Category Archives: HamRadio

Winter and Spring: Comparing Signal Strengths

IRAN INTERNATIONAL’s relay station south of Tashkent/Uzbekistan, received on December 16, 2019 (blue line) and April 2, 2020 (yellow line). Day/night below, top pair for Tashkent, lower pair for DK8OK, on the two dates, respectively.

IRAN INTERNATIONAL is transmitting in Farsi via their relay station just at the outskrits of Uzbekistan’s capital, Toshkent, with 100kW on 6270kHz from 12:00 to 04:00 UTC, directed towards Iran.

I received this station in winter as in spring. In winter (namely 16DEC2019), the whole transmission from sign-on to sign-off can be received, wheras in spring (namely 02DEC2020) a considerable part of the transmission after sign-on has been lost in the noise, plus the time towards sign-off in the morning largely coinciding with fade-out; though still celarly visible.

You see also a clear greyline enhancement at least on the fade-in. Sunrise and sunsetset for both locations can be seen from the bar chart below in the diagram..

Path Tashkent-DK8OK of Apbil2, 2020 at 16:00 UTC, path length 4550km.

The graphs are based on 2 x 86’400 points each, providing a time resolution of one second. To make things more clearly, the bold blue and yellow lines represent a smoothed version (moving average: 601).

This is just one example of how the actual signal strength of a station differs from season to season. With 24 hours’s recordings of the whole HF on both dates, it is easy to compare also other stations and frequency ranges. If I have time, I will add some more examples in the future.

BTW: I passed the big transmission center southwest of Toshkent left-hand, riding M39 on the way to Samarkand; it was not encouraged to take any photos …

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

Fade-in: Voice of Broad Masses, Asmara/Eritrea

Figure 1: Signal strength of VoBM on 7140kHz from s/on around 14:06 UTC to s/off around 18:30 UTC.

The evening transmission of the Voice of Broad Masses from Asmara-Selae Daro in Eritrea signs on around 14:06 UTC and signing off around 18:30 UTC. Figure 1 shows the signal levels with a resolution of one second, marked by red points, and the smoothed level, yellow line, with a moving average of 601 points, or 10 ten minutes. Smoothed levels span a range from -106 dBm/Hz to -80 dBm/Hz.

There occur considerable peaks around 14:30 UTC, 16:15 UTC and 17:30 UTC. Raytracing the signal, transmitted by a Quadrant antenna HQ1/.25, will help to reveal some mechanics behind the curve.

Figure 2: At s/on, we have a four-hop propagation via the F1 layer, carrying the main signal.

Figure 2 shows a four-hop propagation via F1 layer at 140-160km with a relative steep elevation of about 22°. The much shorter hops, reflected at the E-layer at a height of about 100km, are of less to no importance. The signal gets through, but very weak. The path itself still is in full sunshine, see Figure 3.

Figure 3: At s/on just after 14:00 UTC, the path between Asmara and DK8OK still is in full daylight.

There is a very short, but distinctive peak at 14:30 UTC. This coincides with a similar short time of three-hop propagation (Figure 4) from a very low azimuth of 3°. Of course, the full path still is in daylight.

Figure 4: Around 14:30 UTC, signal improved a bit as a three-hop propagation (still via F1) comes into play.

Just after 16:30 UTC and near sunset at the transmitter (16:37 UTC), there is reached the bottom of kind of a “Hillary Step” before the last run to the peak. The way to a (quite short) plateau starts around 17:00 UTC. There we have a textbook-like two-hop propagation (Figure 5) with the greyline covering just more than half of the great circle path (Figure 6). There, an elevation of under 5° is needed.

Figure 5: From around 17:00 UTC, a time of good reception starts. Reason is the textbook-like two-hop propagation.
Figure 6: With more than half of the great circle path in darkness, VoBM puts a fine signal into Germany.

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

Propagation Day by Day: CRI Kashi, 15.260 kHz

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

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

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


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.

SDR Console V3: New and indispensable Software


“Living Sonagram”: On the right window, you see a part of a 24 h recording at 6,1 MHz bandwidth (ca. 2 TB) with 1 line/second. Tagged is the sign on of Dimtsi Hafash which is received by the undocked “Receive” panel of V3’s GUI. At the bottom: signal strength on 7180 kHz over 24 hours reveals e.g. s/on, s/off and fade in.

Just a small note on a real real big event: Simon Brown, G4ELI, has published V3 of his indispensable SDR Console software on June 18th, 2018 – after three and a half years of heavy coding. Download it here and donate. Or vice versa.

V3 is a quite universal software for most SDRs on the market. For all, it provides the same graphical user interface (GUI) and the same functions (plus those specific to some devices).


DXer’s delight: On top the sonagram to visually catch signals (here: JDG from Diego Garcia; tagged). Bottom, from left to right: receive GUI for fine tuning, decoder W-Code showing “JDG”, below this “Playback” panel for controlling the recording (back/forward, e.g.), and on the right a database.

There are many unique functions and modules which will take DXing with SDRs to the next step. For now, let me mention just two of them:

  • 24 parallel demodulators within the SDR’s bandwidth – fully independent in e.g. mode, bandwidth and AGC to receive, record and decode 24 signals/channels in parallel.
  • a sophisticated File Analyser  which presents a recorded band as “living sonagram” – whre you see and click to a signal which then is played via the basic GUI


Up to six parallel demodulators can be seen on the main screen (from up to 24 possible).



1520 kHz from 18:00 to 05:00 UTC (local SR/SS: 19:43/02:58 UTC) with 100 Hz bandwidth and 0,0031 Hz resolution (= +65 dB over 10 kHz!) reveals at least 27 stations and their offsets.

Each of these just two features mentioned will open new worlds for DXing and even serious professional monitoring. I will be happy to come back to some applications of V3 in more detail.

Thank you very much, Simon, for providing this excellent tool for free!


4’800 kHz: First CNR1 with sign on at 20:15 UTC and fade out, then AIR Hyderabad with the same, but s/on around 00:06 UTC.



You may export levels over time on one frequency or level over frequencies at a given time. This graph visualizes the activity on 7435 kHz with 86’400 levels (on per second over 24 h). The data had been exported to QtiPlot for further investigation.

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