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A daily view of all the goings-on at ASTRON and JIVE.

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    © A. Stroe

    Red weather alert: dangerous cosmic weather forecast, in light of galaxy cluster mergers! Clusters grow through mergers with other clusters, events which give rise to the largest cosmic shock waves, as well as turbulence. Shocks travel like giant tsunamis through the electron plasma located between them, while turbulence stirs the intra-cluster medium.

    I will discuss how merger shocks and turbulence accelerate electrons to relativistic speeds, producing diffuse synchrotron emission extended over Mpc regions. I will touch upon the theoretical framework for their formation as well as their observational effects.


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    © Mulcahy et al. 2017

    Spiral galaxies host large-scale magnetic fields that evolve over millions of years via turbulence in the Interstellar Medium and the rotation of the galaxy itself. These galactic-sized magnetic fields contain an ordered component, primarily located in the regions between the spiral arms, where randomness imposed by the star formation process is low. Such ordered magnetic fields and their directionality can be efficiently observed with cm-wavelength radio synchrotron radiation, and its degree of linear polarisation.

    The above picture shows an optical image of the face-on spiral galaxy NGC628 as observed with the Calar Alto 1.23-m telescope in Spain, superimposed with flow lines showing the direction of the ordered large-scale magnetic field as observed with the Jansky Very Large Array (JVLA) at radio frequencies between 2-4 GHz.

    The image is presented as part of new work by a team including George Heald (CASS, formerly ASTRON and Kapteyn Institute) which was recently accepted for publication. The research also found evidence for two drivers of magnetic turbulence in the disk-halo region of NGC 628, namely, Parker instabilities and superbubbles. These findings are published in A&A and can be found at https://arxiv.org/abs/1701.04829


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    © ASTRON

    Since 2010 software engineers from various NWO institutes and the like get together every year to share experiences and to see something of their sister institutes. In 2010 we visited Amolf, in 2011 FOM Rijnhuizen, in 2012 NIOZ, in 2013 NIKHEF, in 2014 SRON (Utrecht), in 2015 NLR (Marknesse), and on the 26th of January this year we met at ASTRON.

    The day was well organized by Ina Doorten and Ger van Diepen. The group got to observe with the Dwingeloo telescope with help from Tammo Jan Dijkema and Michel Arts, and Gijs Schoonderbeek explained the Uniboard2. The rest of the day was spent listening to presentations given by the participants on a broad range of software engineering topics. The next meeting will likely be hosted by the NL eScience Center.


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    © P. Salas

    LOFAR is able to observe at high spatial, time and spectral resolution. The high spectral resolution allows us to detect and map low frequency radio recombination lines at unprecedented sensitivity. These lines provide an excellent diagnostic of the physical conditions of cold diffuse gas clouds in the interstellar medium. In a recently accepted paper Pedro Salas (PhD student at Leiden Observatory) and his team, including ASTRON astronomer Raymond Oonk, explore the use of the lowest frequency lines observable from Earth in the 10-33 MHz range. This frequency range is typically believed to be very difficult to calibrate due to increased presence of radio frequency interference and ionospheric scintillation. None the less Pedro achieved line detections towards the bright supernova remnant Cassiopeia A all the way down to 11 MHz - a new record! The resulting line spectra are shown on the left hand side of the figure and are associated with clouds of cold gas located between us and the supernova remnant. These detections also clearly show for the first time that at these low frequencies the lines are in local thermal equilibrium - consistent with a key prediction in our new line models (Salgado et al. 2016a,b). Finally the detections also show the excellent diagnostic power of low frequency radio recombination lines. In particular we find that the combination of low frequency radio recombination lines from carbon with the far-infrared [CII] 158 micron line provides a good thermometer of the cold gas. This is shown by the red shaded region in the right hand side of the figure. The results are published in Salas et al. (2017) and available at: https://arxiv.org/abs/1701.08802

    Figure: (Left) Spectra showing radio recombination line absorption from carbon in the frequency range from 10-33 MHz. The lowest frequency detection at 11 MHz corresponds to a line transition with principal quantum energy level n=843. From this we can infer that the electron responsible for the observed line emission orbits the carbon nucleus at a distance of 1 micron. (Right) Constraints of the physical conditions of the radio recombination line emitting gas from two low frequency absorption line measurements with, (i) an emission line measurement (blue shaded region), and (ii) the far-infrared [CII] 158 micron line (red shaded region). From just these 4 measurements we determine the temperature and density of the gas to within 25 percent and find it to be in good agreement with the detailed analysis of Oonk et al. 2017 (yellow asterisk).


