Category Archives: Digital

WSPR & MH370: Facts against Fake News

How Aircraft Scatter generally works. This adaption from Gary S. Sales’ paper “OTH-B Radar System” (University of Masschusetts, Lowell/USA, 1992) should add to some other entries on my website. Double-click the picture to enlarge it.

Furthermore, there are people who claim against all facts and reason that they can prove aircraft movements with aircraft scattering of WSPR signals from their log data. Surprisingly or not, they find enthusiastic approval in the popular press, but also in technical-scientific organizations like many ham radio associations, first and foremost the notorious German DARC. Whether one deals with supporters of “conspiracy theories” at all (Nobel laureate Joe Taylor, K1JT, said having too little time for such obvious and non-scienctific nonsense), or whether one meets their convoluted theories with technical-scientific arguments, is quite controversial and a topic more of social psychology than one of physics.

Nevertheless, “Never Give a Sucker an Even Break” as the great comedian and juggler, W.C. Fields stated 1941. And that is why I would like to deal with some “arguments”, which would not be difficult because of the subject matter, but because of how these people “argue”. For the sake of clarity and brevity, let’s do this in the form of a question and answer game.

Do aircraft affect RF signals?
Certainly. HF signals are scattered on the electrically conductive metallic hull of aircraft.

How does Aircraft Scatter work at all?
The drawing at the top explains it: Radio waves from a transmitter reach the receiver directly on the one hand, and via aicraft scatter on the other. On the receiver side, both signals add up. Thanks to the Doppler effect, which the signal part scattered by the aircraft has, both signals can be separated from each other again with a method called FFT; see my website for a couple of examples. However, this is not possible with WSPR log data, here only the total signal is noted.

How big are these influences?
They mainly affect the signal strength and are around 35 to 50dB+ below the original signal. There are exceptions. Downward, there are far more cases than the exceedingly rare constellations where the scattered signal may be larger than the original signal. Above 30 MHz this occurs more often, below 30 MHz I have never observed it as there always was at least some backscatter of the original signal.
Signals or field strength can be measured and calculated. Generally speaking, a suitable form of the “Radar Equation” will do the calculation, see here. They largely match the values being measured by the method “separate original signal and scattered signal”.

Facts, please – how big … ?
Sorry, yes. Say, a booming signal by a broadcaster in the 19 meter band hits your antenna with a level of -40 dBm. Then a Boeing 747, flying over your house to touch down at your airport nearby (“in your backyard”, as they say) at a distance of 500m only, this will peak at -86dBm.
Not bad, and easily visible by FFT analysis.

How much does this scattered signal adds to the original signal?
Good, with this you steer to the central point, because WSPR measures only this total signal. You just have to add -40dBm and -86dBm and with this most favorable constellation you get a total signal of -39.999890911528446dBm.
Believe me: you cannot distinguish it from the level of the original signal, being -40dBm.

Oh, that’s disappointing … but they tell they can identfy aircraft not only 500m, but some/many 1000km away?
First, physiscs may be disappointing. Secondly, I took a most favourable case – booming broadcaster, short distance. The effective power of a stronger WSPR transmitter may reach 40dBm, compared to 100dBm+ of many broadcasters. The difference of 60dBm and more is whopping.

“Whopping” – what do you exactly mean by this?
Take the example of the broadcaster, reading -40dBm on my S-Meter. If the transmitter were an even above-average WSPR transmitter it reading of the S-Meter would be -100dBm. Still readable, and WSPR would give a decode.

So, it works?
Wait a moment, for introducing the scattered signal, also 60dB down. It will peak at -160dBm, and it reliably is eaten by noise which will start between -130 and -140dBm.
By this, the orginal signal of -100dBm will be enhanced and strengthed to -99.999995657057354dBm. Quite an achievement!

I understand, it cannot work. Does a greater distance improve things?!
By no means. A greater distance worsens things even exponentially.

OK, but what the hell are they measuring to come up with such far-reaching results?
They are measuring indeed fluctuations of the signal but without knowing the reason. And there are much more and of stronger influence to the received signal level than aircraft scatter. Prevailing is multi-path leading to near-normally distributed changes of the signal level of around ±8dB from second to second, and often more than 30dB within just a few seconds!

But – they mention “drift” … and “Doppler” means “drift”?!
Yes, but the “moon shapes” of a few signals surely have other reasons, much more obvious – just think of bad power supplies, meteor scatter (stronger and more often seen compared to aircraft scatter) and travelling waves within the ionosphere itself. Have you ever asked yourself, why in the presented cases the whole signal is shifted, instead of seeing a Doppler signal branching out from the original signal? „They don‘t know what they do“, says K1JT into their direction.

