I have an experimental 440 MHz analog repeater that has been converted to D-Star. The GM300 radios have been interfaced using a Mark Phillips, G7LTT GMSK node adapter clone. The node adapter is in a duplex configuration, so in reality it has nearly all the functionality of an Icom D-Star repeater.
A D-STAR repeater is an expensive proposition. And many people are not happy with the Icom D-Star repeater performance. It's a number of things, most notable the poor receiver sensitivity. ~.45uV... In many cases the "repeater" is nothing more than two 28XX series radios in a rack mount box ... Pictures in the d-star digital yahoo group confirm this. Receiver desense is also on the list due to the use of plain-jane RG-58 inside the units. In addition, the receiver is prone to overloading by out of band high power FM broadcast signals.
Apparently the Icom G2 software is also not impressive, as discussed on the D-Star Gateway mailing list back in November 2009.
To build this adapter the cost about $100 (+ your analog radios) as compared to the cost of a Icom RPC-2 Controller plus a RF band module at about $2900.
For the longest time I was running Mark, KB9HKM's DVAR Hotspot Windows based software to compliment the board. For remote repeater site use I haven't been real keen on the idea as Windows computers seem to need reboots at inconvenient times.
So I have had a watchful eye on two Linux developments.
The first is by David, G4ULF, but he is still in the midst of releasing the program.
The other (probably less prominent) is by Scott, KI4LKF. His "rptr" program is available now.
All-in-all, I'm happy to report, version 2.93 has been running stable for me. Under Linux at least I have been able to script some ideas by trapping the debug messages with Perl.
For now, the frequency is 441.4625 +5 (SNP) The 40 watt GM300 radios are running cleanly at 20 watts.. The repeater is located in the village of Allouez near Heritage Hill State Park. The antenna is a Comet GP-6 Omni (9 dB), at about 35 feet. It is fed with LMR-400 coaxial cable. It appears to have about a 15 mile coverage radius.
Maxtrac/GM300 radios have a jumper inside (JU551) that sets whether the external connector will have flat or discriminator audio. You want discriminator. You may also need to add some 10 uF DC blocking caps on the RXA and TXA lines.
For more Information on the GMSK/ DSTAR Node Adapter/ Hotspot, please visit the websites below:
http://www.dutch-star.eu
http://www.gmskhotspot.com
http://d-star.dyndns.org/
Specifics on node adapter setup
If you are seeing what else you can do on a Linux platform with D-Star, I'd love to hear more about it.
{Edit Oct, 2010}
You may also want to take a look at John, K7VE's recent blog where he converts a Kenwood repeater for D-Star.
{Edit Nov, 2010}
And a Cincinnati OH, club using a Kenwood TKR-850