Category Archives: Aviation

Guest Post: Decoding Inmarsat L-Band AERO and STD-C messages using the SDRplay RSP SDR

Many thanks to SWLing Post contributor, Mike Ladd (KD2KOG), who shares the following guest post. Note that the following tutorial is also available as a PDF (click here to download).


Basics to decoding Inmarsat L-Band signals using the RSP SDR

by Mike Ladd

Note: CHECK WITH YOUR LOCAL LAWS BEFORE DECODIING ANY SIGNALS FROM THE INMARSAT SYSTEM

Hardware used

SDR: RSP1a SDR from SDRplay? https://www.sdrplay.com/rsp1a/

Antenna: Modified GPS patch antenna for L-Band from SDR-Kits, model A154.? https://www.sdr-kits.net/L-Band-Receive%20Antenna

Software used

SDRuno v1.32
https://www.sdrplay.com/downloads/

VBcable (Donationware) vPack43
https://www.vb-audio.com/Cable/

VAC (Paid for use) v4.60
https://vac.muzychenko.net/en/

JAERO (Free) v1.0.4.9
https://github.com/jontio/JAERO/releases

Tekmanoid STD-C Decoder (Paid for use) v1.5.1
Requires Java JRE, check your local laws before using this decoder.
http://www.tekmanoid.com/egc.shtml

https://www.java.com/en/download/

Introduction

(some text taken and edited from the RTL-SDR Blog website)

This document is not a definitive guide to Satcom, L-Band transmission or the Inmarsat system. This is a collection of information that I have found scatter throughout the internet and re-compiled into a document, this document. My aim is to help you get started and hopefully guide you in the right direction. Expect typographical mistakes, inaccuracies, or omissions

Inmarsat is a communications service provider with several geostationary satellites in orbit. Inmarsat provides services such as satellite phone communications, broadband internet, and short text and data messaging services. Geostationary means that the Inmarsat satellites are in a fixed position in the sky and do not move.

The Inmarsat 3-F(x) satellites have transponders transmitting data in L-Band (1.5 GHz) that can be decoded. 

The modes we will cover in this document are Aeronautical (Classic Aero or ACARS) and Inmarsat-C (STD-C) using an RSP1a, RSP2/2pro or RSPduo connected to the SDR-Kits modified L-Band patch antenna. The Inmarsat system is not limited to only these types of networks. We are limited to the decoders available.
https://en.wikipedia.org/wiki/Inmarsat

Some regions that use the I-3 satellite services moved and migrated to the Inmarsat I-4 Satellites.  See the following document.  https://www.inmarsat.com/wp-content/uploads/2018/09/INM_C_I3_I4_migration_guide_V3.0.pdf

Two of the most popular decoding applications are JAERO used for ACARS and Tekmanoid STD-C Decoder used for decoding STD-C NCS transmissions on the Inmarsat 3-F(x) satellites

https://www.sigidwiki.com/wiki/Inmarsat_Aero

https://www.sigidwiki.com/wiki/Inmarsat-C_TDM

Software installation

Virtual Audio Cable: A virtual audio cable allows you to pipe audio from application (SDRuno) into another application (a decoder like JAERO) digitally. I will assume SDRuno is already installed with your device attached and functioning properly. 

You can now download a virtual audio cable package.  If you already have a virtual audio cable package installed, you can skip to the next section. If you don’t have a virtual audio cable application installed, you only need to choose one and only install one of the two, either one works fine

Close any running apps, install the virtual audio cable and reboot your computer. When your computer boots back to your desktop, your computer will now have a virtual audio cable pair installed on the system. 

You can verify by going to your Control Panel and double clicking the Sound icon. VB-Cable and Virtual Audio Cable will only install a single virtual audio cable pair, one is for the input (Recording) and one is for the output (Playback). A single pair is all that is needed (as shown below).

