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 Frequency (MHz) 157.420 159.685 159.6875 161.975 162.025 162.975 163.000 164.525 167.420 169.435 169.41875 172.420 173.075 173.175 173.200 173.960 Type approval Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Note 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2, 3 Page 13 BiM1 transceiver, TX1H high power transmitter data sheet 155.725 Note Yes 1, 2 180.175 - 1, 2, 3 1: Complies with the ETSI standards but NOT approved 2: For specialised application, NOT for general purpose e.g: 121.500MHz is an international distress frequency 3: NOT a European Harmonised frequency. Consult local radio regulatory authority. Type approval The BiM1-173 module is meets European harmonised standard ETSI EN 300 220-3 for UK use within the following categories: (a) General applications in the band 173.2-173.35MHz but excluding 173.225MHz. (b) Industrial/commercial applications at the same frequencies as category (a). (c) Fixed/in-building alarm applications at 173.225MHz. (d) Medical/biological applications (including airborne use for the tracking of birds) in the band 173.7174.0MHz. REQUIREMENTS FOR CONFORMANCE TO ETSI EN 300 220-3: 1. Transmitted ERP (effective radiated power) must not exceed the limit of 1mW (0dBm) for category (a) or 10mW (+10dBm) for categories (b), (c) and (d). Equipment in category (a) must include a 10dB attenuator between the RF output pin and the antenna or feed, as specified on page 6 of this leaflet. 2. Any type of antenna system may be employed provided that the applicable ERP limit is not exceeded - i.e. transmitting antenna structures which exhibit ERP gain (such as yagis) are not permitted. See pages 10-13 of this leaflet for details of suitable antennas. 3. The module must not be modified or used outside its specification limits. 4. The module may only be used to transmit digital or digitised data. Speech and/or music are not permitted. Breaching any of these conditions will invalidate type approval. Radiometrix Ltd., BiM1 transceiver, TX1H high power transmitter data sheet Page 14 Radiometrix Ltd Hartcran House 231 Kenton Lane Harrow, Middlesex HA3 8RP ENGLAND Tel: +44 (0) 20 8909 9595 Fax: +44 (0) 20 8909 2233 sales@radiometrix.com www.radiometrix.com Copyright notice This product data sheet is the original work and copyrighted property of Radiometrix Ltd. Reproduction in whole or in part must give clear acknowledgement to the copyright owner. Limitation of liability The information furnished by Radiometrix Ltd is believed to be accurate and reliable. Radiometrix Ltd reserves the right to make changes or improvements in the design, specification or manufacture of its subassembly products without notice. Radiometrix Ltd does not assume any liability arising from the application or use of any product or circuit described herein, nor for any infringements of patents or other rights of third parties which may result from the use of its products. This data sheet neither states nor implies warranty of any kind, including fitness for any particular application. These radio devices may be subject to radio interference and may not function as intended if interference is present. We do NOT recommend their use for life critical applications. The Intrastat commodity code for all our modules is: 8542 6000 R&TTE Directive After 7 April 2001 the manufacturer can only place finished product on the market under the provisions of the R&TTE Directive. Equipment within the scope of the R&TTE Directive may demonstrate compliance to the essential requirements specified in Article 3 of the Directive, as appropriate to the particular equipment. Further details are available on The Office of Communications (Ofcom) web site: http://www.ofcom.org.uk/radiocomms/ifi/ Information Requests Ofcom Riverside House 2a Southwark Bridge Road London SE1 9HA Tel: +44 (0)845 456 3000 or 020 7981 3040 Fax: +44 (0)20 7783 4033 information.requests@ofcom.org.uk European Radiocommunications Office (ERO) Peblingehus Nansensgade 19 DK 1366 Copenhagen Tel. +45 33896300 Fax +45 33896330 ero@ero.dk www.ero.dk