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  • 02/21/17--16:00: First ARTS busy week
  • © R.H. van den Brink

    In week 6 of 2017, the team interested in the time-domain capabilities for APERTIF, organized their first Busy Week. A group of about 20 people participated from both ASTRON and the Anton Pannekoek Institute for Astronomy from University of Amsterdam to work towards a first set goals of goals. These revolved around the APERTIF Radio Transient System (ARTS), which is the new pulsar-timing, transients-search and VLBI back-end for APERTIF, and around ALERT, the APERTIF pulsar and transient survey.

    One of the main goals for the busy week was getting delay tracking up and running and tested. For APERTIF this came at the right moment so it fitted within the APERTIF plans as well, creating great progress for both projects.

    The second main goal was a demonstration of the pipeline for the real-time detections of Fast Radio Bursts (FRBs), with APERTIF. We managed to test and combine various parts of the pipeline, including an FPGAs demonstrator streaming simulated data to a GPU-accelerated development machine, and analyzing the data there.

    One of the smaller goals was to move beyond the X-polarisation data used up to now, and to implement and start using the Y polarization. Such dual-pol observing is beneficial for both ARTS and APERTIF. We were excited about our managing a first dual-polarisation pulsar observation, with XY polarization on one dish.

    In the mean time, many of the astronomers from API worked on their presentations for the first-ever FRB conference in Aspen, which was held right after the busy week. In various talks, the APERTIF progress was a highlight there.

    The team had a very fruitful busy week, where several goals were met. Also people joined who did not directly contributed to the set goals, but worked on other parts of the project. Due to easy interaction with the team progress was for instance also made on the other ARTS sciences cases, and on hardware monitoring by RO.


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    © ASTRON

    On the daily image of december 14th 2016 two different RF shielding cans for the MFAA LNA were shown. To see if there is a difference between the shielding properties of these shielding cans a measurement setup consisting of a waveguide was used to measure the shielding of them. To measure the shielding cans they were mounted on a PCB.

    The first picture shows the measured PCB's with the shielding cans mounted on it. The open PCB and solid PCB were used for reference measurements. Shielding cans 2 and 4 are the ones that are shown in the daily image mentioned previously. Shielding can 1 is from another manufacturer. Shielding can 3 is the same as shielding can 4. Only the production process is different.

    The second picture shows how a PCB is mounted in the measurement setup. The third picture shows the total measurement setup. The shielding of the different cans is determined by measuring the transfer function between the two connectors of the waveguide. By comparing the measured transfer function with the one of an open PCB without shielding can the shielding can be determined. The graph shows the measured transfer function with respect to the transfer function of an open PCB without can. One can see that the shielding below 4 GHz is around -30 dB for all cans. For higher frequencies resonances resonances occur in the transfer function. The conclusion is that there is no significant difference between the four shielding cans.


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  • 02/23/17--16:00: Polygoonjournaal april 1956
  • © Polygoon bioscoopjournaal, Beeld en Geluid

    Click here for the Polygoon Bioscoopjournaal of the week of 17 april 1956, which covers the opening of the Dwingeloo Telesope. People filmed include Queen Juliana, professor Oort and professor Muller.

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    © NOVA Optical IR Instrumentation Group

    The cleanroom at ASTRON is upgraded with a crane and now equipped for assembly of the WEAVE spectrograph.

    The sub-units of the Spectrograph are that large and heavy that manual lifting is not possible. The Collimator Unit and Camera Unit are up to 350 kg of weight.

    Also other smaller units like detector/cryostat system needs a crane support.

