Galactic 21cm measurements using a small static antenna
Frans de Jong, CAMRAS
When trying to do simple radioastronomy at home, one will search the internet for examples, ideas and experiences. It is not hard to find a number of inspiring examples using dish antennas down to 3 meter diameter with astounding results. This includes mapping the arms of the Milkyway and also finding the rotation curve of our galaxy. Smaller antennas however were hardly used for observations but merely used for detection of the faint 21cm signal. This is already an enormous achievement in itself. My quest is to do a real observation including some measurements and explanation of the findings, using an available 1.5 meter dish . How far will I get with this?
The total assembly consists of the prime focus dish and a cantenna type of feed horn. The LNA and line amplifier have a filter in between and should be sufficient for this weak 21cm signal. The real question is whether such a small dish will provide enough signal gain and if the large beam width will destroy any details in the reception of the milkyway profile. So, will the received signals allow useful calculations? The receiver is a simple RTL-SDR dongle and the software used is SDR#. To make the 21cm signal really visible, integration is needed. This was found in a plug-in designed for this puspose called ‘IF-Average’.
With this equipment a 24 hour scan is executed while aiming at a fixed point in the sky. Every 13 minutes a curve of integrated samples around 21cm is stored. After 24 hours the series of observations clearly show the passing-by of the milkyway, but also in between these events a 21cm signal is continuously visible. So sensitivity is certainly available. When lining up all curves, the received 21 cm signal shows a remarkable wave-shaped Dopplershift that requires explanation. Several aspects are researched and a viable explanation laid down in relation to the movements of the Earth through space. The very last refinement of a 6% deviation found during this process needs an additional explanation. The reasoning seems logical but remains open for proof and –obviously – for discussion.
Concluding can be said that such a small set up already provides more than sufficient capabilities to perform some real radioastronomy. Next steps are obvious; get a working setup to point at different known positions in the sky and also to follow the sky movement. Then also mapping the gaaxy and potentially integrate for longer times, finding weaker signals may be realized.
Refurbishing and modernizing an old Haystack „SRT“
The „Small Radio Telescope (SRT)“ developed originally by the MIT Haystack Observatory has been a popular telescope for education at schools and universities for quite some time. The Astropeiler Stockert team has been donated such a telescope by the Bamberg University. This 2.3-m telescope has been completely modernized with a new RF-chain, SDR based backend and a new control system by the Astropeiler team.
The talk will describe the steps that have been taken and the design choices which have been made. The characteristics of the enhanced telescope have bean measured, and first light was achieved in November 2020. The first observational results and future plans will be presented.
Mapping the sky at 21 cm with a small-aperture telescope and manual pointing
Apostolos Spanakis-Misirlis, Vasilis Spanakis-Misirlis
The 21-centimeter Hydrogen Line
Ard Hartsuijker (CAMRAS volunteer, The Netherlands)
After the theoretical prediction by Van de Hulst in 1944, the 21-centimeter Hydrogen Line (H I line) was first detected in the USA by Ewen and Purcell on March 25, 1951. Shortly thereafter the HI line was detected In the Netherlands by Muller and his team.
The Dutch team led by astronomer Oort began to observe the neutral hydrogen in our Milky Way. Their 7.5-meter Kootwijk Radio Telescope was constructed of an Würzburg radar remaining from the Atlantic wall. The Dutch observations made spiral arms visible in the Milky Way and were presented by Van the Hulst in 1953 at the Halley Lecture in Oxford (UK).
In order to observe the Galaxy in detail, all the time Oort urged for a 25-meter radio telescope and on April 17, 1956 the 25-meter Dwingeloo Radio Telescope was opened by queen Juliana. On this EUCARA-2021 conference day that is exactly sixty-five years ago.
This presentation reviews some aspects of the prediction, the detection (seventy years ago), the opening of the Dwingeloo Radio Telescope (sixty-five years ago) and the astronomical relevance of the H I line.
Tjipke de Beer, Aran Benner, Simon Bijlsma, Paul Boven, Harry Keizer, Marc Wolf
The SETI@CAMRAS workgroup was established in November 2014. The workgroup is an interdisciplinary team and includes (amateur) radio astronomers, radio amateurs, software developers and RF specialists. SETI@CAMRAS strives to make a scientifically reliable contribution to the search for extra-terrestrial intelligence. The workgroup maintains contact with the Berkeley SETI Research Center.
During the initial phase, it has been decided to use the SETI@home software using the Berkeley Open Infrastructure for Network Computing (BOINC). The so-called mb_splitter software module, written in C/C++, reads a formatted data stream containing 2.5 MHz bandwidth of signal over time and splits this file into 256 work-units (WU’s). BOINC distributes the WU’s to the clients, i.e., software applications which analyse WU data for interesting signals using pattern-recognizing algorithms such as Fast Fourier Transform (FFT). The objective is to detect artificial signals which might be generated by extra-terrestrial intelligent civilizations.
The search for ET started about 60 years ago and until today no evidence of ET has been found. But the pressing question “Are we alone?” remains, so the search is still going on. Also because of developments in Astrobiology, the search for life beyond the Earth is intensified. Furthermore, the Breakthrough Listen project tries to get the answer in the next couple of years.
SETI@CAMRAS has almost completed the software pipeline and is able to receive and detect artificial test signals. The team needs to finalize the assimilator software module to complete the pipeline. A number of tests using the Dwingeloo Radio Telescope and other signal generators show that the pipeline is working as expected. The next step for SETI@CAMRAS is to start working on the observation strategy, in cooperation with the SETI scientific community.
The Dwingeloo Radio Telescope is an attractive means to run the SETI@CAMRAS project. The pipeline is almost finished, so the CAMRAS team needs to develop an observation, participation and outreach strategy. The ultimate goal is to contribute to answer the question: “Are we alone?”.
