WebSDR node based on a Raspberry PI

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• WebSDR node based on a Raspberry PI
  • General hardware requirements
  • Running on a Raspberry PI 4 or newer?
  • Required setup and software
  • Clone this repository
  • Missing libraries
    • libpng12
    • libssl-1.0.0
  • RTL SDR direct sampling (500KHz - 28.8MHz without upconverter!)
  • Install WebSDR
  • Single band WebSDR
  • Time-controlled, dual band WebSDR
    • Antenna controller
    • Enable WebSDR for dual band operation
    • Cron
    • Manual control
    • GPIO Setup
  • Software reset
  • Blacklist RTL modules
  • SD Card wear

This WebSDR setup covers a dual band receiver (80/40 meters bands) time-based switched. It uses a relay to switch between antennas who is managed by one GPiO pin on the Raspberry PI (using a driver transistor).

Very special thanks to Pieter PA3FWM, Mark G4FPH and Jarek SQ9NFI for the helpful hand on configuring the progfreq setting.

General hardware requirements

• Raspberry PI 3 or greater.
• Raspberry Pi OS (Legacy) installed and working.
• Internet access setup and working
• RTL-SDR USB Dongle

Running on a Raspberry PI 4 or newer?

Raspberry PI 4 or newer runs on a different (but similar) architecture than older hardware like the PI 3. Since websdr-rpi is not fully compatible with this newer arch (mostly due to outdated dependencies) you may face some of these errors:

websdr-rpi: cannot execute: required file not found

or

websdr-rpi: error while loading shared libraries: libfftw3f.so.3

Some of the steps listed below have specific instructions for setting up a newer Raspberry PI hardware and overcome these issues.

Required setup and software

sudo apt update && sudo apt upgrade
sudo apt install -y \
  g++ \
  make \
  libsigc++-2.0-dev \
  libgsm1-dev \
  libpopt-dev \
  tcl8.6-dev \
  libgcrypt-dev \
  libspeex-dev \
  libasound2-dev \
  alsa-utils \
  libsigc++-2.0-0v5 \
  cmake \
  groff \
  rtl-sdr \
  libusb-1.0-0-dev \
  unzip \
  git \
  rsync

If you are running a Raspberry PI 4 or newer (arm64 architecture) install the armhf arch:

sudo dpkg --add-architecture armhf
sudo apt install -y \
  libsigc++-2.0-dev:armhf \
  libgsm1-dev:armhf \
  libpopt-dev:armhf \
  tcl8.6-dev:armhf \
  libgcrypt-dev:armhf \
  libspeex-dev:armhf \
  libasound2-dev:armhf \
  libsigc++-2.0-0v5:armhf \
  libusb-1.0-0-dev:armhf \
  libc6:armhf \
  zlib1g-dev:armhf

Clone this repository

cd /home/pi/
git clone https://github.com/reynico/raspberry-websdr.git
cd raspberry-websdr/

Missing libraries

Over the time, some required libraries were deprecated in favor of newer and incompatible versions.

libpng12

If you're running a Raspberry PI 4 or newer (arm64 architecture), compile libpng like this:

sudo apt install gcc-arm-linux-gnueabihf g++-arm-linux-gnueabihf

tar xf libpng-1.2.59.tar.xz
cd libpng-1.2.59/
CC=arm-linux-gnueabihf-gcc \
CXX=arm-linux-gnueabihf-g++ \
./configure \
  --host=arm-linux-gnueabihf \
  --prefix=/usr/local \
  --libdir=/usr/local/lib/arm-linux-gnueabihf

make
sudo make install
sudo ldconfig
sudo ln -s /usr/local/lib/arm-linux-gnueabihf/libpng12.so.0 /lib/arm-linux-gnueabihf/libpng12.so.0
cd..

If you're running a Raspberry PI older than a PI4, compile it this way:

tar xf libpng-1.2.59.tar.xz
cd libpng-1.2.59/
./configure
make
sudo make install
cd ..

libssl-1.0.0

If you're running a Raspberry PI 4 or newer (arm64 architecture), compile libssl like this:

cd openssl-1.0.0k/

CC=arm-linux-gnueabihf-gcc ./Configure linux-armv4 shared \
  --prefix=/usr/local/arm32 \
  --openssldir=/usr/local/arm32/ssl \
  -Wl,--version-script=openssl.ld \
  -Wl,-Bsymbolic-functions

make
sudo make install_sw

sudo ln -s /usr/local/arm32/lib/libcrypto.so.1.0.0 /usr/lib/arm-linux-gnueabihf/libcrypto.so.1.0.0
sudo ln -s /usr/local/arm32/lib/libssl.so.1.0.0 /usr/lib/arm-linux-gnueabihf/libssl.so.1.0.0

sudo ldconfig

If you're running a Raspberry PI older than a PI4, compile it this way:

tar xf openssl-1.0.0k.tar.gz
cd openssl-1.0.0k/
cat << EOF > openssl.ld
OPENSSL_1.0.0 {
    global:
    *;
};
EOF
./config shared --prefix=$HOME/libssl/openssl --openssldir=$HOME/libssl/ssl -Wl,--version-script=openssl.ld -Wl,-Bsymbolic-functions
make
sudo make install_sw
sudo ldconfig
ldd $HOME/libssl/openssl/bin/openssl
sudo cp $HOME/libssl/openssl/lib/libcrypto.so /usr/local/lib
sudo chmod 0755 /usr/local/lib/libcrypto.so
sudo ldconfig
cd ..

RTL SDR direct sampling (500KHz - 28.8MHz without upconverter!)