How much can I rely on the quality of WSPR signals?
Look yourself at the screenshot below, showing three hours of WSPR signals, showing drift, over-modulation, noisy signals. All fine for decoding WSPR but on only very few you consider those rocks where you want to build your church on (Mathew 16-18). You see instabilities at many scales, and also the duly repeating (!) half-moon footprints which for some ghostseers are the evidence of aircraft.

Drifting away: Three hours of WSPR signals on 20m. Their quality works for decoding WSPR, but it is difficult to use them as reference …

They work with the concept of “tripwire”. Any comment on this?
Well, they seem to consider propagation working by distinctive, laser-like “rays”, not fields of energy. (This is just a guess from this blog entry.) Each object crossing this ray causes a-normal propagation which they fail to precisely specify. This is a fundamental misconcept of how HF propagation works plus an incomprehensable application of PropLab Pro 3.1, the propagation software, which they seem not to understand. Propagation doesn’t produce “tripwires”. And if you need some parallel, you should more think of a booby trap, thanks to which not only signals are pulverized, but with them all the dream fantasies that this or that plane may have caused them to go off.
They must use “Broadcast Coverage Map” with PropLab Pro to get a realistic view of electromagnetic fields and their propagation, see secreenshot below.

No “tripwire”: HF propagation doesn’t work by laser-like rays, but by electromagnetic fields. This PropLab 3.1 Broadcasting Coverage Map screenshot gives a general impression of this – transmitter Tiganesti/Romania, simulated a sector of ±30° of the antenna’s direction. And you can try to get your own impression for free with e.g., VOACAP online.

Can I understand your assertions?
Absolutely! In theory, as well as in practice. You can find many examples on my website. A SDR and software are all you need. Oh, and, last but not least: and unbiased view not on the possibly desirable, but on the physically possible!

But why do they still spread their charlanteries with great success?
Look around you. The world is full of castles in the air. That’s actually not so bad. Here, however, they are built by those who could know better and they are spread with enthusiasm by those who know better. Or at least should know better.
But that is the usual pattern of Fake News. Only that it undermines the technical-scientific competence of the radio amateurs and makes them look ridiculous.

RTL-SDR Active Patch Antenna

Weather-proof: and this is only one of the benefits of this nice tool.

Since August 2021, the RTL-SDR Active Patch Antenna delights the community worldwide. It is small, yet highly efficient. With RTL-SDR Dongle and some software, it combines to a surprisingly high performance receiving post for INMARSAT, IRIDIUM (which I first used with a mobile phone 20 years ago on a tour through Mongolia and China with stunning quality), and GPS – all for just about 100 US-$.

Plug the USB stick into your PC, connect the patch antenna to the stick’s by a cable and set it on a flexible tripod (all contained in the set!), and the sky becomes open. In the screenshot below, I used the nuandRF to show at least half of the bandwidth of the antenna, because this SDR covers 60 MHz:

The 60MHz wide window of the nuand bladeRF SDR shows half of the bandwidth and sensitivity of the RTL-SDR Patch antenna. Caveat: With the bandwidth of the antenna being nearly 140MHz and the bandwidth of the SDR only ca. 60MHz, this screenshot still doesn’t show the complete performance of the antenna. The seemingly (sic!) reduced sensitivity at the lower and upper end of the signal/noise is due to the receiver, not the antenna!

Aero makes a good start with powerful signals and free software JAERO which can also run in multi instances to cover all the channels in parallel.

In the upper window you see the SDR GUI, namely free SDRC software. It shows some aero channels with their signal-to-noise radio, or SNR, achieved with the active patch antenna and the RTL-SDR dongle. The two windows at the bottom show the JAERO decoder in action on a 1200bps channel.

You may also set sails for some maritime experience with the std-C Decoder (full version: 55 US-$). It even visualizes e.g., buoys and areas (rectangle, circle and free format) a Open Street Map.

Top: a maritime satellite channel. Bottom: Safety Message for the marked area in the Gulf of Bengal, off the coast of Cuttack/India.

You may also receive the GPS C/A code signal on 1.575420GHz, and IRIDIUM on which John Bloom wrote the pageturner “Eccenctric Orbits – The Iridium Story“, which I can only highly recommend as a truly thrilling backgrounder. As low-orbiting satellites, the channel has to be handed over to another satellite after about nine minutes.

