Category Archives: Propagation

Propagation Day by Day: CRI Kashi, 15.260 kHz

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Signal strengths of CRI/Kashi, day by day, from 08:58 UTC to 09:58 UTC on the nine consecutive days March 15 to March 23, 2020; see text.

Propagation on HF differs from day to day. The nine diagrams at the top show the signal strengths of China Radio International’s Kashi transmitter, 500 kW, beaming to Romania; 08:58 UTC to 09:58 UTC from March 15 to March 23. The basic resolution (black grey points in the background) is 100 milliseconds, whereas the blue line marks the moving average with 601 points. The “moving average” can be best understood as a lowpass filter, revealing possible trends on a coarser scale. In this case, you cannot see such a trend.

If you compare a part of each transmission on a much finer scale, you even see sheer chaos, as the Figure below is showing:

All nine signal levels drawn together into one diagram (top), and a small part of it zoomed (bottom) reveals sheer chaos.

There seems to be no visible correlation on any scale in this case. There are other cases where, however, some correlation can be found – to which I will come back in some future entries.

The last diagram at the bottom of this pages shows a much more forgiving picture of the signal: the average level changes not more than ±4 dB between best and worst days. This so-called box diagram illustrates best the actual receiving quality of the broadcast, demodulated with an synchronous detector to largely avoid severe distortion by selective fading. The difference of deciles 90% and 10% marks the fading range, a key figure in describing the quality of reception – see “Ionospheric Radio” by Kenneth Davies [London, 1990/96, pp. 232].

The box plot shows very similar signal strengths, day by day. You should concentrate on their each center of gravity. You will also see that the distribution of the signals strengths relative to the center is not symmetrically, with a clearly visible advantage to the percentalge below the average strengths. THis will be covered in some future entry.

Analyzing signal strenghts, is an interesting tool to get to know more about propagation. I will continue this topic – stay tuned!

Receiver: Winradio’s Excalibur Sigma
Antenna: active vertical dipole (2 x 5 m) MD300DX
Software: V3 by Simon Brown, G4ELI, QtiPlot

FAX from Shanghai: Pacific Pressures

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This FAX broadcast was new to me and received on December 16, 2019 at 08:20 UTC on 16557,1 kHz. It was transmitted via Shanghai Coastal Radio, presumably directed into the Pacific, of which it shows the 48h surface pressure.

It was demodulated from a 25 MHz wide HF recording over 24 hours. This recording was made with Winradio’s G65DDCe Sigma SDR, connected to an active vertical MegaDipol MD300DX (2 x 5 m), and decoded with Wavecom’s W-Code. The recording was scheduled with software SDRC V3 by Simon Brown, and directed via USB3.1 to a 20TB hard disk, WD Duo Book. The resulting one file was 8TB, format WAV RF64.

It was also played back from this hard disk, also via USB3.1. Doing so, it is most remarkable that this setup worked smoothly without any glitches which would promptly have been seen at such a time-critical mode like this FAX., 120/576. So, this reception is also a proof that one can work smoothly with such ‘big data’ even on a hard disk – and not only on expensive SSDs. A FAX transmission is that sensitive that you even see a very weak echo (best seen of the big vertical black stripe at the right which echoes from around 115° East). This originates from a mixed short/long path reception. The strong short path’ flight time is 28.7ms, whereas the weak long path needed 104.7ms. As one FAX line covers 500ms, you can easily measure the delay of roughly 80ms, almost exactly matching the difference of long and short path.

The screenshot has been left un-retouched.

Ghosts in the Air Glow: HAARP on March 26th, 2019

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Just after the spring equinox, interdisciplinary artist Amanda Dawn Christie did another performance of her ionospheric transmission art project “Ghosts in the Air Glow” via the High Frequency Active Auroral Project HAARP near Gakona/Alaska. I took an HF recording of a range, covering all frequencies and times scheduled – see here. At my location, on March 26th, 2019, reception was possible only on 5.100 kHz (best), 6.900 kHz, 7.900 kHz and 8.000 kHz. Signal strength was too low to hear any modulation, but the characteristics of the signals did exactly match the schedule – see screenshots and captions below.

Receiver: Elad’s FDM-S2, Antenna: Active Dipole MD-300DX (2 x 2.5 m), Software: V3 from Simon Brown


5.100 kHz, 01:16 to 01:26 UTC, West beam, gave the best signal.
The signal on 6.900 kHz on the East beam from 01:16 to 01:26 UTC was considerably lower.
On 7.900 kHz, the signal was transmitted by an electronically rotated beam, one rotation per minute, from 01:03 to 01:09 UTC on the West beam. This is clearly seen on the the Signal window below the spectrogram.
On 7.900 kHz, the signal was transmitted by an electronically rotated beam, two rotations per minute, from 01:09:30 to 01:15:30 UTC on the West beam. This is clearly seen on the the Signal window below the spectrogram.
On 8.000 kHz, the signal was transmitted by an electronically rotated beam, one rotation per minute, from 01:03 to 01:09 UTC on the East beam. This is clearly seen on the the Signal window below the spectrogram.
On 8.000 kHz, the signal was transmitted by an electronically rotated beam, two rotations per minute, from 01:09:30 to 01:15:30 UTC on the East beam. This is clearly seen on the the Signal window below the spectrogram.

      TDoA Direction Finding: First Experiences on the KiwiSDR Net

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      6465_5

      With some iteration, as described in the PDF, the former unknown site of a CIS-12 transmission on 6.465 kHz has been disclosed as the Russian Navy from Baltysk, Kaliningrad.

