Category Archives: Aero

WSPR & Flight MH370; Richard Godfrey & DARC e.V.: Zwei erledigte Fälle

Seit Wochen führt Richard Godfrey, ein Renter aus dem Hessischen, die Fach- und Publikumspresse mit folgender These an der Nase herum: Mit historischen Logdaten von WSPR, einem Amateurfunk-Mode geringer Leistung, ließe sich der Todesflug MH370 verfolgen.

Ich habe diese These lange ignoriert, weil deren Unwissenschaftlichkeit für mich auf der flachen Hand lag. Als sie allerdings immer mehr Publizität gewann, sah ich das technisch-wissenschaftliche Image des Amateurfunks ins Lächerliche gezogen und schaltete mich mit eigenen Untersuchungen zu diesem Thema ein. In diesem und in diesem Beitrag versuchte ich auf technisch-wissenschaftlicher Basis und mit einer Unmenge von Daten die Scharlatanerien von Godfrey zu widerlegen.

Da war ich nicht der erste und schon gar nicht der einzige. Siehe unter anderem hier.

Zugleich schickte ich dem DARC e.V. eine kurze Information über meine Untersuchungen und deren Ergebnis. Erst 2019 hatte dieser “Bundesverband für den Amateurfunkdienst” Nobelpreisträger (Physik, 1993) Prof. Joe Taylor, K1JT, als Entwickler von WSPR (2008) endlich seinen “Horkheimer-Preis” zuerkannt, wofür ich mich schon Jahre zuvor erfolglos eingesetzt hatte – der Verein hat es offenbar immer noch nicht so mit moderner Technik. Mit meiner Information wollte ich erreichen, dass Godfrey nicht weiter den Amateurfunk und auch die Arbeit eines Nobelpreisträger lächerlich macht:

WSPR und MH370: Eine kritische Würdigung
Immer wieder gibt es in der Fach- und Publikumspresse Nachrichten darüber, dass Logdaten des WSPR-Datennetzes bei der Lokalisierung von Flugzeugen helfen können. Insbesondere geht es darum, den tatsächhlichen Absturzort des Fluges MH370 festzustellen. Diese Bemühungen laufen im Wesentlichen darauf hinaus, in den archivierten WSPR-Logdaten “ungewöhnliche” Pegelsprünge und Frequenzänderungen (“Drift”) festzustellen und diese Reflexionen bestimmter Flugzeuge zuzuschreiben (“Aircraft Scatter”). In einem Blogeintrag unterzieht Nils Schiffhauer, DK8OK, diese Theorie erstmals einer kritischen Würdigung. Diese fußt einerseits auf der jahrelangen Beobachtung von Aircraft Scatter auf Kurzwelle sowie einer Untersuchung von gut 30 Dopplerspuren. Die Ergebnisse dieser aufwendigen Analyse von über 10.000 Daten allein in einem Beispiel lesen sich ernüchternd: Die Auswirkungen von Aircraft Scatter auf das Gesamtsignal bewegen sich fast immer deutlich unter 0,3 dB. Eine Korrelation zwischen Pegelveränderungen des Gesamtsignals und Flugzeug-Scatter nachzuweisen, erscheint anhand des WSPR-Datenmaterials kaum möglich. Die Gründe sind vielfältig, liegen aber vor allem in der Kurzwellenausbreitung, bei der Pegeländerungen von 30 dB innerhalb weniger Sekunden eher die Regel als die Ausnahme darstellen. Da bei den bisherigen Untersuchungen am WSPR-Datenmaterial jedoch der örtliche und zeitliche Zustand der Ionosphäre nicht bekannt ist – er wird in professionellen OTH-Radar-System parallel erfasst und aus dem Empfangssignal herausgerechnet -, lassen sich Pegelsprünge allein aus dem Summensignal kaum eindeutig zuordnen. Dieser Befund wird im Blog durch weitere Argumente gestützt.

