First measurements with prototype radio antennas for the IceTop detector array

Max Renschler (for the IceCube Collaboration)

REVIEW 3 major objections 5 minor 19 references

First measurements with prototype radio antennas for the IceTop detector array

T0 review · 3 major / 5 minor · reviewed 2026-08-14 · deepseek-v4-flash

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Pith's one-line read South Pole radio antennas pick up unexplained peaks every 10 MHz

desk verdict A useful, honest engineering status report; the deployment and LNA work are solid, but the RFI/background excess rests on an uncalibrated absolute baseline and should be read with skepticism. read the letter →

arxiv 1908.10565 v1 pith:4NEU6DUX submitted 2019-08-28 astro-ph.IM astro-ph.HEphysics.ins-det

Max Renschler (for the IceCube Collaboration) This is my paper · ORCID

classification astro-ph.IMastro-ph.HEphysics.ins-det

keywords radiodetectionofairshowersIceToparraySouthPolebackgroundradio-frequencyinterferenceSKALAantennahybridDAQcosmic-rayPeVgammarays

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

This paper reports the first field measurements from two prototype radio antennas deployed at the South Pole in January 2019, as a test for extending the IceTop air-shower array with radio detectors. The central result is that the antennas, their low-noise amplifiers, and the shared hybrid data-acquisition system survived deployment and produced usable spectra, but the measured radio background near the central laboratory building is higher than the sky-noise prediction used in the analysis. The spectra also show unexplained radio-frequency-interference peaks that start at 50 MHz and repeat every 10 MHz. These findings matter because the planned full array of 96 antennas depends on a clean radio environment, and understanding the excess and periodic peaks is a necessary step for measuring highly inclined air showers and searching for PeV gamma rays from the Galactic Center.

What carries the argument

The central object is the SKALA-2 prototype antenna, a wideband antenna covering roughly 70 to 350 MHz with a low-noise amplifier whose gain stays constant within about 2 dB from 20 °C down to -70 °C. It is paired with the hybrid TAXI data-acquisition system, a DRS4-based readout platform that digitizes scintillator and radio signals at 1 GHz, preceded by a radio front-end board that filters the signal to about 50 to 350 MHz. The comparison baseline is the expected amplified sky background, built from the sky-noise model, the simulated amplifier gain, and a fixed 30 K thermal-noise contribution; this predicted curve is the reference that makes the measured field spectra look higher than expected.

What would settle it

Replace the simulated amplifier gain in the expected spectrum with the low-noise-amplifier gain actually measured at low temperature (shown in the paper's Fig. 2) and recompute the comparison; if the excess over the sky-noise prediction disappears or the 10 MHz peaks no longer sit above the recalibrated baseline, the paper's central interpretation is not supported.

Watch

Extended reading notes

Core claim

On the paper's own terms, the SKALA prototype antenna with its internal low-noise amplifier and the TAXI-based hybrid DAQ that digitizes both scintillator and radio signals operated successfully at the South Pole. In two one-hour background measurements taken about 25 meters from the central laboratory building, the measured spectra exceed the expected amplified sky background computed from the sky-noise model together with a simulated amplifier gain and a 30 K thermal-noise contribution. Both spectra show RFI peaks that become visible at 50 MHz and reappear every 10 MHz; the source is unknown, with nearby electronics inside the laboratory a plausible origin. The antenna polarization aimed toward the laboratory records more noise than the perpendicular polarization, as expected from a nearby noise source.

Load-bearing premise

The load-bearing premise is that the simulated low-noise-amplifier gain, the 30 K thermal-noise contribution, and the sky-noise model together give an accurate absolute calibration, because every claim of an unexpected excess or periodic peaks is read against that predicted curve.

Editorial extensions

If this is right

The prototype station's mechanics and electronics can survive South Pole conditions, so the deployment method can be scaled to the planned 32-station, 96-antenna array.
The hybrid DAQ successfully samples particle and radio signals together, demonstrating the technical basis for a combined surface detector that records both air-shower components.
The radio environment within about 25 meters of the central laboratory building carries periodic interference at 10 MHz intervals, so any physics array must either move away from such infrastructure, shield it, or identify and remove the source.
If the excess over the sky-noise prediction is real, the absolute calibration of the full array will need to include additional thermal or local noise contributions beyond the model.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

