A Comparison of Digital Voice Modes of Amateur Radio

Understanding the different modes of Digital Voice gives an amateur a clear picture of the bandwidth and transmission rate used by the digital voice mode. It also helps them understand which mode is easier to start with and which should be experienced later on.

There are three digital voice modes, namely C4FM Fusion, D-Star, and DMR. We will compare these modes based on several parameters, as listed below:

  • Technical Specification
  • How User Identification is done
  • How Repeaters are connected
  • Operating Features
  • Signal Readability
  • Before we start comparing C4FM Fusion, D-Star, and DMR, let us have a quick overview of “Digital Voice.”

Overview of Digital Voice

Digital voice is a transformed version of digital data that we can hear. With the use of A/D converter, digital data is converted into digital voice, which is then processed through a Vocoder. Vocoder analyses and synthesizes the voice signals and compresses them to make the transmission easier and faster. The transmitted data has two parts. The first part is called Header, and the second part is called the “Data Part.” The Header carries the routing information and the information to identify user’s identity. On the other hand, the second portion called “Data Part” carries text, pictures, and other details.

Let us move ahead toward the comparison of C4FM Fusion, D-Star, and DMR.

Comparing Technical Specifications

There are several technical aspects that help comparing all the three digital voice modes.

All three voices modes are compared to the below listed technical parameters here:

  • Vocoder
    • C4FM Fusion uses AMBE+2, DMR uses AMBE+2, and D-Star uses AMBE+
  • Forward Error Correction
    • All three digital voice modes use the Voice Only forward Error Correction method.
  • Modulation
    • Fusion uses C4FM (Continuous 4-level Frequency Modulation), DMR uses 4FSK (4-level Frequency Shift Keying), and D-star uses GMSK (Gaussian Minimum Shift Keying)
  • Multiplex Method
    • DMR uses TDMA (Time Division Multiple Access) and the remaining two use FDMA (Frequency Division Multiple Access )
  • Transmission Rate
    • Fusion has a transmission rate of 9.6 Kbps, DMR has a transmission rate of 4.8 Kbps x 2, and D-star has a transmission rate of 4.8 Kbps
  • Bandwidth
    • Fusion and DMR have 12.5 KHz bandwidth utilization while D-Star has 6.25 KHz bandwidth usage
  • Channels Supported
    • D-Star and Fusion support only one channel while DMR supports two channels

How User Identification is done

Different modes may have similar or different methods to identify users. These methods may include user registration, user identity verification, user’s ID display, and so on.

Given below is the comparison of the factors that are used for user identifications:

  • Requirement of the user’s registration
    • D-Star and DMR require user registration, but for Fusion, user’s registration is optional
  • User identity verification
    • D-Star and Fusion identify a user with the Call Sign while DMR identifies a user with the Subscriber ID
  • User’s ID display
    • D-Star and Fusion display Call Sign as the user’s ID on the radio screen while DMR displays the Subscriber ID
  • Compatible to FCC ID
    • D-Star and Fusion are compatible to FCC ID while DMR is not

How Repeaters are connected

Connectivity to repeaters can be compared based on the factors listed below:

  • Local connectivity
    • All three voice modes support local connectivity
  • Connectivity to another repeater
    • Only D-Star supports connectivity to another repeater
  • Multi-repeater connectivity
    • D-star supports reflectors multi-repeater connectivity, DMR supports Talk Groups, and C4FM Fusion supports Wires-X Room
  • Connectivity to another ham
    • Connectivity to other hams is supported only by D-Star
  • Connectivity selection
    • D-Star selects connectivity through UR entry, DMR confirms connectivity through Channel Dial, and Fusion selects connectivity through the Room name
  • Echo test support for connectivity
    • Fusion does not support Echo test, but D-Star and DMR supports Echo test for repeater connectivity

Operating Features

Every ham wants ease of operating an amateur radio and digital voice mode, but depending upon the type of their selection or the availability of the radio, the level of easiness may vary. The presence of more features may make it difficult to operate an amateur radio; however, with the time, the level of expertise of ham increases as well making it easier to use any radio and digital voice mode.

Listed below is a comparison of D-Star, DMR, and Fusion based on their operating features:

  • Level of Easiness
    • Working with DMR and C4FM Fusion is easier than D-Star. New hams should start with either DMR or C4FM Fusion than D-star. After getting experience with these two, D-star should be used. Whereas D-Star radios are difficult, it is believed that the latest D-star radios with digital voice mode are easier than their older versions.
  • Selecting Memory
    • The process of memory selection is different in all three modes. D-star supports the Dial method. It also supports the GPS search method. DMR supports the Key Press method. And, C4FM Fusion supports the Dial method for memory selection.
  • Mode selection
    • The mode selection method in D-star is key press. The DMR supports Fixed in memory mode selection. And, Fusion has AMS (Automatic Mode Selection) support via Key Press.
  • Selecting a repeater connection
    • The repeater connection method in D-Star and DMR is Dial while the Fusion supports Key Press for repeater connection.

Signal Readability

It is one of the most important factors to ensure that the quality of voice is good. Better signal readability means better voice quality.

Let us compare the signal readability between D-star, DMR, and Fusion:

  • Voice quality
    • As far as the quality of voice is concerned, all three modes have good voice quality.
  • Signal Noise
    • All three modes are free of signal noise, which means crystal clear voice quality.

These are the important factors comparing which one can have enough information to judge which of these three digital voice modes is perfect. As you see, some of the factors in all three modes are similar, which means there is not much difference in the quality of these modes except the level of usage. Fusion and DMR are pretty easier to use than D-Star. However, if you experience the latest D-star radio then you will also find it easier. Apart from the factors that we have compared herein above, there could be many more factors like Bandwidth comparison and Network connectivity that you may compare to collect more information to distinguish the three digital voice modes.

 

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16.05.2012 · From OE8APR
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