I was originally going to write this article specific to one of the digital modes used in ham radio, Digital Mobile Radio (DMR), which is becoming very popular. However, I’ve taken a step back and thought it would be better to take baby steps.
“Conventional” repeaters are FM analog and “wide band.” Wide band signals use a 25KHz wide channel (band width) with a 5kHz deviation. Your local (usually state) repeater coordination council creates a frequency plan and allocates repeater frequencies to make sure that one repeater doesn’t interfere with another.
A number of years ago the FCC mandated that all commercial radio systems switch to narrow band. Narrow band uses a 12.5kHz wide channel with 2.5kHz deviation. This allows frequencies to be closer together, allowing more repeaters. Amateur Radio and the General Mobile Radio Service (GMRS) as well as the Marine Band Radio Service were exempt from this requirement. This actually created a lot of surplus commercial equipment that was reutilized within the Amateur and GMRS radio services.
Internet Radio Linking Project (IRLP)
In 1997 David Cameron, VE7LTD, invented the Internet Radio Linking Project (IRLP), or voice-over-IP (VoIP). IRLP enabled a user to connect one repeater to another by entering a series of DTMF tones from the keypad of a radio. The software is Linux based. As the network grew, ‘reflectors’ were created. A reflector is a server that allows multiple repeaters to be connected simultaneously, basically a large conference call. Today there are over 2,000 IRLP capable repeaters and 29 reflectors each with 10 channels. The system requires the user to use a radio to connect. More information can be found at irlp.net
In early 2002 Jonathan Taylor, K1RFD, developed a VoIP system called Echolink. Much in the same way IRLP a user can connect repeaters to over 2,000 repeaters anywhere in the world. Where IRLP has reflectors Echolink has conference servers where up to 99 connections can be made. Unlike IRLP, Echolink allows the application to be installed on a computer and, more recently, it is available as a smart phone app. There is a process whereby the user is validated as having an Amateur Radio license.
Digital Smart Technologies for Amateur Radio (D-STAR)
Around 1998 a group of hams in Japan, and later the US, developed a digital mode called Digital Smart Technologies for Amateur Radio (D-STAR). The mode uses less bandwidth than analog and provides better quality audio given similar parameters of propagation. Icom brought D-STAR compatible radios to market around 2004 with 2-meter, 70cm and 23cm (1.2GHz) digital voice (DV) repeaters to the amateur market. They also produced a 23cm digital data (DD) module that would provide 128 kbit/sec and provide internet capability with the Icom ID-1 radio and its RJ-45 Ethernet jack. Because of the encoding of the digital voice D-STAR is capable of simultaneous voice and data (text chat), using a program called D-RATS. D-RATS allows forms to be sent and became a very useful tool for emergency communications.
As with the other VoIP capabilities D-STAR repeaters can be connected to other repeaters as well as reflectors (conference servers). However, where IRLP and Echolink use an assigned number, D-STAR uses call signs to route and connect, this also provides the ability to link directly to another user, commonly called private call. Developing programming for a D-STAR radio and understanding the routing ‘codes’ can be tricky but the D-STAR web page provides a ‘calculator’ to help. You select your origin and destination and it provides the correct routing information. Radio programming software by RT Systems makes it even simpler as the software contains a database of all the D-STAR repeaters and reflectors, so you just make menu selections and then program to your radio. The initial manufacturer of D-STAR compatible radios was Icom but Kenwood now also makes D-STAR compatible radios.
Yaesu System Fusion
System Fusion (usually just called Fusion) is a digital mode developed by Yaesu for Amateur Radio. It uses open source C4FM modulation. The major difference between D-STAR and Fusion is its backwards compatibility with its repeaters. A Fusion repeater can be set to accept and retransmit what it hears, so if the transmission is analog it will work, or if it is Fusion it will work. Fusion radios have a Group Monitor mode, whereby you can set a group of radios on a specific frequency and code. The radios will ‘talk’ to each other and, depending on the radio, indicate direction and distance to the other radios and allow communications only between radios that have the same group code set. You can also send pictures to other radios in the Group Monitor mode.
WIRES-X (Wide-coverage Internet Repeater Enhancement System) is the internet connectivity for Fusion radios, the Yaesu WIRES-X HRI-200 is the interconnect unit between a radio and the internet. A node (host) station or repeater is connected to the internet. The user can then connect to other nodes (stations) or to rooms (same as a reflector or conference server) where multiple users can be.
Digital Mobile Radio (DMR)
Digital Mobile Radio (DMR) is a digital mode that is gaining rapid popularity in the ham community. DMR was originally developed as a commercial radio application for businesses and initially in the European markets. It uses Time-division Multiple Access (TDMA) technology on a 12.5kHz channel. This provides 2-channels, called time slots, on a given frequency. DMR standards have three Tiers. Tier I is for simplex ‘free channel’ radio in Europe, similar to our FRS. Tier II is conventional systems, which is where all ham communications are. Tier III is for trunking radio systems, which are not used in ham radio. As DMR was adapted from commercial systems, which were all using UHF frequencies for DMR, it has only been in the past few years that dual band DMR capable radios have come on to market aimed at hams. This is why in most areas DMR repeaters are on 70cm frequencies, as the commercial repeaters were only made for the UHF band.
DMR repeaters can be stand-alone but many are built into networks. There are numerous possible configurations – for a more in-depth article see the article Basic DMR Programming.
Project 25 (P-25)
P-25 is a suite of standards developed for commercial radio systems, mostly for public safety. There are a few areas that have P-25 capable repeaters and they are mostly in the 33cm (902-928MHz) band.
There are no radios directly marketed to the ham community with P-25 capabilities so ham use commercial radios modified for the 900MHz frequencies. There are usually Motorola radios. To program Motorola radios you need propriety software (Computer Programming Software – CPS) and the license costs can be expensive.
This article is intended to give you a basic understanding of a number of the different radio capabilities you might find as a new ham and what you might want to look for when buying a radio. You should look at the article What Radio Should I Buy and Develop a Communications Plan as these articles will give you information on determining what radio systems are in your area. There is no point buying a D-STAR capable radio if you do not have any D-STAR repeaters near you to use.
To determine what types of repeaters are in your area go to RepeaterBook.