DRM.md

DRM broadcasting with Dream

Pulseaudio loopbacks

Let's have a Pulseaudio sink where to feed the input audio for the encoder.

pacmd load-module module-null-sink sink_name=to_radio

gr-limesdr

sudo apt install cmake
git clone https://github.com/myriadrf/gr-limesdr
cd gr-limesdr
mkdir build
cd build
cmake ..
make
sudo make install

Dream

Dream is a free software DRM encoder. The code quality varies but it is usable.

Building

Get the sources:

git svn clone svn://svn.code.sf.net/p/drm/code/dream

Compiling Dream without GUI for tx use to ease running it from a systemd service. To do that, replace CONFIG at the beginning of file dream.pro with the following:

CONFIG += warn_on qtconsole

Then run:

qmake
make

If you want to have the graphical user interface as well you can now rename the binary as dream-console and then rebuild the project with default config.

Configuration

Setup Dream.ini:

[Transmitter]
currenttime=CT_OFF
hqiq=0
ifamp=1
ifformat=OF_IQ_POS
iffreq=-4510.0000000
interleaver=SI_LONG
msc=CS_3_SM
protlevel=1
robustness=RM_ROBUSTNESS_MODE_A
samplerateaud=48000
sampleratesig=48000
sdc=CS_2_SM
snddevin=to_radio.monitor
snddevout=-2
spectocc=SO_4

[Transmitter Service 1]
codec=Opus
description=15
id=0
label=MyStation
language=0
Opus_Application=OA_AUDIO
Opus_Bandwith=OB_FB
Opus_Channels=OC_STEREO
Opus_FEC=0
Opus_Signal=OG_MUSIC

The important part is to have snddevout=-2 as it is a magic number which enables writing I/Q samples to stdout when used with ifformat=OF_IQ_POS.

TODO Other options still need investigating, especially high quality IQ mode

TODO setting up limesdr transmitter

Transmitting

First, find your LimeSDR serial number and type by running:

LimeUtil --find

See ./lime_iq_tx.py --help for usage instructions. For sure, you need to define device type (-d), serial number (-s), band setting (-b), frequency (-f), and gain (-g).

The following example is for my LimeSDR Mini:

{ sleep 6; chrt --rr 95 ./dream -t; } | ./lime_iq_tx.py -f 144.7M -s 1D3AD649AC230B -g 60

Scaling:

chrt --rr 95 ./dream -t | sox -t raw -r 48k -e signed -b 16 -c 2 - -n stat