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Boost your ZigBEE range for a few bucks (or even cents!) Since ZigBee (which we introduced last month) is on the same licence-free 2.4GHz band as other microwave services, many compact WiFi antenna designs can also be conveniently used with ZigBee devices. A side from range extension, especially valuable, given the tiny 1mW XBee transmitter power, such antennas may also help reduce unwanted RF noise picked up from the myriad of devices (WiFi, cord- by Stan Swan less and Bluetooth phones, microwave ovens, video senders etc) now flooding that same 2.4GHz spectrum slice. Rev.Ed’s XBee units come with a small factory-fitted wire radiator, although this looks shorter than the theoretical quarter-wave whip (31.5mm) of a 125mm 2.4GHz wave. Outdoor range checks gave a good You can make a variety of parabolic (and near parabolic) reflectors for ZigBee and even WiFi using simple (and cheap!) materials. More details are on Stan’s website: www.orcon.net.nz 100  Silicon Chip siliconchip.com.au 50-100m between bare units but were hugely influenced by the usual microwave line-of-sight (LOS) limitations. Even shielding at 100m with your body will completely cut signals, as will vegetation in full leaf (it’s actually the water in both which knocks the signal about). Indoors, through timber and plaster walls, gave ~20m range. Remember that brick walls, especially external ones, absorb moisture so are always likely to be more of a problem. Wireless data links likely to be subject to such obstacles may show more “punch” with cheaper (but slower) UHF 433MHz modules (see SILICON CHIP, December 2005). Since each 6dB antenna gain doubles range, a simple 6dB antenna “point to point” at each end should yield 12dB (or four times) the bare range. You can solder different antennas (such as a Biquad) to the XBee but rather than modifying the existing whip to improve coverage, it’s perhaps easier to just position the entire XBee unit at the focal point of a simple concentrating reflector. 0 00 $10 IZE R P ! OL PO Outstanding LOS range extensions were shown by the 12-15dB gain parabolic “cookware” dish designs we first promoted for USB WiFi (see “WiFry Antennas”, SILICON CHIP, September 2004 or www.usbwifi.orcon.net.nz). XBee trials over water readily gave 3km links with these at both ends (see www.picaxe.orcon.net.nz/zigscoop.jpg) – quite amazing for 1mW and only modest receiver sensitivity. Such performance implies LOS ranges with swapped out XBee Pros (100mW transmitter and superior receiver) may only be limited by the curvature of the earth, as a DefCon WiFi shootout in dry-air-Nevada recently achieved ~200km LOS point-to-point with standard WiFi adaptors and (very) large dishes. Naturally ZigBee setups won’t have to stretch that far but may need a “helping hand”. If parabolic maths leaves you numb, consider diverse DIY cardboard and foil template parabolas or corner reflectors that usefully enhance 2.4GHz signals , although accurate measuring and profiling may be needed. Again, see www.usbwifi. orcon.net.nz/carwifi.jpg and www. usbwifi.orcon.net.nz/cnr.jpg The catenary curve of hanging chains approximates a parabola very closely (even Galileo in 1669 was fooled!) – see www.usbwifi.orcon.net. nz/catcurve.jpg But an even simpler DIY design, based around flexible plastic or metal sheet offcuts, has evolved – www. usbwifi.orcon.net.nz/plaspara.jpg. This exploits the little known fact that end-clamped rods and “bendy” sheets assume a roughly parabolic shape when flexed. A few minutes with some springy plastic offcuts, string, glue and cooking foil can give you around 9dB gain – use the old “finger at the hot spot” trick to carefully find the focal point via reflected sunshine. Even “bendy rulers” can be used, although a wider strip will give better performance. One at each end will give ~18dB system gain, enough for a 1km LOS XBee link. Since offcut ends are cord secured, the concentration may be more cardioid (“heart shaped”) than true parabolic but this is not too crucial – even the Arecibo Observatory’s huge radio telescope reflecting dish is spherical. SC 2006 S ILICON C HIP Excellence in Education Technology Awards NOW OPEN SILICON CHIP magazine aims to promote the education, development and application of electronic technology in all fields throughout Australia. As part of that aim, we are announcing the SILICON CHIP Excellence in Education Technology awards, with a prize pool of $10,000. Separate awards will be made to students of secondary schools throughout Australia and to students of universities and TAFE colleges throughout Australia. The secondary school awards will have three categories: AWARD FOR EXCELLENCE (a) Best final year assignment of an individual student involving electronics technology (b) An award to the school sponsoring the winning individual student (c) Best school project involving electronics technology The university and TAFE college awards will have three categories: (a) Best project from a student as part completion of a degree, diploma or certificate in electronics or a related field (ie, mechatronics) (b) Best research project from a post-graduate student working in an area of applied electronics (c) An award to the university faculty or school sponsoring the best research project. Entries and judging The awards will be judged by the editorial staff of SILICON CHIP, convened as a judges panel. The decisions of the judges will be final. Entries for the 2006 awards are now open, with final submissions to be made by September 30th, 2006. All submissions will be confidential, until the winners are announced, in the December 2006 issue of SILICON CHIP. Each award will take the form of a cash prize and a commemorative plaque. All enquiries about these awards should be directed to the editor via email to: awards<at>siliconchip.com.au siliconchip.com.au May 2006  101