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arxiv: 2605.19697 · v1 · pith:TJE4JHVQnew · submitted 2026-05-19 · 🌌 astro-ph.SR · astro-ph.IM

The Small Phased Array DEmonstrator (SPADE) -- Description and first results

Christophe Marqu\'e (1) , Antonio Mart\'inez Picar (1) , Jasmina Magdaleni\'c (1 , 2) , Elisa Tassan-Din (1) ((1) Solar Terrestrial Center of Excellence - Royal Observatory of Belgium , (2) Center for mathematical Plasma Astrophysics , KU Leuven) This is my paper

Pith reviewed 2026-05-20 02:21 UTC · model grok-4.3

classification 🌌 astro-ph.SR astro-ph.IM
keywords phased arraysolar radiodecameter observationssoftware-defined radiocoronal turbulenceradio propagationsolar burstsspace weather
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The pith

A compact digitally operated phased array using commercial receivers achieves temporal and frequency resolution for solar decameter observations comparable to larger facilities.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper introduces SPADE, a small phased array spectrograph built for continuous monitoring of solar radio activity in the decameter band where many bursts relevant to solar physics and space weather occur. All Sun tracking and spectrum generation are handled digitally through open-source software libraries and standard commercial software-defined radio hardware rather than specialized equipment. Observations of the Sun and Jupiter's magnetosphere collected from September to December 2024 are presented to illustrate the instrument's performance. The work emphasizes that the resulting time and frequency resolution opens access to coronal turbulence studies and radio-wave propagation effects that have previously required much larger, non-solar-dedicated arrays.

Core claim

SPADE performs Sun tracking and spectrum production entirely through digital processing on commercial generic software-defined radio receivers and open-source libraries. First solar and Jovian data obtained between September and December 2024 demonstrate that the instrument's temporal and frequency resolution suffice to address topics such as turbulence in the coronal medium and propagation effects on radio waves that are currently accessible only with larger phased arrays not dedicated to solar work.

What carries the argument

The SPADE phased array spectrograph, which executes all tracking and spectral operations digitally with open-source libraries and commercial software-defined radio receivers.

If this is right

  • Solar bursts can be monitored continuously at high time resolution with a compact ground-based system.
  • Coronal medium turbulence becomes observable through radio signatures in the decameter range.
  • Propagation effects on solar radio waves can be studied without access to large dedicated facilities.
  • Digital processing pipelines using off-the-shelf receivers reduce hardware complexity for routine solar observations.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Multiple low-cost copies of the same design could be deployed at different longitudes to increase continuous coverage of solar radio events.
  • The digital architecture may allow straightforward addition of polarization or direction-finding modes in future versions.
  • Data streams from such arrays could be combined with optical or X-ray solar monitors to cross-calibrate propagation models.

Load-bearing premise

Commercial generic software-defined radio receivers together with open-source libraries can supply the sensitivity, calibration stability, and interference rejection required to reach the stated temporal and frequency resolution for solar science.

What would settle it

Solar radio burst spectra in which fine temporal or frequency features remain unresolved or are masked by interference when compared against simultaneous data from established larger arrays.

Figures

Figures reproduced from arXiv: 2605.19697 by 2), (2) Center for mathematical Plasma Astrophysics, Antonio Mart\'inez Picar (1), Christophe Marqu\'e (1), Elisa Tassan-Din (1) ((1) Solar Terrestrial Center of Excellence - Royal Observatory of Belgium, Jasmina Magdaleni\'c (1, KU Leuven).

Figure 1
Figure 1. Figure 1: Left: Configuration of the eight antennas of SPADE; right: top, north-south cut of the result￾ing beam for a uniform 20×20 m ground plane, bottom, same but along the east-west direction. 1972 until 2001. Since 2008, new radio instruments have been set up at the station, making use of refurbished existing telescopes (6-m telescopes and 4-m telescopes from the heliograph, see Koeckelenbergh (1971) for a desc… view at source ↗
Figure 2
Figure 2. Figure 2: Analytical calculations of the beam pattern resulting from the chosen array configuration at different frequencies. The Sun is marked by a yellow dot not up to scale. ing a ground dielectric constant of 15 (according to the International Telecommunication Union (ITU) Recommendation P527.3) and a conductivity of 0.009 S/m (ITU Recommendation P832.1). Aluminium was assumed for the antenna elements, and steel… view at source ↗
Figure 3
Figure 3. Figure 3: View of the SPADE array from the roof of the cabin containing the receivers, showing the eight antennas and the uniform ground plane on the platform. In the background, some of the 4 m dishes of the old radio heliograph can be seen. derground pipes converging to an environment controlled cabin (about 27 m away from the array center) hosting the solar receivers already operating at the station. For each ant… view at source ↗
Figure 4
Figure 4. Figure 4: Schema of the SPADE receiver programs, showing both the physical connections between the receivers (the two square boxes on the left with the external reference signals and the sharing of the LOs between the daughterboards), and from then the dataflow within the program. The individ￾ual boxes from multiply matrix to zeromq push sink are program blocks and their naming matches the ones available in GNU Radi… view at source ↗
Figure 5
Figure 5. Figure 5: Overview of the eruptive event of 18 November 2024, showing the GOES light curves (top) together with a composite plot of radio observations from HSRS (Humain station, 1495 – 275 MHz), ORFEES (Nanc¸ay Observatory, 275 – 144 MHz), SPADE (Humain station, 66.7 – 33.3 MHz) and WIND-WAVES (14 – 1 MHz). The two black arrows under the GOES light curves mark the peak times of the flares mentioned in the text. top … view at source ↗
Figure 6
Figure 6. Figure 6: Excerpt of the quasi-periodic bursts observed during the type II event of 08 December 2024, with time and frequency cuts displayed on the right-hand side. Figure C.2 shows another type II burst that occurred on 08 December 2024. Associated with an X2.2 class flare (09:06 UT, peak time), the radio event is remarkable by its high number of fine fre￾quency structures in shock-accelerated type III bursts. Thes… view at source ↗
Figure 7
Figure 7. Figure 7: Observations between 13:30 and 13:33 UT of the group of type III bursts on 02 October 2024, made by SPADE (top), NDA (middle), and the GERMANY-DLR CALLISTO station (bottom). The intensity scale represents dB over background. on how fast spectra can be written on disc, on the PC that currently controls the receivers. For solar observations, the pointing of the instrument is made specifically for 50 MHz, and… view at source ↗
read the original abstract

