Raspberry Pi + RTL SDR dongle = APRS Rx only gate (Part one – FM Radio)

rtl

Introduction

I have couple of raspberry pi’s laying around doing nothing useful. I decided it’s time to use it better than dust collectors. This tutorial is placed here for reference for any OM who would like to setup APRS Rx only node based on R.pi. Here’s what you’ll need (hardware):

… and software:

Preparation

I searched web for instructions and I found nice step-by-step tutorial here: http://www.algissalys.com/index.php/amateur-radio/88-raspberry-pi-sdr-dongle-aprs-igate

1. download RASPBIAN Debian Wheezy:

raspbian

 

It’s 900MB+ image and you may consider P2P torrent for downloading. It has huge seed pool.

After downloading it’s tme to write the disk image to your SD card.

2. Download and install the Win32Diskimager software http://sourceforge.net/projects/win32diskimager/files/latest/download

3. Extract the  RASPBIAN Debian Wheezy *.zip image to a directory. It is one single file with .img extension.

4. Format your SD card to FAT32

5. Run Win32Diskimager and select *-wheezy-raspbian.img from the directory where you extracted it.

6. Select your SD drive letter for the “Device” and write the image. Confirm overwrite warning and wait about 10 minutes, depending on your SD card speed.

sdwrite

7. Writing image should finish with “Write successfull” info

sdcomplete

8. Plug the card in the Raspberry Pi, plug the LAN cable and power-up the fruit

9. Find the IP of your raspberry. How do you manage this depends on your LAN configuration. I have m0n0wall and it’s easy to check the IP of any device in DHCP lease table:

IP

DHCP assigned IP address 192.168.1.192.

10. Start your favourite SSH client and connect to Raspberry Pi. I am using TeraTerm

ssh1

Login to your Pi with:

Login:  pi

Password: raspberry

11. Expand filesystem

sudo raspi-config

and select option 1: Expand filesystem

piconfig

12. Select Finish and when asked for reboot select Yes.

 

 

Update, configure and install

13. You should have internet connectivity, then update the pi

sudo apt-get update
sudo apt-get upgrade
sudo apt-get dist-upgrade
sudo rpi-update
sudo reboot

This will take more than 10 minutes

14. Remove Pulse audio

sudo apt-get remove --purge pulseaudio
sudo apt-get autoremove
rm -rf /home/pi/.asoundrc /home/pi/.pulse
sudo reboot

15. Edit /etc/modprobe.d/raspi-blacklist.conf

sudo nano /etc/modprobe.d/raspi-blacklist.conf

and add the three lines to the end of the file to prevent the OS from loading the default drivers for the dongle

# blacklist spi and i2c by default (many users don't need them)
 
blacklist spi-bcm2708
blacklist i2c-bcm2708
blacklist snd-soc-pcm512x
blacklist snd-soc-wm8804
 
# dont load default drivers for the RTL dongle
blacklist dvb_usb_rtl28xxu
blacklist rtl_2832
blacklist rtl_2830

Finish editing with Ctrl-O and Ctrl-X

16. Reboot

sudo reboot

17. Create new directory for the RTLSDR software, install new driver and the software

mkdir ~/rtl
cd ~/rtl
sudo apt-get install git build-essential cmake libusb-1.0-0-dev
sudo git clone git://git.osmocom.org/rtl-sdr.git
cd rtl-sdr
sudo mkdir build
cd build
sudo cmake .. -DINSTALL_UDEV_RULES=ON
sudo make
sudo make install
sudo ldconfig

18. Install Sox

sudo apt-get install sox

 

Connect and test the RTL dongle

19. Run rtl_test

pi@raspberrypi ~ $ rtl_test

The response should be something like this:

Found 1 device(s):
  0:  Realtek, RTL2838UHIDIR, SN: 00000030
 
Using device 0: Generic RTL2832U OEM
Found Elonics E4000 tuner
Supported gain values (14): -1.0 1.5 4.0 6.5 9.0 11.5 14.0 16.5 19.0 21.5 24.0 29.0 34.0 42.0
Sampling at 2048000 S/s.
 
Info: This tool will continuously read from the device, and report if
samples get lost. If you observe no further output, everything is fine.
 
Reading samples in async mode...
lost at least 28 bytes
 
Samples per million lost (minimum): 0

20. Now you can tune to your local FM radio

Change the frequency to your favourite local station.

rtl_fm -M wbfm -f 90.9M | play -r 32k -t raw -e s -b 16 -c 1 -V1 -

Don’t forget earphones 🙂 Now you have multiband radio player.

21. Connect proper 2m antenna and tune to APRS frequency (in Europe it’s 144,8MHz):

rtl_fm -M fm -f 144.800M | play -r 24k -t raw -e s -b 16 -c 1 -V1 -

you should hear APRS packets.

—=== This is the end of part one ===—

 

Stay tuned for more (RTL calibration and installing multimon software and the python APRS igate script).

5 Comments

  1. Bob, VK2BYF says:

    Hello Om, could not find your name on the website.

    Everything went like clockwork. Easiest install I have tried.

    Both rtl_fm on broadcast and on local APRS frequency 145.175 in Australia looks like is working but no sound

    I did not go further and install the decoder yet.
    I know very little about Linux. Running Raspbian jessie latest version Sept. 24 2015 on Raspberry pi 2. and Bitvise xterm client

    I did remove pulseaudio (was not installed) What handles audio now? I have HDMI TV plugged in which has working audio form other experiments.

    Thanks for providing this excellent tutorial and hopefully helping me over the last little hurdle

    73 Bob vk2byf

  2. Mare says:

    Hi Bob

    You have to force audio output via HDMI with
    sudo amixer cset numid=3 2

    change back to 3,5mm jack with
    sudo amixer cset numid=3 1

    Or do it via config tool
    sudo raspi-config

    under advanced settings, audio output

    Hope this helps.

    Marko

  3. Bob, VK2BYF says:

    Hi Marko

    sudo amixer cset numid=3 1 worked

    Thank you very much
    Now to install the rest and see.
    I’ll let you know

    Bob

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