My inference: the strict 10 MHz spacing of the RFI peaks points to a digital clock or switching power supply near the antennas; because the high-pass filter starts near 50 MHz, a single 50 MHz or 100 MHz harmonic source could produce the observed comb.
My inference: the comparison against an absolute sky-noise curve rests on the simulated amplifier gain, so redoing the prediction with the measured gain from the paper's own Fig. 2 would show how much of the reported excess is calibration-dependent.
My inference: repeating the same background measurement with the antenna moved kilometers away from the central laboratory, at the position of the permanent prototype array, would determine whether the excess and peaks are local infrastructure or a genuinely unexpected South Pole background.
My inference: if the 10 MHz comb extends across the 50 to 350 MHz band, it could also mask the radio air-shower pulses the array is designed to detect, so a time-domain check of whether the interference is continuous or intermittent would be a cheap next step.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

Quick take: this is a proceedings-style engineering report, not a physics result. It does what it claims: two SKALA antennas were deployed at the South Pole, the hybrid TAXI DAQ worked with the scintillators, and first background spectra near the ICL were recorded. If you are planning a radio array in Antarctica, the mechanical and LNA data are worth having.

What's new: first use of SKALA antennas at IceTop and the first site-specific spectra near the ICL in the 50–350 MHz band. The paper also gives a clean LNA temperature test: gain stable to about 2 dB between +20 and -70 °C. A deployment rate of two antennas in two days by two people is directly relevant to the proposed 96-antenna array. Citations are appropriate; ARA and the earlier South Pole field measurements are the right comparators, and the paper notes those did not see the peaks.

Soft spots: the main quantitative claim—that the measured background is higher than sky noise and contains RFI peaks every 10 MHz—is not as solid as the text suggests. Fig. 6 has no error bars, and the expectation is built from a simulated LNA gain, not the measured Fig. 2 gain, plus a flat 30 K thermal term and the Cane sky model. The authors flag some of this themselves, noting the origin of the discrepancy is unclear and extra thermal noise might explain it. But 10 MHz-periodic ripples are exactly what cable reflections or impedance mismatches in the 30 m chain would produce, so calling them RFI is premature without a system-noise-only run or a cable-length scan.

Nothing here is circular; the comparison against Cane sky and simulated antenna response is external and standard. But the absolute calibration is unvalidated, and the stress-test concern is correct: without end-to-end calibration, the 'environment noisier than expected' conclusion is conditional, not established.

Who this is for: people working on IceCube-Gen2 surface detectors or planning South Pole radio deployments. It is a legitimate proceedings paper, and it deserves referee time—but a referee who insists on error bars and a calibration check. My recommendation: accept as an engineering status report, and don't treat the RFI/background excess as a measured property of the South Pole environment until a calibrated follow-up confirms it.

Referee Report

3 major / 5 minor

Summary. This ICRC2019 proceeding reports the deployment, in January 2019 at the South Pole, of two prototype SKALA radio antennas for a future hybrid IceTop extension, together with a TAXI-based DAQ system that reads out both scintillation detectors and radio antennas. The paper describes the mechanical design and deployment, presents a laboratory characterization of the LNA gain as a function of temperature (20 C to -70 C), and gives first background spectra measured about 25 m from the IceCube Laboratory (ICL). The authors state that the measured spectra show RFI-like peaks recurring every 10 MHz starting near 50 MHz and that the overall level is higher than an expected sky-noise prediction based on the Cane model and an antenna/LNA simulation. The conclusion is explicitly preliminary: the origin of the RFI and of the discrepancy with the prediction is said to be unclear, and further measurements with the deployed antennas are planned.

Significance. If the reported behavior is taken at face value, the paper demonstrates that the SKALA mechanical structure and the hybrid TAXI DAQ can be operated at the South Pole, and it provides an early indication that the radio background near existing South Pole infrastructure is not purely sky-noise limited. The careful LNA temperature characterization is a useful engineering contribution. The strength of the environmental conclusion, however, is limited by the absence of an end-to-end absolute calibration and the lack of statistical error bars on the spectra; these are acknowledged as open items in the text but currently prevent the quantitative 'higher than expected' and 'RFI' claims from being fully supported. The paper is appropriately modest in tone and is best read as a progress report rather than as a definitive measurement of the South Pole radio environment.

major comments (3)

