Several digital voice modes are available and can be used on ham radio, including:
- APCO Project 25 (P25)
- D-STAR
- DMR
- NXDN
- System Fusion
APCO Project 25
P25 is most widely used by public safety agencies. It’s actually a set of open interfaces that define the various parts of a radio system. Because it’s designed for commercial use, most radios are single-band only, with a few exceptions.
P25 Phase I uses the IMBE voice codec with C4FM modulation, and operates in a 12.5kHz-wide channel. Phase II uses the AMBE+2 codec and supports a 2-slot TDMA, which allows two separate conversations to happen in one single 12.5kHz channel – effectively making each of the two voice slots 6.25kHz wide.
Examples of P25-capable radios include the Motorola Astro Saber, XTS, APX7000. Many different manufacturers make P25 radios, and they’re all interoperable with each other. At the time of this writing, P25-capable Astro Sabers were available on eBay for around $200 or less. XTS radios were around $500.
Advantages for amateur use: Higher-quality and more rugged radios and efficient use of spectrum – Phase I is half the bandwidth of a standard FM analog ham radio channel, Phase II is 1/4 the bandwidth per voice channel.
Disadvantages: Equipment can be expensive. Not widely deployed in the amateur bands.
D-STAR
D-STAR. which stands for Digital Smart Technologies for Amateur Radio, was created by the Japan Amateur Radio League. It was the first digital voice mode designed specifically to be used in the amateur service.
D-STAR uses the AMBE voice codec, and also supports 128kbps digital data on the 1.2GHz band.
Currently, D-STAR radios are only available from Icom. Handheld radios start around $300 retail.
Advantages for amateur use: D-Star is widely deployed in the amateur community, and repeaters can be easily linked together.
Disadvantages: Vendor lock-in.
DMR
DMR stands for Digital Mobile Radio. It is typically used for commercial business purposes – such as shopping malls, towing companies, and sports venues. It uses 2-slot TDMA in repeater operation, which provides for two voice slots in a single 12.5KHz channel.
DMR uses the AMBE+2 voice codec, with 4-state FSK modulation.
DMR radios are available from a number of manufacturers, including Harris, Motorola, Vertex Standard, and Connect Systems. Handheld radios start around $200 new.
Advantages for amateur use: Equipment is relatively inexpensive, can fit 4 voice slots in the same bandwidth as 1 analog FM repeater.
Disadvantages: Not widely deployed in the amateur bands, not as much of a secondary market for equipment.
NXDN
NXDN was designed jointly by Icom and Kenwood.