Digital Systems

Digital amateur radio systems can be divided into two main categories; voice and data. A sub-category of  digital voice systems is linking networks. We'll briefly describe the primary protocols of each category here. Several of them also have their own pages with more information.

 Digital Voice
Digital Data
     D-Star      Morse Code
     DMR      NBEMS
     System Fusion
     Project 25       D-PRS
     NXDN       D-RATS
  Linking Networks      RTTY
     EchoLink      AMTOR
     IRLP      PACTOR
     AllStar      FT8


Digital Voice
Digital voice radios convert the audio they receive in their microphones into a digital signal before transmitting it. The received digital signal is then converted back to analog audio before sending it to the speaker. This requires the radio be specifically designed for digital communications. As of this writing, most radios on the market will work with only one of the below protocols, although multi-protocol radios are beginning to be introduced.

The main advantages of digital modes are almost crystal clear received sound most of the time, and much more efficient bandwidth use. The digital signal is not susceptible to fading, static and most interfering noise sources, resulting in very clear sound. Of course, the actual quality of the sound depends on the quality of the circuit that does the digital/analog conversion, called the vocoder (voice coder-decoder). A poor quality vocoder can create audio that sounds more like Donald Duck than a typical human. Also, current digital protocols transmit signals using between one-half and one-quarter the bandwidth needed by a typical analog amateur radio.

The main disadvantage of digital voice radios is that they are more complicated to program and use. Many can't be programmed without the use of a computer.

Most digital voice protocols also use a network of repeaters connected to the internet, allowing users to talk to others practically anywhere in the world from a handheld or mobile radio.

The primary digital protocols in amateur radio are:

D-STAR (Digital Smart Technologies for Amateur Radio) was developed in the late 1990s by the Japan Amateur Radio League. It's the first that was designed specifically for amateur radio use. Today, radios for D-Star systems are made primarily by Icom, though a few other manufacturers are now making some compatible equipment. MDARC has a D-Star repeater on Mt. Diablo. See our D-Star page for more information.

DMR (Digital Mobile Radio) is an open digital mobile radio standard created by the European Telecommunications Standards Institute (ETSI). It was established for public safety, business and commercial applications and is widely used as such around the world. Radios for DMR use are made by several manufacturers. MDARC does not have a DMR repeater, but there is one on Mt. Diablo, as well as many more around northern California. See our DMR page for more information.

System Fusion (C4FM)
System Fusion is a protocol developed by Yaesu in 2013 specifically for amateur radio use. It uses C4FM (Continuous 4-level Frequency Modulation) FSK technology to transmit digital voice and data. Fusion radios can inherently recognize transmissions in both standard analog FM or C4FM, then automatically respond in kind. Like the other digital systems, Fusion repeaters are available. However, as the technology is still young, few are available as of this writing. For more information, see Yaesu's What is System Fusion page.

Project 25 (P25 or APCO-25)

P25 is a protocol suite developed by the Association of Public-Safety Communications Officials-International (APCO) for the North American public safety sector, intended to provide trunked radio systems with efficient spectrum use. The technology was soon adopted by large corporate users and others, and has spread to other parts of the world. Over the years, as the technology developed and equipment replaced, used equipment became available in the amateur market. Otherwise, it would be much too expensive. Although some P25 repeater systems exist for amateurs; they are few, as the equipment remains expensive and complicated to use. See this Wikipedia page.

NXDN (Next Generation Digital Narrowband) is an open standard protocol, developed jointly by Icom and Kenwood. Icom's implementation is called "IDAS" (Icom Digital Advanced System) and Kenwood's is "NEXEDGE". NXDN was intended for commercial Private Land Mobile Radio (PLMR) and public safety communications systems, but has since come to be used by some hams. It uses Frequency-Division, Multiple-Access (FDMA) technology in which different communication streams are separated by frequency and run concurrently. See this Wikipedia page.

