Project 25 (P25) or APCO-25 is a set of standards for digital radio communications for public safety, security, public service and commercial applications. It is standardized by Telecommunications Industry Association (TIA) and supports both voice and data transmissions. APCO-25 compliant technology is being deployed in several phases. Wavecom decoder currently supports only Phase 1 systems.

The common air interface of the APCO-25 Phase 1 system is described in TIA-102.BAAA-A. The devices may use both the C4FM and CQPSK modulation techniques which can be demodulated with a single demodulator. The system uses frequency channels of 12.5 kHz bandwidth to transmit 9600 bits per second. Analog audio is digitized by using the full rate IMBE vocoder (7.2 kbps) before transmission (TIA-102.BABA).

The system allows group and individual calls, where each device has its own ID as well as one or more talk-group IDs.  Each call is marked as a group or individual call with its source and destination addresses. The decoded voice calls can be monitored live using the default sound card of the system and they are also automatically saved under the default Data-Output directory as .wav files. Live sound streaming can be disabled using the mute button on the upper pane.

The contents of the decoded data packets are printed out as raw data and are not further analyzed.

The Offset should be set to the center frequency of the channel to be decoded. The Polarity of the signal is detected automatically.