APCO-25

Project 25 (P25 or APCO-25) is a suite of standards for digital mobile radio communications designed for use by public safety organizations in North America. P25 radios are a direct replacement for analog FM radios but add the ability to transfer data as well as voice, allowing for a more natural implementation of encryption or messaging. P25 radios are commonly implemented by dispatch organizations, such as police and fire, using vehicle-mounted radios combined with walkie-talkie handheld use.

Starting around 2012, products became available with the newer phase 2 modulation protocol, the older protocol known as P25 became P25 phase 1. P25 phase 2 products require the more advanced AMBE vocoder, which allows audio to pass through a more compressed bitstream and provides two TDMA voice channels in the same channel spacing (12.5 kHz) that phase 1 provides one voice channel. The two protocols are not directly compatible. However, phase 2 radios are capable of using both phase 1 modulation and analog FM modulation, per the standard.

P25 fills a similar role as TETRA or DMR protocols. However, TETRA and DMR both use TDMA technology, similar to P25 phase 2, and are generally only used for trunked radio systems (using a control channel), whereas P25 phase 1 is not TDMA and can more easily directly replace a conventional (non-trunked) radio system.

Public safety radios have been upgraded from analog FM to digital since the 1990s because of an increased use of data on radio systems for such features as GPS location, trunking, text messaging, metering, and encryption.

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