    A cable feedthrough and guide system is also installed for electrical (control) cabling, optical fibres, cooling and LN2 feeding.

    The optical table of the WEAVE Spectrograph is already installed inside the cleanroom.

    The slit unit (first part of the optical train) is in assembly phase.

    The collimator unit is in production in Dwingeloo and lenses at TNO in Delft.

    Camera lenses are in production at INAOE in Mexico and camera mechanics production will start soon in Dwingeloo.

    WEAVE is a new multi-object survey spectrograph for the 4.2-m William Herschel Telescope (WHT), on La Palma in the Canary Islands.

    WEAVE is build by several institutes at several countries.

    The Spectrograph team is lead by Johan Pragt, NOVA.

    Dutch PI is Scott Trager, Kapteyn Astronomical Institute, RUG.

    http://www.ing.iac.es/weave/index.html

    http://www.astron.nl/dailyimage/main.php?date=20130319

    http://www.astron.nl/dailyimage/main.php?date=20150414

    http://www.astron.nl/dailyimage/main.php?date=20151015


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  • 02/27/17--16:00: NGC 6951
  • © Albert van Duin

    NGC 6952, in the constellation of Cepheus, was discovered in 1877 by Jerome Coggia. Earlier, Lewis Swift had independently found a nebula nearby in 1885 that was named NGC 6951. Denning later showed that these were duplicate observations of the same object, but Coggia had reported a position that was off by 20 arc minutes. The designation NGC 6952 was later dropped and Dreyer issued a correction in the IC2.

    NGC 6951 is classified as SAB(rs)bc, a barred spiral galaxy. Its bright core also suggests it is a Seyfert galaxy (a mild active galactic nucleus or AGN). Its distance is about 65 million light years, and two supernovae have been detected in recent years: 1999el and 2000E. The galaxies location in the sky also means that it is partly obscured galactic cirrus (interstellar dust) as this deep image shows. The galaxy is interesting because it is showing both strong star formation activity and an active core. As the galaxy is an isolated system it is not clear what has triggered the current round of star formation.

    The image is a result of 16 hours integration time through LRGB filters with a 0.4m reflector equipped with a cooled CCD located in Beilen.


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  • 02/28/17--16:00: Operations BoF at the ADASS
  • © YG / ADASS XXVI LOC

    During the last Astronomical Data Analysis Software and Systems (ADASS) conference, we organised a Birds of a Feather* session. The goal of this session was to bring together people involved in the operations of large, distributed radio interferometers and share their experience with each other, and the audience.

    The session was very informative and it is clear that mananging a telescope that heavily depends on computing is a complex task. We concluded that we share many concerns and exchanged information on how the different groups manage to tackle some of those issues.

    The interested reader can have a look at the session here. A summary of the points discussed will appear in the proceedings of the conference. The submitted manuscript can be accessed via arXiv).

    * Wikipedia: "[…] an informal meeting at conferences, where the attendees group together based on a shared interest and carry out discussions without any pre-planned agenda"


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  • 03/01/17--16:00: The Making of...
  • © ASTRON

    Regional broadcast station RTV Drenthe recently requested for ASTRON's cooperation in a program they were preparing in the context of their 'Week of Technique' in February. Of course, they were welcome at ASTRON.

    The 26th of January appeared to be a perfect day for filming at the LOFAR telescope; it was rather cold but very sunny! Michiel Brentjens went with Annelies Hemeltjen of RTV Drenthe to the LOFAR telescope in Exloo and showed her around.

    After finishing the�interview with Michiel and taking many shots on location, they returned to the ASTRON office for an interview with Andr� Gunst in the�digital lab. After that Annelies had an interview with Nico Ebbendorf in the analog lab. At the analog lab, we also see some colleagues working on ASTRON equipment.

    Michiel, Andr�, Nico, Gijs, Albert, Michel and Sander, thank you for your cooperation!

    The item was broadcasted at the beginning of February, you can watch it here: https://youtu.be/7-d1DoT6sQY It's in Dutch only.