Wenngleich ich nichts vom DARC hörte, so landete diese Information jedoch auf mir unbekanntem Wege bei Richard Godfrey. Der reagierte in seinem Blog wie folgt:

Sie sind in diesem Blog nicht willkommen! Sie wurden 1992 aus dem Deutschen Amateur-Radio-Club (DARC) ausgeschlossen. Trotz 3 Einsprüchen auf regionaler und nationaler Ebene sowie vor Gericht sind Sie auch 29 Jahre später noch von der Mitgliedschaft ausgeschlossen. Dafür gibt es sehr gute Gründe. […]
Ich habe mich bei Christian Entsfellner DL3MBG, dem derzeitigen Vorsitzenden des DARC, über Ihre Forderungen beschwert, gegen meine Arbeit und die von Dr. Robert Westphal (DJ4FF) offiziell auf der DARC-Website zu MH370 und WSPRnet zu protestieren.
Ihr Papier ist schlichtweg falsch und Ihre Argumente sind unangebracht.
Ich schlage vor, Sie gehen woanders hin, denn ich bin sicher, dass es andere MH370-Websites gibt, die Leute wie Sie willkommen heißen. Und Tschüss!

Also: keine inhaltliche Diskussion, sondern eine denunziatorische Mail an “Christian Entsfellner, DL3MBG, den derzeitigen Vorsitzenden des DARC”. Da Entsfellner das Produkmanagement eines Unternehmens verantwortet, das mit HF-Technik handelt, dachte ich, er werde beide Ansichten fachlich prüfen und natürlich zur Erkenntnis gelangen, dass Godfreys Thesen technisch-wissenschaftlich nicht überzeugend sind. Ob jemand überhaupt Mails mit denuziatorischem Inhalt ernst nimmt, ist freilich eine Charakterfrage – wie jene, solche Mails zu schreiben.

Allerdings lief alles so, wie Godfrey es sich gedacht haben mag: von Stil und Inhalt her hatte er genau ins Schwarze getroffen! Denn daraufhin veröffentlichte der DARC eine Presseinformation, in der er die Godfrey’schen Schwurbeleien in den Himmel hob. Verantwortlich dafür: das “Presseteam“* des “Bundesverbandes”, dem man dafür den “Aluhut mit Raute” verleihen sollte.

Warum sich die Vereinsfunker nicht kundig machten, wenn sie schon nicht selbst die Sachkenntnis gehabt haben sollten, ist mir ebenso ein Rätsel wie die Frage, warum sie zwar Godfrey in die Sache einbanden, nicht jedoch K1JT, wozu eine E-Mail an den Preisträger ihres Vereins gereicht hätte!

[Das heißt: So groß ist das Rätsel wiederum auch nicht. Und hätte ich eine Versuchsanordnung mit unfehlbar diesem Ausgang designen müssen – exakt diese wär ‘s gewesen!
Du glaubst es nicht? Hier der Beweis: Am 8.12.21 schrieb ich in Godfreys Blog dazu:
“Ganz ohne Zweifel wird Ihr ‘Protest’ (nicht: irgendwelche Argumente) bei DARC-Präsident Christian Entsfellner, DL3MBG, auf fruchtbaren Boden fallen. Er wird sich Ihre Meinung zu eigen machen. Denn, so vermute ich, er wird sich nicht von den technisch-wissenschaftlichen Argumente leiten lassen. Sie scheinen die gleiche Voreingenommenheit zu teilen.”
Und: Horch, Glöckchen! Am 9.12.21 gab der DARCs eine diesbezügliche ‘Presseinformation’ raus.
Siehste, ist doch gar nicht so schwierig, den DARC zu einer Pawlow’schen Reaktion zu bewegen!]

Auch wenn es zwecklos ist, Scharlatanerien mit sachlichen Argumenten zu begegnen, hatte daraufhin der US-amerikanische Physiker Dr. Victor Ianello sich bei K1JT zu dessen Meinung zum Thema “WSPR und MH370” erkundigt. Die Antwort des Nobelpreisträgers fiel zum wiederholten Male eindeutig aus:

“Wie ich bereits mehrfach geschrieben habe, ist es verrückt zu glauben, dass historische WSPR-Daten dazu verwendet werden könnten, den Kurs des verunglückten Fluges MH370 zu verfolgen. Oder, was das betrifft, jeden anderen Flugzeugflug… Ich verschwende meine Zeit nicht damit, mit Pseudowissenschaftlern zu streiten, die nicht verstehen, was sie tun.”

