Electronics

The reason why WiFi USB adapters suck

Juli 9, 2006 von Franz Hieber

People use USB WiFi adapters for a number of reasons, maybe their laptop doesn’t have built-in WiFi, or like me, there are no cards yet available that fit the tiny pseudo-PCMCIA slot of the MacBook Pro. Yes, I know the MBP has built-in WiFi, but my personal interest and professional activity involve using WiFi in alternative ways, so I need to test antennas, adapters, software and so on.

A few weeks ago, I bought a D-Link DWL-G122, the thought being that since it could be connected to a long USB extension cable, there wouldn’t be any of the RF losses associated to coaxial cables – and so I could go wardriving with a potentially better setup than the usual PCMCIA card with a pigtail and coax running to a roof-mount antenna. And I was wrong. The results were appaling – even the Vaio’s internal IPW2200 card was much better, detecting over twice as many access points as with the D-Link.

How could this be? Logically, having the antenna attached directly to the RF port of the WiFi adapter should reduce loss considerably – but it wasn’t the case. To be sure, I went shopping again, and this time bought a Conceptronic C54RU. One would think that the D-Link, costing around 39$, would have better performance, since the Conceptronic only cost me 25$ – there just had to be something there to justify the price difference. To my surprise, performance was almost identical. This prompted me to pry open the two adapters, and this is what I found:

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No, I didn’t just photoshop a clone of the first PCB. It is the same PCB for both adapters – which means that some OEM/ODM company is manufacturing these devices, and selling them in customized plastics to whoever wants them. Paying attention to quality? Probably not their very first priority.

The next two photographs show a little explanation on the structure of the RF section of these adapters. Do not confuse the PCB antenna as a diversity arrangement, it is basically a center-fed dipole. The designer paid no attention to the large mass of grounding material right next to the large pads of the antenna, and the matching circuit could probably not do much to alleviate the poor design. Here is the actual stripline [click the image for a larger version]:

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And the test connector:

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Bottom line: if you are close to your access point, and don’t really care about the range and quality of the link, this may be the adapter for you. But, if your intention is to take these devices for a wardrive, well, don’t.

No A2DP in OSX – maybe if Apple made a Bluetooth stereo headset…

Juli 2, 2006 von Harald Puhl

Last night I was watching a DVD on my MacBook Pro, and remembered that I still kept a Motorola Bluetooth stereo headset from the time I was working at SouthWing and we designed such devices.

Bluetooth stereo headsets use a profile called Advanced Audio Distribution Profile (A2DP), which allows them to receive medium-quality audio at 16kHz from compatible devices. Most USB Bluetooth dongles sold recently have the profile in their drivers, and there are some mobile phones from Nokia, Samsung and Motorola that also feature this profile. The advantage is that you can listen to music wirelessly, and also control the player from the headset, as they feature the usual forward, back, play and pause controls.

Once I found the headset, I switched on Bluetooth on the Mac, and started the pairing process. The headset was recognised just fine, and pairing completed, but I noticed that it had been connected as a Handsfree device, with A2DP nowhere to be found. Since there doesn’t seem to be a method of connecting the headset permanently, so the audio is always routed from the Mac to it, the attempt was frustrated – I couldn’t even listen to the DVD in low-quality audio.

Why has Apple left out this profile, is it a blunder, or a calculated approach? As to this date, Apple doesn’t manufacture or resell any Bluetooth wireless headsets (only one can be found at their store, and it comes with a dongle for the iPod, so it doesn’t count). So, why would they have an interest in adding the A2DP profile, so that we could use any other headset? If they are in the process of designing their own, they might want to keep the profile away from Macs until they launch it.

Then again, if we give Apple a vote of confidence that they are not that insidious, it could be a blunder. And a big one. Windows has been able to work with A2DP headsets since late 2005, so they have had plenty of time to add the profile to their Bluetooth stack.

A few myths and facts about Bluetooth, versions and profiles for the curious:

1. Profiles are mostly independant of the Bluetooth version. It is perfectly possible to have A2DP in a V1.2 Bluetooth device, just the same as a V2.0 + EDR can have just two profiles and miss many of the usual ones – the mix is up to the manufacturer and driver supplier.

2. EDR stands for Enhanced Data Rate – this does not increase the range, just increases data throughput from around 700kbps to around 2.1kbps, by using a different modulation scheme. The Bluetooth protocol and profiles stay just the same – the advantage is that since data takes almost 1/3rd of the time to send compared to non-EDR devices, there is a considerable power consumption reduction.

3. “Device Y doesn’t support profile Z”. Again, this is up to the manufacturer, and it’s hard to add new profiles, specially in embedded devices. Some chipsets use masked ROM, which means that the Bluetooth stack, profiles and other settings are burned at the time the silicon is printed – so, no software updating on these. Masked ROM is considerably cheaper, although has an initial setup cost of $100.000, so it’s only good for high-volume production runs. The chips can drop $1 to $2 compared to the flash EEPROM counterparts.

As an example of a very poorly implemented Bluetooth solution we can find the Logitech MX5000 keyboard and mouse combo – it sucks. A lot. I am preparing a review that will try to investigate why it does the stupid things it does, such as repeating the first letter you type when it wakes up a dozen times, or why the mouse starts wondering around the screen as if it was possessed by a poltergeist.

TomTom’s hidden all-terrain mode

Juni 2, 2006 von Harald Puhl

Sometimes, I feel like a human GPS navigator. And there are probably many more of us out there. Ever get a call from your wife, asking you to direct her to some remote place she is trying to drive to? My solution was to get a TomTom 500 navigator for her birthday. It comes with the maps for Spain in full detail, and a basic map of Europe, with main roads and cities. It can also be used as a Bluetooth handsfree for your mobile phone, so it’s quite a convenient device.

We set about trying it during a trip to visit my mother – since I knew the way, it would be a good sanity check on the navigator’s ability to lower our phone bills. When I told it where we wanted to go, and it told us to turn west instead of east, I started imagining what would happen. After a few minutes of following the navigator’s instructions without even looking out the window, this is where we ended up:

tomtom Yes. It wanted us to go up a dirt path that only horses (and fit ones at that) can manage. Take a close look at the full-resolution picture, and judge by yourself.

After turning around, and following the route we always take, we had to turn off the sound for almost half the trip, as it kept insisting that we should “turn around as soon as possible” so we could take the easy-going dirt track.

GPS navigator manufacturers only make the devices, but not the data that’s in them. There are a few companies, such as Navtech and TeleAltlas, who take care of that, and license the use of the data. In this case, it seems that overzealous cartographers had simply taken anything that looked like a road in survey maps, and turned them into navigable paths. The result is my unfortunate experience. The collateral is that my wife doesn’t trust the device, unless it’s for navigating within city limits – thus limiting it’s usefulness, and not limiting my phone bill so much.