[Section 5, Fig. 6] The absolute baseline used to conclude that the measured spectra are 'higher than the expectation of the sky noise' is assembled from the simulated LNA gain of de Lera Acedo et al. [17], a constant 30 K thermal-noise contribution, and the Cane sky model, rather than from the LNA gain actually measured in Section 2, Fig. 2. Since the measured LNA gain is available, using the simulated gain introduces an avoidable and unquantified calibration uncertainty; a frequency-dependent difference between the simulated and the deployed LNA gain would translate directly into an apparent spectral excess or deficit. I request that the comparison use the measured gain (with any necessary corrections for the cable and filter chain) and that the expected absolute level be propagated with explicit uncertainties.
[Section 5, Fig. 6] The two one-hour average spectra are shown without any error bars, confidence bands, or estimate of systematic uncertainties, so the visual 'excess' over the black dashed prediction cannot currently be distinguished from statistical noise or from systematic baseline effects. In addition, the claimed 10 MHz periodicity of the peaks is a spectral ripple pattern that can be produced by impedance mismatches and reflections in the 30 m cable and front-end chain; without a system-noise-only measurement, a calibration-source measurement through the same signal path, or a cable-length scan, the identification of these features as ambient RFI is premature. The paper's own statement that the origin of the discrepancy is unclear reinforces this point, but the current wording of the results and conclusion still presents the peaks and the excess as established measurements.
[Section 5, paragraph 3] The description of the expected background is incomplete for reproducibility: the paper does not state the absolute units of Fig. 6, the assumed antenna elevation/azimuth response, the cable attenuation as a function of frequency, or how the 'amplified sky radio background' combines the Cane-model sky temperature with the individual gain and loss terms. Without these definitions, the quantitative comparison in Fig. 6 cannot be independently checked, and the statement that 'a slight deviation of the expectation and the measurement is expected' is not sufficient to interpret the size of the observed discrepancy.

minor comments (5)

[Section 5, Fig. 6 caption] The caption should specify the y-axis units and the exact frequency binning used for the average spectra, as well as whether the solid and dashed black lines correspond to the sky temperature before and after amplification, respectively.
[Section 6, last sentence] The phrase 'radio antennas wthat share one DAQ system' contains a typo; it should read 'that share one DAQ system'.
[Section 2, Fig. 2] The caption states that the LNA gain was measured with a 50-ohm calibration source, but the text does not give the absolute power level or the number of repeated measurements used to quote the 'about 2 dB' temperature stability; adding this information would strengthen the reproducibility of the test.
[Section 3] The sentence 'The trigger is realized with a comparator as a signal-over-threshold trigger' would be clearer if it distinguished the comparator threshold for the scintillator channels from the threshold used for the radio channels, since the current text says that the trigger is based only on scintillation detectors.
[Section 1] The abbreviation 'GFK' (glass-fiber reinforced plastic) is used without expansion; I suggest using the more common GFRP or defining GFK at first use.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: the measured spectra and external-model comparisons are not derived from the paper's own inputs.

full rationale

All scientific claims in the paper are either direct hardware/DAQ reports or empirical spectral measurements. The expectation line in Fig. 6 is built from external, published inputs: the Cane sky model [18], the simulated LNA gain from de Lera Acedo et al. [17], a constant 30 K thermal-noise contribution, and known filter/cable losses; none of these are fitted to the measured spectra shown in Fig. 6, and no target quantity is defined in terms of the measurement. The paper explicitly flags the calibration limitations: 'As LNA response, the simulated LNA gain from E. de Lera Acedo et al. [17] has been used' and 'The deviation could come from an additional thermal noise contribution which has not been included in the amplified background estimation' (Section 5). This is an unvalidated absolute calibration pointing to a correctness or systematic-uncertainty concern, not circularity. The 10 MHz periodic RFI peaks are read directly from the averaged measured spectra, not generated by inverting a model or by a fitted parameter. No load-bearing self-citation occurs: [17] is an external antenna/LNA design simulation, [18] is the standard Cane sky-noise model, and [13] is the TAXI DAQ reference; none of these is used to import a uniqueness theorem or to forbid alternative interpretations. Therefore no fitted input is relabeled as a prediction, and no equation reduces to the paper's own inputs.

Assumptions & free parameters 0 free parameters · 3 assumptions · 0 invented entities

The paper introduces no fitted parameters or new entities. Its quantitative expectations rest on external inputs: the Cane sky-noise model, the simulated SKALA LNA response from [17], and a nominal 30 K thermal noise. The interpretation of the measured RFI peaks as environmental noise is an assumption the paper itself leaves open.

assumptions (3)

domain assumption The simulated SKALA LNA response from [17] accurately represents the deployed LNA at South Pole temperatures.
The expected sky-background curve in Fig.6 uses this simulated gain rather than the measured response from Fig.2.
domain assumption The Cane model provides a valid sky-noise prediction for the South Pole.
Used to define the expected background; the authors note that averaging over the whole sky can cause deviations.
domain assumption The observed 10 MHz-spaced RFI peaks are environmental rather than artifacts of the DAQ or front-end chain.
The paper treats them as real RFI of unknown origin since ASC excludes known sources; the hardware chain is assumed not to introduce periodic spectral lines.

