Thanks to work by Serge Schneider at Raspberry Pi, dl-fldigi can now be installed using:

sudo apt-get install dl-fldigi

dl-fldigi can then be started from the Internet section of the menu, or manually from a terminal session.

Since the Pi does not have an audio input device, you need to add one. Do this before running dl-fldigi for the first time, so that the setup process can see the device. You can check that the device has been installed by running lsusb which should show something like:

Bus 001 Device 005: ID 0d8c:0014 C-Media Electronics, Inc.

When you start dl-fldigi for the first time, it will step you through basic setup; enter your receiver callsign and then on the Audio page select “PortAudio” and checking that your USB device is selected in the drop-down box.

Connect an RTL SDR to a spare USB port on the Pi.

Install the RTL_FM program with

sudo apt-get install rtl-sdr

The audio from RTL_FM needs to be directed to dl-fldigi, and this is most simply done with a loopback driver. Create a file .asoundrc in the home folder (/home/pi) and populate with the following:

# .asoundrc
pcm.multi {
    type route;
    slave.pcm {
        type multi;
        slaves.a.pcm "output";
        slaves.b.pcm "loopin";
        slaves.a.channels 2;
        slaves.b.channels 2;
        bindings.0.slave a;
        bindings.0.channel 0;
        bindings.1.slave a;
        bindings.1.channel 1;
        bindings.2.slave b;
        bindings.2.channel 0;
        bindings.3.slave b;
        bindings.3.channel 1;
    }

    ttable.0.0 1;
    ttable.1.1 1;
    ttable.0.2 1;
    ttable.1.3 1;
}

pcm.!default {
	type plug
	slave.pcm "multi"
} 

pcm.output {
	type hw
	card 0
}

pcm.loopin {
	type plug
	slave.pcm "hw:Loopback,0,0"
}

pcm.loopout {
	type plug
	slave.pcm "hw:Loopback,1,0"
}

Now load the loopback device with:

modprobe snd-aloop pcm_substreams=1

and run RTL_FM with:

rtl_fm -M usb -f 434.100M -s 192000 -r 8000 - | aplay -f S16_LE -t raw -c 1

Sound from the RTL SDR will now play through the Pi audio output, as well as being available for dl-fldigi.

When you start dl-fldigi for the first time, it will step you through basic setup; enter your receiver callsign and then on the Audio page select “PortAudio” and select the “loopout” audio device. dl-fldigi will then receive audio from the RTL SDR.

NOTE: The installed version of rtl_fm provides a means of adjusting the frequency that it is tuned to; a client program for this will be available soon

NOTE: If you change the output device using the volume plugin in the settings panel, the .asoundrc file will be overwritten.