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  • 03/02/17--16:00: Famous in the Donald Duck
  • © Sanoma media

    These images appeared in the Donald Duck special issue on Drenthe, issue 21, 2012.

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  • 03/05/17--16:00: De Inrichting van de Hemel
  • © P.C. van der Kruit / Amsterdam University Press

    Last year former chair of the ASTRON-board and former director of the Kapteyn Institute Piet van der Kruit published a biography of Jacobus Kapteyn. The title of the biography De Inrichting van de Hemel (The Construction of the Heavens) refers to William Herschel. He used this expression to mention the problem of spatial distribution of stars. Indeed a subject Kapteyn worked on.

    The biography describes the whole career of Kapteyn. He studied mathematics and physics at the University of Utrecht where he got his Ph.D in 1875. After working a few years as observer at the Leiden observatory he was appointed as professor in Groningen in 1878 (at the age of 26). This appointment was a direct result of the new higher education act which resulted in an increase of the number of professors at Dutch universities. Around the same time Kapteyn's brother Willem was appointed as professor in mathematics at the University of Utrecht.

    Contrary to the universities of Utrecht and Leiden, there was no observatory at the University of Groningen. After failed attempts to get an observatory in Groningen he started a co-operation with the observatory of Cape Town. This observatory was performing a survey to measure the positions and magnitudes of stars: the Cape Photographic Durchmusterung. The observatory didn't have enough manpower to process the photographic panels that resulted from this survey. Kapteyn didn't have an observatory, so a solution was found.

    Using the proper motion of stars Kapteyn investigated the spatial distribution of stars. This investigation resulted in a model of the universe we nowadays know as the Kapteyn universe. Already shortly after the publication of this model it turned out that it was incomplete. The problem of attenuation of light due to dust in the universe was known by Kapteyn but the effect was underestimated.

    This biography is a must-read for everyone who is interested in the history of (Dutch) astronomy. It is written in Dutch, however Piet van der Kruit has also written a more extensive scientific biography in English. Together with the book of David Baneke and the Ph.D thesis of Astrid Elbers this is the third book about the history of Dutch (radio) astronomy published the last two years.


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    © Marc Ribo (UB) & Benito Marcote (JIVE)

    MWC 656 is the first known binary system composed of a Be star and a black hole (BH). Be/BH binaries are important in the context of binary system evolution and sources of detectable gravitational waves because they are possible precursors of coalescing neutron star/BH binaries.

    MWC 656 was discovered as a transient gamma-ray source and X-ray emission was later revealed, indicating its nature as a new high-mass X-ray binary. Although radio observations at different epochs and with different interferometers have been conducted during the last years, most of them have only provided upper-limits on its putative radio emission. MWC 656 was only detected in a single epoch with the VLA up to now, suggesting a variable behavior also at radio frequencies. Optical observations provided an estimation of the orbital period of 60.37 days and the mass of the black hole of 3.8-6.9 solar masses.

    We conducted simultaneous X-ray and radio observations with Chandra and the VLA, reporting a faint X-ray and radio emission. These data allowed us to detect one of the faintest quiescent luminosities observed in stellar-mass black holes so far. Additionally, we find that the obtained luminosities are fully compatible with those expected from the X-ray/radio correlation derived from quiescent BH/low-mass X-ray binaries. Given that only one Galactic BH/high-mass X-ray binary was known to date, Cygnus X-1 (always located in the high end of the correlation), the addition of MWC 656 (located in the low end) allow us to study this X-ray/radio correlation for the first time in high-mass X-ray binaries. These results show that the accretion/ejection coupling in stellar-mass black holes is independent of the nature of the donor star.

    The figure above shows a representation of MWC 656 (right), the radio map together with the optical position (top left), and the X-ray/radio correlation including low-mass and high-mass X-ray binaries and the position of MWC 656 on the diagram.

    These results have just been published in Ribó et al. (2017, ApJL, 835, 33).


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    © Ajinkya Patil

    On the 22d of Nov 2016 Ajinkya Patil defended his thesis with the title: LOFAR Epoch of Reionization: Statistical methods and First Results. Profs Saleem Zaroubi and Ger de Bruyn acted as promotors. The defence took place in the beautiful aula of the University of Groningen.

