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product review WM232-UHF Short range, high-performance wireless modem The applications for radio as a medium to connect devices is virtually unlimited. Some applications demand wireless connection, due to difficult access or for mobility reasons. Others, such as metering and data acquisition systems can benefit greatly from wireless technology. No network cabling and no direct access to equipment is needed, reducing costs right from the installation stage and beyond. T he WM232-UHF, an Australiandesigned and manufactured radio modem, is a low-cost, plug’n’-play connectivity solution for devices that communicate via serial links. It supports on-air data rates of up to 14.4kbps and features data encryp32  Silicon Chip tion, error checking and acknowledged data transfer. The basics The modem is housed in a small ABS plastic case, measuring about 103mm (L) x 62mm (W) x 24mm (D). Antenna hookup is via an SMA connector that protrudes through one end of the case. A tiny (60mm) helical stubby antenna can be mounted directly onto the SMA connector, making a very tidy little package. Power for the unit can be provided www.siliconchip.com.au by Peter Smith Fig.1: Point to Point mode allows simple, transparent connections between any two devices with RS232 ports. by either an internal 9V PP3 battery or around 500m line-of-sight. Of course, dressing system, composed of “unit” an external 7-15V DC source. A 9V DC you could also fit a more elaborate and “site” addresses. plugpack was supplied with our evalu“gain” antenna for much greater range, Up to 16 pairs of modems can operation unit. The average current drawn but that wouldn’t be legal, now would ate within a single site address, with during transmit/receive is quoted at it? up to eight possible site addresses. 40mA, falling to 15mA when idle. This corresponds to a maximum of 127 Wireless simplicity This means that an external power possible point-to-point links. source will be necessary for most In their simplest configuration, two Site addressing effectively partiapplications. In power-down mode, WM232-UHF modems can function as tions groups of modems for repeating consumption drops to a more respecta reliable two-way wireless link. purposes. Any WM232-UHF can able 400µA. operate as a dedicated repeater unit. Apart from a certain amount of Connection to the modem is made latency in the data exchange, the Up to three repeaters can be used via a 9-pin female ‘D’ connector. modems appear transparent to the within a network to extend the opPin assignments conform to the PC connected devices, functioning just erating range. A repeater retransmits modem (DCE) standard, so for conas they would if they were hard-wired any data it receives with the same nection to a PC (DTE) serial port all together. This mode of operation is site address, allowing very flexible that’s required is a 9-way pin to pin called “Point-to-Point”. networks to be constructed. cable (supplied). For more demanding applications, It is important to note that effecThe unit operates in the 433.920MHz multiple pairs of modems can operate tive data throughput for any pair in a LIPD (license-free) band, with transmit within the same air space. network will decrease as the network power limited to is expanded, as the available airtime This is achieved with a two-tier ad10mW (ERP) to satalways remains constant. isfy the regulatory An LBT (Listen requirements. Before Transmit) √ Easy configuration via PC, laptop or PDA Receiver sen scheme is employed √ Point to point or multip sitivity is quoted to minimise the inoint network capability at -100dBm for a √ Repeater support terference that ocfor increased range 1ppm BER (Bit Er- √ Se curs when multiple rial port speeds of 600 to 115200 baud ror Rate), giving modems attempt to a range of about √ On-air data speeds of 600 to 14400 transmit simultanebaud 300m line-of-sight √ On-air data encryption ously. and error checking and 50m indoors √ Diagnos tic “Radar” and “Ping” More about netfunctions with the helical √ DTR-controlled “slee stubby fitted. p” mode working A n o p t i o n - √ Internal 9V battery or externa A common requirel DC plugpack a l c o a x - f e d , √ Range of up to ment within a wire500m with coax-fed ha lf-wave antenna ground-inde- √ less network is to CE & Australian C-Tic k approval for use on pendent halfbe able to monitor licence-free UHF Band wave dipole exand control multiple tends the range to nodes from a central Features www.siliconchip.com.au February 2003  33 product review (continued): Telelink Communications WM232-UHF Fig.2: before data exchange can occur in Point-to-Multipoint mode, the host first programs the desired slave address into the master modem. location. This is the purpose of the “Acknowledged-Point-to- Multipoint” mode, where a single modem is configured as the master and all other modems as slaves. Each slave is assigned a unique address, using the same addressing scheme employed in Point-to-Point mode. In order to communicate with a particular slave modem, the host must first program the desired slave address into the master modem. In Acknowledged-Point-to-Multipoint, the master modem must initiate a link with a slave before data transfer to or from that slave can occur. By contrast, “MultiMaster” mode allows up to 15 slave modems to initiate connection with a single master unit. In this mode, data transfers must be kept as short as possible to prevent “hogging” of available airtime. Design your own network If none of the above modes suit 34  Silicon Chip your requirements, then it is possible to design your own network from the ground up using “Broadcast Multi-drop” mode. In this mode, all aspects of network management, including routing, node addressing and error recovery, are assumed to be host-controlled. Data sent to a modem over its RS232 link is transmitted (broadcast) to all modems within range. Receiving modems simply decode the data and pass it on to their hosts. Configuration Modem configuration is accessible, strangely enough, via configuration mode. A PC, laptop, or PDA with an RS232 port and suitable terminal software (such as HyperTerminal) are required for the job. Normally, modems automatically enter data transfer mode at power up. To exit data transfer mode and enter Fig.3: any modem can function as a dedicated repeater. Up to three repeaters can be added to a network, greatly extending the operating range. www.siliconchip.com.au short range wireless modems configuration mode, it’s just a matter of sending an “escape” sequence from the terminal program. The factory default sequence is three consecutive “+” characters. Typing “help” at the configurator prompt displays all possible commands, whereas “list” displays current settings (see Figs. 4 & 5). A variety of useful commands allows mode and address selection and fine-tuning of network parameters. It’s also possible to modify most of these settings remotely, from a second modem via a wireless link. Of course, this feature can be disabled for security purposes if so desired. Link testing Two diagnostic commands have also been included to aid network setup and testing. The “ping” command looks for a modem within range with the specified address and returns its status. This is a useful “go-no go” test and it allows verification of which unit addresses are in use. The “radar” command allows link range and reliability to be quickly determined. This mandatory feature will help to eliminate most of the guesswork from a simple network installation. Impressions Setting up a simple, reliable wireless network with these modems should be a painless exercise. And if you have something more elaborate in mind, the WM232-UHF can probably handle that too. Getting more information Fig.4: configuring the WM232-UHF is dead easy. Here, we’ve used the “list” command to show all configurable parameters. The WM232-UHF Wireless Modem is manufactured and sold in Australia by Telelink Communications, phone (07) 4934 0413 or email sales<at>telelink .com.au You can reach them on the ’net at http://www.radiotelemetry.co.uk/ SC WM232-UHF Modem and Accessories Prices (inc. GST) WM232-UHF Modem:......$361.90 WM232-PSU Power Pack..................................$ 27.50 ANT-UHF-H SMA Helical Antenna.............................$ 26.40 ANT-UHF-Q SMA 1/4 Wave Antenna.............................$ 28.60 ANT-UHF-D 3dB Industrial Dipole................................$ 42.90 Fig.5: the “ping” command is a handy “go-no go” test and allows quick verification of modem addresses. www.siliconchip.com.au A PC Board only version of the WM232-UHF is available for OEM’s. (prices on application) February 2003  35