Raspberry Pi Installation

Get the Raspian onto your SD card

The current version of Jessie Lite is OK to use as we aill not need the desktop environment.
Note - SSH is not enabled by default on Jessie - You can enable it when you expand the SD card (below) it is in Interfacing Options (5) and P2 Enable/Disable SSH.

and expand disk partition (to use the full SD card capacity):

sudo raspi-config

Select the advanced option (7)
Select A1 Expand Filesystem
Select OK to reboot
Select Finish on the main Menu
Select Yes when asked would you like to reboot now.

Upgrade OS and firmware

For the GPU code to work, you need the up-to-date OS:

sudo apt-get update
sudo apt-get upgrade
sudo rpi-update (This command is no longer needed for Jessie as the above update and ugrade commands now update the firmware)

Install rtl-sdr

Installation

sudo apt-get install rtl-sdr

For other distributions than debian/ubuntu/debian-deriavates, there is a detailed guide here: http://osmocom.org/projects/sdr/wiki/Rtl-sdr#Software

Now, once the DVB-T dongle is plugged into the USB port, you should find a corresponding message in dmesg

Prevent some kernel modules to lock the use of USB DVB-T stick

(Only required if rtl-sdr was manually build and installed)

At some point in time the standard Raspian distribution began to contain drivers for the DVB-T dongles, likely to make easier for multimedia users to receive digital TV.
These drivers however are not of any use for us and they overtake the rtl-sdr driver, thus making it unusable. Here is how to disable them:

Create a file (with sudo):

sudo nano /etc/modprobe.d/rtl-glidernet-blacklist.conf

then insert the following lines

blacklist rtl2832
blacklist r820t
blacklist rtl2830
blacklist dvb_usb_rtl28xxu

Save the file, then

Install required packages

sudo apt-get -y install libconfig-dev fftw3-dev libjpeg-dev libconfig9 libjpeg8

Download the binary and unpack it

For Raspberry Pi 1, choose

wget http://download.glidernet.org/rpi-gpu/rtlsdr-ogn-bin-RPI-GPU-latest.tgz
tar xvzf rtlsdr-ogn-bin-RPI-GPU-latest.tgz

For Raspberry Pi 2 and other arm systems, choose
wget http://download.glidernet.org/arm/rtlsdr-ogn-bin-ARM-latest.tgz
tar xvzf rtlsdr-ogn-bin-ARM-latest.tgz

There are also binaries for x86 and x86_64 targets, see http://download.glidernet.org/.

Create named pipe

Since v0.2.2 rf-reception and decoding are separate processes. They communicate via this fifo.

cd rtlsdr-ogn
mkfifo ogn-rf.fifo

Set file permissions (only on Pi 1 for GPU usage)

The following five lines are only necessary if you are running the GPU code on Raspberry PI 1 - if you run without GPU (higher CPU usage) or run on other platforms (for which we don't know how to use the GPU) do not execute these commands.

sudo chown root gsm_scan
sudo chmod a+s gsm_scan
sudo chown root ogn-rf
sudo chmod a+s  ogn-rf
sudo mknod gpu_dev c 100 0

If running on Kernel 4.1 or higher (check it with command "uname -r") replace the last command with
sudo mknod gpu_dev c 249 0

Receiver configuration and tuning for best performance

Now power system down, insert the USB DVB-T stick and repower on..
Attach your aerial.

The very first thing you need in order to receive the signals is to be on the correct radio frequency.
Cheap SDR receivers use cheap crystals and their frequency tolerance is about +/-50-100ppm.
At 868MHz 100ppm error makes you 86.8kHz away from the correct frequency, while frequency deviation for FLARM signals is +/-50kHz.
Technically, the software receiver can search a wide range of frequencies for radio packets but this inflicts lot of CPU, thus can only be done for stronger CPU boards, but not for Raspberry PI.
Thus you need to know how much off is the crystal of your DBV-T dongle before you proceed.

You can measure the crystal with the gsm_scan tool, run it like this:

cd rtlsdr-ogn
./gsm_scan --ppm 50 --gain 20

it should receive some GSM broadcast channels and measure the frequency correction.
Notice the GSM frequency with a strong broadcast channel, even better: with one or two directly adjacent channels.
Adjust the gain (--gain) and initial crystal correction (--ppm) for best reception of as many as possible channels with consistent correction measurement.
GSM signals are very strong, thus too much gain is not good. You need to find an optimal setting here.

Rename the file named either Example.conf or Template.conf so that the name corresponds to your receiver's location (e.g. LFLE.conf, EPZR.conf, myPlace.conf)

(this assumes you are still in the rtlsdr-ogn directory, if not you need to "cd rtlsdr-ogn" first)

cp Template.conf myPlace.conf

Then edit the file, to set-up the receiver:
enter your crystal correction, GSM frequency for calibration, geographical position, APRS name. (You will find more details about receiver's configuration here)

nano myPlace.conf

Run the receiver

sudo nohup ./ogn-rf myPlace.conf &

and

 sudo nohup ./ogn-decode myPlace.conf &

to stop it, kill the process-numbers shown on startup or retrieved with the top command:

kill <processnumber>

The output of these commands is redirected to 'nohup.out' if possible, '$HOME/nohup.out' otherwise.

Install as service

If you don't want to start the receiver by hand every time the RPI boots, then install it as a service:

sudo apt-get -y install procserv telnet
sudo wget http://download.glidernet.org/common/service/rtlsdr-ogn -O /etc/init.d/rtlsdr-ogn
sudo wget http://download.glidernet.org/common/service/rtlsdr-ogn.conf -O /etc/rtlsdr-ogn.conf
sudo chmod +x /etc/init.d/rtlsdr-ogn
sudo update-rc.d rtlsdr-ogn defaults

Update /etc/rtlsdr-ogn.conf according to name of your configuration file, by replacing SampleConfigurationFileNameToChange.conf by the name of your config file and pi with your actual username

sudo nano /etc/rtlsdr-ogn.conf

Note that the path should be to rtlsdr-ogn, not the directory of the version you have installed. This is a symbolic link and will be updated with each version.

Start the service

sudo service rtlsdr-ogn start

Remark: When the service starts it waits for time synchronisation (NTP). It may takes up to 30mn on just booted RPi. Gossip says if you install ntpdate it synchronizes much faster.

Your service is now running and will start automatically at next boot.

If you wish to re-run gsm_scan after this point you will have to stop the service.

sudo service rtlsdr-ogn stop
cd rtlsdr-ogn
./gsm_scan --ppm 50 --gain 20

You can see console output of your receiver at any time with:

telnet localhost 50000

containing infos regarding to the decoding-process and

telnet localhost 50001

containing infos regarding to the APRS datatraffic.

And to finalize

Please don't forget to add your new receiver to the receiver list.
Some words on how to increase Raspberry Pi stability

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