The RTL-SDR Active Patch Antenna is a great, little tool providing high SNRs at a small form factor of 17.5 x 17.5 cm. Its low noise amplifier (powered via bias tee from the SDR stick) together with the SAW filter to suppress any signals outside its passband from 1.525 to 1.660GHz shows unsurpassed performance at this price tag. It is a must, and absolutely a no-brainer. Did you miss a large suction cup to mount it on your window? Wait a minute – it is also included in the turnkey package …

WSPR & Propagation [MH370] – an Experiment

Completely unintentionally, my last blog on WSPR and MH370 had led to more of a social psychology experiment than a technical science discussion. I expressed my doubts whether it is possible to recognize aircraft scatter from the historical WSPR data by “unusual signal changes” without essential knowledge of further circumstances.
As a reminder: WSPR works with weak transmission power at modest antennas in a rhythm of 110.6 seconds. Apparently this average value is noted and made available as SNR at the receivers.

I objected that practically all other influences on the signal on its way from the transmitter to the receiver (“channel”, with refractions both at the dynamically in three dimension, plus density, changing ionosphere and at the ground) exceed those effects by far, as they are to be expected by airplane scatter. I proved this with 3 x 10’000 level data and 30+ Doppler tracks.

The main proponent of the theory, that the proof is possible against all those odds, reacted with a juicy complaint to the German amateur radio association DARC, in which he argued exclusively personally, but not technically-scientifically. A behavior even more bizarre than trying to prove his actual thesis. The DARC immediately jumped over the stick held out to it, and published few hours later – apparently without or against better knowledge – a sweetish-mendacious “press release“, in which a so far not by technical-scientific papers noticed employee praised that as only beatifying truth.

[Auf Wunsch einiger deutschsprachiger Leser erfolgt in einem weiteren Blog eine Erläuterung dazu.]

WSPR vs. high-resolution data

For all those, however, who are interested in technical contexts, this blog answers a still open question from my last blog:

  • What is the smoothing/generalizing influence of the evaluation of mean values over 110 seconds – which is how the WSPR logbook is supposed to work – on the mapping of the actual signal changes?

Let’s simply test it
For this purpose I have analyzed on September 22nd, 2021 with the professional SDR Winradio Sigma between 07:00 and 12:00 UTC the broadcasting station CRI Kashi, which transmits continuously on 17’490 kHz with 500 kW towards Europe – 5’079 km, two hops. My antenna is a professional active vertical dipole antenna with 2 x 5 m long legs, namely MD-300DX.

With the software SDRC 17’930 level values were noted in dBm/Hz, every second. The FFT analysis was performed with a high-sensitivity resolution of 0.0122 Hz, resulting in a process gain of 53.1 dB compared to the data from WSPR, measured in a 2’500 Hz wide channel. Assuming the carrier power of the transmitter to be 250 kW and the gain of the transmitting antenna HR4/4/.5 to be typically 21 dBi, this results in an additional gain of 47 dB compared to a WSPR transmitter of 5 W on a dipole, which is already strong by its standards. Thus, the total gain of this experiment is 100 dB compared to a WSPR signal. If we assume that signals with SNRs between -20 and -30 dB can still be evaluated, the gain is still a robust 70 to 80 dB. Thus, if aircraft scatter were to be detected on a WSPR signal, it would be even more striking with this factor.

The spectrogram of the five hours’ recording see below, followed by an explanation of the annotations (as with all screenshots: double-click to get the original resolution):

Kashi’s carrier over 5 hours, shown within a window of ±50Hz and a resolution bandwidth of 0.0122Hz at an dynamic range of 90 dB. Explanation see the following text.

The spectrogram reveals a couple of different strong influences to level and frequency of the carrier. Most prominent is the Doppler shift by a moving ionosphere, plus the split-up into o- and x-rays due to the magnetionic character of the ionosphere. You may simulate it with PropLab 3.1, but only in 3D mode. Aircraft Doppler is very weak. It has been verified as such by a different spectrogram with better time resolution, not shown here. You see also some Doppler from meteorite’s plasma in the vicinity of the carrier.

The level of the carrier can be seen from the following screenshot at a time resolution of 1 second, enriched with some statistical data:

Levels over 5 hours. Mean = -44.02 dBm, Standard Deviation 7.872, Range 58.81 dBm. Max/min: -21.97 dBm/-80.78 dBm

The next screenshot shows the whole 17’930 datapoints, split up into consecutive groups of 110 each. This should simulate the the 110.6 seconds which the WSPR logbook boils down to one SNR value plus on “drift” value. To read this contour map:

Vertically you see 163 columns. Each column contains the levels 1 … 110, and 110 x 163 = 17’930 total level values. For the first time, you can see here the dynamic within a column of 110 values each.

