Earth: Mostly Harmless

It’s my birthday today so I’ll be taking some time out from blogging - I promise!

Also, welcome to the hundreds of visitors coming in via the Make: blog, after my antenna design got featured. Look at the spike in visitor numbers over the past 12 hours or so!

Catch you all soon.

UPDATE (10th August 2006)- My antenna may no longer be needed soon!

UPDATE (3rd August 2006)- Better pics added - see bottom of post

(Or, to be more accurate, where 20ft of solid stone was blocking line-of-sight to the nearest transmitter.)

I just got a Nokia E61 on T-Mobile. When I signed up, I knew that the signal was really weak in the back of our house - the building forms a large square, and my bedroom faces into the centre of the square. I could get a signal in the living room (just), but wouldn’t it be great, I thought, not to have to go through there every time the phone rings. Although outside my house full-strength UMTS signals are readily available, the building’s construction prevents them diffracting into the internal ‘courtyard’.

All I needed was enough reception to receive and send SMS messages. I have home WiFi for data access, and I can potentially make calls over that too. I planned to aim for UMTS reception rather than GSM since: a) I didn’t know which GSM frequency to aim for and b) E series Nokia phones maintain their batteries better if they have UMTS signals (otherwise they constantly search for a UMTS signal).

I tried two car-type external antennas that I got via eBay - but unfortunately the gain on both of these was just too low (barely even compensating for the losses in the cable running to the phone). Also, neither were sufficiently directional to catch enough of the reflected signal to give me anything to work with.

The first step was the figure out what the extent of the problem was. I located my nearest T-Mobile base station using the government’s Sitefinder service. This also confirmed the frequency that the transmitter used - 2100Mhz. This is the standard frequency for UMTS (i.e. 3G) services in Europe.

By drawing a line between the transmitter’s location and my building in Google Earth, I was able to confirm the approximate distance and angle of the signal I needed to catch.

Buying a directional antenna wasn’t really an option - for a start, they are expensive - and anyway I couldn’t be sure that such an antenna would actually help. If it didn’t, I’d have wasted £60-£100.

However, in an incredibly geeky flash of inspiration, I realised that there really isn’t much difference in operating frequency between WiFi (around 2.4Ghz) and UMTS (2.1Ghz). And there are loads of different clandestine WiFi antenna ideas floating around the Internet. If I could find an easy-to-build directional WiFi antenna, perhaps I could reverse-engineer its dimensions and adapt it for 2100Mhz use.

So I set about the task. I decided on the biquad antenna type, as it’s fairly compact and easy to build, yet provides decent (10-14dB) gain and is quite directional. My primary sources of information were the many WiFi biquad and double bi-quad antenna tutorials and blog entries, such as: Engadget’s; Trevor Marshall’s tutorials. More can be found on my del.icio.us page for the tag ‘antenna’.

Both WiFi and UMTS operate in microwave frequencies - however, there’s a substantial difference between the middle WiFi channel (around 2.4Ghz - what people usually tune their WiFi antennas to in order to give a good amplification factor across the channel range) and UMTS’ 2.1Ghz. To my knowledge no-one has built a homebrew biquad UMTS antenna before, so there wasn’t much to go on. What also didn’t help was that most WiFi biquad tutorials just give you the measurements verbatim - not the calculations of formulae.

Having done no physics since school, my expertise in antenna building is poor to say the least. Still I did realise a few things about most of the designs floating around the Web: all of the dimensions were multiples of the wavelength at 2.44Ghz (122mm or 0.122m). So then, I just needed to figure out the multiplication factors in each case and I was sorted.

My list is as follows: (λ = wavelength)

• Emitter wire total length: 2λ
• Emitter ’square’ side length: 0.25λ
• Emitter offset from reflector: 0.125λ
• Reflector width/height: 1λ
• Reflector ‘lips’ height: 0.25λ

So, at 2.1Ghz (2,100,000,000Hz - λ = 142.8mm),these dimensions are:

• Emitter wire total length: 285.6mm
• Emitter ’square’ side length: 35.7mm
• Emitter offset from reflector: 17.85mm
• Reflector width/height: 142.8mm
• Reflector ‘lips’ height: 35.7mm

I made the reflector out of galvanised steel mesh and mounted an N-type connector to the centre. I made an N-type coaxial to FME coaxial cable to hook up the phone to the antenna. The emitter itself is made from the copper centre conductor taken from a length of high-quality satellite TV coaxial cable that I had left over. I used some scrap wires to connect the ends of the biquad ‘bow-tie’ back to the reflector, and placed some of the original dielectric insulation from the satellite cable back on the ends of the bow-tie’ shape to prevent the antenna from ’shorting’ (in an RF sense). The emitter is then soldered into the N-type connector in a most slapdash style.

I didn’t have enough mesh to make the ‘lips’ of the antenna’s reflector match the measurements I’d planned, but made them the longest equal lengths that I could. In other respects, I managed to get the dimensions down to within a couple of millimeters of my target measurements.

High-quality cable is a must - I only used 50cm or so of RG-58 type cable to go between the phone and antenna, and unless you’re using something very high-grade (like LMR-400), I wouldn’t go too much further than that.