Prof. Joe Taylor, K1JT

Verrückt” und “Pseudowissenschaftler, die nicht verstehen, was sie tun” – das ist deutlich genug. Aber auch die Konsequenz, sich mit solchen Leuten erst gar nicht zu beschäftigen. Sollen sie weiterhin unter ihresgleichen auf Dummenfang gehen.

Der DARC, mit unten zitiertem Anschreiben davon in Kenntnis gesetzt mit der Bitte, diesen dem technisch-wissenschaftlichen Image des Amateurfunks schädlichen Scharlatanerien keinen Raum zu geben, reagierte bislang nicht. Das Anschreiben:

Guten Tag – nachdem ja einiges Wunschdenken zum Thema “WSPR und Flug MH370” die Publikums- wie Fachmedien beherrschte und auch der DARC mit einer Pressemeldung Partei für diese Scharlatanerien ergriff, hat nun Nobelpreisträger Prof. Taylor selbst diesem “verrückten Glauben” eine deutliche Absage erteilt.
Ich meine, dass ein weiteres Festhalten an diesem Wunschdenken das technisch-wissenschaftliche Image des Amateurfunks untergräbt. Irren und erst recht Wunschdenken ist menschlich. Aber man sollte sich, wenn schon nicht durch technisch-wissenschaftliche Argumente, so doch durch das Machtwort eines Horkheimer- und Nobelpreisträgers (was immer davon die härtere Münze im DARC sein mag) überzeugen lassen.
Vielleicht ist ja im nächste Deutschland-Rundspruch Platz für folgende Meldung, deren Inhalt auch gerne für eine erneute Pressemitteilung des DARC zu diesem Thema genutzt werden mag.

Godfrey aber kann sich gratulieren: er wusste genau die richtigen Fäden zu ziehen, um dem DARC-Vorsitzenden, dessen Verein sich trotz vielfacher Aufforderung nicht gegen Denunziation als Mittel der Diskussion im Amateurfunk ausgesprochen hat, seine schrägen Thesen schmackhaft zu machen. Christian Entsfellner wiederum hätte diese technisch und unvoreingenommen überprüfen können und müssen, das “Presseteam“* ebenfalls. Wer es nicht kann, ziehe Experten hinzu.

Dass in der technisch-wissenschaftlichen Community der Amateurfunk immer weiter zur Lachnummer verkommt, ist insofern nicht verwunderlich, sondern mit Fleiß selbstgestrickt.

Zwei nur halbwegs ernstgemeinte Prognosen, nun: zum einen wird Richard Godfrey Ehrenmitglied des DARC e.V. (mit vollem Recht, denn er hat mit den dafür goldrichtigen Methoden dem Ansehen des Amateurfunks einen schweren Schlag versetzt), zum anderen wird man die Black Box von MH370 an der prognostizierten Stelle finden – was dann aber auch ganz & gar nichts mit WSPR zu tun haben wird. Und die “Pseudowissenschaftler” werden jubelnd ihre Aluhüte in die Luft werfen.

* Wenn auch technisch-wissenschaftliche Themen nicht so ganz die Kragenweite des “Presseteams” sein mögen, so leistet es doch geradezu Herausragendes bei der “Anpassung von Vorstandshemden”:
In einem kürzlichen “Mitgliedertreff” äußerte sich ein Vorstandsmitglied des DARC ganz begeistert darüber, wie er “vor Steffi strammstehen durfte” (gemeint ist Dipl.-Soz. Stephanie “Steffi” Heine, DO7PR, stellv. Geschäftsführerin des DARC e.V. und offenbar leitende Presseverantwortliche), um sich ein “Vorstandshemd” anpassen zu lassen. Der DARC-Vorständler war darob ganz hin und weg: “Top und schick … mit Stickereien!” Worauf besagte “Steffi” flötete: “Das machen wir doch gerne!”
Man glaubt es unbesehen. Und dass es dafür dann beim “Bundesverband” mit technisch-wissenschaftlichen Themen gelegentlich ein wenig hakt, wollen wir gerne nachsehen: Das “Vorstandshemd” sitzt halt näher als der Rock.