    Dr Patil's thesis is one of the many theses that have been delivered in the past 8 years at the University of Groningen on the subject of the LOFAR EoR project. However, it is the first that contains LOFAR results on the highly redshifted 21cm signals that we are aiming to detect.

    His thesis contains a paper on the "variance statistic", an efficient way to constrain the redshift evolution of the HI signal, and a paper on the nature and possible cause of the systematic biases in the calibration. The latter reveal themselves as "excess noise" and have occupied us for several years. Both papers have already been published.

    A thorough analysis of a single night of LOFAR data was presented in chapter 4 of his thesis. A journal version of that chapter, including all the details of the calibration and subsequent processing, has just been accepted for publication in the Astrophysical Journal (see arXiv 1702.08679). The limits on the spatial power spectra of HI signals for three redshift ranges centered at z=10.1, z=9.1 and z=8.3 are presented in Fig. 4.5 of his thesis and in Fig. 8 of the paper referenced above. These limits are still some factor away from a detection of the elusive signals. We are currently working on a paper with results based on many nights which we trust will produce significantly deeper limits.

    At an age of only 25.5 years Ajinkya must have been the youngest PhD student to graduate in the history of the Kapteyn Astronomical Institute. Unfortunately, for us, he has decided to accept a job outside of astronomy. The EoR group is already missing him.


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    © Robert Schulz, Cornelia Mueller

    Radio-loud active galactic nuclei belong to the most powerful and persistent sources in the Universe. They exhibit highly relativistic jets, which emit light across the electromagnetic spectrum up to gamma-ray energies.

    High-resolution observations with radio telescopes using Very Long Baseline Interferometry (VLBI) combined with simultaneous multiwavelength monitoring from the radio to the gamma-ray regime provide the most complete insight into the physics of these sources.

    In this talk, I will present recent results and developments of VLBI observations in the Southern hemisphere. I will focus on TANAMI, which is the largest multiwavelength project that monitors the brightest southern extragalactic jets, and the current efforts towards observations with the Event Horizon Telescope. In particular, I will highlight the results of our multiwavelength study of the nearest radio-loud galaxy Centaurus A. The parsec-scale structure in conjunction with broadband properties give valuable information on intrinsic jet parameters and help us to further constrain the high energy emission origin.


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  • 03/09/17--16:00: JUMPING JIVE kicks off
  • © JIVE

    February 21st marked the official start of the JUMPING JIVE project with a kick-off meeting in Leiden – of which an impression is shown above. The JUMPING JIVE project was awarded nearly 3 million euros by the Horizon 2020 Framework Programme of the EU. The project combines 12 institutes from 8 countries, and is led by JIVE.

    The first action of the meeting was to select a chair of the board, which will be René Vermeulen (ASTRON). The vice-chair will be John Conway (Onsala Space Observatory). During the kick-off meeting the work packages were presented and discussed in more detail. The ambition of the project is high, as is the motivation to make the European VLBI Network (EVN) a truly global instrument, and a world leader in VLBI science and innovation.

    JUMPING JIVE stands for Joining up Users for Maximising the Profile, the Innovation and Necessary Globalization of JIVE. The project aims to expand the membership base of JIVE, as well as to boost the functionality of the EVN. The latter will involve a coordinated discussion with European and global VLBI experts to define the necessary technical innovation based on scientific requirements for radio astronomy, geodesy and space science applications.

    The project also has resources for integrating new telescopes into the existing EVN network. The Square Kilometre Array (SKA) and other African telescopes will significantly increase the sensitivity and resolution of VLBI observation of targets in the Southern celestial hemisphere. Consequently, the project has dedicated work packages to stimulate radio astronomy developments in Africa and include telescopes across the African continent. JUMPING JIVE also provides for a scientist to work with the SKA Organisation on future VLBI operations that include the SKA.

    In the top pictures you can see (left to right): René Vermeulen (ASTRON), Tiziana Venturi (INAF), the JUMPING JIVE logo, and the meeting room. All participants are included in the group photo.

