LOFAR Technical Issues

M.A. Brentjens

ASTRON, Dwingeloo, The Netherlands

2019-05-20 Windmills: time line

2018 Raad van State dismissed all appeals 2018 spring manufacturer selected: Nordex NOW Development detailed measurement procedure 2019 summer windturbine RFI assessment 2020 H1 start construction 2020 Dec wind farm operational Windmills: covenant EM interference reduction Consequence < 35 dB No permission to build 35 dB ≤ improvement < 40 dB 56–62× 12 h idle 40 dB ≤ improvement < 50 dB Reduced idle time to be negoti- ated improvement ≥ 50 dB No restrictions

• Astron must find 7 dB additional improvement in signal processing. (WMM project) • Agentschap Telecom establishes method to measure improvement in cooperation with Astron and wind farm developers. Being adapted to LOFAR • In case of conflict: binding arbitration. • Neither party will claim damage due to wind farm or lack thereof.

RS509

RS508

RS407

RS406

Solar parks

RS409

Planned solar parks near the LOFAR core 52.96

Nieuw-Buinen RS503

Paardetangendijk Buinerveen 52.94 Nieuw-Buinen HooghwegHooghweg Energy Energy Buinen Buinen Nieuw-Buinen

Nieuw-Buinen 52.92 Daalkampen

52.90 RS305 Westdorp Latitude [deg]

RS306 Westdorp Exloo 52.88 RS106

Valthermond M2883 Valthermond M3006

52.86 RS205

6.75 6.80 6.85 6.90 6.95 Longitude [deg]

RS307

RS310

RS208

RS210 Other Spectrum Management

• 52–54 MHz range: no amateur digital broadband allowed • 70–74 MHz range transferred from military to radio astronomy • Prevented bat-based transmitters at 150 MHz • Special liaison to government for coordination of clean energy initiatives (solar PV, wind, LED (street)lighting, . . . ) and LOFAR: Ilse van der Waaij. Data inspection: goals and status • ML for data inspection “Goal: automatic “operator email” suggestion” • HDF5 MS summary • Full complex dynamic spectra • 1000s plots: cluster first • Browser to explore clusters DAB+ spurious: spectrum Ger de Bruyn BREAKING! DAB spurious understood! BREAKING! DAB spurious understood!

• PAGER = DITHERING SIGNAL! • P2000 only on when transmitting • KPN ERMES pager system decommissioned AT SAME TIME DAB+ rollout ended • Just a happy accident. . . • Possible solutions: I inject artificial dither I insert (and later remove) artificial delays I insert analogue DAB-suppression filter LOfar BEams: LOBEs David Prinsloo

“The primary objective of the LOBEs project is to derive, implement, and commission beam models for all low- and high-band antenna elements within the international LOFAR telescope.” Phase I LOfar BEams: LOBEs David Prinsloo

“The primary objective of the LOBEs project is to derive, implement, and commission beam models for all low- and high-band antenna elements within the international LOFAR telescope.”

Phase II • Actual simulation of all antenna’s in the ILT • Implementation of new LOFAR beam library based on database of simulated element beams • Full-band verification of this library using 24-h cross-calibration of several flux density calibrators at all their azimuths and elevations LOBEs: Altair-FEKO sims David Prinsloo Total power spectroscopy: main problems

Mean spectral power (PPF)

1.0

0.8

0.6 Power

0.4

0.2

0.0 0 200 400 600 800 1000 Channel

• Station subband bandpass correction on Cobalt insufficient for narrowband work • Core not coherent, particularly in LBA Total power spectroscopy: cobalt vs BG/P

Subband bandpass correction versions FFT of subband bandpass correction versions 1.0 Cobalt 64 ch 1.04 Cobalt 256 ch BG/P 0.8

1.02

0.6

1.00

0.4 Normalized power Normalized power 0.98

0.2 Cobalt 64 ch 0.96 Cobalt 256 ch BG/P 0.0 0 50 100 150 200 250 0 20 40 60 80 100 120 Channel Fourier mode Total power spectroscopy: core coherence

• Reasonable in HBA • Horrific in LBA • New LBA (and HBA) core cal solutions by Tied Array Beam holography • More permanent solution: replace clock distribution by WhiteRabbit technology: CSYLOPHON project Tied Array Holography: HBA pre cal Tied Array Holography: LBA pre cal Tied Array Holography: LBA post cal Summary

• Windmills: clarity this fall • Solar parks: covenants being signed • Data inspection: new tools available internally at ASTRON • DAB spurious: understood and solution underway for DUPPLO • Beams: Phase I modelling underway • Tied array spectroscopy: LBA beams solved, bandpass not yet