Under the headings of democratizing and demystifying technology, here’s a group of open-source folks making ways of receiving the digital signals with which, under what’s called “P25” (Project 2025), public safety agencies will be conducting their radio communications by the year 2025. Those handy with soldering irons and reading circuit diagrams will find this especially interesting.  Those of us with a less sophisticated understanding will, for the moment, stand in awe and admiration:

OP25 is a not-for-profit project to bring together folks that are interested in implementing APCO P25 using a software-defined radio. Our goal is to build a software-defined analyzer for APCO P25 signals that is available under the GNU Public License (GPL).

APCO Project 25 is the digital communications standard used by many police and emergency services throughout the world. Most notably the US, Canada and Australia deploy systems based on P25. Compared to existing analogue systems P25 offers improved spectrum use, coverage and flexibility. Provision is made to ensure the confidentiality of traffic, to allow the use of trunking and the provision of data in addition to voice services.

Hardware scanners such as the Uniden BCD996T offer APCO P25 functionality but software-defined radio (SDR) offers significantly improved flexibility. For example, software radio approaches can receive many channels at once, handle both voice and data (including the trunking control channel), decrypt encrypted traffic when the key is known and log traffic to disk for later analysis. With the right software an SDR is a powerful analysis tool for debugging and monitoring of P25 networks.

That’s the sales message. The reality is software-defined radio isn’t yet as simple as the plug-and-play of hardware radios. You will need a lot of patience and a fair amount of software skills to get working. To get an idea of the work involved you can check out Hardware for Your Software Radio By Stephen Cass. In that sense this really is an amateur radio project and requires the same kind of skill and dedication but we’ve a few people who will help out if you run into trouble. A project like this needs many different skills so even if you’re not technical you maybe able to help in other ways.

A short video that demonstrates OP25 transmitting audio from a PC’s microphone input, then to a USRP being received by a GRE scanner is available on Youtube.

via OP25.

Thanks to Dangerous Prototypes for the link.

Cassidian Communications has a helpful explanation of P25 in .pdf (Acrobat) form; see also their P25 Land Mobile radio page. If this subject is of interest but daunting, start with Wikipedia’s excellent Project 25 entry.

OP25 itself notes that there are other projects exploring these issues: “OP25 is only one of a number of projects in this area and you should check out  Project54,  OpenP25 and  Unitrunker for related work. “