NXDN digital voice
A narrow digital two-way radio standard.
What does it sound like?
A tight, buzzing digital sound.
Who uses it?
Businesses, utilities and some public agencies.
Where and when can I hear it?
VHF and UHF business and public safety channels.
The science
NXDN gives each conversation its own narrow channel (FDMA, frequency division multiple access) of either 6.25 kHz or 12.5 kHz, using four-level frequency shift keying that carries two bits per symbol. In the 6.25 kHz form the channel runs at 4,800 bits per second with 3,600 bits per second for the AMBE+2 voice codec; in the 12.5 kHz form those double to 9,600 and 7,200. Trunked systems use one of two designs: Type-C, which relies on a dedicated control channel, or Type-D, which uses no control channel and lets every channel carry traffic.
Why use it?
The 6.25 kHz version fits two voice paths into a single 12.5 kHz allocation, and a 2016 DHS Office of Emergency Communications fact sheet notes it can use interleaved 6.25 kHz channels that 12.5 kHz systems cannot. The same fact sheet describes 6.25 kHz FDMA infrastructure as less complex than TDMA, allowing quicker recovery from failures, and NXDN radios can coexist with analog FM.
Lore
NXDN grew out of the FCC's push toward narrower channels: Icom and Kenwood began working together in 2003, announced the protocol at IWCE 2005, and shipped the first products in 2006. JVCKENWOOD says NXDN is documented by the ITU in Report ITU-R M.2014.
Easily confused with
- DMR digital voice: DMR pulses with its two time slots