Category Archives: SDR

FM-DX: How to Identify very short openings – a few examples

42 seconds in a recording of 12 hours length – a “blob” in V3’s “Analyser” module reveals a DX chance.

In the last weeks, I had used Sporadic-E conditions to stroll a bit in the FM broadcast band in search for DX. Elad’s FDM-S3 covers the whole 20 MHz wide band, and Simon Brown’s SDRC V3 software again provides an unique and most valuable tool to dig out DX. Antenna is an active Dressler ARA-200 (R.I.P.).

This blog entry shows how to make use of short openings of only some (ten) seconds.

First step is to record the whole FM broadcast band for hours on external HD. Then you make up so-called “spectrograms” by V3’s Analyser module. This provides you with a picture of activity (signal strengths color-coded) over time and frequency – see screenshot at top of this blog.

Scrolling through this spectrogram, you can make out even the shortest openings. Just click onto one of them, and the software instantaneously tunes into it. The sensitive RDS decoder of V3 is doing the last step – showing its RDS identification.

The short video below gives one example from a recording of June 26, 2020. On 91.8 MHz, I received semi-local transmitter NDR 1 NDS at Visselhövede (5kW@67 km distance), with “Stand by me”. From the spectrogram, I saw a “blob” (see screenshot at the top of this blog), stretching over around 40 seconds. It turned out to be Algerian’s Akfadou transmitter with Chaine 2 programme, 70 kW ERP@1’810km distance! RDS did tell me. Just have a look at the short video below which was made with V3’s video recorder …

First “Stand by me” by a local transmitter, then CHAINE 2 drops in for about 40 seconds, after the local transmitter takes over again.

V3 software provides also an a-symmetrical tuning of bandwidth, even at wide FM/BFM. This is important to identify some stations “in the clear” – if they are prone to some spillover from a local/regional station right on an adjacent channel. The following example spots Radio Marca/Mallorca from Spain on 91.6 MHz, suffering not only from a a strong local just 100 kHz below, but also from a very short appearance “out of the blue”, to where it disappeared again after less than 30 seconds. The latter is shown in the spectrogram, made by the Analyser, where I magnified the small/short signal of Radio Marca over 1’541 km. The video at the bottom shows how to evade the interference from the channel below to get the RDS code “B002 R.MARCA” correct.

On an empty channel, a stations pops up for 28 seconds. Pinpointed by V3’s “Analyser”, decoded as RDS “B002” Radio Marca from Na Burguessa/Mallorca in Spain by the RDS decoder.
With a strong local just 100 kHz below, a-symmetrically tuning the bandwidth helps to identifythe very short pop-up of Radio Marca/Mallorca on 91.6 MHz by RDS.

Sometimes propagtion is too short for any identifcation, neither RDS, nor by announcement. Take the next screenshots as example: The spectrogram shows some very short openings revealing similar pattern which cropping the recording (Crop – > Apply) confirms. It turns out to be an English-speaking stations for a maximum of ten seconds. Parallel listening reveals the same programme on the following eight frequencies: 88.3MHz, 88.4MHz, 88.5MHz, 88,7MHz, 88.9MHz, 89.1MHz, 89.7MHz and 89.8MHz. The only intersection turns out to be Raidió Teilifís Éireann from different locations with their Radio 1 programme.

Up to ten seconds in a ten hours’ recording, marked by a rectangle in the spectrogramme: whodunit?
All nine stations carried a broadcast in English, eight of them in parallel, only that on 89.6MHz remaining unidentified. The solution is easy …

RTE transmitter usually do have RDS onboard, but here the time with a modest signal was too short to raise the alarm. On the other hand, there are stations with RDS, but not programmed or even without RDS at all. Take Radio Tisnath/Algeria in Tamazight, a Berber language, as an example for the first and Radio Blagovestiye/Russia as an example for the latter:

Radio Tisnath from Djebel Tissalah/Algeria [2’091km] should carry RDS-ID of “2202 CHAINE2”, which didn’t pop up – in spite of the good signal. At least a station identification was heard, alas, a bit distorted after a programme in Tamazight in the clear
As with all OIRT band stations, also Radio Blagovestiye from Voronezh/G-Tsa Brono in Russia [1’984km) doesn’t carry any RDS information. You have to wait for the announcement – as here – or to collect some other information to identify such a station.

