Category Archives: Aero

Visualizing HF Networks

G-VIFT

A flight of G-VFIT from Atlanta to Heathrow, and its HFDL communications – visualized by GEPHI.

Gephi does it

Each communications has a structure. Visualization reveals this structure. This is also valid for HF communications with its networks with different stations, (even moving) locations, hierarchy …

Recently, I made my first steps with free visualization software GEPHI to get a deeper look into some aeronautical networks. The graph at the top shows the gephi’ed result of 125+ HFDL messages, transmitted by a flight of G-VFIT from Atlanta to Heathrow. I monitored six HFDL channels in parallel, one channel from New York, two from Shannon, and three from Reykjavik.

Each point represents a message, tagged by its time in UTC. The positions of the points are geo-referenced, as I used HFDL messages containing these information.

Wheras the longitude’s positions are to scale, their latitude’s positions had been spread for better reading.

This visualization shows that Reykjavik on 6.712 kHz did the main work. But it is surprising that the first contact just leaving the U.S. coast was made with Shannon, and not with nearby New York.

GEPHI also helps in visualizing the hiearchy of networks, see screenshot below:


In the Russian Aero Net on 4.712 kHz, Rostov plays a pivotal role.

Here the strength of the connecting lines and the position of the city’s names represents to hierarchy of this network, i.e. who is calling whom, and how often. There are several strongholds like Rostov, Yekaterinburg and Samara, but also some mere outposts like Novosibirsk and Syktyvkar.

This picture isn’t geo-, but social-referenced, to say so: you know that e.g. Chelyabinsk on the left is geographically situated east of Rostov. You may also geo-reference these data, turn it into a kml file and see it in Google Maps of Open Street Map. If the co-ordinates are correct, zooming will take you exactly to the feeding point of each of their Nadenenko dipole, see below …

The above visualized hierarchy has been changed here into a geo-referenced kml file, opened in Google Earth.

There are many more applications of such a great tool for visualization which will further enrich monitoring.

INMARSAT: Decoding 12 Aero-channels in parallel

Jaero12

Action: Free software allows for decoding twelve INMARSAT in parallel

A recent post in Carl’s rtl-sdr-blog informed about the ebay-lability of some surplus Outernet patch antennas for just – see here. For just 29 US-$, I got this small antenna with integrated SAW filter (1525 – 1559 MHz) plus LNA. A real bait for me to jump over the limit of 30 MHz reception! Soon I fired up my AirSpy R2 receiver, providing the LNA with power supply (Bias-Tee). It worked fine, and I received a whole bunch of excellent signals by this setup.

As I wanted to receive some aircraft information, so I downloaded free JAERO decoder of Jonathan “Jonti” Olds, also from New Zealand. This fine software can be opened in many instances. In combination with the up to 24 decoders of SDR-Console V3 of Simon Brown, this modest setup turned into a multi-channel satellite reception post.

AeroGUI

Here 12 decoders had been assigned – one on each INMARSAT channel. You see also quite good SNRs from the Outernet patch antenna.

Next steps worked as usual with the mutli-channel approach:

  • make up 12 channels in SDR-Console and tune each channel to a different signal. Mode must be USB, and as bandwidth I choose 1200 Hz for 600 bps and 2400 Hz for 1200 bps channels. That’s a bit wider than necessary, but doing so there is some room for the AFC in JAERO decoder always to stick to the signal even if the SDR should drift a bit over 24 h or so
  • The output of each channel is then routed to a different Virtual Audio Cable, or VAC 1-12.
  • Then you have to install twelve instances of JAERO software in different folders, e.g. JAERO 1-12. You should name each JAERO.exe file accordingly, e.g. JAERO_1.exe to JAERO12.exe.
  • Open JAERO_1.exe, assign its input to VAC 1, and set the matching speed of the signal. If all is ok, you will be rewarded by a sharp phase constellation, and soon decoding will start.
  • Repeat the above steps until you have reached JAERO_12.exe, connected to VAC 12.

12Matrix

The “Matrix” of SDR-Console V3 shows the twelve channels with different signal strengths and width, depending on the data rate (600bps/narrow, 1200bps/wide).

The result can bee seen from the screenshot at the top of this page. The whole setup ran stable and unattended for hours.

Thanks for all smart people having developed the smart software and hardware!

PC-HFDL Display: Receive, decode and analyze the biggest net on HF!

HFDL is a net for data communications between airplanes and ground. The results can be shown on Google Earth . This screenshot shows a part of 29.000+ entries, received and processed on August 15th, 2016.

HFDL is a net for data communications between airplanes and ground. The results can be shown on Google Earth. This screenshot shows a part of 29.000+ entries, received and processed on August 15th, 2016.

 

Communications between air and ground is mostly done on VHF, UHF and SHF. But if an aircraft is out of reach of a ground station station due to the limited “radio horizon” of these bands, it has to maintain communications by either satellite or HF. This HFDL net is in fact the most massive professional user of HF right now. Within 24 hours, I get more than 40.000 live messages with a modest equipment.

