Sporadic-E Reception: Some Notes

Running from top to bottom: that’s DX! The spectrogram runs from 87.5 MHz to 94.5 MHz. The lower part shows Sporadic-E conditions around 18:00 UTC, the upper part was switched to 19:37 UTC when Sporadic-E had largely disappeared. 29May2020.

When HF collects new power for the autumn season, it’s time to thrown an ear onto VHF. I did so in May 2020, and the spectrogram at the top should give you an impression of the power and glory with with Sporadic-E fills the ORT band and the FM broadcast band. Having published some audio examples from both bands in the two recent posts, I now want to make some comments on this exciting propagation mode.

One signature of Sporadic-E is a highly selective propagation in respect to geographical regions – resembling a laser pointer. Please find below an example of just 90 seconds on 93.9 MHz on 29May2020, around 18:00 UTC (the vertical interruption at the last quarter of the audio spectrogram. It starts with a powerful-modulated, yet unidentified, Italien station with pop music. Then, Radio Constanine from Kef El Akhal (per RDS 2425) takes over with a distinctive (lower) sound, gevoerning the channel for a time, until the Italian comes through again. If play the audio clip and following its spectrogram in parallel, you surely will see what I mean.

93.9 MHz: Two stations on one channel, see text. The vertical frequency is in the logarithmic style to enhance the visibility of the most important speech formants. Listen to audio clip below.
Here you can listen to what is shown in the spectrogram above: two different stations fighting on 93.9 MHz.

Parallel listening on two channels is an essential tool to identify the same station on different channels. Place one (e.g. the left) audio channel on one frequency, and the other audio channel with a 2nd RX on the other (in this case: right channel). This can be done easily with SDRC V3 software. There will always be a time lag between both channels for at least two reasons: the main reason is that two frequencies are usually coming from two different locations, fed over different lines from the studio which causes a slight time difference. The other reason: different RXs in SDRC V3 software ore not phase-synchronized, so there is a small difference. Another difference might occur from different propagation time from two locations (300 km = 1ms!).

The screenshot below shows a typical setup: on 87.7 MHz a station in Arabic was heard. It was set onto RX1/left audio channel. To identify this station, RX2 was set to the right audio channel. Leaving RX1 on its frequency as the reference channel, RX2 was tuned to other channels with Arabic programme. The first hit was made on 87,6 MHz, second on 90,8 MHz, third on 92.5 MHz – all carrying the same programme. Hence, it was very likely SNRT Al Idaa Al-Watania from Morocco from four different locations at distances from 2312 to 2613 km.

Searching parallel programs: right (as basic) audio channel on 87.7 MHz, left audio channel on 90,9 MHz showed programmmes being (largely) in parallel – see the spectrum, and listen to the audio, both below.
Spectrogram of both channels of the audio clip below: left audio = top, right audio = bottom In the first few seconds, including the time-beeps, 87.7 MHz produces “Radio Chlef” from Bou Kadir/Algeria (1963 km), according RDS. Then SNRT Al Idaa-Watani from Midell (2498 km) takes over.
Listen to the above spectrogram in stereo. Soon you will hear that 90.8 MHz lags a bit in time. And that in the first seconds both channels are not in parallel.

The Radio Data System RDS provides an identifcation and often some additional information. First, you see the “Programm Identification Code – RDS-PI”. This is used to support an automatically scan of the receiver to tune always the best channel of this programme. Hence, it designates a programme which is used throughout a chaine of programmes. The “Programme Service Code – PDS-PS” needs a bit longer and gives, if programmed, additional information. As the RDS signal sits on edge of the channel and is quite slow, it is a bit delicate to receive from weak stations under interference. The first example below gives a full-blown RDS signal from a local broadcaster, followed by some RDS signals from DX stations.

Here you see all elements of an FM multplexed (local) stereo signal. The double-peak on the righ is the DSB-modulated RDS signal.
A selection of received RDS signals, in reading direction: 92AA Top Albania (1356 km), 505F Radio Sound/Italy, 5264 RDS/Italy (1304 km), 11DE Radio Epirus/Greece (1648 km), 5201 RAI Radio 1 /Italy (1635 km), Radio Soummam/Algeria (1810 km), E2ED Europa FM/Spain (1364 km), 2202 Chaine 2/Algeria (1802 km)

Fading can be nerve-wrecking. Stations come and go. And they reliably go at top of the hour when the listener expects a station identification … Below I compared the signal from a still near-regional transmitter at a distance of 83 km with that of Radio Constatine/Algeria, 1802 km away. The grey block marks the limit, whre Radio Constanine can be demodulated.

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