Make 2.4GHz parabolic mesh dishes from cheap but sturdy Chinese cookware scoops & a USB WiFi adaptor ! The largest (300mm diam)shows 15-18dB gain (enough for a LOS range extension to 3-5km), costs ~US$5 & comes with a user friendly bamboo handle that suits WLAN fieldwork- if you can handle the curious stares!
DIY antenna details best followed from these pix -click on a thumbnail for full size 800 x 600 images
Note -the phrase "Poor Man" is not usually considered insulting, but indicates (possibly with a degree of DIY pride) a desire to "make it do, use it up, wear it out" while laterally solving a problem. New Zealand Kiwi's are champions of such #8 wire ingenuity,with electric fences a typical appropriate technology example. Guess our project even has East meets West cross cultural aspects- in the style of Kiwi Fruit evolving from Chinese Gooseberries !? Lab note jottings below pix rather blog style,but arose during an educational WiFi workout & are intended to stimulate others into similar DIY investigation. The author- who first wrangled antenna as a radio ham in the 1960s- is a career educator with a flair for innovation,& has had extensive hands on DIY WiFi experiences - www.manuka.orcon.net.nz has insights into "his" Sardine Can Biquad antenna. LAB NOTES text below intended to document rather than entertain- suggest you stay with images for the latter! 21 April 2004: The long awaited NetStumber 0.4 ( + PDA MiniStumb.) is just out ! ( www.netstumbler.com~1.2MB). Of course we've been trying all sorts of Wi-Fi cards to hand! Originally NS only favoured Orinoco PCMCIA, but the latest flavour IS talking to such cheapies as the popular NZ Dick Smith Electronics (DSE) NZ$69 USB thumb
dongle adaptor (cat XH6822). This DSE sweetie is based on a ZyDAS chipset,& seems to perform almost as well as esteemed Orinocos under XP. Yah! Can't say things look
bullet proof with NS 0.4 yet, but it's certainly a tempting way to go, since USB
cables & active extenders are dirt cheap,& being just digital are
lossless compared with COSTLY microwave coax cable & connectors. Will
maybe do a roof top "sweet spot" trial from here in central Wellington, New Zealand
& perhaps upload a NS file,but picked up a AP ~500m LOS away OK. 25th April 2004: Well - ANZAC day dawned fine here in Wellington (NZ), so in best military
tradition we ran a few LOS(Line Of Sight) scouting trials,supporting the
USB device on a broom handle tied to the roof,fed by ~5m of regular el
cheapo USB cable from an XP laptop running the new NS 0.4 inside.
As always LOS means just that at 2.4GHz, & assorted in line trees &
buildings caused massive signal losses, so ~100m was all we managed
while walking around the house/yard/street with a Dell Axim PDA & a
Socket low power CF WiFi card.
We'll give it a further trial tomorrow across the inner city Basin Reserve to
Mt.Vic, where a standby Orinoco Sardine can biquad easily handles
the 2km from work ( Massey University). Experiences however indicate already that such
simple food can reflectors at each end look only good for ~2km LOS, & this USB receiver doesn't seem as sensitive as an esteemed PCMCIA Orinoco. Sniff ! That USB adaptors
ceramic antenna may be the culprit - anyone fancy a "hack" &
installation of say a Biquad ?!
THOUGHT - fit this thumb at the focal point of a directive antenna?
Quick trials with NS 0.4 showed useful gain with even a bare metal
plate behind it. Perhaps the classic "Sardine can" biquad reflector?
Simple metallic plates behind the unit gave significant weak signal
boost, espec. when spacings were ~32mm ( which of course is 1/4
wavelength at 2.4GHz). With DIY dishes (each 15-20dB ?) then range
increases to say 5-10km may result - dB maths says each 6dB
gain will double the range.
The real attraction with USB of course is the jelly bean cheapness of
cable & connectors-we paid NZ$95 for just a 1/2m Orinoco pigtail in
2002 that eventually broke it's tiny connector! Grr... In contrast the entire box of tricks used here today came to ~NZ$75, & with a USB active extender (~NZ$30) cables could be run on
to the basement. With USB cables in place you can swap out the WiFi
unit for a golf ball web cam up there for an improved view too-
cheaper than moving house maybe ! USB cables are so cheap that they're almost worth cutting up as DC hookup wire - 5m USB 2.0 extension cables( the USB 1.0 limit) wholesale here for under $NZ4 each. Woops- broom handle still outside in the dark. Stay tuned... 26th April 2004: Rustled up a simple corner reflector
(folded aluminium)to good effect & NetStumbler 0.3/W98 Orinoco
detected OK ~1km LOS away. Gain of such quickee antenna typically 5-8dB,& a
simple open mesh dish (bird netting etc) will usually be MUCH better.
