A Weak Signal Propagation Reporter based on a Raspberry Pi and an RTL-SDR Software Radio Dongle

Foreword

This is an ambitious and very rewarding project for a young engineer who is interested in radio-frequency engineering and propaggation. There is an opportunity to install a portable, low cost wsprnet (Weak Signal Propagation Reporter Network) station at an ANU site. This project will become part of a world-wide research collaboration that is supported by the amateur radio community in Australia.

What is it?

The Weak Signal Propagation Reporter Network is a group of amateur radio operators around the world who use K1JT's MEPT_JT digital transmission mode , this and this to probe radio frequency propagation conditions using very low power (QRP/QRPp) transmissions. The software is open source, and the data collected are available to the general public at these sites 1, 2 and 3.

The MEPT_JT transmitter is also described here .

Despite the jargon, this a very low cost project. The aim is to implement a portable wsprnet reporter station with a few simple components, demonstrate data acquisition and report this to the wsprnet database. The wsprnet reporter station can be located at any low noise site of choice on the ANU campus.

Unfortunately we will not be able to transmit on the wspr network without an amateur radio license. But we can do low power tests on the LIPD bands.

Equipment:

For this project you will have to obtain the following.

  • A raspberry pi (RPI) . This is a versatile and inexpensive (~$35) single board computer popular among radio amateurs. The RPI will be used to acquire wspr signals and upload these to the internet. The RPI can also be employed as a radiofrequency transmitter without additional hardware and has therefore been used as a wsprnet transmitter. Software for a wsprnet transmitter can be found here .

  • An RTL_SDR is a DVB-T (digital TV broadcast) USB dongle) that has been hacked so that it can acquire 8-bit IQ samples at 2.5 Msps. This is too is very low cost (~$25) and can be easily found on ebay. Some modifications to the electronics (oscillator crystal) to make local oscillator tuning more stable.

  • An antenna, an RF cable (trasmission line) and an Internet connection to upload the data to the wsprnet database (supplied by ANU).



The figure shows some propagation channels across the atlantic ocean.

Scope and learning outcomes:

This is a build, package and test project.

  • You will learn about the WSPRNET transmission protocol and how to decode it.

  • Obtain all the components for the project and check proper operation using RF test equipment.

  • Implement and test the reporter.

  • Install the reporter at an ANU test site.

  • You will learn and implement signal processing for wireless communications and do some data analysis of massive data sets.

  • Do signal propagation research using data from the wspr database.

  • Investigate practical and social applications of wsprnet.

Quick Start Guide:

Note that a more detailed and specific procedure will be available if you take up the project.

  • Obtain the components and install linux on the RPI

  • Learn to code in C

  • Obtain a copy of the wsprnet reporter daemon code from the github and study how it works.

  • To obtain the code simply type git clone github URL at the linux command line.

    • The folder also contains copies of the code.

    Sample usage of rtl-sdr:

    $ rtlsdr-wsprd]$ ./rtlsdr_wsprd

    rtlsdr_wsprd, a simple WaSPR daemon for RTL receivers

    Use: rtlsdr_wsprd -f frequency -c callsign -l locator [options]

    -f dial frequency [(,k,M) Hz], check http://wsprnet.org/ for freq.

    -c your callsign (12 chars max)

    -l your locator grid (6 chars max)

    Receiver extra options:

    -g gain [0-49] (default: 29)

    -a auto gain (default: off)

    -o frequency offset (default: 0)

    -p crystal correction factor (ppm) (default: 0)

    -u upconverter (default: 0, example: 125M)

    -d direct dampling [0,1,2] (default: 0, 1 for I input, 2 for Q input)

    Decoder extra options:

    -H do not use (or update) the hash table

    -Q quick mode, doesn't dig deep for weak signals

    -S single pass mode, no subtraction (same as original wsprd)

    Example:

    rtlsdr_wsprd -f 144.489M -c A1XYZ -l AB12cd -g 29 -o -4200


  • Download and install the wspr-GUI program to view your stations received wspr signals

  • Obtain a copy of the rtl-sdr source code.

  • Download rtl_decode which can be used to decode IQ signals from rtl-sdr