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Cite this review

Pith. "Pith review of First measurements with prototype radio antennas for the IceTop detector array." pith.science (2026). https://pith.science/paper/4NEU6DUX

@misc{pith2026190810565,
  author       = {Pith},
  title        = {Pith review of: First measurements with prototype radio antennas for the IceTop detector array},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/4NEU6DUX}},
  note         = {Machine review of arXiv:1908.10565}
}

abstract

Extending large-scale air-shower arrays with radio antennas can increase the detector's performance, as the radio emission by cosmic-ray air showers provides an additional measurement of the electromagnetic component. Instrumenting the IceCube surface detector IceTop with radio detectors as well as with new particle detectors in a hybrid approach will enhance the measurement and reconstruction accuracy and allow for the characterization of highly inclined air showers. This will enable a better understanding of the atmospheric background for the in-ice neutrino measurements. It also opens the opportunity for new science cases, e.g. the search for PeV gamma rays from the Galactic Center, which is visible from the IceCube site year-round at an inclination of 61$^{\circ}$. Adding to several scintillator particle detectors already running at the South Pole, two prototype radio antennas have been deployed at the IceCube site in January 2019 using the same DAQ system as the scintillators. The antennas serve as a test setup for a future deployment of radio antennas extending the scintillator array planned inside the IceTop footprint. In this proceeding, the antennas considered for deployment and the hybrid DAQ system processing the signals of the particle and radio detectors will be introduced. First measurement results at the South Pole will be presented and future plans for a full hybrid particle and radio detector array inside the IceTop footprint will be shown.

Figures

Figures reproduced from arXiv: 1908.10565 by the authors.

**Figure 1.** SKALA-2 antenna of the South-Pole design with a height of 0.3m from ground to the lowest lobe. The left picture shows a test setup at the Karlsruhe Institute of Technology (KIT). The right picture shows the deployed antenna at the South Pole. A prototype version of an antenna developed by the Square Kilometer Array (SKA) [12] is used. Desirable characteristics of the antenna include the gain of the antenna for incli… view at source ↗

**Figure 2.** Measurement of the LNA gain. The gain is measured in a temperature range of 20◦C to -70◦C and a frequency range of 50 MHz to 600 MHz. As input, a 50 Ω calibration source has been used. range up to 600 MHz are shown. The LNA gain stays constant within about 2 dB throughout the whole temperature range, allowing for stable operation in the cold and temperature-dynamic environment of the South Pole. 3. Hybrid particle a… view at source ↗

**Figure 3.** Block diagram of the hybrid TAXI DAQ system. in channel-cascading mode which reduces the available DRS4 channels to two per DRS4 but increases the number of sampling cells to 4096 for each channel resulting in a radio-trace length of about 4 µs. Radio-specific components are placed on a radio front-end board before the TAXI inputs. The radio front-end electronics consist of a bias tee (JEBT-4R2G+), a protection aga… view at source ↗

Figures from the paper (3 more)

**Figure 4.** Figure 4: Not-to-scale layout of the deployed scintillation and radio detectors with scintillation detectors as rectangles, IceTop tanks as circles and radio antennas as stars (January 2019) [PITH_FULL_IMAGE:figures/full_fig_p006_4.png]

**Figure 5.** Figure 5: Detector site with scintillation detectors (1), radio antennas (2) and elevated IceAct camera (3). camera. The antenna mechanical structure was found to be fast and easy to deploy, an important criterion for a future deployment of 96 antennas in the footprint of IceTop…

**Figure 6.** Figure 6: Measurement of the background frequency spectrum near the ICL. The black dashed line shows the expected background noise originating from the Galactic Center and other sources in the sky. ICL (blue) and perpendicular to the ICL (red) are shown. Comparing the two measur…

Discussion (0). Continue with ORCID to comment.

Reference graph

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Pith tools

Reviewed August 14, 2026 · model on record in the stance chip above.

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E. de Lera Acedo, N. Drought, B. Wakley, and A. Faulkner, 2015 International Conference on Electromagnetics in Advanced Applications (ICEAA) (Sep., 2015) 839–843

work page 2015

[2] [1]

IceCube Collaboration, M. G. Aartsen et al., JINST 12 (2017) P03012

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[4] [3]

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work page 2019

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