The eventual idea of course is to have a lowish profile antenna that
can be mounted inside something like an empty plastic blank CD "cake"
tin or bowl 28th April 2004: Update- predictions on use with a dish confirmed, since we noted a
(nameless!) AP some 8km LOS away when positioned at the focal point of
an old 600mm parabolic reflector (~21dB). Compared with the expense & lossy
cable runs of regular devices, this USB approach just COULDN'T be
easier. ~1/2dB loss per m is typical with microwave coax, with maybe another 1dB at each connector. A 10m cable hence may "cost" you 7dB of gain that spiffy roof dish provides... We'll try next some DIY smaller reflectors, with aluminium foil coated curved
plastic lamp shades ($2!) showing particular promise. Only downside seen so far is that the USB units run rather warm, although an
overnight soak test gave no hassles. Surely we're not the only ones evaluating these USB adaptors - any other feedback ? With their tiny size & bargain NZ$69 (~US$40) price
(plus jelly bean cheap lossless USB cable/fittings) they look a winner.
30th April 2004: Have contacted DSE (Aust.),who inform these XH6822 dongles are a NZ only item, & they've no plans to retail in OZ- yet! However they DO sell a similar USB
WiFi adaptor, the Spirit XH4268 @ A$59. Anyone had experience with
these? Can they use NS 0.4 ? 1st May 2004: Poor Man's WiFi ? You can thank an impromptu visit to a Chinese emporium for our latest variation- a 300mm diam mesh parabola (gain ~15dB ?) that
fits this USB dongle beautifully. It's based on a NZ$8 Chinese cook vat scoop c/w bamboo handle. Asian students here inform this classic Chinese cookware item is known as a "Spider Skimmer", & is usually made of brass rather than cheaper galvanised mesh. Sizes are 6", 8", 9", & largest 12" (300mm) as we used. Total setup B.O.M <$NZ80 (~US$50 ) & that
includes the ZyDAS ZD1201 WLAN adaptor, USB cable,& dish antenna with
environmentally friendly bamboo support handle. Field trials anyone ? 2nd May 2004: While in the Asian Emporium diverse other cookware was noted, much of it stainless steel. Customers gave sideways glances as assorted woks, lids and pans were measured up& focal points calculated! Although tempting, normal woks are of course TOO solid & have serious wind resistance - a major factor here in Wellington even when closely attended ! Have just hilltop trialled that spider skimmer mesh scoop & managed an AP 5km LOS away ( NS 0.4 showing -80dB ). The whole development suits "Poor Man's WiFi", since for ~NZ$100 (~US$60) one could have the works ! Being appropriate technology fans, it's envisaged such a setup could have immense appeal in less developed, rural areas or schools etc. Naturally USB connectors are easy to maintain too. 5th May 2004: Finishing off quest & prowling hardware stores for antenna supports & tripods. The very thing-a garden hose mender makes a PERFECT mount for the USB socket, & only modest mesh trimming needed. To allow USB cable placement hack saw an angled slice cut in the hose mender- the screw on rings will secure OK. The plug in adaptor even fits in the recess at just on the desired 94mm too when internal joiner plastic trimmed/drilled off. As a "just how far can USB cables go " trial today, we had 5 x 5m cheap USB 2.0 M-F extenders cobbled together for a 25m ( 75') run, for which the USB adaptor never missed a beat. Yah ! Visions of WLAN PC at ground level & USB adaptor/antenna in a tree top sweet spot arise. Well - why not ? There's been a similar but corporate Power Over Ethernet (POE) approach for some time of course.