Contour diagram, showing all 17’930 level data, grouped to 163 blocks of 110 data points each.

So far, we retained the level information of all 17’930 data points. What happens if WSPR boils them down to chunks of 110 seconds only? This question answers the next screenshot:

What is lost by boiling down the 17’930 level values at 1 second’s distance to 163 chunks of the mean of 110 values? This screenshot shows the answer.

If it still isn’t understood that information which simply are not palpable in the 110-seconds’ chunk cannot be “interpreted” as this or that, a zoom-in must convince you:

Same as above, but zoomed into. WSPR logbook will keep only the Chunks. So all information has to be derived from just the red line! Imagine that you don’t have any more information – no “Raw”, no “Spectrogram”.

Looking at the both screenshots above: are you still sure to see any faint details (refer to spectrogram on top of this blog) like any Aircraft Doppler just from the chunks? You have also seen that the “drift”, shown in the WSPR logbook, may have manifold sources, ionospheric Doppler prevailing.

Stanag 4285 & PSKSounder – a better mode

There, of course, is a way out of this dilemma: since many years free PSKSounder provides an excellent tool to extract many more information from STANAG 4285 signals, see the following screenshot:

PSKSounder shows relative “time of flight” of a Stanag 4285 signal. Here with FUV, French Navy in Jibuti. You see that the structure of the spectrogram of the signal at the right has it source in two strong and different paths of the signal. Their times of arrival differ by about one millisecond. This procedure is very sensitive and is also used to reliably reveal meteorites and – aircraft!

Finally two things: The path between two stations does not always have to be exactly reversible – that is, if two stations are equipped exactly the same, it is very likely that a different signal will be detected in each case. And if the black box of MH370 should indeed be found in the area supposedly designated by WSPR, it is due to many things, but certainly last of all to WSPR.

After which methods it might be tried nevertheless, one can read already now in Grete De Francesco’s “The Power of the Charlatan”, Yale University Press, New Haven/USA, 1939.

ALE [MIL-STD-188-141A]: Which one is the best Decoder?

This is an update from my post two days ago. I have expanded the number of test signals and added some hints.

Does your decoder read this track? Buried in noise and plagued by multipath fading, the recordings below will separate the wheat from the whaff.

Often I am asked – and sometimes even asking myself! – “Which one is the best decoder for ALE?” This means: Which one delivers the best decoding under demanding conditions?

To test this, I made a recording of twelve stations “on the air” plus one weak signal, buried in Additive White Gaussian Noise, AWGN. All signals are correctly tuned, no one invers. All were read by at leastby one of my decoders “in a row”.

To test your decoders, you should download this WAV file of 131 seconds length and play it. It can be either directly opened by some decoder, or feed it via virtual audio cable (VAC) into a decoder. I used Audacity for this.

I am as interested in the results as you are – so please drop me a line to dk8ok [at] gmx.net. I like to encourage you to try all ALE decoders you have at hand – the more, the better.

Already the first results were surprising. This concerned both, the decoding ability of the decoders and the repeatability of the test. So far, the following decoders had participated: go2monitor, Krypto500, MARS-ALE, MultiPSK, Sorcerer, and W-Code. Steve, N2CKH, had written some valuable hints to optimize his MARS-ALE software for SIGINT purposes – please see his comment.


This WAV file contains the calls of thirteen ALE stations. Download and save this file (point to the icon, press right mouse button …). Then feed it to your decoders. Copy the results and send them to me. Have fun!

GMDSS & Display Launcher: Monitoring seven Channels in parallel

DiplayLauncher_4

GMDSS-Display reading decoded data streams from seven MultiPSK’s instances in parallel, presenting all information neatly in one database.

GMDSS is a system of ship-coast and coast-ship digital communications on six main HF channels. At an average location in Germany, you will receive about 5000 messages altogether during 24 hours.

In the past, I mostly used the excellent and free YaDD software to decode all channels in parallel (yes, YaDD can be opened in multi instances, each one in a separate folder).

During HFDL monitoring, I came across Mike Simpson’s free software Display Launcher which neatly collects now up to 24 different data streams, coming from up to 24 HFDL channels in a clear database format.
Mike’s software also contains a module called “GMDSS-Display” which now works similar in collecting datastream from up to seven GMDSS data streams, decoded by MultiPSK software.

