For maximum Wi-Fi performance, you want maximum range and reception. Phil Chia shows you how to get just that, with the most common of household bits.
So let's get the legal stuff out of the way. Atomic and AJB accept no liability in the design or execution of the projects contained within this article. These projects and the information contained within are purely for informative purposes and are deemed correct at the time of publication, however are subject to change without notice. Users construct these projects at their own risk. Atomic and AJB will not be held liable for any damage to hardware, health or financial loss, nor any prosecution from any third party as a result of constructing these projects. It is up to the reader to seek appropriate information and approval from the appropriate governing bodies prior to the construction of any of these projects.
Why do we have to do this? Because Wi-Fi treads a very thin line in the wireless community. Who does this include? If you have a cordless phone, a TV, a mobile phone or a radio, (chances are, as you're reading Atomic, you've answered 'yes' to all of the above} then welcome to the community!
Wi-Fi 101
Wi-Fi in the US has caused quite a bit of controversy, and it's only just begun happening over here.
The major problem is that Wi-Fi works in the public unlicensed microwave band. That means that everything from garage door openers to cordless phones and AV repeater devices use the same band. Wi-Fi, or IEEE 802.11, comes in several distinct flavours. For simplicity's sake, I'm going to use the term 'Wi-Fi' instead of 'IEEE802.11'.
All Wi-Fi products work in the Industrial Scientific and Medical (ISM) band which includes 2.4 - 2.5GHz and 5.2 - 5.8GHz microwave frequency. Stuff working in this band generally goes unlicensed, with the proviso that some interference is inevitable. Basically, it works on a fair-play principle. It's free to use for everyone, so long as we don't abuse it or deliberately interfere with other persons' devices. In line with this principle is the limitation of transmission power to purposely limit the amount of interference that can be caused. Wi-Fi A and G are able to operate at up to 10W while all the other flavours must operate at no more than 4W. Wi-Fi G users, however, should be aware that if their systems default back to DSS mode (see later), the maximum signal that they are able to transmit is 4W. That being said, the average power of an access point is a piss-weak 30-60mW.
Of course, if you happen to have a 25-metre yagi antenna hanging off your roof and it starts to make your neighbours' cordless phones and garage doors open up, expect a visit from the Australian Communications Authority (ACA); the equivalent of the US FCC. They're the good guys here, so do the right thing and take your PiMPed antenna down!
Wi-Fi Tech 101
Wi-Fi A is almost extinct in the public field as its range was limited and the hardware was expensive to deploy. Wi-Fi A exists in the corporate market as it had (until recently) the corner on high-speed wireless networks. Wi-Fi A used a technology called orthogonal frequency division multiplex (OFDM) that allowed it to pump through up to 54Mb/s. Luckily, the frequency that Wi-Fi A operates at isn't badly cluttered. It's also this technology that allows Wi-Fi A and G to technically transmit a maximum signal of 10mW.
Wi-Fi B and its speedy cousin, Wi-FiB+ (which isn't a standard; it's just the Texas Instruments' stop-gap between Wi-Fi B and G. It actually works well and is found in some D-Link products) aren't so lucky. The 2.4GHz band is a pig's breakfast, with noise from hundreds of transmission sources. To get around the clutter, Wi-Fi B/B+ uses Digital Spread Spectrum or DSS. This is the same tech used in several cordless phones, and it means that the receiver and transmitters 'jump' subtly around the frequency range. In all, Wi-Fi B cards stay on the same frequency for just 0.8 seconds, meaning that if there's interference, only a few packets need to be resent. From our and the OS's perspective, it's invisible (see Logan Booker's article in Atomic September 03). Also, Wi-Fi B allows for 11 discreet 'centre' channels with which cards can communicate on. Think of each channel as a TV station and this is a simple way to avoid interference. However, each channel uses 22 MHz of bandwidth, resulting in some overlap. You need to be at least five channels apart to get zero overlap. This is one of the biggest issues with new Wi-Fi users. So if you're having trouble with your current Wi-Fi setup, try changing the channel! Note that you need both the transmitter and receiver to be on the same channel.
Wi-Fi G is the latest and greatest implementation. Recently ratified by the IEEE, it melds the speed of Wi-Fi A with the distance and inexpensive tech of Wi-Fi B. It uses the OFDM encoding, and has a fallback measure to use DSS if either OFDM fails, or if it comes across a Wi-Fi B access point. This is the stuff to invest in; however in field trials with FreeNode, the fastest we got was 50Mb/s, with an average of 46Mb/s.
The killer: 802.16
Just a small footnote on what the industry is calling the next 'killer app'. . . the 802.11x standard was never meant for long-distance coverage. 802.16 is designed to solve that problem. The spec will use frequencies from 2 - 11GHz and 10 - 66 GHz to span metropolitan areas with 'commercial quality' speeds. That being said, the spec is really intended for building-to-building, although the idea of being able to walk down the street, catch a bus/tram into town and into work whilst being constantly connected and receiving streaming multimedia is pretty cool.
Antennas already!
Ok, no doubt now all you Dremel heads are raring to go, but first a short rundown on antenna designs and how they work. You'll need it to get the best out of your setup.
First and foremost, understand that antennas are excellent conductors. They collect and concentrate energy, which is essentially what radio waves are. This also makes them perfect candidates for lightning, so, never go waving your antenna around in the park during a rainstorm, or you'll be sorry!
If you're thinking about mounting your antenna outside, be sure to include a gas-tube lightning arrester in the design and don't forget to properly ground the bloody thing! There are lots of stories of people forgetting this essential element and ending up with fried equipment.
OK, enough with the scare tactics. One of the first things to understand about antennas is that they are converters. In a nutshell, an antenna converts radio waves into electrical impulses or signals or vice-versa. Another aspect of antennas is that signals are received in ¼ wavelengths. That means that an antenna works best if it is tuned to either receive ¼, ½, ¾, or full wavelengths.
Issue: 133 | February, 2012