JAERO

(some text taken and edited from the JAERO website)

JAERO is a program that decodes ACARS (Aircraft Communications Addressing and Reporting System) messages sent by satellites (in this case Inmarsat) to Airplanes (SatCom ACARS). This is commonly used when airplanes are well beyond VHF range. 

JAERO also allows for decoding and demodulation of voice calls, due to local laws and privacy, I will not show or discuss how to do this. You can find more information about that JAERO feature online.

JAERO can be downloaded from the link provided on the first page of this document. After downloading the installer, simply double click the setup file and install it on your primary drive.

Tekmanoid STD-C Decoder

(some text taken and edited from the USA-Satcoms website)

Inmarsat STD-C is a data or message-based system used mostly by maritime operators. An Inmarsat C terminal transmits and receives on L-Band to various geosynchronous satellites that service each major ocean region. 

The Tekmanoid STD-C decoder will decode STD-C Inmarsat EGC (enhanced group call) and LES (land earth station) messages. Some of these messages contain private information. Reception of these messages may not be legal in your country; therefore, your local laws should be checked.

The Enhanced Group Call (EGC) service is a message broadcast service with global coverage (except the poles) within the Inmarsat-C communications system. Two of the services provided are:

FleetNET and SafetyNET

FleetNET is used to send commercial messages to individuals or groups of subscribers (for example, individual companies communicating with their own Mobile Earth Stations (MES). SafetyNET is used for broadcasting Maritime Safety Information (MSI) such as Navigational warnings, meteorological warnings, meteorological forecasts and other safety related information (including Distress Alert Relays) from official sources.

The LES station acts as an interface (or gateway) between the Inmarsat space segment and the national/international telecommunications networks. 

The Tekmanoid STD-C decoder requires Java JRE in order to run. The link for the Java runtime environment is on page 2 of this document. For information contact the developer direct admin@tekmanoid.com

There are alternatives to using the Tekmanoid STD-C decoder, but in my opinion the other decoders available do not perform as well on low end systems or even work without needing “helper” applications to be installed. Tekmanoid STD-C decoder is very easy to use and works great on my low-end system using minimal system resources.

Putting all the pieces together

ACARS and STD-C messages will transmit via the Inmarsat satellite deployed within your coverage area/region, you will need to choose the Inmarsat satellite that is closest to your coverage area. 

Note that only different frequencies are used between ACARS transmissions and STD-C transmissions. You will only need to receive from one of the available 3-F(x) Inmarsat satellites. 

L-Band ACARS transmissions are in the 1.545 GHz range but STD-C messages are on fixed frequencies (shown on page 8)

Since STD-C transmissions are broadcasted on fixed frequencies, we want to monitor the TDM NCSC channel, again these are fixed for the following Ocean Regions. Choose the region closest to your location (page 9).

Again, some regions that use the I-3 satellite services moved and migrated to the Inmarsat I-4 Satellites.  See the following document.  https://www.inmarsat.com/wp-content/uploads/2018/09/INM_C_I3_I4_migration_guide_V3.0.pdf

STD-C transmissions are broadcasted on fixed frequencies, NCSC channel. The NCSC frequency per region is noted below.

Inmarsat satellite: Inmarsat-4 F3 (AOR-W)
Direction: 98° West
Frequency: 1.537.70 GHz

Inmarsat satellite: Inmarsat-3 F5 (AOR-E)
Direction: 54° West
Frequency: 1.541.45 GHz

Inmarsat satellite: Inmarsat-4 F1 (IOR)
Direction: 25° East
Frequency: 1.537.10 GHz

Inmarsat satellite: Inmarsat-4 F1 (POR)
Direction: 143.5° East
Frequency: 1.541.45 GHz

I will assume you have located the Inmarsat satellite that covers your region. I suggest using a compass on your mobile phone to pinpoint the general direction. The direction is in ° (degrees). I am referencing true north, not magnetitic north (traditional analog compass). https://en.wikipedia.org/wiki/Magnetic_declination