Yes, also MultiPSK can be opened in many instances, each one in a sperate folder. By this way, it accepts e.g. the audio input of seven different GMDSS channels from an SDR via each different VACs, and decodes each of them.
To do so, the decoded data of each MultiSPK instance has to be backed up regularly:
Configuration -> Regular back-up -> 20 sec
Then, decoded data is automatically written into the appropriate QSO.txt file. This, in turn, is read by GMDSS-Display. Of course you first have to set the paths to guide the software to the appropriate sources.

It takes a bit time of setting it all up, but then you may run this combination until a Windows’ update forces the PC to re-boot 😉

With Mike’s development, you have a unique and mighty tool at hand for a 360° view now also in the field of GMDSS – thank you very much!

Please find below the results of a 24 hours’ session on all seven GMDSS HF channels – coast stations only, automatically drawn onto DX Atlas. All stations received in Germany with SDR FDM-S2 and MD300DX, an active vertical Megadipole of just 2 x 2.5 m of stunning performance.

DXAtlas_5

Received coastal stations on all GMDSS channel/HF during 24 hours in Germany world-wide and …

DXAtlas_6

… those with a focus onto Europe.

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.

Decoding the whole DGPS band

This screenshot shows the automatically visualized result of a 15 hours’ session receiving the DGPS band, March 11th/12th, 2017. You clearly see the propagation effect during night (marked yellow).

For years, Chris Smolinski of Black Cat Systems offers a fine selection of Mac software, among them many pieces for hams and shortwave listeners.

He now presented an unique software dubbed Amalgamated DGPS which decodes, analyzes and visualizes all DGPS stations on long wave at once. This is done from an I/Q wav file of e.g. Perseus SDR. DGPS stand for “Differential Global Positioning System” and is a system of long wave transmitters in the range of 283,5 to 324,5 kHz transmitting FSK data in 100 and 200 Baud to correct for GPS signals. Look here for a short introduction to this topic.

[Einen deutschsprachigen Test der aktualisierten Software habe ich in der April- Ausgabe 2017 der Fachzeitschrift FUNKAMATEUR veröffentlicht.]

These transmitters are of regional coverage, like non-directional beacons, or NDB, in the same band. This makes them interesting for DXing and propagation studies as well.

All you have to do is to let the software analyze your I/Q files of a receiving sessions. Yes, it is automatically “chaining” your files. You then get a detailed list of decoded stations with some additional data. You also can visualize these data, as I did in the screenshot at the top. This is based on a 15 hours’ session resulting in 56 wav files of 675 MB each.

The software runs on both, Mac/iOS and Windows. On both systems it works fine, covering .0 and .5 kHz channels as well as both baud rates.

Here you see the complete list of stations and the number of their receptions. “Amalgamated DGPS” has decoded 516.918 logs in roughly 15 hours!

 

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.

20 MHz HF: “HackRF One” on Shortwave

world Kopie

The world is full of software-defined radio (SDR), but HackRF One has a rather unique position – thanks to its vast maximum bandwidth of 20 MHz. With an up-converter, this combination covers more than 70 percent of the whole HF range from 3 to 30 MHz. Even better: with proper software you can record and play this enormous band!

However, this stunning bandwidth is achieved by a moderate resolution of 8 bit, resulting in a dynamic range of just nearly 50 dB. Or the half of SDRs like Elad’s FDM-S2.

Anyway. I wanted to know in practice what you can actually do with such a set at a budget price plus mostly free software. The results surprised even me: Properly used, this combination convinced as a quite decent performer on HF! The world map above shows some of the stations received with the set (see insert bottom left) to test its performance.

I laid down my experiences and recommendations for best reception in a paper of 17 multi-media pages full of examples – including 55 screenshots, 21 audio clips and one video. The PDF shows how to optimize reception of broadcast, utility and amateur radio stations. It covers many examples on how to analyze recordings, to decode data transmission with free software plus live decoding of 14 channels in parallel. It also gives some examples of combining HF reception with the internet, e.g. regarding the reception of signals from airplanes (ARINC, HFDL) and vessels (GMDSS).

My experiences really left me enthusiastic about this set.

You may share this enthusiasm and download the PDF of 43 MB here. Save it on your hard disk or USB stick, and open it with a most recent Adobe Reader. Otherwise, the multimedia content will not work.
[Einen deutschsprachigen Test  habe ich jeweils als Titelgeschichte in der April- Ausgabe 2017 der Fachzeitschrift  Radio-Kurier – weltweit hören und in der Mai-Ausgabe der Fachzeitschrift Funktelegramm veröffentlicht.]

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