In solchen Händen sind die technisch-wissenschaftlichen und die ethisch-charakterlichen Grundlagen des Amateurfunks ebenso vorzüglich aufgehoben, wie genau diese Eigenschaften für viel Geld in alle Welt geblasen werden!

Wer das nicht noch weiter mit seinem Geld unterstützen möchte, sondern wer für ein seriöses technisch-wissenschaftliches Hobby eintritt, das vom Ham Spirit getragen wird, sollte, falls er wirklich noch Mitglied im DARC ist, aus diesem austreten. Noch heute.

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 …

MH370 and WSPR: Aircraft Scatter on HF – A Critical Review

Some articles had been published stating that processing of WSPR logs can assist in reconstructing the route of an aircraft (i.e., MH370) by a method known as bistatic radar. Nils Schiffhauer, DK8OK, has some doubts. Read his reasoning below.

Some Doppler traces in vicinity of the carrier of China Radio International from Xian-Xianyang, broadcasting with 500kW (250kW carrier) on a curtain array antenna providing nearly 25dBi gain towards 190°. More on the lower than on the upper sideband you see some aircraft Doppler traces at distances of 8Hz to 17Hz (LSB), corresponding to a relative velocity of the aircraft from about 200 to 600 km/h. Frequency resolution: 0.0047 Hz.

Again and again, efforts by radio amateurs make the rounds to have identified the crash site of MH370, for example, on the basis of the evaluation of WSPR logs. For this purpose, they primarily evaluate “unusual” level changes in the WSPR logs.
The fact that RF signals are scattered by the metal hull of aircraft is nothing new. The best way to see this effect is to look at the Doppler tracks that form at a certain distance from the actual carrier frequency of the transmitter. This is based on the theory of bistatic radar (see for example “Bistatic Radar” by Nicholas J. Willis, Raleigh NC, 1995).

Aircraft Scatter: Bistatic Radar

This concept has been used worldwide for decades, in the HF range primarily in the form of various over-the-horizon (OTH) radars.
In principle, a signal with known properties (amplitude, waveform …) is transmitted and received again after having passed through the “channel”. Comparing the transmitted signal with the received signal, the properties of the channel can be deduced.
Professional systems with powerful transmitters, beam antennas with high gain and signals with precise characteristics, whose scattering is evaluated with highly specialized algorithms, allow the detection of even small aircraft and ships in rolling seas. Intelligent evaluation includes the extensive elimination of interference factors, from sea clutter to changes in the ionosphere. These also have a considerable influence on the received signal – including amplitude and frequency (Doppler and split-up into x and o rays).

WSPR: A challenging mode

Transferring this technology to the evaluation of level and frequency of WSPR signals faces a couple of challenges:

  • The effective transmit power of WSPR signals is only roughly known at best, but in terms of magnitude it is at least 50 dB below that of professional OTH equipment.
  • The quality of the transmitted signal in terms of frequency stability, noise and possible amplitude changes (power supply!) is not known.
  • The changes of the ionosphere (attenuation, Doppler, multipath …) is not known.
  • The waveform WSPR, as well suited as it is for QRP communications, has not been developed for its use as bistatic radar.

All previous evaluations, especially in connection with flight MH370, are based primarily on evaluations of level changes, measured as just one mean value of a 110 seconds long transmission. It has been postulated that aircraft scatter increases the overall level of the signal. (“Drift” seems not to be a proxy for “Doppler”, see below). A possible evaluation of the Doppler shift fails so far largely because of the data situation. This also prevents the inclusion of the current state of the ionosphere and its local fine structure. Catching up ray tracing – moreover only two-dimensional! – can by no means compensate this disadvantage.

Correlation vs. Causality

However, far-reaching expectations are attached to the existing and modest material [Sensational new finding for MH370 flightpath], which in my opinion are already epistemologically, but also technically on feet of clay. This is like one can make Mozart’s “Kleine Nachtmusik” sound out of pure noise by suitable filtering. This also happens to high-ranking scientists, for example, when they detect neuronal correlates in the brain of a dead salmon and erroneously conclude that it is solving mathematical problems … there has been everything. Correlation doesn’t always mean causality.