If you are running a RTL-SDR.com V4 receiver, a special version of the rtl-sdr driver is needed in order to receive 500KHz-28.8MHz

git clone https://github.com/rtlsdrblog/rtl-sdr-blog
cd rtl-sdr-blog/
mkdir build
cd build
cmake ../ -DINSTALL_UDEV_RULES=ON
make
sudo make install
sudo cp ../rtl-sdr.rules /etc/udev/rules.d/
sudo ldconfig

If you are running a different SDR device, but if it supports direct sampling (such as RTL-SDR.com V3 receiver), there's a way to receive 500khz-28.8mhz without an external upconverter hardware, easing the node build.

unzip rtl-sdr-driver-patched.zip
cd pkg-rtl-sdr/
mkdir -p build/
cd build/
cmake ../ -DINSTALL_UDEV_RULES=ON -DDETACH_KERNEL_DRIVER=ON
make
sudo make install
sudo ldconfig
cd ../../
cp -r pkg-rtl-sdr/ /home/pi/
cd ..

Don't forget to remove the progfreq line from the websdr configuration file(s).

Use the following systemd unit for direct sampling:

sudo cp etc/systemd/system/rtl_tcp_direct_sampling.service /etc/systemd/system/rtl_tcp@.service

Install WebSDR

• This is a good time to reboot your Raspberry PI, do a sudo reboot.
• Ask Pieter to get a copy of WebSDR.
• Copy the websdr-rpi binary and files to your home directory (/home/pi/)
• Edit websdr.cfg (for single band use), or websdr-80m.cfg and websdr-40m.cfg (for dual band use) to fulfill your configuration
• Create Systemd units to manage websdr and rtl_tcp

sudo cp etc/systemd/system/websdr@.service /etc/systemd/system/websdr@.service

Copy this systemd unit only if you're NOT using the RTL SDR direct sampling method. RTL-SDR.com V4 receivers don't need the Direct Sampling mod to work, it just works out of the box.

sudo cp etc/systemd/system/rtl_tcp@.service /etc/systemd/system/rtl_tcp@.service

Single band WebSDR

The setup described in this section is the most usual: a single band SDR receiver (say, 40m band).

• Create systemd units to manage websdr and rtl_tcp:

sudo cp etc/systemd/system/websdr.service /etc/systemd/system/websdr.service

• Enable the rtl_tcp systemd unit:

sudo systemctl enable rtl_tcp@0.service

• Enable the websdr unit:

sudo systemctl enable websdr.service

Time-controlled, dual band WebSDR

The setup described in this section is a more powerful one, where the Raspberry PI switches the WebSDR bands according to the time you define in crontab.

Antenna controller

This WebSDR setup uses one RTL-SDR dongle for two bands (40/80 meters), crontab takes control of which band is working. As wave length isn't the same on both two bands, I'm using a GPiO port to switch between them using a DPDT relay. GPIO3 is controlled by the check_band.sh cron script.

Enable WebSDR for dual band operation

• Enable just the rtl_tcp systemd unit. Websdr is managed by crontab

sudo systemctl enable rtl_tcp@0.service

Cron

• I built a crontab configuration to switch between 40m and 80m bands time-based. Just import the crontab lines into your crontab.

Manual control

You can always control band changes manual way. Disable cron lines to avoid automatic setup changes. Then you can use

sudo systemctl stop websdr@40.service
sudo systemctl start websdr@40.service

Where 40 is the band you want to receive. You can use and setup almost any band you want, as long as you had setup your websdr-{{band}}m.cfg

GPIO Setup

• Copy the etc/rc.local file to your /etc/rc.local

sudo cp etc/rc.local /etc/rc.local

• Check and match GPIO ports for relay control to switch antennas and a button to soft reset the Raspberry pi.

Software reset

• There is a Python script that handles Raspberry PI reboots from a hardware switch without killing power.
• Check the /etc/rc.local file and match the desired GPIO port for this task.
• Copy etc/systemd/system/reset.service to /etc/systemd/system/reset.service

sudo cp opt/reset.py /opt/reset.py
sudo cp etc/systemd/system/reset.service /etc/systemd/system/reset.service
sudo chmod 644 /etc/systemd/system/reset.service
sudo systemctl enable reset.service
sudo systemctl start reset.service

This is the software reset schematic. It has a 5v pull-up signal between a 10k resistor.

Blacklist RTL modules

You'll need to blacklist some modules in order to get rtl_tcp working. Edit or create the file /etc/modprobe.d/blacklist.conf with the following content:

blacklist dvb_usb_rtl28xxu

SD Card wear

To reduce the SD Card wear due to writes from logs, I recommend you to install log2ram, a tool which creates a ramdisk mountpoint for /var/log.

echo "deb [signed-by=/usr/share/keyrings/azlux-archive-keyring.gpg] http://packages.azlux.fr/debian/ bookworm main" | sudo tee /etc/apt/sources.list.d/azlux.list
sudo wget -O /usr/share/keyrings/azlux-archive-keyring.gpg  https://azlux.fr/repo.gpg
sudo apt update
sudo apt install log2ram

sudo systemctl enable log2ram

You may want to increase the ramdisk partition size up to 200M, edit the file /etc/log2ram.conf and set SIZE=200M.

While Websdr has an option to prevent logs to be written to the card (logfileinterval 0), there are two log files that are written anyway: log-cpuload.txt and userslog.txt. Create a logs folder inside /var/log and link both files in a symbolic fashion.

sudo rm /home/pi/dist11/userslog.txt
sudo rm /home/pi/dist11/log-cpuload.txt
sudo mkdir -p /var/log/websdr
ln -s /var/log/websdr/userslog.txt /home/pi/dist11/userslog.txt
ln -s /var/log/websdr/log-cpuload.txt /home/pi/dist11/log-cpuload.txt