Nĭ hăo, Xinjiang Broadcasting Station!

Still going strong since 1949: Radio Xinjiang, here their banner in Chinese and Mongolian; from their Mongolian website.

Okay, the birthday flowers are already letting hang their heads – but better late than never: Happy birthday, Radio Xinjiang, XJBS!

It was founded in the same year as the People’s Republic of China itself. Only the 1957 edition of the authorative World Radio Handbook took a first notice of their shortwave transmitters at Ürümqi. One of these frequencies, namely 4500 kHz, is still active today.

Among DXers, Radio Xinjiang is a welcomed signal from their transmitters at Ürümqi-Hutubi and at Ürümqi-Changii, some ten kilometeres northwest of Xinjiang’s capital Ürümqi, all in the north-west corner of China.

XJBS’ shortwave transmits in Uighur, Kazakh, Mongolian and Mandarin (“Chinese”) to serve the majority of listeners in each their mother tongue. Please find below their station’s announcement in each of those language. I especially like the “Nĭ hăo, Xinjiang” of the Mandarin recording at second 20. The announcer must have seen Good Morning, Vietnam, undoubtedly echoing Adrian Cronauer [the late Robin Williams].
Just for conaisseurs: in the YouTube clip, Adrian mentioned “Hanoi Hannah”, or Trịnh Thị Ngọ, a popular radio announcer at Radio Hanoi from 1965 airing three shows per day in English, directed towards US GIs. She left microphone only in 1973, after the USA fled from her country.

The following audio clips from my 25MHz/24h recording of December 16, 2019, received with Winradio’s Über-SDR Excalibur Sigma, connected to MD300DX antenna, an active dipole, hung vertical, with 2 x 5m legs.

Mandarin: “Gooood moorning, Xinjiiaaaaang!” 5960kHz, 02:00 UTC
Uighur: 6120kHz, 00:00UTC
Mongolian: 6190kHz, 02:00UTC
Kazakh: 6015kHz, 03:00UTC

I will come back to this interesting station with an analysis of their alltogether 24 HF frequencies between 3950kHz and 13670kHz here in Northern Germany in December 2019, as well as in early April 2020.

P.S. Below a QSL of this station, from 1984 on 4735kHz.

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

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

Greyline enhancement

Signal level on 4750 kHz, observed over some hours: After s/off of Bangladesh Betar, People’s Broadcasting Station at Hulun Buir emerged, showing a peak just after their local sunrise

Today’s SDRs plus able software allow for some new insights into propagation. The figure at the top shows but one example: greyline enhancement. It follows the signal levels on 4750 kHz with a resolution of one second. Smoothing this cloud of points, reveals the more general course of signal level. Here we see, after sign off of Bangladesh Betar, the 10 kW transmitter of People’s Broadcasting Station at Hulun Buir coming up. Most interesting is its short-living enhancement just after sunrise at Hailar in China’s Inner Mongolia, squeezed at their borders to Russia and Mongolia.

This greyline enhancement can be observed regularily on frequencies under, say, 10 MHz: at sunrise at the transmitter’s site, first the F2 layer of the ionosphere is building up, being responsible of the signal of, here, about 5 dB. The lower and attenuating D-layer needs a bit more time to build up, leaving a short-living window for an enhanced signal.

This is to encourage also other HF aficionados to to use this technique.

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

CIS Time Signals on VLF

Locations, callsigns and starting times of the received VLF time signal stations, 25 kHz

On January 10, 2020, I did a round-up of VLF time stations from the Commonwealth of Independant States (CIS). They are controlled by the Russian Navy and start their main transmission on 25.0kHz. Then they change to a couple of four other VLF channels. See here for some detailed information in Russian. The diagram below shows a panorama of all received station (Khabarovsk in the Far East missing, as they skip transmission on the 10., 20. and 30. each month) on all frequencies versus time and signal level.

Five locations, six transmissions, five frequencies – this diagram puts it all together.