My doubts about using WSPR logs for the purpose of locating aircraft are based on two main points:

  • We know little to nothing about the actual state of the fine structure of the ionosphere, which primarily affects the signal.
  • We have only guesses about the extent to which (amplitude, Doppler …) an object flying in an unknown direction scatters the signal (type, height, direction, speed …).

Furthermore, raytracing in those examples calculates with unusually low elevation angle of under 3°. PropLab 3.1 [most recent build #43] sees the main elevation of, e.g., a vertical dipole at more than 20°.

Just as an aside, when the central paper on “WSPRnet Propagation Technical Analysis” states, “Flat ice or calm ocean provide the best surface’s for WSPRnet signal reflection.”, the opposite is true, at least as far as the conductivity of ice is concerned. It has the worst conductivity and thus reflectivity of all soils on the earth’s surface and, at 10-4 S/m, is in last place in this respect according to ITU-R P.527-4.

HF Scatter: What the Experts say

The relevant literature on HF radar deals with such central matters as radar cross section (which defines the return power of an modeled object, which can vary by several 10 dB under different circumstances), scatter in Rayleigh and Mie regions (dependence on wavelengths and dimensions of the object), and inhomogeneities of different layers of the ionosphere – concepts of which most previous studies on the subject of “WSPR and MH370” make sparse use at best.
I do not want to bore now with long-tongued recounting of these things, but to pick out thesis-like only some points from the NATO paper HF-OTH Skywave Radar for Missile Detection” as a quotation (bolded by me):

* We must deal with heavy propagation losses due to the very long travelling distances as well as strong absorption losses mainly due to the D layer of the ionosphere. The whole loss contribution can be up to 100-150 dB.

* The apparently simple propagation mechanism hides the complexity of the ionosphere structure. This implies a challenging target localization that could be achieved by a smart system calibration combined with a three dimensional reconstruction of the signal path through the ionosphere.

* OTH radar system functionalities are strongly dependent on the ionosphere and on the environment noise level that means geographically dependent performances. Accordingly the radar siting represents one of the key choices.

* High values of peak power are necessary in such systems to deal with strong losses.

* It is essential a simulative approach that can provide a predicted radar cross section variability as a function of the operating frequency and of the aspect angles that are unusual for ordinary radar systems.

Certainly, these military requirements do not have to be transferred 1:1 to our more semi-professional approach. Nevertheless, they set such narrow limits to even our modest approach that their meaningful application threatens to disappear almost completely in fading and noise.

Amateur’s Choice: +70 dB – and more

In order to verify at least some basic assumptions in practice, I have conducted a series of investigations on carriers of shortwave broadcast transmitters. These have several key advantages over WSPR:

  • They provide a known signal in terms of frequency stability and amplitude.
  • Their effective transmit power is about 70 dB higher than that of WSPR transmitters.
  • Each station transmits continuously for at least 30 minutes, allowing relatively large integration times to improve the frequency resolution (up to 0.005 Hz, or adding another 57 dB in a 2’500 Hz channel) and thus the sensitivity for detecting the Doppler signals.
  • This setup allows a clear separation of original signal (via ionosphere) and aircraft scatter by shape and frequency. This eliminates what I consider to be the biggest unknown of the WSPR approach.

However, there is one drawback: only between 0 and 10% of even these strong transmitters can be used to detect Doppler traces from aircraft. Only with a smart match of frequency, time, flightpath, propagation … you will have some success.

Let me pick a typical example from a series of experiments – all with similar outcomes. The Chinese transmitter at Xian is received with 500 kW (carrier: 250 kW) on a GPS-locked SDR Elad FDM-S3. Its carrier on 17’530 kHz was first displayed under magnifier of two software, namely PSKOV (screenshot on top of this blog, for a first introduction click here) with 0.005Hz resolution, and SDR software SDRC with 0.39 Hz resolution, see screenshot below. The latter provides the numerical output used in the following post-processing.

Situation with software SDRC, compared to the PSKOV-screenshot at top of this blog.

Needle in a Haystack?

