tcd

tcd is a hybrid digital voice transcoder for ham radio used by the new URF reflector.

Introduction

This will build a new kind of hybrid transcoder that uses AMBE DVSI-based hardware for vocoding digital voice streams used in DStar/DMR/YSF and David Rowe's open-source Codec2 used in M17 as well as the open-source P25 vocoder, IMBE.

This is the only transcoder that will work with the URF reflector.

This software is loosely based on LX3JL's ambed, but is easily different enough to be considered an entirely original work. Here are some major differences with ambed:

• tcd uses both hardware-based and software-based vocoders, providing a bridge between the closed source vocoders used in DStar, DMR NXDN and YSF and open-source vocoders used in M17 (Codec2) and P25 (IMBE).
• TCP Sockets are used to communicate between the reflector and this transcoder. This guarantees that packets moving between the reflector and transcoder are never lost and the arrive at their destination in order.
• Each configured module has a dedicated encoding and decoding instance running on a different thread. This prevents overloading when processing multiple voice streams and provides the best possible performance for the reflector's clients.

Constraints and Requirements

Only systemd-based operating systems are supported. Debian or Ubuntu is recommended. If you want to install this on a non-systemd based OS, you are on your own. Also, by default, tcd is built without gdb support.

The DVSI devices need an FTDI driver which is available here. It's important to know that this driver will only work if the normal Linux kernel ftdi_sio and usbserial drivers are removed. This is automatically done by the system service file used for starting tcd.

Download the repository

In the parent directory of you urfd repository:

git clone https://github.com/nostar/tcd.git
cd tcd

To be perfectly clear, the urfd reflector repository clone and this clone must be in the same directory. If your transcoder is a remote installation, you still need to git clone https://github.com/nostar/urfd.git even though you won't compile anything in the urfd repository. Both tcd and urfd repositories need to be in the same directory as several of the source files in tcd are symbolic links to the adjacent urfd reflector source code.

Compiling and configuring tcd

Copy the three configuration files to the working directory:

cp config/* .

Use your favorite text editor to edit the following files:

• tcd.mk defines some compile time options. If you want to use the md380 vocoder, software only vocoding, or change the installation directory, specify it here. Once you've set these options, do make to compile tcd. If you change BINDIR, you need to also change the ExecStart in your tcd.service file.

• tcd.ini defines run-time options. It is especially important that the Modules line for the tcd.ini file is exactly the same as the same line in the urfd.ini file! The ServerAddress is the url of the server. If the transcoder is local, this is usually 127.0.0.1 or ::1. If the transcoder is remote, this is the IP address of the server. Suggested values for vocoder gains are provided.

• tcd.service is the systemd service file. You will need to modify the ExecStart line to successfully start tcd by specifying the path to your tcd executable and your tcd.ini file.

Transcoding options

By default, tcd requires 2 USB AMBE dongles; one for AMBE+(D-Star) and one for AMBE+2(YSF/DMR/NXDN). Using the following combinations in tcd.mk, there are other transcoding options:

• swambe2 = false, swmodes = false : 2 dongles required, all modes transcoded.
• swambe2 = true, swmodes = false : 1 Dongle required for AMBE+(D-Dstar), all modes transcoded.
• swambe2 = false, swmodes = true : No Dongle required, only IMBE(P25), Codec2(M17), and USRP(AllStar/EchoLink) modes transcoded.
• swambe2 = true, swmodes = true : No Dongle required, All modes except AMBE+(D-Star) transcoded.

The md380_vocoder library for arm32 linux OS is located here: https://github.com/nostar/md380_vocoder

The md380_vocoder library for all Intel/AMD 64-bit and ARM 64-bit platforms (including Android) is located here: https://github.com/nostar/md380_vocoder_dynarmic

Installing tcd when the transcoder is local

It is easiest to install and uninstall tcd using the ./radmin scripts in your urfd repo. If you want to do this manually:

sudo make install
sudo make uninstall

Installing *tcd when the transcoder is remote

Use:

• make to compile tcd.
• sudo make install to install and run tcd.
• sudo systemctl *something* is used to manage the running tcd, where *something* might be start, stop or other verbs.
• sudo journalctl -u tcd -f to monitor the logs.
• sudo make uninstall to uninstall tcd.

When started, tcd will establish a TCP connection for each transcoded reflector module. If the TCP connection is lost, tcd will block until the connection is reestablished. A message will be printed every 10 seconds suggesting that the reflector needs to be restarted.