Digital Voice Protocols
digital voice Protocols
Digital voice modes on amateur radio are becoming increasingly popular, so we thought we would try to assist new users by clarifying a few details. There are several different digital voice modes that can be used in ham radio - most digital voice is used on VHF / UHF, but significant advantages can be achieved using digital voice on HF. Common protocols include DMR, D-Star and System Fusion, but others are available and new protocols are being developed.
How does digital voice work?
Whatever the digital protocol that is used, there are several basic concepts that are common to all types, whether used for amateur radio or form commercial or other applications.
Audio enters the transmitter in the normal way from a microphone and is amplified. It is then passed to an analogue to digital converter and as the name suggests it converts the signal to a digital form.
The resulting digital data is then compressed and encoded in a particular format by an item known as a Codec.
Once in the right format the digital data from the codec is fitted into the system data format and then modulated onto the signal.
Obviously the receiver is the reverse of the transmitter so that the incoming signal is demodulated, and data removed from the transmitted signal structure, passed through a codec, and then through a digital to analogue converter to reconstitute the audio.
Digital voice modes have the advantage that they provide much a good signal to noise ratio even in the presence of interference, and they can sometimes be copied at much lower levels that an equivalent analogue system.
One of characteristics of digital systems is that they can operate down to low signal levels and then suddenly disappear. They move from 100% copy to nothing for a small signal change. This is rather different to analogue systems where there is a gradual degradation in performance.
D-Star
D-Star standards for Digital Smart Technology for Amateur Radio and it is a digital voice standard that was developed by the Japan Amateur Radio League, JARL in conjunction with a number of universities and amateur radio companies. D-Star is an open standard, although it does use an AMBE codec which is proprietary and it is not possible to radio amateurs to obtain licences for the code development. The first D-Star equipment were mobiles and handhelds from Icom, but others have since joined and offer D-Star compatible equipment.
DMR
DMR stands for Digital Mobile Radio and it was a digital voice standard developed by Motorola for mobile radio systems, especially those used for commercial applications. In view of its original applications, it has many features that are aimed at commercial / business users. Nowadays there are several manufacturers supplying DMR equipment to the amateur radio market.
System fusion
Although properly called System Fusion, it is often referred to simple by the name Fusion. It is a digital voice system for amateur radio designed by Yaesu and as such it is not an open standard. Yaesu is the only manufacturer of radios for this mode.
System Fusion is incorporated into the Yaesu repeaters and as a result it is available on many repeaters. Despite this, many of the users of the repeaters that have Fusion simply use them as analogue repeaters.
connecting
Connecting to a digital voice protocol requires a digital radio (or computer/smart phone). These usually require some programming via computer software to enter the setting required to connect to the digital protocols. If you intend to use DMR you will first have to obtain a free, unique ID number from https://radioid.net/ As described above, the digital radio can connect directly to another digital radio or to a digital enabled repeater using RF. If outside of the range of another digital radio or digital repeater, another device such as a Pi-Star hotspot (Raspberry Pi computer fitted with a RF module) or a digital node can be used. The Pi-Star receives the digital RF signal from the radio and passes it to an internet connection. From there it can be routed via servers to emerge at a Reflector. These Reflectors can be a talk group or 'room' where other users of similar interests or local connect. The transmission can be routed from the Reflector to a node or repeater and back out to a digital enabled radio. Reflectors can be interlinked to provide cross protocol operating.
Cross protocol
Using the system above, it is possible to allow the different protocols to communicate with each other.