Beside this search, SETI@CAMRAS is a perfect way to engage people to science and technology in general. In this way, CAMRAS hopes to enable a wide group of people to enjoy working with the Dwingeloo Radio Telescope.
Repeating a historical observation of an occultation of the Crab Nebula (M1) by the Moon
Hans van der Meer, Paul Boven, Cees Bassa, Tammo Jan Dijkema
During an 18.6 year period there are two series of lunar occultations of the Crab Nebula (M1) by the Moon. In 1955 the construction of the Dwingeloo Radio Telescope was temporarily interrupted to observe the lunar occultations M1 on 3 November and 30 November on 400 MHz. The lunar occultation of M1 on 18 July 2020 was visible from the Netherlands. This occultation was observed with the Dwingeloo Radio Telescope on 1.3 GHz and 430 MHz.
The presentation will focus on repeating this historical observation. We will discuss the differences, both the results and the way the observations were organised and data was captured. We further discuss the impact of having additional data for 1.3 GHz that was not available in 1955.
Finally some learnings will be shared for future occultations (not before 2030).
Introduction to Interferometry
Paul Boven, Daniel Estévez, Wael Farah, Derek Kozel, Alexander Pollack, Ellie White and many other GNU Radio / ATA enthusiasts.
Most radio amateurs don’t have access to large radio telescopes, despite a few notable exceptions. Smaller dishes of course have lower gain, and poorer resolution. This makes it difficult to detect even the strongest sources, as they will be well below the system noise level.
Interferometry is a technique in radio astronomy where the signals from multiple antennas are cross correlated against each other. The cross correlation is sensitive to the signal that is common to the two receivers, whereas the system noise and to some extent even the RFI get averaged down. It is also less sensitive to gain level fluctuations, as the correlated signal can easily be contrasted against the adjacent noise level.
The resolution of an interferometer depends not on the size of the individual dishes, but on the largest distance between them. As will be shown in this talk, actually resolving a source is still going to be quite a challenge for amateur astronomers. But advances in signal processing hardware and open source software such as GNU Radio and Astropy help a lot in making this goal more accessible.
In this talk, the basics of interferometry will be presented. They will be illustrated with some GNU Radio flowcharts that do all the required signal processing, and allow live monitoring of the signals and correlation signal. Their usage will be illustrated with recordings and results observed at the Allan Telescope Array (ATA) at Hat Creek Radio Observatory in the USA.
Polarimetric interferometry at Allen Telescope Array
Daniel Estévez (GNU Radio), Paul Boven (GNU Radio), Wael Farah (SETI Institute), Derek Kozel (GNU Radio), Alexander Pollack (SETI Institute), Ellie White (Berkeley SETI Research Centre)
Since September 2020, SETI Institute and GNU Radio have joined forces to develop signal processing at Allen Telescope Array. As part of this collaboration, some members of the GNU Radio community have some observing time at the telescope, as a testbed to run their own experiments and software. Even though the ATA is a large scientific installation, a pair of its 6 metre dishes is not so far from what a resourceful amateur astronomer may build, so it can be an excellent platform to test ideas of what could be achieved with amateur means.
Polarization of radio waves is an interesting topic, that can be understood in simple terms as the plane of oscillation of waves, but also has deep ties with concepts in quantum mechanics and quantum computing. Beautiful mathematical constructs such as the Bloch sphere and Stokes parameters emerge. Many astronomical sources are polarized. The study of their polarization parameters gives insight about their physical properties.
As a first step in polarimetric interferometry experiments, I will present an observation of the quasar 3C286 done with two dishes at ATA. 3C286 is a strongly polarized compact source, and it is one of the primary polarization calibrators for VLA, so its polarization properties are well known. A polarimetric correlator was made in GNU Radio, and its output visibilities were studied using Python code written from scratch and also the radio astronomy software package CASA.
The Sharjah 40-meter Radio Interferometer
I. Fernini, A. Alhameed, A. Noorani (SAAST)
The Sharjah Academy for Astronomy, Space Sciences, and Technology (SAASST), located in the United Arab Emirates, has built a 40-m radio interferometer, unique in the MENA world. This system consists of three 5-meter SPIDER 500-A radio telescopes placed at the vertices of a scalene triangle with baselines of 30, 40, and 50 meters. The resolution of the array is 0.36 degrees and operates at 1.4 GHz. We plan galactic and extragalactic radio source observations to use our system as a radio astronomical educational tool to promote radio astronomy for students, amateurs, and professionals astronomers who would like to conduct radio astronomical observations using a state of the art facility. Our presentation will describe the technical aspects of the 40-m radio interferometer and the many types of astronomical objects that can be observed.
Galactic Navigation using the Pioneer Spacecraft Pulsar Map
This paper analyzes the Pioneer and Voyager spacecraft pulsar map. The analysis includes the interpretation and identification of the pulsars in the map and the technique to triangulate the Sun’s position using basic geometric measurements. The use of this map to navigate from an extrasolar planet to the Sun is also explored.
Adventures with a Lunar satellite
T.J. Dijkema, Mingchuan Wei, Reinhard Kühn, Cees Bassa, Paul Boven, Daniel Estévez.
As part of the Chang-e 4 mission, China launched two lunar orbiting satellites (called LongJiang / DSLWP), of which one managed to reach lunar orbit by itself. These satellites carried amateur radio payloads by Harbin University. The Dwingeloo telescope was used as a primary downlink station for this amateur payload. In this talk I will report on radio experiments we did with this satellite, and present many pictures that were taken with an amateur-built camera that was part of the amateur radio payload. The satellite crashed on the lunar farside in August 2019, where it now is one of the 10 man-made objects there.