Category: RTL-SDR

Using an RTL-SDR to decode VOR Aircraft Navigation Beacons in Real Time

VOR stands for VHF Omnidirectional Range and is a way to help aircraft navigate by using fixed ground based beacons. The beacons are specially designed in such a way that the aircraft can use the beacon to determine a bearing towards the VOR transmitter. VOR beacons are found between 108 MHz and 117.95 MHz, and it's possible to view the raw signal in SDR#.

Over on RadioJitter author Arnav Mukhopadhyay has uploaded a post describing how to decode VOR into a bearing in real time using an RTL-SDR dongle. His post first explains how VOR works, and then goes on to show an experimental set up that he's created using a GNU Radio program.  With the software he was able to decode an accurate bearing towards the VOR transmitter at a nearby airport.

Arnavs post is a preview of an academic paper that he's worked on, and the full paper and code is available by request on the radiojitter post. We've also seen on YouTube that Arnav has uploaded a video showing the software working in action, and we have embedded it below.

Bearing to nearby airport VOR transmitter determined with an RTL-SDR and GNU Radio.
Bearing to nearby airport VOR transmitter determined with an RTL-SDR and GNU Radio.

Real Time Demo of VOR Bearing

Reverse Engineering Wireless Blinds with an RTL-SDR and Controlling them with Amazon Alexa

Amazon Alexa is a smart speaker that can be programmed to control home automation devices via voice commands. For example, Stuart Hinson wanted to be able to control his wirelessly controlled blinds simply by verbally asking Alexa to close or open them. Stuart's blinds could already be controlled via a 433 MHz remote control, so he decided to replicate the control signals on an ESP8266 with 433 MHz transmitter, and interface that with Alexa. The ESP8266 is a cheap and small WiFi capable microchip which many people are using to create IoT devices.

Fortunately replicating the signal was quite easily as all he had to do was record the signal from the remote control with his RTL-SDR, and use the Universal Radio Hacker software to determine the binary bit string and modulation details. Once he had these details, he was able to program the ESP8266 to replicate the signal and transmit it via the 433 MHz transmitter. The remaining steps were all related to setting up an HTTP interface that Alexa could interface with.

If you're interested, we've also previously posted about another Alexa + RTL-SDR mashup which allows Alexa to read out ADS-B information about aircraft flying in your vicinity.

[First seen on Hackaday]

The ESP8266 with 433 MHz Transmitter
The ESP8266 with 433 MHz Transmitter

More KerberosSDR Passive Radar Demos

KerberosSDR is our upcoming low cost 4-tuner coherent RTL-SDR. With four antenna inputs it can be used as a standard array of four individual RTL-SDRs, or in coherent applications such as direction finding, passive radar and beam forming. More information can be found on the KerberosSDR main postPlease remember to sign up to our KerberosSDR mailing list on the main post or at the end of this post, as subscribers will receive a discount coupon valid for the first 100 pre-order sales. The list also helps us determine interest levels and how many units to produce.

In this post we're showing some more passive radar demos. The first video is a time lapse of aircraft coming in to land at a nearby airport. The setup consists of two DVB-T Yagi antennas, with KerberosSDR tuned to a DVB-T signal at 584 MHz. The reference antenna points towards a TV tower to the west, and the surveillance antenna points south. Two highlighted lines indicate roughly where reflections can be seen from within the beam width (not taking into account blockages from mountains, trees etc).

The second video shows a short time lapse of a circling helicopter captured by the passive radar. The helicopter did not show up on ADS-B. On the left are reflections from cars and in the middle you can see the helicopter's reflection moving around.

We are expecting to receive the final prototype of KerberosSDR within the next few weeks. If all is well we may begin taking pre-orders shortly after confirming the prototype.

KerberosSDR Passive Radar Timelapse 2

KerberosSDR Passive Radar Helicopter Detection

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Spektrum SV Mod: RTL-SDR Spectrum Analyzer Software Now with Improved UI

Spektrum is a popular spectrum analyzer program that is used with RTL-SDR dongles. It is based on the command line rtl_power software and is compatible with both Windows and Linux. Thanks to it's easy to use GUI it is an excellent piece of software for scanning and determining where active signals exist, or for measuring filters and antenna SWR with a noise source.

Recently SV8ARJ (George) and SV1SGK (Nick) have been working on extending the original open source Spektrum code. Their improvements focus around the UI and making it more functional and easier to use. Currently the updated branch is in alpha, and they are hoping that any testers could help report bugs, issues and wishes to them. The code is available on their GitHub and the latest Windows test build can be downloaded from their DropBox.

The changelog reads:

  • 2 Cursors for Frequency axis.
  • 2 Cursors for Amplitude axis.
  • Absolute and differential measurements with cursors.
  • Zoom functionality of the cursors's defined area (gain + frequency).
  • Mouse Wheel Gain adjustment on graph (Top area for upper, low area for lower).
  • Mouse Wheel Frequency adjustment on graph (left area for lower frequency, right for upper).
  • Mouse Wheel in the centrer of the graph performs symetric zoom in/out.
  • View/settings store/recall (elementary "back" operation, nice for quick zoomed in graph inspection).
  • Right click positions primary cursors.
  • Right Double Click positions primary cursors and moves secondary out of the way.
  • Left Double Click zooms area defined by cursors (Amplitude + frequency).
  • Left Mouse Click and Drag on a cursor moves the cursor.
  • Middle (mouse wheel) Double Click resets full scale for Amplitude and Frequency.
  • Middle (mouse wheel) Click and Drag, moves the graph recalculating limits accordingly.
  • Reset buttons to Min/Max range next to Start and Stop frequency text boxes.
  • Cursor on/off checkbox now operate on all 4 cursors.
  • ZOOM and BACK buttons.
  • Filled-in graph option (line or area).
  • Display of frequency, Amplitude and differences for all cursors.
  • Modified: Button layout.
  • Fixed: Save/Reload settings on exit/start. IMPORTANT : delete the "data" folder from the installation location if you have it.
  • Filling in graph option (line or area).
Spektrum UI Updates
Spektrum UI Updates

GammaRF: Distributed Radio Signal Collection and Analysis with RTL-SDR and HackRF

Thank you to Josh for submitting news about his project called GammaRF. GammaRF is an client-server program that is used to aggregate signal information via the internet from distributed SDRs. Currently the RTL-SDR and HackRF SDRs are supported.

ΓRF (“GammaRF”, or “GRF”) is a radio signal collection, storage, and analysis system based on inexpensive distributed nodes and a central server. Put another way, it is a distributed system for aggregating information about signals, and a back-end infrastructure for processing this collected information into coherent “products”.

Nodes utilize inexpensive hardware such as RTL-SDR and HackRF radios, and computers as small and inexpensive as Intel NUCs. Each node runs modules which provide various radio monitoring functionality, such as monitoring frequencies for “hits”, watching power levels, keeping track of aircraft (through ADS-B), and more. Nodes are distributed geographically and their data is combined on the server for hybrid analysis.

A web-based system allows users to view information from and about each station in its area. Below shows the server landing page. Markers are placed at each station’s last known location (stations can be mobile or stationary.)

GammaRF Server Landing Page
GammaRF Server Landing Page

From the currently implemented modules it appears that you can monitor ADS-B, scan and monitor the power of a set of frequencies, forward the output from trunk-recorder (a P25 call recorder), scan the spectrum and monitor power levels, monitor a single frequency for activity, take a picture of a swath of RF spectrum, and collect 433 MHz ISM data. Some example applications might include:

  • Monitoring ham radio activity on repeaters in a city
  • Creating timelines of emergency services activity in an area
  • Distributed tracking of satellites and other mobile emitters
  • Monitoring power at a frequency, for example as a mobile node traverses an area (e.g. signal source location)
  • Building direction finding networks (e.g. for fox hunts)
  • Spectrum enumeration (finding channels and guessing modulation) [under development]
Monitoring Activity of an Amateur Radio Repeater
Monitoring Activity of an Amateur Radio Repeater via the 'scanner' Module

Listening to the Sound of Molecules via Nuclear Magnetic Resonance and an RTL-SDR

Over on YouTube user aonomus has uploaded a video showing how he's used an RTL-SDR to observe and listen to the radio signal generated via a chemistry lab's nuclear magnetic resonance machine. To do this he simply taps the RF output of the NMR machine which allows the RTL-SDR to listen to the signal and play it as audio. In the video he shows the sound of a sample of chloroform in acetone-d6. The demo has no real scientific purpose other than to hear the sound of the molecule. Normally the RF output goes straight into a spectrum analyzer for visual analysis.

Nuclear magnetic resonance is a technique used in chemistry for the analysis of chemicals, as well as in MRI medical imaging machines. Very basically, it works by applying a chemical sample to a strong magnetic field, exciting it with a strong pulse of RF, and listening to the echo. An echo will only occur when the radio waves are transmitted at the chemicals resonant frequency. The frequencies used are typically between 60 to 800 MHz.

A few years ago I came up with a demonstration for some high school students interested in chemistry. This demo is a modern take on a classic NMR experiment, using a low cost software defined radio to observe the FID signal as audio. In short, this demo allows you to hear the proton FID echo from the liquid sample inside the NMR magnet.

Nuclear Magnetic Resonance Demonstration Using Software Defined Radio

A Step by Step Tutorial to Receiving GOES-16 Images with an RTL-SDR, Raspberry Pi and Goestools

Aleksey Smolenchuk (lxe) has recently uploaded a step-by-step guide to setting up a GOES weather satellite receiver with an RTL-SDR dongle, Raspberry Pi and the goestools software.  GOES 15/16/17 are geosynchronous weather satellites that beam high resolution weather  images and data. In particular they send beautiful 'full disk' images which show one side of the entire earth. Compared to the more familiar and easier to receive low earth orbit satellites such as NOAA APT and Meteor M2 LRPT, the geosynchronous GOES satellites require slightly more effort as you need to set up a dish antenna, use a special LNA, and install Linux software.

Aleksey's tutorial first shows where to purchase the required hardware and notes that the total cost of the system is around $185. Next he goes on to show the hardware connection order, and then how to install and configure the goestools decoding software onto a Raspberry Pi.

Aleksey's RTL-SDR Based GOES Receiver setup
Aleksey's RTL-SDR Based GOES Receiver setup

Russian RTL-SDR USB Filter Video Review

Over on YouTube, Alexander from the Russian channel РАДИОБЛОГ с Александром Никитенко has uploaded a video review of a Russian USB filter product, designed for USB SDR dongles. The video is narrated in Russian, however you can use the YouTube auto-translate feature to get somewhat understandable subtitles. The actions he takes in the video are also easy to understand.

The USB filter is designed by Maxim who runs a small company called ExpElectroLab. Back in August we posted about another ExpElectroLab product which was the SDR# tuning knob. Since then we've seen that a few people outside of Russia have been able to order the product by contacting him at [email protected], and have been happy with it.

When using USB SDR dongles, the USB cable can pick up lots of interference from the PC and monitors, providing a direct path for this interference to enter the RTL-SDR. A USB filter can be used to remove this interference. There are several USB filters on the market designed for improving USB audio devices, but this is the first one we've seen designed for SDRs in particular. 

In the video Alexander tests an RTL-SDR with and without the USB filter connected. With the USB filter not connected, the SDR# display shows several spikes of interference in the spectrum, and once the filter is connected these spikes disappear. He also tests it on a USB powered shortwave radio, and the filter appears to remove the hiss caused by the power supply.

Note: Non-Russians can order this product by contacting Maxim at [email protected]

Фильтр для SDR-приёмника и не только.