The diagram features a time resolution of 1s and has a resolution bandwidth of about 0.12 Hz. It is part of a 24h session, made with Winradio’s Excalibur Sigma SDR, active dipole MD300DX (2x5m) and Simon Brown’s software SDRC V3. This software delivers also the values for level over time, which were visualized and combined with QtiPlot software.

Only seemingly, Vileyka and Krasnodar are transmitting on two channels at the same time (from 07:06 UTC/11:06 UTC). This is not the case, but their transmitters show a bit wider signal in their first part of the transmission. Thus, the much weaker (ca. -30dB) “signal” at the same time, but 100Hz up, is some kind of sideband, but not the carrier!

You will see some variation of the carrier power, especially following sign on, but also during the transmission. This can bee seen with tenfold time resolution (i.e. 100ms) and magnifying the dB-scale, see diagram at the bottom as just one example. Fading can be largely excluded for several reasons, artificial characteristic of changes and VLF propagation during short periods among them.

Under the microscope: This rise of 1.5dB of the carrier is part of the workflow of switching on/tuning the transmitter. There are many such details, and they may differ from transmitter, location and performance. Such details might be used for “fingerprinting”.

P.S. The map at the top was made with free software Tableau Public. The locations are geo-referenced, and a satellite map as background will you lead directly to the antennas. Please try this here.

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.

Looking at Things: Elad FDM-S3 [beta]

The new FDM-S3. Made in Italy, by ELAD.
19.7 MHz alias-free for receiving, recording and playing

As seen from now, ELAD’s FDM-S3 is still to come. It features a 16 bit SDR with up to 24 MHz bandwidth (19.7 MHz alias-free) for receiving, recording and playback. It will become the great brother of the renowned FDM-S2 of also 16 bit, but with just 5 MHz alias-free bandwidth which was State-of-the-Art when this radio hit the market. Still, this remarkable FDM-S2 sets the standard in its price class.

The file format of the S3 is the same as with the S2, so Simon Brown’s software SDRC V3 works on S3 files also (see screenshot at the bottom). This opens V3’s File Analyzer plus up to 24 demodulators when playbacking files. SDRC V3 will support also live reception when the radio will be more widely available.

Simon Brown’s software SDRC V3 is reading FDM-S3’s files also.
The FDM-S3 cover the whole FM band. Here shown with receiving six stations in parallel, including demodulation and RDS deocding. The lower half of the the spectrogram shows the performance without pre-amplifier, the upper part with pre-amplifier switched in.

Airspy HF+ Discovery & Spurious Signals – Much Ado about Nothing

Worst case: Those very few and low-level spurious signals of the “Discovery” disappear completely in the atmospheric noise after you connect an antenna – leaving even faintest stations in the clear.

There had been some discussion about the “real” performance of the brand new Airspy HF+ “Discovery”. It is not only my experience that this great little SDR is a perfect performer at a ridiculous low price.

The discussion focuses on “spurious signals”. I measured them with the Winradio SIGMA as spectrum analyzer, compared it to the two past Airspy HF+ models, plus Discovery, and did some work on how this effect might touch reception.

The result is clear: this discussion in the Ivory Tower is “Much Ado about Nothing”. You may read more about method & findings, with many diagrams, in this PDF.

3 x CW: Kagoshima Fishery Radio, JFX

Parallel DXing: JFX on 6421,5 kHz, 8690 kHz and 12704,5 kHz

Morse Code or CW has become rare among professionals (in the West). But there is a busy net of small Japanese Fishery Stations literally pounding the brass. One of them is Kagoshima Radio, JFX. They are not daily heard in Europe, but a combination of receiver Winradio Sigma, active antenna MD300DX (2×2.5 m, vertical) and SDRC V3 software did the trick even under this grim summer propagation. See screenshot above, from 24 hours’ recording of 25 MHz HF. All channels clearly readable – as far as the expressive handwriting (see detailed screenshot at the bottom) of their CW allows for … Yeah: CQ CQ DE JFX JFX QRU QSX 6 / 8 /12 MHz K

First part of the CQ call of JFX in good ol’ hand-made CW … from 12704.5 kHz

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