The next step is to answer the following question: Is it possible to detect the influence of the Doppler tracks in the overall signal? After all, this is the method that is tried using WSPR.
For this I first divide the total signal of 100 Hz width into three channels: Carrier, Doppler and Noise, see below. The Doppler signals are clearly visible, the respective correlation coefficients between the channels “Carrier”, “Doppler” and “Noise” are all well below 0.1, which shows the independence of the three different signals from each other and their separation. Mean Level of Carrier is -59.1 dBm, standard deviation 5.71. Mean Level of Noise is -108 dBm, standard deviation 4.5.

Signal levels over 10’000 seconds for all three channels.

In the following step, I sum up the channels “Carrier” and “Doppler” (de-logarithmize the dBm values in mW, addition, re-logarithmize the mW values to dBm).

If I now compare the data “Sum level of Carrier and Doppler” with the “Carrier”, the correlation diagram shows a near-complete agreement between both data sets – see screenshot below:

Correlation diagram fo Carrier and Carrier+Doppler (blue marks) shows only miniscule differences from 100% identity (red line).

Are rounding errors the reason for those miniscule differences? No, as we see in the following screenshot where you can see that the Doppler trace increases the signal of the carrier by 0.2 dB to 0.3 dB at most, except for a single exception: 0.6 dB.

But these values are almost completely lost in the overall signal with its standard deviation of 5.71, if they are not anyway below the measurement accuracy of many SDRs and their software.

The screenshot below draws the difference between [Carrier+Doppler] and [Doppler] – values left Y-scale – together with the original Doppler signal – right Y-scale. Judge for yourself …

The Doppler traces are practically lost in the fluctuations of the carrier signal.

For the complete overwiew of the steps see the workflow below:

Workflow, done with Elad FDM-S3, SDRC, MatLab R2021a.

WSPR & Aircraft Scatter? I have my doubts.

We started with the challenge to see some signal enhancement by scattering from aircraft in WSPR logs. Those should lead to “unusual” changes within the signal. A WSPR transmission lasts for 110.6 seconds and delivers just one mean SNR value representing his time (plus drift with a resolution of 1 Hz only).

It was suggested that from these signal levels (and drift data) aircraft scatter can be derived. This had been tried to underpin with 2-dimensional ray-tracing propagation simulation, based on statistical, rather then real data.

I tested those assumption with 10’000 level data at one second resolution, +70 dB in transmitting power, added by a few 10 dB of processing power. Doppler traces from 30+ aircraft had been analyzed. Backed by this, it can be stated:

  • On HF over longer paths (from two hops/with multipath propagation), usual aircraft scatter has nearly no effect on the overall reception level. Without prior knowledge, it is hard, or even impossible, to conclude aircraft scatter from the sum signal.
  • Doppler effects occure in the region of about 5 Hz to 20 Hz and don’t coincide with the much lower “drift”, I saw in the WSPR logs.
  • The power of a typical WSPR setup is many ten dBs down to what it should be to reliably identify aircraft scatter.
  • We usually know near nothing about the transmitter’s and receiver’s site – power, noise, drift etc.
  • We know near nothing about the channel (propagation) at the refracting points. This makes it difficult to separate different effects from each other, of which aircraft scatter is just a minor one, with multipath fading being the absolutely prevailing one.
  • The statistical population/resolution of the data one gets from the WSPR logs is too small (due to the 110 seconds) to apply robust statistical methods to cope for a dynamic environment.
  • The simulation capabilities of PropLab are not sufficient for such long-range statements due to, for the given case, poor temporal and spatial resolution of the usable ionospheric data. In addition, the simulation with PropLab was, to put it mildly, not optimally implemented – 2D instead of 3D, airy assumptions about the angle of incidence of the signal, and wrong assumption about ground conductivity.

My final conviction is: the detection of aircraft scatter and its assignment to specific flights from WSPR data is far more wishful thinking than reality. Only with considerable prior knowledge and using other data sources as well as possible coincidences these statements can be explained. WSPR in itself is not likely to contribute to this.
There are far more RF signals that are far better suited for this purpose for a variety of reasons. Trump, however, would be digital beacon project, whose waveform is suitable for also qualitative studies of the propagation path. Here, a private initiative seems to be active, after amateur radio clubs continue to stick to analogue technology (NCDXF, once meritorious).

