Homebrew D-Star HF Today

I recently tuned into the wonderful Thursday Night D-Star/DV Round Table net on XRF002A (7pm Pacific) and heard a question — he has an ICOM IC-7000 transceiver and he’d like to adapt it to be able to have D-Star QSOs on HF.

Before answering that question, of course the simplest (if not the cheapest) answer is to get an ICOM HF radio that supports D-Star, for example the IC-7100 or IC-9100.  But, that was not the question, and the IC-7000 is a terrific radio.

Digital Voice advocates, particularly those using D-Star, solved this problem in the early days of amateur radio DV, but with all the focus on internet-connected hotspots and multi-mode, I’m not sure it is still easy to find the hardware that will work with existing software.

Old Solutions That Should Work Today

Solution 1 is the more interesting, but has a “gotcha”, in that you will need to find or build the “simple interface”.  Solution 2, assuming the GMSKClient software works with a DVMEGA GMSK modem,  is similar to the first one, but easier.  Therefore (with the above disclaimer), I recommend Solution 2 for most people.

Solution 1 – Soundcard approach
Use the G4KLX program SoundCardClient with a simple soundcard dongle.

This approach is pretty simple.  The pc program passes the mike’s analog audio to the AMBE device, which converts it to a compressed digital bitstream, which is then modulated to audio tones by the 2nd soundcard and sent to the transmitter.  On receive, the audio tones need to be demodulated back to a digital bitstream, sent to the AMBE device for decompression to analog audio and sent to the pc’s speaker via its 1st soundcard.

What’s needed:

  • G4KLX’s SoundCardClient software (available in the Digital Voice package on the “dstar_development” Yahoo Group’s Files/Beta folder). This program will run on a computer (no internet needed) with pc mike and speakers.
  • A  low-end USB soundcard dongle – it’s important there be no filtering in the audio chain, and the better soundcard dongles often add filtering.  Get the cheapest dongle you can find.  You can search for details on the dstar_development Yahoo Group.
  • An AMBE device, like the original blue DV Dongle or a NWDR ThumbDV.
  • A transceiver providing access to the modulator on TX and the discriminator on RX with audio paths unfiltered — typically a radio supporting 9600 baud Packet data will do the trick.
  • An interface that will provide TX and RX audio along with a PTT line.  This is the one thing you’ll have to build or find yourself.

Looking at the manual, the IC-7000 does support 9600 packet and has the traditional data socket (6-pin mini DIN) on the back.   Caution:  I don’t have this radio and have not tested it in this mode, but chances are very high that when packet data rate is set to 9600, the radio will not introduce audio filtering and it should be able to do D-Star.

The interface is the most interesting part of this project.  What we are doing here is quite similar to people doing classic digital modes like PSK-31.  So you can search for digital mode interface products (my search term was “ham digital mode interface”.   They all just want to route RX and TX audio to the appropriate pins on the radio’s digital data connector.  Some have a built-in soundcard.  Some have built in VOX to key TX, or they use the radio’s vox.  BUT — there are two problems with many of these interfaces:  1)A built-in soundcard may have audio filtering that will work for classic digital modes, but will filter out the low audio frequencies used by D-Star’s GMSK modulation; 2)VOX PTT keying may cause a delay such that the radio will fail to transmit the very beginning of the D-Star transmission, which is when then routing headers are transmitted.

Back in the day, I used a spare BuxComm Rascal interface.  This does not do VOX PTT.  Instead, it has a PTT circuit keyed by  the pc’s serial port (these days, one would use a USB to serial cable to the interface).  The Rascal had a filter capacitor in the audio path that I had to bypass, but then it worked well on D-Star.  Today, one would search the internet for something similar.  When I get time, I will do that myself and update this article.

I suspect the UDRC-II (Universal Digital Radio Controller) from Northwest Digital Radio would also do the interface job, but I have not tried it for this function.  I notice they are currently out of stock, but NWDR produces great products, so I would consider this if they get it back in stock.

Solution 2 – GMSK modem approach

OK, I “think” the software will support the DVMEGA GMSK modem, but I have not tried it.  So before proceeding, get assurance from someone who’s tried this that it works.

Similar to the soundcard solution, but easier.  While most GMSK modems are no longer available, DVMega has a good one that pairs with an Arduino Uno controller.  This approach has the advantage of being designed for GMSK modulation and allows the computer to control PTT.

Other solutions, no longer available

  • DVRPTR modem hardware, G4KLX DVRPTRClient software. If you have an old DVRPTR modem, just get the software from the dstar_development Yahoo Group, same place where you can find SoundCardClient.  The interface is part of the solution; you just need a 6-pin mini DIN cable.
  • Star*DV AMBE device, Star*Board GMSK modem and SDV software.  This was a terrific solution from Matrix Circuits.  Their engineer, Rick KD0OSS, designed the AMBE device and wrote the SDV software.   While originally designed to work with the ircDDBGateway for linking to reflectors, you can just not run ircDDBGateway and use the modem to drive your analog radio.  SDV features the ability to change TX Invert settings when changing bands.  It was a great D-Star HF solution!

There could easily be better, simpler solutions out there that I am not aware of, or have forgotten.  If so, please let me know!