Linking Networks
Linking networks are similar to several of the digital voice protocols mentioned above in that they connect repeaters together via the internet, allowing people to chat worldwide with a handheld or mobile radio. The difference is that those radios and repeaters are typically standard analog FM systems, rather than digital ones designed for that particular network, and the linking network uses a now well-developed technology called Voice over Internet Protocol (VoIP) instead of a protocol specific to the digital system. The primary linking networks in amateur radio are:

EchoLink is by far the most popular linking network; and is also the only one of the three described here that can be implemented for little or no cost. It works via internet-connected computers to allow people to talk practically anywhere. Some descriptions of EchoLink refer to it as something like "Skype for hams". It has multiple working methods. The main ways EchoLink connects are:
*    Direct User- The EchoLink-connected computer's speaker and microphone are used to directly connect to the network. Alternatively, cell phone apps are also available. With this method, no ham radio is needed; and only the computer's user can participate in the conversation.
*    EchoLink Enabled Repeater- The amateur uses his handheld, mobile or base station to connect to a local repeater which has an EchoLink computer attached. With this method, everyone within range of the repeater can hear and participate in the conversation.This is the most common EchoLink method.
EchoLink also allows the connection of multiple repeaters to the same link, creating a "Conference".
*    EchoLink Enabled Simplex Link- Similar to the EchoLink enabled repeater, except that the EchoLink computer is attached to a base station instead of a repeater. With this method, those within range of the local base station can hear and participate in the conversation.

MDARC's 2-meter repeater on Mt. Diablo is connected to an EchoLink computer. See our EchoLink & IRLP page for more information.

IRLP (Internet Radio Linking Project) is similar to EchoLink in that it uses VoIP technology to link amateur radio stations around the world, using a computer (called a "gateway") connected to a radio. Some differences are a) no Direct User mode (see EchoLink section above) is allowed, requiring radios to be used for all contacts; and b) the software is proprietary and embedded into IRLP boards that are not free. As such, IRLP is used mostly with repeater systems. Although a one-node-to-one-node link is the most common, a user can also connect to a Reflector. A Reflector is a computer connected only to the Internet; no radio attached. It allows many repeaters to be inter-connected together by streaming the received audio back to all other connected stations, creating a conference similar to EchoLink's conference.

MDARC's 2-meter repeater on Mt. Diablo is connected to an IRLP computer. See our EchoLink & IRLP page for more information.

Like EchoLink and IRLP, AllStar uses VoIP technology to link amateur radio stations around the world. It's internet-linked computer is actually an open-source telephone PBX system called Asterisk, and so is occasionally referred to by that name. An advantage of AllStar is that one PC running Asterisk can control up to 8 separate radio links or repeaters, more than the other networks. It also has the capability to operate EchoLink connections. AllStar is not intended to link radio systems worldwide, but to extend a repeater's "coverage" by linking to other repeaters or base stations within a wider, but still local, area. The San Francisco Bay Area is an example. The three connection methods described in the EchoLink section above are also available with AllStar.

MDARC does not have an AllStar link. See the AllStar Link web site for more information.

Digital Data
Digital data systems transmit information other than sound, usually by using an encoding scheme to speed the information transfer, better ensure reliable reception or otherwise improve the communications. Some of the digital data methods used by amateurs include:

Morse Code
Morse Code (also known as CW, or Continuous Wave) is considered the original digital system. No longer required to earn a ham license, it has nonetheless grown in popularity. See our Morse Code page for more information.

Narrow Band Emergency Messaging System (NBEMS)
NBEMS is more frequently known by the software it typically uses, Fldigi, or Fast Light Digital modem application, a free, open-source program which allows an ordinary computer's sound card to be used as a simple two-way data modem. The software is free, and requires only a computer to run it and a two-way radio or other communications device with a microphone and speaker. As such, it's rapidly growing in popularity. See our NBEMS page for more information.

Packet and APRS
Packet for amateur radio began in the 1970s, with the development of the AX.25 (Amateur X.25) protocol. As is common in today's internet (but new then), the protocol breaks the message into small chunks, or packets, each able to find its own way to the destination. The packets are then reassembled into the complete message for presentation to the user. A further enhancement is that each packet station can also serve as a "digipeater" or digital repeater, allowing the message to travel long distances, even worldwide. See this Wikipedia page for more information.