You can also download an app for your smartphone called Satellite AR (Android and IOS). After you locate the correct direction of the Inmarsat satellite, you will want to place the L-Band patch on a flat metal surface. I have read that the receive pattern of this patch antenna is z (about 85-90°, straight up). Point the top of the antenna facing the Inmarsat satellite. Using the roof of my car worked just fine, just remember to point the front of the antenna at the satellite.

https://www.u-blox.com/sites/default/files/products/documents/GPS-Antenna_AppNote_%28GPS-X-08014%29.pdf

Launch SDRuno and click the PLAY button, remember that if the RSP(x) is in ZERO IF mode, give frequency separation between the VFO (top frequency) and LO (bottom frequency). In LOW IF mode this is not needed. I suggest running a sample rate of 2 MHz, larger bandwidths are not needed. 

The SDR-Kits patch antenna requires that the RSP(x) Bias-T be enabled. The Bias-T option is enabled within the MAIN panel of SDRuno. See the SDRuno manual located here. https://www.sdrplay.com/docs/SDRplay_SDRuno_User_Manual.pdf view page 17.

With the Bias-T enabled. Set the RSP(x) RF GAIN to max. The RF GAIN slider is located on the MAIN panel. See the SDRuno manual located here. https://www.sdrplay.com/docs/SDRplay_SDRuno_User_Manual.pdf view page 17.

For more information about the RF GAIN settings of the RSP(x)
https://www.sdrplay.com/wp-content/uploads/2018/06/Gain_and_AGC_in_SDRuno.pdf

Select the Virtual audio cable as the output in SDRuno, this is selected via the RX Control panel. SETT. button and clicking on the OUT tab.

Have SDRuno’s Volume slider (RX Control) at about 35-40%

Upper sideband is recommended but I found the best mode to use for L-Band ACARS or L-Band STD-C decoding is DIGITAL with a filter width of 3k. 

Be sure to set a proper step size (right click the RX Control frequency readout). The step size is not important for STD-C transmissions because these signals are only on one frequency for the satellite in your region but L-Band ACARS signals will be on many frequencies. Setting the proper step size will avoid issues when you point and click on signals you want to decode using the JAERO decoder.

You will want to center the signal with a little breathing room within the AUX SP filter passband. The filter slopes are very sharp. Keep the signal centered and away from the extreme edges (red markers). 

Select your virtual audio cable within the decoder’s audio input preferences.

The Tekmanoid STD-C decoder sound properties are located under Settings in the toolbar menu.

JAERO’s sound settings is located under the Tools menu and Settings.

For STD-C decoding use the frequency from page 8 of this document, remember we only want to monitor the TDM NCSC channel in the Tekmanoid STD-C decoder.

For JAERO decoding, I suggest you start in the 1.545 GHz portion and observe the constellation in the JAERO decoder. 

The signal to noise ratio (SNR) needed for successful decoding in these decoders will need to be greater than 7dB. When working with a weak satellite signasls, try decimating the signal using SDRuno’s decimation feature. (MAIN panel, DEC).

Click here to view on YouTube.

Additional resources

Videos:

Click here to view on YouTube.

Click here to view on YouTube.

Click here to view on YouTube.

Click here to view on YouTube.

SDRuno:

L-band frequency bank
https://mega.nz/#!jRFRiSaA!CcmRRRpjToxPzyGV9bf7MkDkKnqCYZCwwjC5curWj6g

PDFs:

https://www.inmarsat.com/wp-content/uploads/2018/08/Aero_Service_External_Com_Kit_I3_to_I4_Transition_21AUG2018.pdf

http://seaworm.narod.ru/12/Inmarsat_Maritime_Handbook.pdf

Websites:

https://usa-satcom.com/

https://uhf-satcom.com/

I hope this document helps you get started decoding Inmarsat L-Band transmissions from the I3-F(x) satellites. I am sure I missed some key features, remember this is only a primer/basics to decoding these types of transmissions.

