In May of 2011 the Sangamon Valley Radio Club, my local club, was awarded a free D-STAR repeater from Icom. I volunteered to be the computer system administrator for the project. What follows are some notes I've written as I've learned about D-STAR and a series of links to information on the Internet.
So, the question a lot of local people asked along the way was “What Is D-STAR?” The following is some very basic information.

D-STAR offers digital voice and data communications on some of the same frequencies we use on VHF and UHF FM. Currently radio equipment is available for the 2 meter (146 MHz), 70 centimeter (450 MHz), and 25 centimeter (1.2 GHz) bands. There are both “low speed” and “high speed” data modes. The high speed mode offers 128 kbps speeds but also requires 1.2 GHz radios, etc. so I won’t reference it further in this discussion.

Slow speed data and digital voice is transported over the air at 4800 bps. This is about one third the bandwidth of a VHF or UHF FM radio signal which is around 16 kHz wide. 3600 bps is used for voice and error correction. The remaining 1200 bps is used for synchronization and data. There is no provision for using all 4800 bps for data. Digital Voice is often referred to as “DV Mode”.

All current D-STAR capable radios also include traditional FM capability in addition to DV Mode. You cannot use an analog FM radio to send or receive DV mode either simplex or through a repeater.

A key feature of D-STAR which has yet to be fully exploited is dynamically linking D-STAR repeaters together. In a linked FM repeater system such as exists here in Central Illinois, the audio quality from distant repeaters may be slightly degraded and users must wait for the links to come up and down as carriers are sensed, etc. In the D-STAR network everything happens by moving around bits and bytes so the audio quality remains constant.  The linking can occur via RF or Internet depending on which is available. In the US this is typically done via Internet connections, in Japan 1.2 GHz radio links are common. To the users at either end there is no difference. With everything being moved around in the digital domain you cannot tell from the sound quality whether someone is in the same town as you are or thousands of miles away.

Typically we think of making a transmission and sometimes announcing to anyone listening that we are available for a contact. We do this by “calling CQ” or on FM you may frequently here some one say “This is WD9EDT listening”, etc. With D-STAR the radio always has an address it is trying to connect with. Very often that address is “CQCQCQ” which has special meaning and causes the system to behave as if you were on an FM repeater or operating simplex. Everyone tuned in hears you and everyone with a D-STAR radio can talk back and forth.

Another D-STAR feature is called “Call Sign Routing”. This is where the addressing starts to become more useful. If your friend is travelling and has used a D-STAR repeater anywhere, the network knows where the friend was last heard. If WD9EDT is here in town and you program the radio to talk with K9EIV who happens to be in Florida the system will take your call and route it to the repeater where he was last heard. If he answers your call you can chat back and forth just like you were both in the same town.

That covers the very basics of “What Is D-STAR?”. I didn’t really tell you how to do anything and didn’t say anything about data transmission, etc. I hope to revise and expand this paper in the future. In the mean time a good book that covers a lot of detail is Nifty E-Z Guide to D-STAR Operation by N6FN.

The W9DUA D-STAR repeater operates on 443.78125 MHz (TX) / 448.78125 MHz (RX)
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D-STAR Users Information Site

W9DUA D-STAR Repeater Status and Information
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