APRS (Automated Position Reporting System) uses packet networks to send multiple types of short messages, including
the station's location coordinates, weather station data, text messages, announcements, queries, and other telemetry. The APRS software includes a map, which can display the location of APRS-enabled stations, weather stations and other information. See this Wikipedia page for more information.

MDARC has a Packet/APRS digipeater on Mt. Diablo. See our Repeater Systems page for more information.

D-PRS is a method of converting D-Star GPS data into a format that can be transmitted over APRS systems. The D-Star protocol is a 4800 bps data stream, of which 3600 bps are for voice, while 1200 bps is for synchronization and user-defined capabilities. One of the uses Icom developed for the user-defined space is GPS information, but it's not APRS compatible, hence D-PRS. See, and the developer's description.

D-RATS is another application for using the user-defined space in the D-Star protocol. D-RATS can send email, chat messages, transfer files and other information. A D-RATS reflector, also known as a ratflector is required for use as a gateway, which passes the data to its destination over the internet. See, a Quick Start Guide, and this operating guide.

High-Speed Multimedia Radio (HSMM)
HSMM can be thought of as long distance Wi-Fi for hams. The systems often use commercial off-the-shelf hardware such as 802.11 access points that have had their firmware re-flashed with a ham-specific program, allowing higher power and a somewhat different protocol to be used than with standard Wi-Fi. Some systems also have amplifiers and/or high-gain antennas; providing for communications links that, in some circumstances, can reach into the tens of miles. The protocol automatically builds a mesh network among all other nodes it can connect with, creating a robust and fast network that can be used much the same way as any Wi-Fi network can.

One disadvantage is that it is almost totally visual line-of-sight. Hills, buildings and even trees can block the signal. Another is that, for it to be truly useful, an applications server also needs to be established, to allow for email, file transfer and/or storage, or any other service you need.

MDARC does not have an HSMM mesh node. See this Wikipedia page for more information.

RTTY (Radioteletype) is an evolution of the old land-line teletype systems that began in the mid-1800s. Early radio teletype systems were developed by the U.S. government and corporations in the 1920s and 1930s. After World War II, hams started getting surplus teletype machines and adapting them to ham use. Now RTTY uses mainly PC computers running teletype emulator programs. RTTY is slow, but remains popular as a "keyboard to keyboard" mode. See this Wikipedia page for more information.


AMTOR (Amateur Teleprinting Over Radio) is an improved form of RTTY. It was used extensively in the 1980s and 1990s but has now fallen out of use as improved PC-based data modes are now used and teleprinters became out of fashion.
See this Wikipedia page for more information.

PACTOR is a form of packet radio that is used mainly on the HF band. It was developed in 1991, combining features of both RTTY and AMTOR to improve the reception of digital data when the received signal was weak or noisy. Using PACTOR requires a Terminal Node Controller (TNC). It currently has four generations of improvements; I, II, III and IV. All generations above level I are proprietary and must be purchased from the manufacturer. See this Wikipedia page for more information.

FT8 (Franke-Taylor design, 8-FSK modulation) is a newer entry in the growing WSJT package of computer programs used for weak-signal radio communication. It's intended for use on the HF bands and is capable of getting through in extremely noisy conditions. However, the messages sent are extremely short; little more than the basic contact information of call sign, location and signal report. The software is open source, and so free to use. See the WSJT Home Page and this Wikipedia page for more information.

WSPR (pronounced "whisper" & standing for "Weak Signal Propagation Reporter") is another member of the WSJT package of computer programs used for weak-signal radio communication. It's designed for sending and receiving low-power transmissions to test propagation paths on the MF and HF bands. The software is open source, and so free to use. See the WSPRnet web site and this Wikipedia page for more information.

"Winlink, or formally, Winlink Global Radio Email (registered US Service Mark), also known as the Winlink 2000 Network, is a worldwide radio messaging system that uses amateur-band radio frequencies and government frequencies to provide radio interconnection services that include email with attachments, position reporting, weather bulletins, emergency and relief communications, and message relay." (Wikipedia). See this Winlink web site and this Wikipedia page for more information. Also see this series of short videos (1-5 min. ea.) on how to get started with Winlink and use its various features; hosted by the San Diego, California ARES.