Search results for: VOR

Testing VOR Navigation in the Stratosphere with an SDRplay RSP1 and High Altitude Balloon

Over on the SDRplay blog Jon has posted about the STRATONAV experiment which makes use of the SDRplay RSP1 software defined radio. The STRATONAV experiment uses high altitude balloons to carry the RSP1 as well and a commercial portable receiver. The two receivers were configured to receive aircraft VOR navigation signals in order to test the effectiveness of VOR when used at extreme altitudes of up to 28 km. The VOR navigational data was then compared against GPS tracks, resulting in a measure of how well VOR worked at those altitudes. 

VOR (aka VHF Omnidirectional Range) is a navigational beacon that is transmitted between 108 MHz and 117.95 MHz from a site usually at an airport. In the past we have posted about VOR a few times as it can also be decoded with an RTL-SDR, or used for passive doppler aircraft radar. 

The results showed that VOR navigation does indeed continue to function at extreme altitudes, proving that it can be used as a back up navigation system for stratospheric platforms. They also note that VOR navigation could also be used as a primary navigation system on smaller stratospheric platforms due to its low cost and low complexity to implement.

The full academic paper is available on sciencedirect, or for free via Sci-Hub.

SDRplay RSP1 (seen bottom right behind the metal mount) Flying on a High Altitude Balloon

Passive Doppler Aircraft Scatter with a VOR Beacon and an RTL-SDR

Over on YouTube Meine Videokasetten has posted a video showing how he's been using an RTL-SDR to detect aircraft landing and taking off via the scatter on a VOR beacon. VOR (aka VHF Omnidirectional Range) is a navigational beacon that is transmitted between 108 MHz and 117.95 MHz from a site usually at an airport. Although as it is an older technology it is slowly being phased out in some places. 

An interesting observation can be made that is unrelated to the actual operation and use of VOR navigation. When an aircraft passes near the VOR beacon it results in the signal reflecting and scattering off the metal aircraft body. As the aircraft is moving quickly, it also results in a frequency doppler shift that can be seen on an RF waterfall display.

In his video Meine Videokasetten uses an RTL-SDR and OpenWebRX to receive the VOR signal. He then pipes the audio output of that signal into Speclab which allows him to get significantly increased FFT resolution for the waterfall. This increased resolution allows him to clearly see the doppler scattering effects of aircraft on the VOR transmission. He notes that it's possible from the scattering to determine if an aircraft is taking off or landing.

Passive doppler radar on VOR beacon transmitter .:°:. A let's test it out

We note that back in 2015 we posted about the ability to "fingerprint" aircraft using this technique. Different types of aircraft will result in unique patterns on the waterfall. In that post they used analogue TV carriers which are not very common in most countries anymore, so it's good to see that this can be used with VOR signals too.

Comparing large and small aircraft with aircraft scatter
Comparing large and small aircraft with aircraft scatter with an analogue TV transmitter. From previous post.

A new VOR Decoder Written in Python

Thank you to Martin Bernardi for writing in and sharing with us his new VOR decoder that is written in Python. The program decodes VOR from a wav file, so any SDR such as an RTL-SDR can be used to record the audio initially.

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# with a software defined radio such as an RTL-SDR.

Martin notes that there are already several VOR decoders available, including vortrack written in C, and several GNU Radio based decoders [1][2]. However, Martins is the first in Python, which is a fairly easy to understand language and this should make learning from the code easier.

The GitHub readme for the project is a good read too, as it explains exactly how the VOR decoder works, and shows some results that they were able to obtain. In their testing they were able to obtain measurements at three locations with an accuracy of +/-3°.

The VOR Spectrum
The VOR Spectrum

SignalsEverywhere Podcast EP1: Es’hail-2, Favorite RTL-SDR Blog Posts and What SDR Should I Get?

Corrosive from the SignalsEverywhere YouTube channel is starting up a radio/SDR related podcast, and today has released episode one. The podcast is 22 minutes long, and in that time he discusses Es-hail-2, a geosynchronous satellite with an amateur radio transponder that was recently launched and activated, some of his favorite recent posts from our blog here at RTL-SDR.com, including posts about a 3D printed V-Dipole holder, Radwave RF Analyzer, cloning 433 MHz devices, and finally he ends the podcast by discussing the question of what SDR is right for you.

Podcasts are a great way to catch up on what's happening in the SDR and radio world so check it out below or over on the SignalsEverywhere podcast post.

An Open Source VOR Receiver for Airspy and RTL-SDR

Thank you to Thierry Leconte (TLeconte) for writing in and submitting his new command line based open source software called vortrack. Vortrack is a simple VOR decoder which calculates the angle towards the VOR. It is compatible with both RTL-SDR and Airspy radios, and runs on Linux.

In the past we've seen several other posts about RTL-SDRs being used to decode VOR signals, but Thierry's implementation appears to be the easiest way to get a bearing straight away. You'll get the most use out of the software if you install it on a portable device like a Raspberry Pi and take it out for a drive as you'll be able to see the VOR angle changing then.

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#.

A DVOR Ground Station at an Airport. Source Wikipedia.
A DVOR Ground Station at an Airport. Source Wikipedia.

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.

Decoding and Plotting VOR Signals with an RTL-SDR: Part 4

Previously we posted about Will’s (aka hpux735) project [1] [2] where he has been using an RTL-SDR dongle to help understand and decode aircraft navigation VOR signals. VOR is an acronym for VHF Omni Directional Radio Range and is an older method of navigation used by aircraft which is used to provide a heading towards a VOR transmitter.

In his latest video, Will has been able to finish his code which allows him to actually plot some VOR data that he obtained from a flight on a map. In the video the VOR data is used to draw a heading line between three recorded VOR transmitters and the aircraft. The video clearly shows the accuracy of the VOR signals (about 1 degree) and shows what happens to the heading accuracy when reception is bad.

VORs and SDRs Part 4: Fusion!