Tutorial D STAR

Tutorial: D-STAR

What it is

D-STAR is a digital voice and data system for radio amateurs developed in Japan. Each transmission carries the callsigns, repeater names, a short text message and optionally GPS positions, all in a slow data stream next to the voice. OnAir logs the calls, shows the messages and plots positions on a map; voice needs an mbelib you install yourself.

What you need

• Any SDR that tunes the band: an RTL-SDR covers roughly 24 MHz to 1.7 GHz at up to about 2.4 Msps (see Radio-RTL-SDR), and so do HackRF, Airspy, SDRplay and others (Supported-radios). The narrow signals here need only a small sample rate; the mode asks for 2 Msps.
• Antenna: a 2 m or 70 cm vertical, outdoors.
• Frequencies (database): 145.375 MHz is the IARU Region 1 digital voice calling channel (the default), 145.670 MHz is a common simplex calling frequency, and 433.475 MHz is a 70 cm simplex frequency. Repeaters have their own frequencies: type yours. The channel is 6.25 kHz wide (12.5 kHz in the database).

Before you start

Set the gain so that the ADC level in the status line stays clear of full scale; use Auto-tune or Optimise gain (Your-first-reception). Too much gain makes strong neighbours (paging, FM broadcast, repeaters) leave spurs in the channel. Make sure the radio is on frequency: a cheap RTL-SDR can be several kHz off at 430 MHz, so enter its correction (ppm) in Radio settings or watch the carrier offset the panel shows. Narrow digital voice channels need an offset under about 1 kHz.

Step by step

1. Connect the radio and antenna and start OnAir. Open the group Amateur: voice & packet and choose Digital voice (the entry reads Digital voice, 145.375 MHz; remember that the same label is used by M17).
2. Enter the repeater or simplex frequency. The Calling button jumps to the 145.375 MHz calling channel.
3. Press Start. The panel says start the receiver to hear D-STAR until it runs and then nothing heard yet.
4. When a call arrives, Now shows ON AIR with RPT1 and RPT2, your and the other callsign, a slow-data message and a bit-error figure.
5. Open Calls for the log, Messages for the slow-data texts and Map for D-PRS / GPS positions.
6. Install mbelib yourself if you want to hear voice: Voice-codecs lists the file names and folders. Without it the panel says no mbelib: frames counted only.

What you should see

A call log with rows for each transmission (callsigns, repeaters, length, bit error rate). If the signal is late (you tuned in mid-call) the header is rebuilt from the slow data and marked joined late. Positions on the Map come from the slow data GPS text.

Reading the screen

Now: the current call (RPT1 / RPT2, the callsigns, message, length, BER and EMERGENCY if the flag is set). Calls: Carrier, Time UTC, RPT1, RPT2, Message, Length, BER. Messages: the slow-data text. Map: stations by their reported position, never the position of the receiver. Station / Heard: stations heard.

Options and settings

• Calling button: the 2 m calling frequency.
• Copy the call log row. Code squelch shown if the call has a code.
• Zoom on the map.

Troubleshooting

• Nothing heard. D-STAR is usually quiet; try a busy repeater. Check the frequency offset: the signal is GMSK so a drifting radio loses it.
• Calls with high BER. Weak or off-frequency signal.
• No sound. mbelib is missing (mbelib not found: click ? for the file names and folders).
• Header missing. You joined mid-call: the header is rebuilt from the slow data after a few frames.
• Messages shown garbled. Damaged slow data; the panel counts damaged lines.

Tips

• Record the channel (Tutorial-Record-IQ-then-the-Signal-workbench) while it is busy and replay it to try settings.
• A scan (Main-window, tab Scan) helps to find an active channel.

Legal and privacy notes

Digital voice and data on land-mobile and amateur channels can be private. Receiving is regulated differently in each country: follow the rules where you live. OnAir decodes only what is sent in the clear: encrypted calls are reported as encrypted and nothing is decrypted, and OnAir offers no help to defeat encryption. The AMBE / IMBE vocoders are patented, so the voice sound comes only from an mbelib you install yourself (see Voice-codecs); calls, IDs and data work without it. Do not publish what you hear. Transmit works in OnAir (used on a real radio by the maintainer and in loop-back tests) but needs the right licence for the service; see Transmit and Legal.

Under the hood

D-STAR transmits 4.8 kbit/s with GMSK in a 6.25 kHz channel: about 2.4 kbit/s voice (AMBE), 1.2 kbit/s forward error correction and 1.2 kbit/s slow data that carries the header (RPT1, RPT2, MYCALL, URCALL), a message and optionally GPS. The specification is published by JARL.

Related

Mode-D-STAR, Tutorial-Digital-voice-DMR-D-STAR-P25, Tutorial-M17, Tutorial-DMR, Voice-codecs, Radio-RTL-SDR, Live-map, FAQ