Sunday, August 30, 2009

APCO 25 decoder /analyzer

Matt Robert, VK2TVK writes in the APCO25 ham radio list:

Hi List,

I would like to let you guys know about an open source P25 decoder/analyzer project that has been running for a little while now. OP25 started as the thesis for a Computer Security PHD student that is researching the security aspects of the APCO25 standard. The software is being expanded into a decoding suite that can gives various bits of information about a received signal and there is also provision for a software based repeater.

OP25 is based on the open source GNUradio package, and it is compatible with either the USRP software radio peripheral, or a conventional NFM radio connected to a sound card via a discriminator tap. One contributor is also working on adding transmit code with the intention of giving a software based P25 repeater that can be run off conventional PC hardware. Currently all the major contributors are HAM operators.

At the moment OP25 is considered pre-alpha (i.e. developmental) and we are looking for people that are interested in becoming developers/contributors to the project. The project is designed to run under GNU/Linux and it requires a bit of skill to get it going. It's definitely a HAM radio project at this stage and that's why I figured it would be appropriate for this list.

Shown here are are some sample screenshots for the curious.

Please feel free to have a look at the project homepage at and there is also a discussion list at

Kind Regards,

[Update Dec 2009]
Here is an interesting amateur video, that demonstrates the OP25 code in action with GNU radio using the USRP.

[Update April 2012]
Here is an updated video, showing OP25 code with GNU radio using a cheap USB TV tuner as a replacement to the USRP.


machinegeek said...

Experimentation is dying is ham radio because projects such as OP25 are accessible only with a username/password.

Steve, KB9MWR said...

Here is a copy: