Tagged: VHF Omni Directional Radio Range

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

Showing what VOR and ILS Aviation Signals Look like in SDR#

Over on YouTube user RedWhiteandPew has uploaded two videos showing what VOR and ILS signals look like in SDR# with an RTL-SDR dongle. VOR and ILS are both radio signals used for navigation in aviation. 

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.

RedWhiteandPew writes:

Here I am picking up the VOR beacon from KSJC. The coolest part is at the end of the video. I believe the signal moving back and forth is caused by the Doppler effect, because VORs transmit their signals in a circular pattern. The VOR wiki article has a GIF that shows how it works here https://en.wikipedia.org/wiki/VHF_omn…. If you play and pause the video at different points before I zoom in, you can see that the two signals on the side are the opposite phase.

Listening to a VOR and Doppler Effect Demonstration || RTL-SDR Dongle

ILS stands for Instrument Landing System and is a radio system that enables aircraft to land on a runway safely even without visual contact. It works by using highly directional antennas to create four directional lobes (two in the horizontal plane, two in the vertical) that are used to try and ensure the aircraft is centered and leveled on the approach correctly. The ILS frequencies are at 108.1 – 111.95 MHz for the horizontal ‘localizer’, and at 329.15-335.0 MHz for the vertical ‘glide slope’.

RedWhiteandPew writes:

Here I have tuned into one of KSJC’s ILS frequencies. You are able to hear the faint identifier beeping transmitting its ISL ID code which is ISJC. For comparison, I used to morse code translator website.

The reason I am hearing ISJC and not ISLV even though they are on the same frequency is because the localizers transmitting the signal are directional along the length of the runway. Since I am located to the south east of the airport, and I am within its transmitting beam, I am able to listen to it on a scanner.

Listening to an ILS Localizer (RTL-SDR Dongle)

If you’re interested in these signals then this previous post about actually decoding them might be of interest to you.

Studying VOR Signals with the RTL-SDR

VHF Omni Directional Radio Range (VOR) signals are used in aviation as a short range radio navigational system. Amateur radio hobbyist F4GKR decided to study these VOR signals by recording them using his RTL-SDR, and then analyzing them in MATLAB. On his post he shows his method of analysis and discusses his results.

VOR Spectrum and Waterfall
VOR Spectrum and Waterfall