We present the Small Phased Array DEmonstrator (SPADE), a compact phased array spectrograph designed for the monitoring of solar activity in the decameter range, where a majority of bursts of interest for solar physics and space weather occur. Unlike other existing phased arrays, SPADE operations like Sun tracking and spectra productions are made entirely digitally, and rely on the use of open source library software and commercial generic software defined radio receivers. In this paper, we describe the instrument and its associated software and present the first observations of the Sun and of the jovian magnetosphere performed between September and December 2024. For the solar observations, in particular, we highlight the capacities of the instrument in terms of temporal and frequency resolution, making it capable of addressing science topics like turbulence in the coronal medium and propagation effects affecting radio waves, which are currently only accessible by larger but non-solar dedicated phased arrays.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 1 minor

Summary. The manuscript describes the Small Phased Array DEmonstrator (SPADE), a compact phased-array spectrograph for decameter solar monitoring. It details the instrument hardware, digital Sun-tracking and spectral processing implemented entirely with commercial software-defined radios and open-source libraries, and presents first solar and Jovian observations obtained between September and December 2024. The central claim is that the achieved temporal and frequency resolutions enable studies of coronal turbulence and radio-wave propagation effects that have previously required larger, non-solar-dedicated arrays.

Significance. If the performance claims are substantiated, SPADE would offer a low-cost, replicable platform for routine high-resolution solar radio observations in a scientifically important but under-instrumented band. The explicit reliance on commercial SDRs and open-source software is a positive feature that could facilitate broader community access and reproducibility.

major comments (1)
  1. [Abstract and first-observations section] Abstract and the section describing the September–December 2024 solar observations: the assertion that the instrument reaches temporal and frequency resolutions adequate for coronal-turbulence and propagation studies is load-bearing for the paper’s scientific motivation, yet no measured quantities (system temperature, Allan variance of gain/phase, dynamic range after RFI excision, or direct comparison with component datasheets) are reported to confirm that commercial SDR front-ends plus open-source libraries actually deliver the required sensitivity and stability in the crowded decameter band.
minor comments (1)
  1. Figure captions and axis labels should explicitly state the integration time and frequency resolution used for each displayed dynamic spectrum so that readers can directly assess the claimed performance.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their constructive review and recommendation. We address the single major comment below, agreeing that additional quantitative metrics will strengthen the manuscript's claims, and have revised the relevant sections accordingly.

read point-by-point responses

  1. Referee: [Abstract and first-observations section] Abstract and the section describing the September–December 2024 solar observations: the assertion that the instrument reaches temporal and frequency resolutions adequate for coronal-turbulence and propagation studies is load-bearing for the paper’s scientific motivation, yet no measured quantities (system temperature, Allan variance of gain/phase, dynamic range after RFI excision, or direct comparison with component datasheets) are reported to confirm that commercial SDR front-ends plus open-source libraries actually deliver the required sensitivity and stability in the crowded decameter band.

    Authors: We agree that the manuscript would benefit from explicit quantitative performance metrics to support the central claim. The first-observations section already illustrates the achieved temporal and frequency resolutions through spectrograms that resolve fine structures in solar bursts and Jovian emissions, directly relevant to turbulence and propagation studies. To address the referee's point, we have added a new subsection on instrument performance in the revised manuscript. This includes measured system temperature estimates from on-sky and receiver noise, dynamic range after RFI excision derived from the 2024 datasets, and comparisons against the commercial SDR datasheet values for sensitivity and linearity. Allan variance of gain/phase is not reported because the observation sessions were too short for meaningful long-term drift analysis; instead, we provide short-term phase stability from the array coherence in the solar data. These revisions substantiate the claims without overstating the scope of the initial results. revision: yes

Circularity Check

0 steps flagged

Instrument description and first-results paper contains no derivation chain or fitted predictions

full rationale

The manuscript is an engineering description of the SPADE phased-array spectrograph together with initial solar and Jovian observations obtained between September and December 2024. No equations, fitted parameters, or quantitative predictions appear that could reduce to the instrument's own inputs or to self-citations. Performance statements about temporal and frequency resolution are presented as direct consequences of the digital Sun-tracking implementation and the first data sets rather than as outputs of any prior model or fit. Consequently the paper is self-contained against external benchmarks and exhibits no circularity.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

This is an instrumentation and first-results paper with no mathematical derivations, fitted parameters, or postulated physical entities; the contribution rests on engineering integration and observational demonstration rather than new theory.

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