Tag Archives: electronics

So I thought I’d start a category to contain all the random crap I that seems to drift in and out of my interests list.  It could prove to be amusing and I’m sure someone with a lot of time on their hands could generate some sort of tag-cloud versus time style graph further down the line that will prove deeply embarrassing to all parties involved.  Onwards.

A while I go, I obtained a Radio Scanner for the purpose of entertaining myself without a screen or keyboard right in front of me.  It was kind of nice to be in bed, listening to some arguing bus/truck drivers or PMR users. It really came into it’s own when I moved to the city – there’s lots more activity here than there was in little rural Radcliffe and it was quite exciting to get regular Close Calls* (I wasn’t even sure that feature was really working back in Radcliffe).

I got bored quickly though – there’s only so many things you can hear on a radio scanner before you’ve heard it all – and that happens surprisingly quickly when you’re not moving around at all I suppose.  Looking for something else exciting and interesting, I saw more advanced scanners that just seem to add more compatibility for trunking and storage – these didn’t really interest me so much.  The actual trunking radios are quite clever things – particularly the TETRA standard.  Capable of working in several configurations – Trunked (using the network infrastructure – essentially lots of cell sites – to communicate), Direct (Back-2-Back direct communication between two terminals) and crossovers between the two like Repeater and Gateway (effectively proxying traffic between terminals) – the system is extremely versatile.

Motorola MTP850

It’s not just voice that can be transferred over TETRA, the standard also supports data and an SMS-like text message service (SDS – Short Data Services).  Something I’d love to play with would be implementing IP/TETRA (Read: Internet Protocol over Terrestrial Trunked Radio) between a few machines with attached TETRA terminals.  The interesting network characteristics like the repeater and gateway functionality would make for a great data link layer – albeit with a fairly low bit rate.  Although I feel pretty confident that I’d be able to hash something together in C# or Objective-C to give the idea some legs; unfortunately there’s a few things in the way of experimentation here. The terminals are a little (!!) expensive. Given that they’re normally not purchased by members of the public, their price ranges reflect the target audience of government (Read: public safety, police, fire, ambulance, disaster control et al.) and large corporations.  Secondly, Ofcom are standing by to stomp out the fun – perhaps with good reason.  The terminals tend to operate in the 380-410 MHz area – and that’s not allowed without some kind of licence (exactly what kind, I have not figured out yet – I dare not inquire in case men with black suits and guns start asking questions – there’s no such thing as curiosity and innocence these days).  The airwaves do need to be kept clear for the proper users of the technology though of course.  If I can figure out how to proceed legally and on-record then I shall endeavor to do so.

I should probably say at this point the usual safety clause: Anyone reading this that has put together the words “police” and “listen” – drop that thought now.  One of the other wonderful features of TETRA is it‘s security – it supports End to End encryption between terminals and network infrastructure (and you bet they use it!) – on that note yet another plus for IP/TETRA.  The UK TETRA network is operated by Airwave Solutions (I believe they also have something to do with O2 – God help us!). As far as I can tell – there was once a public TETRA network called Dolphin in the UK – but it didn’t last long – call quality was apparently atrocious and the handsets were more expensive than conventional GSM machines that, for most users, would do the same thing.

Another interesting radio-related thing I came across was the USRP2 from Ettus Research LTD.  It’s essentially a machine that lets you generate and transmit arbitrary waveforms and also receive radio transmissions.  It has been applied to GSM, RFID, FM and many more radio applications.  Unfortunately it’s pocket-burningly expensive and not really the sort of thing I can see myself understanding or owning in the foreseeable future.  The people that do understand it and can afford it have done some really exciting things with it though – definitely worth a look on YouTube.

I’ll keep browsing and I’m open to suggestions on fun wireless things to play with.

* My scanner was a Uniden Bearcat UBC3500XLT.  I sold it last week on eBay! The Close Call feature lets the scanner continually observe the band for activity and automatically emit a sound or tune in when something is detected. Really great feature if there’s a lot going on right across the band.  The only problem I had with the scanner was the squelch setting (Read: the setting that chooses how strong a signal the scanner stops for) was a bit granular – at least I thought it was, maybe it was the best one around and I’m being picky; but it always either seemed too eager to stop for static or too ignorant to stop for anything at all.