Category: Amateur Radio

Measuring Power Line Noise in the Neighbourhood with the RTL-SDR “Driveby” System

Over the last few months Tim Havens has been developing a portable RTL-SDR based scanner that he intends to use for geo-tagged noise floor readings. He hopes to use such a system to map sources of RF noise related to power lines so that he can contact his power company to resolve them.

Tim’s system uses a powerful Odroid XU3 which is a Linux based mini embedded computer that sells for $179 USD. The Odroid XU3 has dual quad core ARM CPUs which is enough power to run rtl_power with 5 RTL-SDR dongles simultaneously. Rtl_power is an RTL-SDR tool which allows you to scan and record the power levels in the frequency spectrum. By using 5 dongles he is able to scan the 49 MHz, 50 MHz, 144 MHz, 222 MHz and 432 MHz bands simultaneously.

From a previous post Tim writes:

The idea behind this project is to be able to MAP real-world Geo-tagged noise floor readings.  This can be used for the primary purpose I intended for this application (mapping of problematic sources of RF Noise related to power lines in the area so that I can approach the local power company to resolve them) or any other sort of RF signal MAPPING.  Such as cellphone/cellsite coverage or FM broadcast coverage (and dead spots) among other things.

RTL dongles are CHEAP, and reliable, although not 100% stable (they drift a bit for the first 5 minutes of warm up) they can be used to measure changes in the RF Noise Floor (once warmed up).  While they don’t really seem to be able to be calibrated to anything less than -87db all we’re really looking for are relative changes to the noise floor while driving around a particular location (there is probably some complex math that could applied to these measurements that could be calibrated).  So for this project these inexpensive receivers are really just fine.

While rtl_power is scanning, the Odroid uses a GPS receiver to tag the timestamped noise readings with GPS coordinates. Then by driving around with the system and combining the GPS coordinates with the noise floor readings from rtl_power he is able to create a heatmap showing exactly where in his neighbourhood noise levels peak, indicating a power line RF noise problem to be fixed by the power company.

Some more information about the hardware build of his system can be found on a previous post.

Powerline Noise Mapped with RTL-SDRs and GPS
Powerline Noise Heat Mapped with RTL-SDRs and GPS Logging
The Insides of the Driveby System
The insides of the driveby system

Tim also has uploaded a video to YouTube showing his system running a stationary test demonstrating the hardware and some of his custom software before everything was boxed up.

Driveby App stationary test

Compiling and using DSD 1.7 for D-STAR on Linux

Amateur Radio hobbyist George Smart has recently written a tutorial showing how to compile and install DSD v1.7 on a Linux computer in order to receive D-STAR digital voice. D-STAR is a digital voice protocol used by hams at a frequency of 145.670 MHz.

The tutorial shows the entire set up process from installing the required dependencies to running DSD 1.7 with GQRX by piping audio through UDP into DSD. He also shows how to run DSD 1.7 on a Raspberry Pi.

Note that DSD v1.7 also runs on Windows, and this previous post links to a precompiled Windows binary file.

GQRX Receiving D-STAR
GQRX Receiving D-STAR

Decoding Oregon Scientific Weatherstation Messages using Gnuradio

Recently a reader of rtl-sdr.com, DO2BJK wrote in to let us know about his project where he used GNU Radio to decode Oregon Scientific V1 and V2 weather station messages. To receive the weather station messages which are sent in the ISM band at 433 MHz, DO2BJK used a USRP B210, but he writes that other SDRs such as an RTL-SDR or HackRF will also work. To decode the signal, DO2BJK took the usual steps of recording the signal and looking at the audio waveform in Audacity. From the waveform he was able to determine the bit string and discover the preamble, sync and data parts of a packet. He then used GNU Radio and wrote a Python program to receive the signal and automatically detect the preamble and extract the temperate data. His code is available on GitHub at https://github.com/bkerler/OregonDecoder/.

Bit string signal interpretation
Bit string signal interpretation

Receiving WSPR with the RTL-SDR

Recently RTL-SDR.com reader DE8MSH wrote in to let us know about his experiments with receiving WSPR with his RTL-SDR. WSPR is an acronym for “weak signal propagation reporter” and is a software program and RF protocol designed for very weak signal radio communications between ham radio users. With less than 5W of transmitting power, a WSPR signal could potentially be copied all over the world.

To receive WSPR, DE8MSH used a direct sampling modified RTL-SDR dongle together with a 9:1 unun, 10m RG58 coax cable from RTL-SDR to unun and a 12m wire antenna outside his house. Then by using SDR# together with the WSPR software he is able to copy signals from all over Europe and Canada/USA from his home in Germany.

Some Received WSPR Locations
Some Received WSPR Locations
WSPR Report Information Including Distance
WSPR Report Information
The WSPR Software
The WSPR Software

Listening to FreeDV Digital Speech with an RTL-SDR

Over on YouTube user BSoD Badgers has uploaded a video showing his reception of FreeDV digital speech at 14 MHz. He uses SDR# combined with the FreeDV software to decode the signal.

FreeDV is a open source software application that allows digital speech to be sent at HF frequencies in a 1.25 kHz wide signal. The same software can be used on the receiving end to decode the signal into speech.

Receiving Hellschreiber with the RTL-SDR and an Upconverter

Over on YouTube user BSoD Badgers has uploaded a video showing reception of Hellschreiber on HF at 20m. To receive the HF frequencies he used a ham-it-up upconverter. He used SDR# to receive the signal and the Fldigi decoding software to decode the signal.

Hellschreiber is a fax-like communications mode used by amateur radio hobbyists.

Receiving BPSK63 with an RTL-SDR and Ham-It-Up Upconverter

Over on YouTube user Java’s Toys has uploaded a video showing a demo of his reception of a BPSK63 signal using his RTL-SDR and the Ham-it-up upconverter. BPSK63 is a text based digital communications mode used by ham radio enthusiasts to make contacts. It is twice as fast compared to the more commonly used BPSK31 mode.

Java’s toys used HDSDR together with Fldigi to receive and decode the signal.

SDR(X): New Upconverter for the RTL-SDR

A new UK designed and manufactured upconverter that goes by the name SDR(X) has recently become available for purchase. This upconverter connects to a RTL-SDR dongle and allows it to receive from 100 kHz up till 1850 MHz. Some of its features include:

  • Four user selectable HF pre-filters (0-2, 2-6, 6-11 and 11 to 30MHz) or single 0-30MHz pre-filter.
  • Band pass filter after mixer and band pass filter after Oscillator
  • User selectable MMIC 18db amplifier external to RTL chip set (lower noise level, than RTL chip and compensates for pre-filters).
  • User selectable HF and VHF/UHF mode (HF 0-30MHz, VHF/UHF mode 24MHz to 1850MHz).
  • Microchip PIC controller for above.
  • Diode protection on RF input.

The board comes as a prebuilt kit which is currently selling for 79.95 GBP which includes an RTL-SDR dongle. The device also comes with complete documentation. The SDR(X) can be purchased from 6v6.co.uk.

Image of the SDR(X)
Image of the SDR(X)