In his short but pithy article in the February 2009 CARC Newsletter David wrote- “ Experimentation has always been at the heart of Amateur Radio, and the latest digital linking system, D-Star is debatably the most wide reaching innovation in Amateur Radio since the introduction of SSB. Whilst currently dominated by one manufacturer, the majority of the D-Star transport protocols are open and published, ripe for a sport of reverse engineering”. Since the publication of this short article David has been working on both the hardware and software elements of D-Star.
On Wednesday 16th September we were treated by David G4ULF to a rundown of the D-Star system. D-Star has been developed in the last few years by Icom in conjunction with JARL (Japan Amateur Radio League) and is gradually being taken up by VHF and UHF users as a means of providing worldwide communications.
The worldwide aspect is achieved by employing the Internet as the bearer for long distance linking of amateur V/UHF repeaters and reflectors. Prime movers in this D-Star community enterprise include Robin Cutshaw AA4RC.
This ability to couple a local repeater into the Internet means that potentially worldwide communications is possible, with the repeater at each end of the link providing the local V/UHF radio communications hub. D-Star uses Gaussian filtered Minimum Shift Keying (GMSK) as the modulation method. This is an effective and relatively simple approach to digital modulation for wireless data transmission.
The particular relevance of D-Star to CARC and Ashdown Forest Repeater Group members is of course that it is one of the modes now operational on our local GB7MH repeater located at St Leonard’s Church, Turners Hill. So, why are we implementing D-Star at this time?
The D stands for digital and, as it is digital, the signal from your D-STAR radio is converted from its original analogue format into a series of zeros and ones. Along with your digitized voice, the data stream contains addressing and routing information - what radio it is coming from, what radio it is going to, and how it is getting there. There are similarities to email in that without the addressing information, the mail won't go.
These concepts will sound familiar to packet radio users and D-STAR does in many ways work like packet e.g. MyCALL (who you are), UrCALL (who you're talking to), RPT1 C and RPT2 C. Even working simplex, your radio needs to know "Who it is" and "Who it is calling"… again, it’s a digital thing. When you transmit a digital voice (DV) signal, the radio's codec digitizes your voice and addressing information is added. In receive mode, your radio runs the data through the codec and turns it back into something we humans immediately recognise and use, analogue sound.
So, Digital Voice is a digital mode, and while it may sound like analogue FM coming from the speaker on your radio, the way it all happens is quite different. Being digital, there are a lot of interesting things we can do... such as sending your traffic to the local 70cm port and 1.2 GHz port. Or sending your traffic to the local 2 metre port and a "Reflector" somewhere across the world, such as the USA... all at the same time!
In the past few months David G4ULF has produced some major D-Star software implementations and he, together with Malcolm G3NZP, Richard G4ANN and Paul Phillips have collected, modified as necessary and installed the necessary equipment to get GB7MH up and running under D-Star protocol. This is a major achievement and whilst still classified as work in progress those equipped with D-Star mobiles or hand portables can now connect in to the D-Star network.
David has produced some notes on the D-Star system, which can be found at http://carc.org.uk/downloads/CARCTalk.pdf .
John G3VLH
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