Just a quick answer …

… to a question, I have been asked:

Q: “WSPR is sampling SNR for 110 seconds, boiling this down to one value. The resolution of your approach is one second. Does this influence the results?”

A: “Surely – higher resolution = more details, better insights!”

Q: “Can you show me?”

A: “I warn curious, but that you are, gladly!”

The screenshot below offers an answer to the question: “What does the WSPR log see, which only notes the sum voltage and also this only as an average value (?) – and also this not every second, but in intervals of 110.6 seconds?” Because with WSPR one has only this one sum value. For this purpose, exactly this situation was simulated with the originally good 10,000 data values collected every second and these were divided into groups of 110 seconds each, whose mean value was formed. This then corresponds to the SNR value in the WSPR logs.I boiled down my data of “Carrier+Doppler” and “Doppler” to 91 groups of 110 seconds each, and then I calculated the mean values of each group. In my view that should match the SNR values of WSPR (“Carrier+Doppler”).

Sum level and Doppler level. Allegedly, one should be able to conclude from “unusual” sum levels to aircraft Doppler. Which without prior knowledge leads predominantly to false-positive (FP) and false-negative (FN) results, of which only some are entered here. Rolling the dice gives a better result.

I then calculated the 95% confidence interval from these largely normally distributed mean values and restricted the plot in the above screenshot to those values that lie above the upper limit of this confidence interval of 58.02 dBm. These are “unusual” values in my eyes, although this is only a reasonable guess, because the authors do not specify further what they mean by “unusual”. The course of the values “Carrier+Doppler” is scaled on the left Y-axis, from -58 dBm to -54 dBm.
According to theory, a Doppler signal should now be lurking behind each of these values above -58 dBm, at least in the “unusual” peaks. Is this true? To check this, I plotted the corresponding processed Doppler levels in the same diagram, scaling on the right Y-axis, -110 dBm to -98 dBm.
Already a first look shows that the connection of both curves is rather random. With FP like “false positive” I marked for clarification at least some of those positions, where due to the “unusual” sum signal an aircraft Doppler would have been expected – but was not present. With FN are marked, vice versa, some of the positions, where there was a Doppler signal, but no “unusual” course of the sum level indicated it. A clear assignment “unusual sum signal -> aircraft Doppler” is therefore unlikely.

Comments welcome: dk8ok at gmx.net

P.S.

Oh, yeah, we had some comment! Richard Godfrey rebuked my technical-scientific based criticism on his website (“Serving the MH370 Global community”), which explicitly invites discussion, with the following “arguments”:

“You are not welcome on this blog!You were thrown out of the German Radio Amateur Club (DARC) in 1992. Despite 3 appeals at regional and national level as well as in court, you are still excluded from membership 29 years later. There are very good reasons for this. …I have complained to Christian Entsfellner DL3MBG, the current Chairman of DARC, about your demands to protest against my work and that of Dr. Robert Westphal (DJ4FF) officially on the DARC website regarding MH370 and WSPRnet.Your paper is plain wrong and your arguments are misplaced.I suggest you go elsewhere as I am sure there are other MH370 websites who will welcome the likes of you. Und Tschüss!”

” Ambition should be made from sterner stuff.” [Shakespeare, Julius Caesar, Act III]

I like to recommend a website where you find much ado about sterner stuff concerning MH370 and WSPR:
MH370 and Other Investigations – Following the Data Towards Discovery.

Decoding ADS-B with free QIRX software

QIRX’ dashboard, decoding ADS-B: in the middle you see spectrum and spectrogram (“waterfall”) of the ADS-B signals. The window at the bottom lists alls received aircraft with additional data, whereas the top window places them onto a map.

In the last two blog entries, I took a look at the DAB capabilities of free software QIRX by Clem Schmidt, DF9GI, from Frankfurt. It directly works with RTL-SDR, Airspy and RSP2 SDRs. I tried this very smart software from my location near Hannover/North Germany now also with ADS-B, mostly with my RSP2.

ADS-B stands for “Automatic Dependant Surveillance – Broadcast” and is an automatic service where aircraft continuously transmits several vital data on around 1.090MHz. Most important part of these data is the 2D location of the aircraft which it gets by GPS plus height by a baromatric altimeter. From this position data, many other data are derived, e.g. climbing/sinking or speed. If matched to databases, you will also see type of aircraft, flight number and many other data.

