# rtlsdr-wsprd -- WSPR daemon for RTL receivers

![rtlsdr-wsprd](art/rtlsdr-wsprd-web.jpg)

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## TL;DR

This project aim at decoding WSPR signals using an RTL device, usually connected to a Raspberry Pi.
To install and use your dongle on a Raspberry Pi with a *Rasbian OS* with a *4.x* Linux kernel:

```bash
sudo apt-get update && sudo apt-get -y install build-essential clang cmake libfftw3-dev libusb-1.0-0-dev librtlsdr-dev libcurl4-gnutls-dev ntp git
git clone https://github.com/Guenael/rtlsdr-wsprd
cd rtlsdr-wsprd
make
make install
rtlsdr_wsprd -f 2m -c A1XYZ -l AB12cd -g 29
```

## Overview

This non-interactive application allows automatic reporting of WSPR spots on WSPRnet. The initial idea was to allow a small computer like a Raspberry Pi and a RTL-SDR device to send WSPR reports for VHF/UHF bands. This kind of lightweight setup could run continuously without maintenance and help to get additional propagation reports. The code is massively based on Steven Franke (K9AN) implementation of Joe Taylor (K1JT) publication and work.

This application written in C does:

- A time alignment (2 mins, required NTPd to run on the OS)
- Start the reception using the RTL lib
- Decimate the IQ data (2.4Msps to 375 sps)
- Decode WSPR signals
- Push any spots on WSPRnet
- Repeat, again and again...

## Installation

  1. Install a Linux compatible distro on your device.
     With *RasberryPi* devices, use a kernel *4.x ONLY*. There is a know bug related to later version 5.x.
     You can use this image : https://downloads.raspberrypi.org/raspbian_lite/images/raspbian_lite-2019-04-09/
     Update your OS as usual:
     ```bash
     sudo apt-get update && sudo apt-get upgrade
     ```
  1. Install dependencies & useful tools (for example, NTP for time synchronization). Example with a Debian based like Raspbian:
     ```bash
     sudo apt-get update && sudo apt-get -y install build-essential clang cmake libfftw3-dev libusb-1.0-0-dev librtlsdr-dev libcurl4-gnutls-dev ntp git
     ```
  1. Clone this repository:
     ```bash
     git clone https://github.com/Guenael/rtlsdr-wsprd
     ```
  1. Build the application:
     ```bash
     cd rtlsdr-wsprd
     make
     make install
     ```
  1. Start the application with your right parameters, ex. for the 2m band, with a fake callsign (A1XYZ):
     ```bash
     rtlsdr_wsprd -f 2m -c A1XYZ -l AB12cd -g 29
     ```

## Tips (for your Raspberry Pi and SDR dongles)

  - Use ferrite bead on the USB cable to limit the QRN
  - Use an external clean power supply
  - Cut off the display (could help to reduce QRN)
    ```bash
    /opt/vc/bin/tvservice -o
    ```
  - Remove unused modules (for example, /etc/modules: #snd-bcm2835)
  - Use an enclosure, and ground it

## Crystal stability

Most of RTL dongles use a cheap crystal, and frequency drift can effect the decoding & performance. The use of no-name RTL dongle for VHF/UHF bands usually require crystal modification, for a better one. External clock could be also used, like GPSDO or rubidium reference clock, aligned on 28.8MHz.

Some manufacturers intergrate a 0.5ppm TCXO. It's the best second option, after an external clock. Based on my personal experience:

- NooElec NESDR SMART : Works fine out of the box
- RTL-SDR Blog 1PPM TCXO : Works with some drift, require additional mass, or a better enclosure
- Other no-name like : RT820, E4000, FC0012, FC0013, can work, but require modification and drift a lot

## OS & Linux kernel requirement for RasperryPi devices

I have no idea why this app works fine for RPi with a kernel 4.x and not 5.x. Using a x86_64, rtlsdr-wsprd works perfectly fine with both versions of the kernel. This is probably related to an issue with pthread, and I have to investinage this point.
If you have some knowledge about this, your help is welcome!!