      The stunning direction finding tool on the KiwiSDR net has hit the community. Most people are enthusiastic about the new horizons, some some smart people had opened for free.

      A few people, however, reported some disappointment as they couldn’t pinpoint each and every transmitter with expected high precision.

      To avoid this disappointment, you have to know what you are doing. The TDoA tool for direction finding indeed delivers automatically stunning results. But you have to think a bit about the setup, and also do some iteration.

      I wrapped up my first experiences with TDoA in this PDF. You may simply download it by double-clicking the link, and open it in a PDF reader. It consists of 22 pages and 37 instructive figures. I greatly stressed the practical part of direction finding with this tool – with 13 explicit case studies from 2,6 MHz to 15,6 MHz.

      The idea is to have more fun by getting the most reliable results.

      GRAVES: Reflections out of the blue

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      A GRAVES reflection from a meteor trail, August 21st, 2017 at 10:51 UTC. Received with FDM-S2 from Elad, a discone antenna and software V3 from Simon Brown

      Undoubtly, a Graves is a fine French wine from the Bordeaux region in western France. So it is so surprise that also GRAVES is an extraordinary Radar station. It was built to detect and follow satellites and their debris. They sequentially cover from 90° to 270° azimut in five big sectors A to D, and change from sector to sector each 19,2 seconds. Each of this sector is further divided into 6 segments of 7,5° width, covered for 3,2 seconds each.

      They are transmitting on 143,050 MHz. If you are in Europe and tune into 143.049,0 kHz USB, you probably will hear/see some reflections of meteors, airplanes and even spacecraft. The distance between the transmitter and my location is about 630 km, and for their southly directed transmissions, there most of the time is no direct reception.

      So, if you tune into 143.049,0 kHz, you will see just a blue spectrogram: noise. If you wait for a while, some signals will appear out of this blue; see screenshot on the top. With Simon Brown’s free software Version 3 you may also take a level diagram in smallest time steps of just 50 milliseconds:

      A level diagram of the meteor trail reflection from the spectrogram at the top, visualized qith QtiPlot.

      This level diagram shows the big advantage of SDRs, working on the signals on HF level, rather than of audio level as with legacy radios. The latter additionally introduce e.g. noise and phase errors. Of course, you may also listen to this signal:

      From this audio, in turn, you may do an audio spectrogram, possibly revealing further details of e.g. of the trilling sound like that from a ricocheting bullet: The Searchers (the 1956’er Western film by John Ford, not the British boy group from 1960 …) on VHF.

      Audio spectrogram of the sound, revealing “packets” of sound which result in the trilling audio. At start, these packet show a width of about 42 milliseconds to be reduced to 37 milliseconds.

      P.S. If you want to donate: my favourite Graves is from Domaine de Chevalier, blanc …

      2,5+ million of Field Strength Data from ITU

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      Tehran-Norddeich_1983-1989_15K1MHz_3D1

      Seven years of hourly field strength data of a transmitter in Tehran/Iran, received at Norddeich/Northern Germany. You clearly see the influence of time, day, season and solar activity.

       

      The International Telecommunications Union recently published many information for free, which had been locked for years behind an often impressive cash house or had been available just for a few blessed.

      Among these information is a bonanza of 2,5+ million of normalized field strength data from the years 1969 to 1993. This time covers two solar cycles and by far doesn’t provide insights of only historical interest: You e.g. may visualize some circuits to see the influence of day, time and solar activity at a glance. And you may use this data to analyze some dependence between field strength and solar/geomagnetic activity.

      As these data so far hasn’t attracted any interest of ham radio magazines, we are just at the beginning to make use of it. Join in!

      The diagram at the top has been made with QtiPlot software. The same software has been used to visualize solar and geomagnetic WDC data, obtained from GFZ Potsdam – see diagram at the bottom.

      Kp_vs-Flux_2

      Solar flux (F10,7) vs. geomagnetic activity (Kp index), 1969-1993.

       

      SDR Console V3: Signal History and six RX Panes!

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      KPL

      NEW: The Receivers’ Pane on top covers spectrum and spectrogram of up to six demodulators – look at different modes and bandwidths. Also new: “Signal History” at the bottom.

      Simon Brown, G4ELI, has further developed his software SDR Console which has become THE platform for a real bunch of very different SDRs. The new public preview has two more exciting features:

      • “Signal History” takes the signal strength of the given bandwidth each 50 milliseconds, which can be saved in a CSV file. It is also shown in three different speeds on a display.
      • “Receivers’ Pane” shows up to six combos of spectrum/spectrogram of the complete up to 24 parallel demodulators (they additionally can be shown in the Matrix, as in former versions).

      See screenshot on at the top.

      “Signal History” offers many applications, to name just three:

      • analyze fading and its structure with an unsurpassed time resolution of 50 ms
      • document fade-in and fade out
      • measure signal-to-noise ratio of signals

      As an First Aid, I have written a PDF of 19 pages with 36 instructive Figures. There you find a step-by-step introduction plus numerous example on how to use this valuable tool in practice. Please download it here. (Another tab opens, where you have to double-click “SDR_COM_Marker” to start download.)

      Surely, I will come back to these most welcomed features in more detail. For now only some screenshot examples regarding “Signal History”, which have been realized by analyzing the CSV files with QtiPlot:

      With some statistics applied on the CSV file of Signal History, you’ll get a deep inisght into fading structures. Top: original data (black), averaged (yellow), median (read line). Bottom: box diagram, histogram, 3D-band. See following screenshots for some examples.

       

      … and this is just the beginning! [Receiver: Elad FDM-S2 & AirSpy with SpyVerter]

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