These signals were captured on 14430.0 kHz (USB) by my colleague ANgazu, who kindly shared them with me. peculiar thanks go to EA1FAQ for providing access to his SDR via the AirSpy Server Network.
The intercepted transmission consists of short time-synchronized bursts, occurring either as discrete pulses or in clusters of five. Occasionally, longer-duration bursts happen with no apparent correlation to the primary pulse train. These signals exhibit a bandwidth of about 3 kHz and a symbol rate of 2400 Baud. Spectral analysis indicates a advanced SNR. Figure 1 illustrates an example of this behaviour (abridged-timeline view).
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| Fig. 1 |
Analysis of the Autocorrelation Function (ACF) exhibits strong peaks all 62.5 ms. At a 2400 Baud rate, this confirms a frame dimension of precisely 150 symbols (2400×0.0625=150). The structure likely consists of 122 unknown data symbols followed by 28 known probe symbols. This indicates that the signal is not a standard MIL-STD/STANAG waveform; based on available non-restricted documentation, no of the established standards utilize a 150-symbol framing structure.
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| Fig. 2: autocorrelation analysis |
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| Fig. 3: rhomboidal (rotated) signalling constellation |
I analyzed 1 of the long bursts utilizing an Octave script from my repository [1], and the consequence of Figure 4 closely approximates the constellation analysis shown in Figure 3.
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| Fig. 4 |
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| Fig. 5 |
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| Fig. 6 |
The explanation of 64/256-QAM is consistent with MS-110D Waveform IDs 10-12 and STANAG-4539, which support:
- 2400 baud in a 3 kHz bandwidth
- High-order QAM (64-QAM, 256-QAM)
- advanced spectral efficiency, with natural data rates of about 14.4 kbps (64-QAM) and 19.2 kbps (256-QAM), calculated at a symbol rate of 2400 baud with 6 and 8 bits/symbol respectively.
Although the constellation alone aligns with both MS-110D and STANAG 4539 standards, the observed 150-symbol periodic structure is inconsistent with the framing specified by either protocol (MS-110D 64/256-QAM modulations utilize 288- and 384-symbol frames, while STANAG 4539 employs a 287-symbol frame).
In HF environments, the Channel Coherence Time — the window during which the ionosphere remains quasi-stationary — typically ranges between 50 and 100 ms. The observed 62.5 ms probe interval offers importantly enhanced robustness compared to the MS-110D and STANAG 4539 standards (which feature durations of 120 ms, 160 ms, and 119.5 ms, respectively). By inserting a training series (probe) all 62.5 ms, the strategy enables the receiver to update its equalizer coefficients more frequently, allowing for more effective tracking of fast channel variations and Doppler spreads that would otherwise degrade high-order QAM performance.
The analysis tends to confirm the detection of a highly optimized narrowband (3 kHz) waveform alternatively than a standard MS-110D or STANAG-4539 implementation. While it utilizes a single-carrier 2400 baud rate with high-order modulation, its unique 150-symbol periodic structure distinguishes it from established military protocols. This emanation may represent experimental investigating or a next-generation waveform presently restricted to non-public documentation or classified mention libraries. At the time of writing, I have no reports of further interceptions, at least not on 14430 kHz.
