Announcement: K0RV-DR on air

I’ve finally got all the pieces/parts cobbled together and we now have a D-star repeater! It went on the air last weekend temporarily using K0JEG for testing, but yesterday afternoon I got the response from the various registration groups to make it all “official”

The hardware:

As seen above, the main radio is a Kenwood TKR-820 repeater. This is a fairly simple repeater, just two radios and duplexer. There is an internal controller, but for d-star that’s not used. I picked it up on eBay. The nice thing is there’s a single connector on the back that brings all the important signals out for an external controller. D-star uses GMSK modulation, which is able to pass through non-linear equipment much like FM. The only caveat is that it uses a lot of low frequency information, which normally is filtered out of the audio chain. However a radio that has either a 9600 baud input/output or (in the case of a repeater), direct modulator input/discriminator output can pass the entire passband without any issue.

Above is the Raspberry Pi running the repeater controller and gateway software. Note the DV Dongle on top is not connected to the Pi in any way (well, technically it is connected with double stick tape) in this configuration. At some point I’ll move everything over to a Model B+ I picked up at Fry’s over the weekend, but for now this will work. The radio interface is in the white plastic box on the right. It is a GMSK modem, made by Jim Moen, K6JM. It uses a USB interface to the Pi and a db-9 breakout cable to the radio. The GMSK modem actually regenerates the digital signal, so it is a true digital repeater. I did try passing a D-star signal using the internal repeater controller and it worked, but I’m sure regeneration is going to output a much cleaner signal. 

That’s all there is to it. Of course there’s an antenna and coax, but for a basic D-star repeater that’s really all you need. Technically we could stop right here, but a single 10 Watt D-star repeater out in Parachute is a fairly lonely thing, so having an Internet connection helps too.

The Software

When D-star was first introduced, Icom put repeater linking in place to allow for callsign routing, using a system called USTRUST. If you wanted to add a repeater, it had to be an Icom repeater. There were some other issues with the system as well. A few enterprising hams in Europe and the US began looking to expand the capabilities of the growing D-star network. 

First, hams in Atlanta GA developed the D-plus system. This allowed repeaters to connect to reflectors, much like IRLP, Echolink, and All-Star systems. It also made it possible to use DVAP and DV-Dongles to link to repeaters and reflectors over the Internet. Here’s a link showing the current reflectors. Click on the status links to see users currently connected, etc. Reflector 30C is very active, along with Reflector 1C and sometimes the PAPA system in Southern CA on 12A.

In Europe, a few hams have developed their own system for callsign routing called ircDDB. Instead of using a database to keep track of callsigns and radio locations, it uses Internet Relay Chat (IRC) servers for repeater updates. This allows for much faster updates (typically the USTRUST system can take up to half an hour for your routing info to show up). It has since become very popular, and there is a “plug-in” for Icom controllers as well as home-brew setups. The Pi is running 2 programs: D-star Repeater and ircDDB Gateway.

The D-Star Repeater controller listens for packets from the GMSK board. When it gets a valid packet, it decodes the header and passes the audio data to the output port(s). Here you can see a station coming through (via Reflector 30C) the gateway interface (K0RV/G) and the repeater is passing it on through the RF interface (K0RV/B). If a station were transmitting locally, RPT1 would be K0RV/B and RPT2 would be K0RV/G. The repeater software also handles the housekeeping functions like PTT and 10 minute legal ID beacon. It also has the capability to play out recorded announcements and pass along some remote commands.

ircDDB Gateway is the repeater interface to the rest of the world. The primary use is for announcing stations to the ircDDB callsign routing system, but it does much more.

The gateway will connect to up to 4 repeaters, either hosted on the same PC or networked. This is primarily for cross-band use, but could easily be used to set up a remote receiver or multiple repeaters over a single Internet connection.

The ircDDB system will allow users to contact each other using callsign routing, without needing to know what repeater the other station may be using. 

One function of D-Star is DPRS, which is similar, but not completely compatible with APRS. The ircDDB software is able to pass D-PRS position information to the APRS-IS servers, so stations can be seen on aprs.fi, for example. Note that this will not transmit APRS information using AX-25 on 144.39MHz, but D-PRS data will pass through to other D-star users.

Another add on is DPLUS, which as mentioned, allows repeaters to be linked using various reflectors. It also allows DVAP and DV-Dongle users to connect to the repeater through the gateway. 

Finally, yet another linking system called StarNet allows for on-the-fly reflectors. I’m still figuring this one out.

This repeater will also support D-RATS, which is a messaging/chat system that uses the low speed data fields built into the protocol.

The System

D-Star continues to grow in popularity. My impression is many of the stations have come on in the last year or so, many on various dongles and access points. The expensive part continues to be the radio, but a company called Connect Systems is getting close to releasing the CS-7000, a 70cm HT with FM, DV and DMR compatibility, and later a mobile rig, and a CS-7000 plus, that will have WiFi built in (make your own hotspot). It is possible to combine an AMBE vocoder chip, GMSK modem and Raspberry Pi to make your own D-star radio. NW Digital Radio is still working on the  UDRX-440, a 70cm digital radio that will also work with d-star. Along with the UDRX-440, NW Digital radio sells a Raspberry Pi compatible AMBE decoder chip for setting up a DV-Dongle or DV-analog gateway. The JARL, who maintains the standard, recently released version 5.0 of the specification (pdf). A translation into English is in progress. I’ll continue to update the club as things progress. In the mean time, if you’re looking for a stocking stuffer, the ID-31a is “on sale” -$5.00 off list price at HRO.