2.2 KiB
APCO-25 Decoder
The APCO-25 decoder will decoder P-25 phase I signals that are using either C4FM modulation or LSM Simulcast (CQPSK) modulation. It will process trunked, conventional and packet data messages.
Audio Vocoder
APCO-25 Phase-1 audio calls use the multi-band excitation model vocoder to compress the digitized audio. SDRTrunk supports the JMBE library for decoding audio, but DOES NOT include the jmbe library in the normal application download. You must download and compile the library and place the jmbe-x.x.x.jar file in the same directory from where you launch the sdrtrunk application. On startup, sdrtrunk will attempt to discover the library and can then decode imbe audio.
Traffic Channel Following
The decoder currently does not automatically follow trunked traffic channels. This feature is planned for a future release
Talkgroups and Addresses
All talkgroups and radio addresses are listed in hexadecimal (base-16) notation and use the digits 0 - 9 and the letters A - F. Talkgroups are four characters in length and radio addresses are six characters in length.
Packet data IP Version 4 addresses will normally show in the from column of the events window and the Logical Link ID (radio address) will show in the from column with the radio's IP Version 4 address listed in the details column. If the data contains UDP over IP protocol, the UDP source and destination ports will be appended to the IP address.
Aliases
You can create an Alias List and attach it to your P25 decoder in the channel configuration window.
When aliasing talkgroups and radio addresses, ensure you include the full 4 or 6 character talkgroup or address with leading zeros.
Modulation
Choose either C4FM or LSM Simulcast (CQPSK) modulation in the channel configuration decoder tab. When you select the P25 Decoder from the drop-down list, the modulation selector list will appear.