“The internet” provides many services showing the results of ADS-B and other data, collected from receivers all over the world, among them Flightradar24, OpenSky, FlightAware and AirNavRadarbox. They each provide many additional data, somtimes available at different schemes. Most provide free access to much of their data, with some more specific data behind their paywall. OpenSky as a scientific and non-profit organization offers billions of datasets for free, see Scientific Datasets. QIRX uses an OpenSky data base with about 650’000 entries.

Backbone of all these services is a net of ADS-B receivers, connected via the internet and curated by each company.

QIRX shows some capabilities of such a receiving station, using a proper antenna and a simple SDR. It decodes the I/Q stream of it. ADS-B is transmitted via pulse-position modulation, or ppm. The system is explained in ICAO Annex 10 Volume IV [free download].

With QIRX, you must set the sampling rate of you SDR to 200000[Hz], as other sampling rates won’t work, see screenshot below.

To decode ADS-B, you must set the sample rate for your SDR to 2000000Hz.

After that, and having started QIRX in ADS-B mode, decoding is done automatically. Release your seatbelts, and simply relax by viewing the activities above your head. Coverage largely depends on the “view” of you antenna and a few other factors like te sensitivity of your SDR and the attenuation of your cable connecting your antenna with your SDR. Some web services, thanks to anticipatory obedience/security reasons/data protection etc., do mute some “special” flights . This is not the case, of course, with this setup. QIRX always provides stable decoding at even low SNRs – great!

Last, but not least, please find below a comparison of FlightRadar24 and QIRX setup with Flight Number TK1554/THY6KG, Hannover->Istanbul, starting from Hannover Airport. One difference between both screenshots is that at my location (Burgdorf), I got the Airbus only after it had climbed to an atlitude of 200m or so, whereas the FR24 receivers are placed at positions allowing for tracking the aircraft from even the runway.

Starting from Hannover to Istanbul: the airbus on track around Hannover. Top window shows the flight via FlightRadar24 web service, and even from the runway. Bottom window shows it received with QIRX from Burgdorf (red point in the northeast).

Also small aircraft is equipped with transponders, but not necessarily with ADS-B transponders, broadcasting the position, derived from their GPS. These small aircraft may haveonly Mode-S transponders on board, transmitting identification, height and squawk (transponder code) as assigned by their responsible ATC, or Air Traffic Control.

Doppler: Following Airplanes’ tracks

Carrier and Doppler trace (left), locations of transmitter, receiver and track of flight NH8406 – March 27, 2021, around 16:45 UTC [click onto the screenshot for richer detail]

Working on a project which will focus on Doppler spread of HF channels (see at the bottom) and other impairements, I also bumped into some more prominent Doppler catches, namely on the VHF aero band. I took the AM carrier of nearby Hannover VOLMET on 127.4 MHz and observed doppler traces about plus/minus 200Hz the carrier frequency. Following the acitvity in the airspace via Flightradar24 in parallel, it is easy to match traces and aircrafts. In this case, I nailed cargo flight NH8406 from Frankfurt to Narita/Tokyo. It is important to remember what is shown in left part of the screenshot: it is the signal of Hannover VOLMET, reflected by this moving Boeing 777-F. Thus, the reflected frequency shows a Doppler frequency shift – depending on the relative speed in respect to transmitter and receiver. A positive Doppler frequency signals that the aircraft is approaching my location. When it turns to the lower frequencies, I see the aircraft passing.

Things get more complex wen it comes to the Doppler shift at HF propagation. You will also see planes, but effects from high winds in the upper atmosphere, coming and fading of ionospheric layers and the influences of the geomagnetic field are prevailing. Due to the much lower frequencies, the effects are just about a tenth compared to thie above example on VHF.

See below a result from my observations on HF as a preview.

Carrier of TRT Emirler, Turkey, in the 19 meter band. Just after sunrise, the carrier splits into two, and you also see double lines due to magnetoionic effects. The window shos about 3Hz in the vertical, and about 40 minutes in the horizontal scale.

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!

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