| Metric | Re (Left) | Im (Right) | |h| (Magnitude) |
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| Marker | Prob | dB rel mean |
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Notes:
Sampling in this tool is performed on complex baseband (IQ) data with the explicit goal of characterizing slowly varying, narrowband propagation channels. The incoming signal is reduced to a single complex channel coefficient as a function of time, capturing the essential fading and Doppler behavior of the propagation medium while remaining independent of the transmitted modulation.
All processing is implemented entirely within a standard web browser, making the tool immediately accessible on any modern platform without specialized software. This design prioritizes portability and interactivity, while remaining well matched to channels whose dominant dynamics evolve on millisecond-to-second time scales.
The channel is sampled using block-based RMS processing of the IQ stream. At a commonly used 100 Hz sampling rate, the channel is observed once every 10 ms, and each sample represents the average channel behavior over that interval. This provides stable, low-noise measurements and clearly resolves fades, correlations, and trends occurring on time scales of tens of milliseconds and longer.
Because the channel is observed at a finite sampling rate, inaccurate results can occur if the channel varies faster than the selected sampling interval. At a 100 Hz sampling rate, channel fluctuations or Doppler components approaching or exceeding approximately 50 Hz cannot be uniquely represented and may appear distorted or underestimated. Similarly, fades shorter than the sampling interval are averaged rather than individually resolved. For this reason, the tool is not intended for rapidly time-varying, wideband, or frequency-selective channels, nor for fast mobile scenarios with large Doppler spreads. When applied to slow, narrowband channels—where the dominant physical dynamics evolve well below these limits—the resulting statistics remain reliable and physically meaningful.
Doppler measurements are aligned with this same operating regime. In live operation, Doppler spectra derived from a 100 Hz sampled channel accurately capture Doppler components up to approximately ±50 Hz, which comfortably encompasses the Doppler spreads seen in most HF and Earth–Moon–Earth links. In file-based operation, Doppler analysis uses decimated IQ data to achieve a higher effective Doppler bandwidth while remaining efficient in a browser environment.
The tool is based on a flat-fading, narrowband channel model, which is an excellent approximation for many radio science and weak-signal experiments. Under this model, the channel is fully described by a single complex gain versus time, enabling classical statistical measures such as amplitude distributions, autocorrelation functions, coherence time, and Doppler spread to be directly interpreted.
A major strength of the tool is the ability to derive a comprehensive set of channel statistics from a single observation. These include envelope PDFs and CDFs, Doppler spectra, coherence metrics, level crossing rates, and average fade durations, all computed in a consistent and physically meaningful framework.
Overall, the tool is particularly well suited to HF ionospheric propagation, Earth–Moon–Earth paths, and narrowband beacon measurements, where channel evolution is governed by slow physical processes. By combining well-established channel theory with a browser-based implementation and a practical 100 Hz sampling regime, the tool provides an effective and accessible platform for studying slow, narrowband radio channels.
In addition, it is also possible to gain partial understanding about unknown narrowband transmissions; after bandpass filtering, the waveform time-domain plot, constellation plot and CCDF can be seen. The filtered and sampled data can also be output as a wav file for further post-processing, and all data exported as a zip file.
Additional demo IQ WAV file AM transmissions for HF ionospheric propagation research:Version History: (Press CTRL-F5 to refresh cache)
001 - 1st stable version