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Monday, October 10, 2011

Super Trunking Scanner: the original idea

Ever since I posted my Super Trunking Scanner project to Hacker News, I've gotten a good stream of questions about how it works. I have decided to go back in my own diary and write up a series of posts about how it came to be.

It started in May, about a week after I set myself free from that place in Mountain View. I had been poking around some forums and discovered that someone had written some code that used GNU Radio to decode Motorola SmartNet control channels for trunked radio systems. It also claimed to be able to record calls in parallel. While it wasn't a full system, what I did see was sufficiently interesting to keep investigating.

I started by looking at GNU Radio itself. What I discovered is that it needs a device called a USRP which costs $1500 for just the one box, and it also needs a $150 daughterboard called the DBSRX2 to get the band I cared about: 800 MHz to 2.4 GHz. Finally, it needs a suitable antenna. If you put this all together, you got a software radio which throws data at you over an Ethernet link. I thought this was promising.

The fact that the USRP is made by a company right by the Taco Bell on Shoreline in Mountain View was also a good sign. I am a big fan of buying local whenever possible. There are plenty of economic and social reasons for it, and I hope anyone else with a choice follows suit.

That's how it started: I discovered gr-smartnet, which lead to GNU Radio, which pointed me at the USRP hardware. It had a nontrivial price tag and promised to be a lot of work, but it did seem possible.

After a couple of weeks of messing with other projects, I came back to this and decided to go for it.

Next: part two: ordering the hardware and starting with GNU Radio.