View source for APCO-25

P25 P-25 APCO 25 APCO-25 APCO Project 25 Astro-25

Police and public service is migrating to P25 digital mode, making it impossible to listen on traditional analog police scanners.  

P25 is a radio system using digital voice via the APCO-25 Common Air Interface (P25 CAI) standard.   P25 is a standard developed for public safety trunked radio systems.  It follows the open APCO Project 25 standard.  

Project 25 uses the IMBE vocoder. IMBE stands for Improved Multi-Band Excitation, and was developed by DVSI Inc. Numerous vendors have produced Project-25 capable subscriber equipment, including Motorola, M/A COM, EF Johnson, Uniden, Racal, and others. There are conventional voice solutions as well as trunking solutions available for this digital voice solution.

Currently, there are two trunking solutions available that use the P25 IMBE vocoder: 
#Motorola ASTRO IMBE
#Project 25 Digital Trunking

===Scanner support for FDMA===
*P25 Phase one is FDMA
*P25 Phase two is TDMA

The following scanners can only decode P25 Phase I, but not Phase II:

*    GRE PSR-500, PSR-600 
*    Radio Shack Pro-96, [[Radio_Shack_PRO-2096_Scanner|Pro-2096]], Pro-106, Pro-197, Pro-651, Pro-652 
*    Uniden BC296D, BC796D, BCD396T, BCD996T, BCD996XT,BCD396XT, HomePatrol-1 
*    Whistler WS1040, WS1065 

Scanner Support for TDMA

*    GRE PSR-800 (with firmware upgrade, not out of the box) 
*    Radio Shack Pro-668 
*    Uniden BCD325P2, BCD436HP, BCD536HP, BCD996P2, HomePatrol-2 
*    Whistler WS1080, WS1088, WS1095, WS1098, TRX-1, TRX-2 

''The TDMA support scanners also do FDMA Phase I''

=== Variations ===

P25 Phase 1:   The phase 1 Project 25 radios can operate in 12.5 kHz analogue, digital, or a mixed mode format. The Phase 1 radios use a form of modulation known as Continuous 4 level FM, C4FM.

Phase 1 P25 compliant systems are backward compatible and interoperable with legacy FM systems. In addition to this, the P25 standards provide an open interface to the RF Sub-System to facilitate interlinking of different vendors' systems.

P25 Phase 2 :   Phase 2 P25 radio systems are based around a 6.25 kHz channel bandwidth> within this they achieve one voice channel or a minimum 4800 bps data channel. P25 Phase 2 uses FDMA - frequency division multiple access and the modulation format is CQPSK. An alternative 2 slot TDMA solution is currently under development. Phase 2 implementation achieves the goal of improved spectrum utilization. Also being stressed are such features as interoperability with legacy equipment, interfacing between repeaters and other sub-systems, roaming capacity and spectral efficiency/channel reuse.

P25 Phase 3:   With the growing need for high speed data in many areas, Phase 3 of the P25 radio standards will address this requirement. Additional features are aimed at providing functionality for a new aeronautical and terrestrial wireless digital wideband/broadband public safety radio standard that can be used to transmit and receive voice, video and high-speed data in wide-area, multiple-agency networks.

=== C4FM ===
Yaesu C4FM amateur radio is not compatible with APCO-25 Phase I C4FM.  The Yaesu C4FM deviation levels are wider than that of Phase 1's levels (approximately 600 Hz of difference).

[[Category:Electronics]]
[[Category:Consumer Electronics]]
[[Category:Radio]]