EXTRA: US contacts inform Texan outlet =>www.axiontech.com sells for ~US$25, this exact ZyDAS adaptor as a ZONET ZEW2000C. Apparently NZ outlet Computer Dynamics also sell a similar EDIMAX WL7117U (ZyDAS) unit ~NZ$65,but have not tried. At these prices a user group could buy a box & sell them at a modest profit while still in stock!? 7th May 2004: Phew- we spoke too soon- is this ever a fast moving field. Dick Smith NZ inform this XH6822 adaptor, after a store life of only months, is about to be replaced by a similar ZyDAS (cheaper ?)XH6859, & that a faster 54MHz IEEE 802.11"g" USB unit (cat XH8227) is on the horizon, but at ~twice the "b" price. With antenna such as we've developed, simply swap out the old & insert the new units as they arrive (or you can afford them !) With 54 Mbps "g" being so rapidly adopted, 11Mbps "b" hardware may become almost free to a good home. 11Mbps is naturally MORE than enough for many users, since even if only 1Mbps achieved with weak links & USB decoding overheads,it's still equiv. to ~20 times the speed of a wired dial up connection, & thus suitable for streaming video/Internet sharing/voice traffic/games/Netmeeting or even impromptu event/sports day/emergency WLANs etc. APPLICATIONS INSIGHTS & FEEDBACK welcome! 19th May 2004: Sacre Bleu- this DIY Kiwi WiFi idea seems to have struck a worldwide chord, since ~10,000 hits in a week & numerous global links & citations. French,Spanish & even Polish mentions are "readable", but the Hindi version, while most exotic, defies our translation! Site overhaul needed, with proper DIY instructions instead of lab notes? Thoughts? 25th May 2004: In spite of wind susceptibility & carrying weight, pressed steel parabolic woks have also emerged as suitable homemade WiFi dishes. Woks sell cheaply & are easily drilled/chassis nibbled for mount holes. Gains ~17dB reported from a North Otago (NZ) user-enough to use an AP 4km away. Having come this far we may as well explore other suitable dishes-cooling fan mesh screens & even umbrellas have caught our eye.Publicity from yesterdays Dominion Post Infotech article shows NZ interest is keen, with schools especially enthusiastic-one had bare APs with just 50m LOS range... Yikes! 27th May 2004: Gadzooks-SlashDotted! Our humble WiFi lab notes went ballistic following a SlashDot mention,with ~43,000 global hits yesterday afternoon. Amazingly the Orcon server & Extreme tracker survived,even at hit rates ~200 a minute. To those who emailed & have yet to get a reply- responses have near swamped us,so please follow DIY instructions-shown as text notes on many pix- while we consider a site rewrite( perhaps a Wiki ?)! Several mirror sites now exist too (US & France). As a tribute to the democracy & efficiency of the Internet, "old conference junkie" Stan reflects that the info we've gathered here would have taken kilobucks & decamonths to circulate traditionally, with far fewer eventual recipients... 30th May 2004:As well as gunpowder & the compass, perhaps the ancient Chinese even stumbled on microwaves & these "scoops" may have been antenna all along? To prevent their secrets falling into barbarians hands,they were disguised as cookware! This could explain the Ming dynasty fascination with ceramics (= semiconductors ?). Such jests aside, parabolic reflectors uniquely have the property of a fixed focal point-unrelated to frequency. Hence our visible light technique in bringing the sun to a focus is valid for showing the WiFi sweet spot. Aha-this means any microwave wireless device at the FP could be enhanced! Bluetooth (also on 2.4GHz) is an obvious swap out, but quick checks indicate GSM cell phones (900/1800 MHz) & even Wellington's new Woosh IPWireless (~2GHz) indeed show better performance. Downlink signal levels came up ~2 bars on the latter, although weak Woosh uplink signals failed to connect when ~10km LOS! Small cell radius maybe too ? Naturally a cradle to hold these devices would be needed, but it could allow indoor coverage in marginal regions without costly external antenna. See pictures above 7th June 2004: Trials with Aluminium foil glued to the fabric of assorted (~600mm diam) umbrellas gave mediocre WiFi results, even though the resulting dishes verified as bringing the sun to a good focus. Such antenna are VERY wind prone & thus hazardous anyway - suggest insect screen mesh used instead if outdoor umbrella dishes developed, even if short term & attended !
Pix & quick web page via Olympus 1.3Mpx digital + Notepad by Stan - email => s.t.swan@massey.ac.nz Ver 0.65 June 7th 2004
