During the past two decades, digital voice communications options have become many. Most digital modes that are available to amateur radio operators are designed for the commercial user (DMR, NXDN, P25) while others were developed specifically for amateurs (D-STAR, M17, System Fusion). Each of these modes offer much the same experience and extras. All of them take up much less bandwidth when compared to the 25kHz-wide FM signal. They all offer "tracking" using GPS connected transceivers. They all even offer the ability to transmit a fair amount of data either along side a voice transmission or separate from it. The major difference, I’ve found, is in the protocol’s development and the radio manufacturer’s ability to implement features in such a way to make them useful to the user.

Table 1. Comparison of VHF/UHF digital modes.

DMR

D-STAR

M17

NXDN

P-25

System Fusion

Channel width

12.5kHz^[1]

6.25kHz

12.5kHz

6.25kHz 12.5kHz

12.5kHz

6.25kHz 12.5kHz

Data bitrate

~2,450bit/s^[2]^[3]

1,200bit/s^[4]

4,700bit/s^[5] 1,600bit/s^[6]

?^[7]^[3]

9,600bit/s^[3]

?^[8]

Vocoder

AMBE+2

AMBE

Codec 2

AMBE+2

IMBE^[9]

AMBE+2

I highly encourage people to read Mike Myers’s, K3DO, article "D-star, DMR, Fusion, Which is right for you?", which is a little dated but still contains a lot of excellent information.

1. DMR is TDMA meaning that it can allow multiple users to use the same "channel" simultaneously only separating the transmissions by time. DMR has two timeslots allowing two users to communicate using the same repeater at the same time. You may also hear this referred to as "achieving 6.25kHz equivalent bandwidth" as that will likely become a requirement in the United States at some point in the future.

2. Wikipedia contributors."Digital mobile radio: Specifications." Wikipedia. Accessed 2022-05-01.

3. In the United States, due to identification requirements, you can’t really use this mode for data communications.

4. Data connectivity in digital voice mode (DV) is available on 2m, 70cm, and 23cm at a rate of 1200 bps (not including the 3600 bps that is used for the AMBE voice encoding). A full 128 kbit/s is available on 23cm in digital data (DD) mode.

5. Transmitting only data.

6. Transmitting voice and data simultaneously.

7. Transmission bit rate is 4,800bit/s. Not sure how much overhead is involved so I can’t judge the available bandwidth.

8. Can send formatted messages and pictures.

9. P25 Phase 2 utilizes the AMBE+2 codec. This is only used over trunking systems, however, and probably won’t be seen in the amateur radio spectrum.

Why is D-Star being pushed so hard for emergency communications?

This morning I received the ARRL's ARES E-Letter (24 Feb 2010) and found it riddled with how Icom's D-Star system was so great and the answer to all our problems. The entire letter seemed to be one big advertisement for Icom, actually. What I can't understand is why the ARRL …

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Why is D-Star being pushed so hard for emergency communications?