Converting a D-Star Hotspot to a Full Duplex Repeater

If you have a gmsk modem and put up a D-Star Compatible Hotspot, it is quite easy to convert this simplex system to a full duplex repeater that supports DPlus linking to other repeaters, reflectors and often to Hotspots, DVAPs and DV Dongles.  With other software, this same equipment can become an ICOM G2-compatible repeater that supports Callsign Routing.

Here's all you need:

• Another analog radio with 9600 baud Data port, or direct access to the Rx radio's discriminator and the Tx radio's modulator
• Cable to connect the GMSK Node adapter to the two radios
• Duplexer to isolate the Rx radio from the transmitted signal (required of all same-band repeaters)
• Appropriate PC and software (which you already have if you are converting an existing Hotspot)
• Internet connection

Details:

• Callsign -- I recommend you get a separate callsign for your D-Star Compatible repeater.  This is required if your chosen software is the G4ULF StarGate gateway.  While not absolutely required when using DVAR software, things will be simpler if your repeater has its own callsign, and if you later move to G4ULF StarGate, the callsign will already be set up. 
  
  Note to US hams -- A club requires only 3 other people besides yourself to get started.  Click here for easy guidance on setting up a small ham club and requesting a club callsign

• D-Star registration -- You need to register your club callsign with a nearby D-Star repeater, and set up at least one "terminal" with a blank "initial".  This is documented on the Building a D-Star Compatible Hotspot page, Step 1.  In Step 1.d, create the "blank" terminal.  You can create a 2nd terminal with initial of "R", or you can keep it simple and just use the "blank" terminal for authentication.  There really are no standards for this.  

• Duplexer -- This is not a D-Star issue, since all repeaters require at least a duplexer.  If you are setting up a "garage repeater" in a low-RF area, you can probably get away with an inexpensive "mobile" duplexer.  I got mine on eBay from seller "mega409shop" for $90 tuned to my frequency pair and shipping included.  Running 35 watts, I have experienced very little desense in the receiver. On eBay, search for "50W UHF Duplexer" or "50W VHF Duplexer".  Prices will vary. 

Caution:  Inexpensive duplexers normally provide about 75 db isolation between Rx and Tx.  When running 50 watts or less, this is probably ok.  This type of duplexer requires a split of at least 3.5 mHz for VHF, or 5.0 mHz for UHF.  If you are hoping to get your repeater coordinated in the US, this split may or may not be acceptable to the coordinators.

If your repeater will be located at a high-RF location, for example on a commercial repeater tower, an inexpensive duplexer will not work for you.  You will need a high quality duplexer with 100 db or more isolation and possibly other equipment.  You can get lots of info from the internet, such as Repeater-Builder website.

• Computer -- Your computer doesn't need to be large or fast.  I started out using an older laptop, but decided since the PC would be on 24 hours a day, I should get something that consumes minimal power.  I built a small, inexpensive PC using a Mini ITX form-factor motherboard.  There are many which will work.  I got an Intel BOXD510MO board with Atom CPU, 1 GB memory, for the "hard disk" I got a cheap 4 GB Compact Flash card and a CF SATA adapter.  I already had a KVM switch so I use the same keyboard, monitor and mouse that my main computer uses.  The entire cost of this PC was about USD 180.  It uses 26 watts of mains power.  Note: some people get an inexpensive solid-state disk unit.  The goal is to have as few moving parts as possible.

My software for now is DVAR Hot Spot, so I needed to load Windows to my new PC, and I wanted a slimmed-down Windows installation.  In addition, since Compact Flash cards have a lifetime limit in write operations, I wanted Windows to avoid all hard disk writes during normal operation.  This page explains how I did that.

• Software -- you have a choice, but for this page I'll assume you will use DVAR Hot Spot by Mark McGregor KB9KHM.  You can get his software from http://www.dutch-star.eu/software/ -- scroll down to DVAR HotSpot and select the latest version.  If you haven't already, refer to Step 5 on Building a D-Star Compatible Hotspot.  

• Cable -- Since I already had a simplex hotspot with a gmsk board to radio cable, I built a simple cable that plugs into that cable and the two radios.

  From the local electronics store I got 1) a ps/2 keyboard/mouse extension cable (6 pin mini DIN female on one end, male on the other) and 2) another one, though any cable with a male 6 pin mini DIN on one end will work.  I cut both in two and tossed one of the halves with a 6 pin male connector on it.  I stripped insulation and used a VOM to identify which color wire went with which pin. So there are 3 cables, one with a female connector, two with males. The resulting Y-cable plugs into the end of the gmsk node adapter cable and the Y-pigtails plug into the Tx and Rx radios.
   

  Using the pin numbering shown here:  6 pin mini DIN connectors -- that is, both female and male connectors are facing you with the slot or notch at the top, wires coming out the back.  Label one of the male cables Tx, the other Rx.

   

  Female Pin   Male Pins

   

     1        -        Tx 1  (Tx audio to transmitter)

     2        -        Rx 2, Tx 2  (ground, from both transmitter & receiver)

     3        -        Tx 3  (PTT to transmitter)

     4        -        Rx 4  (Rx audio from receiver)

     5        -        not connected

     6        -        Rx 6 (COS/Squelch from receiver)

  (If you'd prefer to build a single cable with a 9-pin DSub, the pin numbers are described on page 9 of the DUTCH*Star MHS manual.)

Configuration  

• Load NAWinCFG
• Click on Mode
• Un-check the Half Duplex box
• 
• Note: see Building a D-Star Compatible Hotspot, steps 3.a and 7, for info regarding RSSI Report.  Most boards are configured for "version 4" mode, so RSSI Report should not be checked.  If you have a NQSMHS board and have set the jumpers for V5 mode, then check RSSI Report box here.
• Click SAVE and exit the program