Category: Applications

Updates to the Power Line Noise Detector “Driveby” System

A few days ago we posted about Tim Havens “driveby” project, which is a RTL-SDR based system he developed to help create heatmaps of power line noise in his neighborhood. Upon doing further research, Tim discovered that the main source of power line interference was appearing at a frequency of 44.252 MHz. Then by using his driveby system to create a heatmap of his area at this frequency and also by using a hand held radio he was able to pinpoint a massive source of power line noise.

The noise appears to be coming from a faulty and unsafe power pole near a local school. He writes that the power poles primary ground line has been severed and that a wire from the AC line is simply dangling in the air, ready to be grabbed by school children.

Heatmap showing sources of powerline interference
Heatmap showing sources of powerline interference
The faulty power pole
The faulty power pole with dangling AC line
Severed grounding line
Severed grounding line

Measuring Frequency Deviation of an FM Transmitter with an RTL-SDR

Over on YouTube user KP4MD has uploaded a video showing how she uses an RTL-SDR together with SDR#, a program called Visual Analyzer and an AEA PK-232 Terminal Node Controller to measure the frequency deviation of a Yaesu FT-8800R Transceiver. She writes:

The SDR# receiver is tuned to 145.050 MHz and the bandwidth set to 20 kHz.

The deviation level of the 1200 Hz tone is increased until a null appeared on the carrier frequency.

This is called a Bessel Zero and occurs at various predicted modulation indices (2.4, 5.52, 8.66, etc).

The Modulation Index is defined as the peak frequency deviation divided by the modulation frequency.

This Bessel Zero occurred at a modulation index of 2.4 corresponding to a frequency deviation of ±2.88 kHz (2.4 x 1.2 kHz).

The oscilloscope indicates that a peak to peak amplitude of 54.3% corresponds to ±2.88 kHz deviation.

The 1200 Hz tone modulation is increased to yield a peak to peak amplitude of 66%.

This corresponds to the desired ±3.5 kHz frequency deviation.

Frequency Deviation Measurement with an RTL-SDR Dongle

New Oregon Scientific Temperature/Humidity Data Receiver Software for MacOS and RTL-SDR

Recently programmer Erik Larsen wrote in to us to let us know about a MacOS application he has been developing to receive temperature and humidity data from Oregon Scientific v2.1 sensors. Oregon Scientific manufactures popular electronic weather stations that transmit data from remote sensors wirelessly. Using an RTL-SDR and Eriks software it is possible to receive the weather station data on a Mac computer and display the data on a GUI. The software can be downloaded from the releases section on its GitHub page.

Note that there are also several Linux based Oregon Scientific decoders available including rtl-433m-sensor, rtl_osv21, and rtl-wx.

Oregon Weather Decoder
Oregon Weather Decoder

Receiving VOR Radio Navigation with an RTL-SDR and GNU Radio

Over on YouTube user hpux735 has uploaded a video where he explores the feasibility of receiving VOR radio navigation signals using GNU Radio and an RTL-SDR. VOR is an acronym for VHF Omni Directional Radio Range and is an older method of navigation used by aircraft which is quickly being made redundant due to GPS navigation. VOR uses two signals, one master omnidirectional signal and one rotating directional signal. By doing some calculations on the received phase of these two signals it is possible to determine the angle of the aircraft from the transmitter.

In the video hpux735 explains and discusses the VOR signal and also shows how to use these signals for navigation with an RTL-SDR and GNU Radio flowchart. To receive the VOR signal he uses an RTL-SDR to record the VOR signal while he drives around with a car. Then later he uses his GNU Radio program to generate a plot that shows when he is moving and in which direction.

hpux735 has also uploaded some supplemental material over on his blog. In the future he hopes to correlate his VOR results with GPS coordinates that he will take whilst actually flying around.

VORs and SDRs part 1: Playing with angles

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

Beaglebone Black FM/Internet Radio Combo Receiver using an RTL-SDR

Last year we missed this interesting project by Frederick Vandenbosch where he created a FM/internet radio combination receiver using a BeagleBone Black mini embedded PC and an RTL-SDR dongle.

The idea is that the system will receive FM radio through the RTL-SDR normally, but when reception is poor or unavailable you can switch to internet radio which is received through WiFi. The radio is controlled through an LCD screen attached to the BeagleBone Black.

Frederick used Linux on the BeagleBone and created a custom GUI that allows for easy tuning using rtl_fm as the RTL-SDR back end, setting channel presets and for switching between internet and live FM radio.

BeagleBone Blade FM/Internet Radio Combo Receiver
BeagleBone Blade FM/Internet Radio Combo Receiver
Beaglebone Black Digital Radio with RTL-SDR and Wifi

Monitoring a Trunked P25 LSM Simulcast System with OP25 and an RTL SDR

Over on YouTube user jdlucas78 has uploaded a video showing a P25 LSM modulated digital voice signal being decoded by the Osmocom OP25 software for Linux. Although DSD and DSD+ can decode P25 voice, it seems that the Osmocom OP25 software is better at decoding P25 signals as it implements better error correction algorithms.

Over on the RadioReference forums there is a thread discussing the use of the OP25 decoding software which can be found here. There is a post in the thread that shows an easy Linux install procedure for the OP25 software.

Monitoring a Trunked P25 LSM Simulcast System w/ OP25 and RTL SDR Dongle

Take 2: Monitoring a Trunked P25 LSM Simulcast System w/ OP25 and RTL SDR Dongle

New SDR# Plugin: PAL / SECAM TV

The SDR# plugins programmer over at rtl-sdr.ru has recently released a new plugin which allows the decoding of PAL / SECAM TV images from within SDR# (note link in Russian, use Google translate or see the download link at the bottom of the page). The author also writes that if you are using a newer software defined radio like an Airspy, you can also receive the audio channel using the SDR# multiple VFO plugin.

We note that there is also the TVSharp software by the same author which is a standalone program that can decode PAL and NTSC.

PAL / SECAM TV SDR# Plugin
PAL / SECAM TV SDR# Plugin