Warmest of 73,
Mike-KD2KOG


Many thanks for sharing your tutorial here on the SWLing Post, Mike! This looks like a fascinating activity that really requires little investment if one already owns an RSP or similar SDR. I’m certainly going to give L-Band a go!  Thank you again!


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David Warren: Radio enthusiast who invented the “Black Box” flight recorder

As a schoolboy, David was fascinated by electronics and learned to build his own radio sets (Source: BBC and the Warren Family Collection)

Many thanks to SWLing Post contributor, Paul W4/VP9KFPaul W4/VP9KF, who notes that David Warren, inventor of ‘Black Box’ recorders was a ham radio operator and radio enthusiast.

The following short biography comes from this memorial website:

David Warren (full name David Ronald de Mey Warren) was an Australian inventor. He is most famous for his invention of the Flight data recorder (invented in 1956), or more commonly known as the “black box”

The “Black Box” is a device that records in-flight conversations and data. Warren came up with the idea of recording the flight crew’s conversation on a device that could be protected to increase its chances of surviving the crash. Although it has the name “Black Box”, it is coated with heat-resistant bright orange paint for high visibility in a wreckage, and the Black Box is usually mounted in the aircraft’s tail section, where it is more likely to survive a severe crash.

David Warren was born on the 20th of March, 1925, on Groote Eylandt, an island off the coast of the Northern Territory. He was the first child of European descent born on the island. When he was at the age of four, he was sent to Tasmania and Sydney to spend most of the next 12 years in boarding schools (Launceston Grammar School in Tasmania and Trinity Grammar School in Sydney).

Australia’s first major air crash in 1934 claimed the life of David’s father.

Warren had received a crystal set from his father just before the disaster that started his interest in amateur radio and electronics. Almost 20 years later, when the age of commercial jet aircraft was just beginning, Warren worked as a chemist, specialising in aircraft fuels at the Aeronautical Research Laboratories.

Dr Warren was working as a scientist at Melbourne’s Aeronautical Research Laboratory, where he was helping to investigate the 1953 mystery crash of a Comet jetliner. New fuels being used in Jets in the early 50’s were more likely to become explosive at altitude than conventional aircraft fuels and this was identified as a possible cause of the Comet crash. While listening to the arguments over possible causes of the Crash, Warren realised that the solution could be at hand if someone on the plane had been carrying a device similar to the then newly released “Protona Minifon” portable recorder that he saw at a trade fair.

The device would be fire proof (using steel wire as the recording medium like the “Pocket Recorder”) and erase itself so that the last hours of the flight were always recorded. The device consisted of a single steel wire as the recording medium and provided four hours of recording and automatically switched itself on and off with the aircraft. It was during this period that Dr Warren incorporated the idea of recording instruments on a separate channel – his interest in electronics as a schoolboy was brilliantly applied to turn instrument readings into recordable dots and bleeps.

The recorder was well received in England (where the name “Black Box” was made up by a journalist at a briefing) and also in Canada where the idea was seen as a potential addition to beacons being developed there.

Warren continued to lead the project, developing the Flight Memory device to record more instruments with greater accuracy. This led to the first commercially produced flight recorder-the Red Egg.

A further disaster at Wintoon in 1967 saw Australia become the first country to make both flight data and cockpit voice mandatory on all jets.

While a student at the University of Sydney, David met Ruth Meadows, who became his wife and lifetime supporter. Together, they raised a family and shared an interest in science and education. When he retired, David and Ruth lived in Caulfield South, Victoria, in regular contact with their four children and seven grandchildren.

David died at the age of 85 in 2010, 19 July, Melbourne, Australia. After his death, He was buried in a casket bearing the label “Flight Recorder Inventor; Do Not Open”.

Then in June 2012, the ACT Government named a road, David Warren Road, in the suburb of Hume in recognition of Warren. On 25 March 2014, the Defence Science and Technology Organisation renamed their Canberra headquarters to the David Warren Building.