    This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 730884.


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  • 03/12/17--17:00: Training Ondernemingsraad
  • © OR

    We hebben een flink aantal nieuwe mensen in de Ondernemingsraad (OR). In dat kader zijn we een dag op cursus geweest om beter bekend te raken met de Wet op de OndernemingsRaden (WOR). Hierdoor zijn we nu veel meer op de hoogte van wat juridisch gezien onze rechten en plichten zijn, en welke mogelijkheden we hebben om die uit te oefenen. Zeker ook met de NWO Transitie is het wel van belang dat we hiervan goed op de hoogte zijn. Sommige leden van de OR hebben nu zelfs een favoriet artikel van de WOR. Helaas kon Klaas Visser er op het laatste moment niet bij zijn. De cursus werd gegeven door Ellis van Bellen.

    We have a large number new people in the Works Council (OR). In relation with this we've had a course for a day to learn about the Works Council Law (WOR). Because of this we are now much better informed about what our legal rights and duties are, and what options we have to exert those. Especially because of the NWO Transition it is important that we are well aware of these. Some of our members now even have a favourite article in the law. Unfortunately Klaas Visser was unable to join us at the last moment. Ellis van Bellen taught the course.

    De Ondernemingsraad.


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    © Anthony Rushton et al.

    Black hole X-ray binaries undergo occasional outbursts caused by changing inner ac- cretion flows. These outbursts are often accompanied by collimated ejecta at near relativistic speeds, similar to what we see in the nuclei of active galaxies, therefore these systems are sometimes referred to as microquasars. The microquasar XTE J1908+094 produced a bright radio flare in 2013. Very high angular resolution observations with the Very Long Baseline Array (VLBA) and the European VLBI Network (EVN) detected moving jet knots that appear asymmetric in morphology and brightness, and expand to become laterally resolved as they move away from the binary.

    Initially, the southern component gives rise to a 15-mJy radio flare and generates the observed radio polarization. This fades and becomes resolved out after 4 days, after which a second component appears to the north, moving in the opposite direction. The timing of the appearance of the knots relative to the X-ray state transition, a 90 degrees swing of the inferred magnetic field orientation, the asymmetric appearance of the knots, their complex and evolving morphology, and their low speeds, indicates that the knots are working surfaces where the jets impact the surrounding medium. This would imply a substantially denser environment surrounding XTE J1908+094 than has been inferred to exist around other microquasars.

    The results will published by Anthony Rushton et al. in the Monthly Notices of the Royal Astronomical Society (arXiv preprint: https://arxiv.org/abs/1703.02110 ).


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    © Nico Ebbendorf

    Traditionally, ASTRON has an excellent relationship with the Hanzehogeschool, a University of Applied science in Groningen. One example of the collaboration is the Electronic Product Engineering Design (EPED) assignment, in which a customer provides a technical problem, to be solved by students working in a project team.

    Since the start of LOFAR operations, a local HBA-tile controller has been high on the maintenance and developers wish-list, but never been worked out. It turned out that the development and construction of such a controller would be an ideal EPED project, combining various technical disciplines and challenges.

    Three engineering students expressed interest in picking up the challenge. Their assignment was to develop and construct a HBA-tile controller that can point a single tile beam to a predetermined position in the sky, and to display the RF spectrum of the beam. The deliverables included a portable prototype with a user friendly GUI for the tile control and signal measurements.

    With a little interaction from ASTRON, the students succeeded in this assignment within 4 months. Despite the short development time, the technical solution and quality that they provided were outstanding.

    The pictures show the final project presentation. In the background you will recognize a black box containing 16 HBA front-ends and signal Summator, representing a single HBA-tile. The demonstration showed how the beam direction can be programmed, and the GUI displaying the RF spectrum.

    One picture shows three very happy students, from left to right Sjoerd Kiewiet, Douwe Zijlstra and Jip Kosse, receiving a speech from the Hanzehogeschool supervisor Peter Kamphuis, congratulating them with the success of the project.


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