The NXDN is FDMA-based and was developed to satisfy the FCC “refarming” mandate that called for all LMR use in the VHF and UHF bands to shift to narrowband capability. It can enhance operations and provide clearer and more efficient communication between users. While primarily targeted as a solution for business and industry market segments, the acceptance of NXDN worldwide has now reached a level where virtually all market segments including public safety entities are using NXDN.
These two types of trunking are called NXDN Type-C and NXDN Type-D. Type-C uses a centralized control channel whereas Type-D does not use a control channel. Most of these trunking systems feature automatic roaming, individual group and call capability, short text, GPS, and many other features. NXDN could be the right digital technology for you if you are looking for these key features in your digital technology.
NXDN is a Common Air Interface(CAI) that is part of a consortium of companies. although there are other companies that also produce products. NXDN uses Frequency Division Multiple Access (FDMA), and uses either 6.25khz or 12.5khz of bandwidth. One advantage for amateur radio use of NXDN is Icom and Kenwood repeaters can be used in “mixed-mode”, meaning that traditional analog FM at 12.5khz can be used to allow for legacy equipment. In our testing, we have found mixed-mode works very well, and can be a draw to get legacy users running digital, without having to immediately buy a digital radio. Also, in situations where analog capability is expected for emergency purposes, users can just program a channel on their digital radios for analog use. Another consideration in deploying an NXDN repeater is that it is not compatible with other C4FM modes on the market, such as Yaesu Fusion and dPMR.
Activity on the linked NXDN system is found in a handful of areas in the United States, with large concentrations in Connecticut, Florida, and Massachusetts. We have a few repeaters up in Canada linked in with us also. NXDN tends to be a niche mode for those who want to experiment with a true 6.25khz bandwidth. Also, there is opportunity to experiment and develop more software for amateur use on this platform.
Linking to the amateur radio NXDN network is achieved in a few different ways. Two software programs exist for linking multiple repeaters together. The first is NXREF, written by Alan, W7QO. This program supports a talkgroup (65000) which is used as a “worldwide” group. The second program NXCore, is written by Bob, N1XDN, and allows for multiple talkgroups. Multiple groups help in situations where there are many repeaters covering a smaller area, which helps with spectral efficiency. For example, we use talkgroup 9001 as our “Connecticut only” group, which will allow for local conversations over several repeaters in a state without causing traffic on the entire network. NXREF is compiled for Raspberry Pi and has worked on Beaglebone boards in the past. NXCore source is published on Github and should run on any Linux-based system, in addition to Cygwin on a Windows system.