With his software Display Launcher, Mike Simpson from Australia provides a most valuable tool to analyze up to nine channels in parallel. His software also draws positions and routes onto Google Earth. Mike has spent much energy on coping with many inconsistencies of transmitted data before it all really goes smoothly.

This free software is the vital part of a monitoring project to receive, demodulate and analyze live up to nine HFDL channels in parallel. Other ingredients you need is a software-defined radio (SDR), nine virtual audio cables (in fact, a piece of software) and a decoder software. Don’t forget an antenna and a PC …

This setup comprises a semi-professional monitoring station which will allow you to receive and track many of the nearly 3.000 airplanes using HFDL. This also covers the military, business jets, helicopters and some other delicate users. It maybe used as an important complement to Flightradar24’s web service, whenever their VHF/UHF/SHF-based net is out of range of the aircraft. This is particularly true over vast water masses like oceans and sparsely populated land masses. Furthermore, Flightradar24 erases some sensible flights from the raw material before publication on their website. This is clearly no “censorship”, but some thoughtfulness in regard to those countries where reception and publication of HFDL data is more tolerated than explicitly encouraged by the government.

In a 9-page PDF, I published a step-by-step recipe on how to set up such an HF monitoring station for up to nine parallel HFDL channel. You can download it here.

Audio Log and Google Maps

This is just a first test: I wanted to embed audio logs of some Utility Stations on a Google Map. This is possible only with MP4 files (video) as a link to You Tube. Several kinds of videos are tried: some with HF spectrum and sonogram giving additional information about the signal quality, some with a more static background to optimize file size.

There had been some difficulties to place the spots precisely. It worked fine for e.g. Deutsche Luftwaffe DHM91 (German Air Force) where you see the antennas at satellite view. But it failed a bit for e.g. US Air Force Diego Garcia, where the mark splashed right into the Indian Ocean …

Have fun in clicking to these 15 SSB stations! They should encourage you also to tune into these bands! They had all been received in Northern Germany with ELAD’s FDM-S2 and a quadloop of 20 m circumference.

Critics, suggestions and alternatives to this approach wanted.

Wake up – ICAO Selcals

If you ever had an ear on the aero bands, you are already familiar with ICAO Selcalls. With this 2 x 2 tone signal lasting for about 2,2 seconds, a Ground Station alerts a specific airplane to open up for communications. The short video on top of this page shows a typical initial contact, where Ground an Air are testing the Selcal.

This paper (click this hyperlink) describes on three pages with nine illustrations, one video and one audio the procedure and gives some background information. These may improve correct decoding of the somewhat delicate signals, as it will show how to look up the Selcal and follow the flight. BTW: It is planned to extend the pool of 16 tones to 32 tones by September 1st, 2016.

P.S. Remember to save the PDF and open it with a recent version of Acrobat Reader. Otherwise the multimedia (video, audio) will not work!

Monitoring, State-of-the-Art: In a Nutshell

As I was asked for a look onto my monitoring workbench, I decided to write it down. It’s not to show “the real stone”, but an invitation for discussing efficient workflows which State-of-the-Art technology has to offer.

This PDF of 13 pages contains 25 hopefully instructive illustrations to comprehend my approach to monitoring; or, in this case: Utility DXing. Part of this PDF is also a 2:50 video, showing how to stroll between aero channels and to decode ALE. This video is also placed on top of this page.

The paper explains in detail the advantages of leafing through recorded HF files using the technology of the “living sonogram”. It also discusses some efficient strategies of voice and data reception, eventually touching even documentation.

To make use of the video content, download it on your hard disk, save it and open it by the most recent version of your PDF reader. It works on a PC as well as on a Mac. You can download it here.

Utility DX: Some (actually: 1.000+) Logs, June, 2016

Part of the EXCEL list

Part of the EXCEL list

“HF for the pros is stone-dead, isn’t it?” This rather verdict than question is often heard even by hams. If you are telling them how busy the bands really are (as they cannot read about that in their magazines), they are doubting: “But you need professional equipment plus decoding software, worth my Mercedes Benz?”, they are upset by the answer: “Absolutely bullshit. A software-defined radio at 500 US-$ plus some free software will produce thousands of logs!”

Still don’t believe that? Well, here is the first thousand, caught just in the first half of June, 2016. Received with an FDM-S2 receiver at a quadloop of 20 m of circumference. I mostly concentrated on fixed (rather than: mobile) stations and of modes which can be decoded with free software – if they are not even outright SSB or CW.

You can download this log: Logs_EXCEL from where it may easily be opened not only by EXCEL, but also e.g. free LibreOffice.
If I find time, even more logs from the same HF recordings will be added.

I am greatly indebted to the busy and resourceful friends of UDXF for their work, thanks.

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