Thanks for sharing this, Paul!  Fascinating…

Note that the BBC recently published an amazing piece about Dr. Warren on the 9th anniversary of his passing–click here to read.

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Can you identify this Hallicrafters model onboard the Columbine III?

The Lockheed VC-121E “Columbine III” (Image Source: USAF Museum)

Many thanks to SWLing Post contributor, Robert Yowell, who writes:

I was visiting the US Air Force Museum [Friday] and walked through “Columbine III” which was the Lockheed Constellation used as Air Force One by President Eisenhower from 1954 until he left office. In the back of the cabin was a nice cozy area where this Hallicrafters receiver was installed – ostensibly for the passengers to listen to news or other events while in flight.

I am sure one of your readers will be able to identify which model it is.

Can you imagine flying in this gorgeous Lockheed VC-121E four prop aircraft and listening to HF radio from a built-in Hallicrafters set? Wow…

Thank you, Robert, for sharing these photos. The National Museum of the US Air Force is one of my favorite museums in the world. I bet I’ve visited it more than a dozen times over the past decade–always a treat and always something new to discover!

Post readers: Can you identify this Hallicrafters model?  Please comment!

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Thomas (N1SPY) explores the world of non-directional beacons (NDBs)

Many thanks to SWLing Post contributor, Ivan Cholakov (NO2CW), who shares the following:

Thomas, N1SPY did a follow up video [to this previous post] where he explained a few details about NDBs (Non Directional Beacons).

I knew they existed but had no idea about their historical significance.

Click here to view on YouTube.

Another excellent and informative video, Thomas! Thank you for sharing and keep up the good work!

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Boeing 787 Antennas

Many thanks to SWLing Post contributor, Sally, who writes:

Besides being a bit of a radio geek, I also love aviation and am working on my PPL (private pilot license). I recently discovered this image [above] of the Boeing 787 antenna compliment. It’s amazing to see how many antennas they fit on this heavy bird!

Thank you for sharing, Sally! I can assure you, you’re not the only aviation nut here on the SWLing Post. I’m guilty as well!

It is amazing to see just how many various antennas are install on modern commercial aircraft. Looking at this image, you would think it’s a flying antenna farm!

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Tommy (N1SPY) on monitoring airplane communications

Many thanks to SWLing Post contributor, Ivan (NO2CW), who writes:

If anyone is interested in monitoring aircraft communications across HF, VHF and UHF, Thomas, N1SPY put together a demo video of what you can hear and how:

Click here to view on YouTube.

Brilliant instructional video, Tommy! Like you, I love both radio and aviation so appreciate the effort you put behind this video.  Great primer!

Click here to check out other projects by N1SPY.

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Aeronautical RDS: Ivan’s impressive collection of in-flight FM stations

Many thanks to SWLing Post contributor, Ivan Cholakov (NO2CW), who writes:

Last week I took an Eton Satellit with me on a flight from Tampa, Florida to Washington DC. The radio is very light, portable and packed with features. I have used an SDR radio before for inlight FM reception where I recorded audio, but this time I decided to only count stations with an RDS lock. With so many signals battling RDS is tricky to catch as every 10 seconds or so one station comes on top of another. The flight was just short of 2 hours and I divided my logs into three 30 minute segments. Not suprisingly looking into the technicalities I noticed RDS is commonly received from stations 50 -100 kW of power and tall towers.

Interestingly signals seem to be stronger a lower altitudes. My theory is that FM broadcast antennas heavily favor gain on the horizontal plane parallel to the terrain and send as little signal as possible out into space. I overlaid my logs onto three maps and also a video:

Click here to view on YouTube.

Impressive Ivan! I’m taking a flight later this month and might even try this with the FM radio built into my Moto G6 smart phone which also includes RDS (although I doubt reception can match that of the Satellit.

This is fascinating, Ivan! Thank you for sharing.

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