Presently the antenna is fixed and aimed in a pretty shoddy way - it’s fixed onto a set of ‘3rd hands’ - and there’s a Post-It note there to provide (some) insulation between the stand and the reflector… I plan to investigate more permanent mounting options at some other date.

The biggest problem with the antenna is aiming it - but having said that once it does catch a signal, the phone holds on to it very well. I’m aiming it over the rootfops of the building, hoping to catch some of the signal’s diffraction.

I have no idea how much gain the antenna produces. When aimed correctly (which is very tricky), it gives me a consistent 1-bar UMTS connection, or a 2 bar GSM signal. It works better at night, holding on to a signal for many hours.

UPDATE (3rd August 2006): Here are some better pics. I’ve replaced the post-it note with some pieces of polycarbonate. The pics also show the cradle into which the phone sits, and the cable which links the antenna to the phone.

Also, admire my lovely lavender wall paint :S

Just got my hands on my new phone, a Nokia E61. Very impressed with it!

The new Series 60 3rd Edition operating system is much snappier than the previous incarnations. I’m still getting used to the QWERTY keyboard though- I can type much faster using T9. I expect it won’t take long for it all to sink into muscle memory though. I’ve managed to get through writing this entry on it anyway!

More to follow soon!

SIPPhone Inc, makers of the Gizmo Project voice-over-ip softphone announced today that all landline calls in most ‘northern’ parts of the world (and even mobile calls in some countries) will be free of charge to Gizmo users. The offer applies to North America, Europe and most parts of Asia.

If you choked at the ‘voice-over-ip softphone’ part, fret not. That’s code for ‘it works just like Skype’. What makes it far superior to Skype is its standards compliance.

Skype is a walled-garden. Internet calls can only be routed to other Skype users. Sure, you can call out to a geographic number and talk to ‘old’ phones that way. But wouldn’t a standard enabling all softphone users (and users of physical VoIP handsets) to talk to each other via the Internet be better?

Such a standard already exists, and has done for some time. It’s called SIP, or Session Initiation Protocol. Strictly speaking, it doesn’t actually transfer the audio of your call, but sets up the connection and handles all kinds of signalling during it.

Although it doesn’t have the profile of Skype’s ‘one box’ solution, SIP is actually all over the place - supported not only by the Gizmo client but: softphones like X-Lite; hardware VoIP phones like Grandstream and Cisco’s handsets; standalone WiFi SIP phones like D-Link’s; and, to a limited extent, in some high-end mobile phones such as the Nokia E61 (which I’m getting tomorrow - yay!).

Gizmo give you a SIP account which you can use with any of these hardware and software options. So you can call anyone whose SIP number or address you have - for free. They also have a nice XMPP/Jabber-based instant messaging system which can interoperate with other similar XMPP systems like Google Talk and any standard Jabber service.

The only caveat to the ‘free calls’ offer is that the number you call must be attached to a Gizmo account - so you’d need to get the person you’re calling to sign up and log in once before calling. No big deal though really.

Gizmo Project makes all VoIP to landline calls free. Forever.:

Filed under: Misc. Gadgets

Skype ruffled some feathers in the internet telephony world earlier this year when they announced they’d be offering free SkypeOut calls to the US and Canada for the rest of 2006. We weren’t too interested since it came off as little more than a promotion, and we typically skip over promos (for obvious reason). But we’re kind of left wondering how Skype — deep eBay pockets and all — intends to compete with archrival Gizmo Project’s latest tactic: free Gizmo-to-landline calls anywhere, anytime, any amount, forever. We’ll probably be spending a while trying to make heads from tails of their business plan which pretty much totally gives away the shop, but who’s really going to be reeling here is the rest of the VoIP telephony industry that’s currently clawing desperately to monetize on landline phone replacements. Not everything’s free with Gizmo Project, however; even though you can all over Europe, Asia, and the Americas (to 60 countries and counting), if you want your pals to call you on Gizmo from their landlines, you’re going to have to buy a Call In number. (Fret not though, since those cost as little as $3 a month.) Also, in order to call them up they need to have a number registered to an active Gizmo account, which increases the barrier to entry by a bit. But what started with Captain Crunch’s 2600Hz whistle may now end with Gizmo Project’s capture of the biggest voice trunk of all time; if this is any sign of things to come, we’d say the free voice revolution may finally have a proper flagbearer. So let the free phone wars begin.

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(Via Engadget).

Ars Technica has posted a nice article on the current state of DRM circumvention, and its legal consequences.

The depressing that it confirms a lot of my fears about DRM - that it doesn’t need to be totally ’secure’ to be effective in its real (as opposed to stated) aims - controlling markets and distribution revenues, and not copy prevention as widely touted by Big Media.

Hacking Digital Rights Management:

Like it or not, DRM has become a fact of life in the 21st century. Ars takes a look at some of the more noteworthy hacks of the past several years and what the future might hold as Blu-ray and HD DVD take hold.

(Via Ars Technica).

Passport RFID tag

Originally uploaded by BigRedBall.

I just renewed my passport, and there’s an RFID tag inside.

Agghh! Tin-foil hat time!