# How big a dish do I need for radio astronomy?

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I've recently become interested in the idea of building my own small-scale radio telescope. A quick online search finds a few instructions on how to build this using a satellite dish. These suggest a dish of radius of around 1 metre, but the only objects that you seem to be able to detect are the Sun, the Earth, the Moon (possibly) and communications satellites.

This sounds like it would be become boring fairly quickly, and I would like to observe some deep-sky objects. Some example objects that I fancy observing (depending on how strong their signals are) are Betelgeuse/Sirius, the Crab Nebula and the Andromeda Galaxy.

N.B. I am quite satisfied with pointing the dish at an object and the signal strength increasing. I don't expect to get any kind of image.

Evidently, you cannot pick these up using a metre-wide dish, so what is the minimum size required to pick up these objects (noting that I can't exactly build Arecibo in my back garden)?

In case it matters, I live in a rural area, ~5 miles from the nearest town.

I originally emailed Jodrell Bank this question but they ignored me :P

I am a member of Astropeiler Stockert e.V., and we are fortunate enough to be able to approach this problem coming from the "large side" :-) We have a 25m, 10m and 3m telescopes as well as an interferometer made from two 1m satellite dishes available. All these dishes can be used to do interesting things, but you'll need to match the instrument to your target (and, in a hobbyist setting, often also the target to your instrument).

First of all, you should think about what frequency band you want to work on. 21cm (1420 MHz) is the classical hydrogen line, which lends itself well for mapping neutral hydrogen in the spiral arms of our galaxy. You can expect comparatively strong signals in a quiet frequency band there. Lower frequencies (and large bandwidths) are interesting for pulsars, higher frequencies give access to more interesting phenomena but will require a lot of work on the high frequency side. So my recommendation would be to start out with 21cm.

Secondly, what to look for? In general, the following areas of observation are easily accessible for amateurs:

• continuum emission of the Milky Way, perhaps up to creating maps
• spectral measurements of selected, "bright" (as in "intense radio sources") objects
• Pulsars

Let's look at them in detail:

Continuum measurements are easily done using dishes of any size, but I'd start from 3m upwards to get more interesting results. Calibration of the backend receiver is not trivial, and you should plan a bit of time for it.

Spectral measurements also benefit from larger collecting areas, but you'll also need to set up a suitable backend. They are, however, possible from 3m upwards if you are happy with a bit of mapping of intra-galactic velocities.

Pulsars require a lot of collecting area and bandwidth, so they are mostly the domain of large instruments. We are currently observing several dozens of the brightest pulsars on our 25m dish. The 10m might be sufficient for some of the very brightest. And while there is a report of pulsar measurements using a 3m dish and an RTLSDR frontend, this is a feat that requires experience and dedication. So, I'd recommend this only for 8m and above dishes.

Interferometry with 2x1m dishes (20 GHz) is rather interesting, but very involved in terms of analysis. Two receiving systems help mitigate local fluctuations, and with that setup, we can observe sources down to 2 Jy (with a looong integration time). This setup will give you access to one or two handful of interesting targets like M1, W51 or Cyg A.

Finally, I'd like to recommend the EUCARA conference series (European Conference on Amateur Radio Astronomy) and the SARA group as great starting points. They have conference presentations available online that show what other amateurs are doing.

## How big a dish do I need for radio astronomy? - Astronomy

The wavelengths of radio waves are very large, and as a result large dishes are required to "capture" them. Because radio is of a lower energy than visible light, radio waves can reflect off of non-reflective surfaces. As a matter of fact, a disk does not have to be completely solid since the waves are so large.

 In 1931, Karl Jansky was tasked by Bell Telephone Labs to determine the cause of static over long distance telephone lines. He built a device in an attempt to pick up stray radio waves.

Instead, by 1933 he realized the emission was coming from space along the path of the Milky Way galaxy. By 1935, the first radio disk was constructed by Grote Reber, and radio astronomy was born.

While radio astronomy is used to study a wide variety of topics, the most common use is the mapping of hydrogen emission. Such emissions allowed for the determination of the spiral structure of our galaxy - using Doppler shift.

Hydrogen is the most abundant element in the Universe. It exists scattered throughout the Universe as well as members of larger clouds of dust and gas within galaxies. The hydrogen atom consists of 1 proton and 1 electron, and exist in one of two states: aligned or opposed:

The rotation (spin) of the electron can spontaneously shift to the opposite direction releasing a photon. This energy is detected at 21cm, or 1.42GHz (1420MHz). This shifting occurs about every 400 years for a single hydrogen atom, but is detected often due to the abundance of hydrogen.

 The radio dish is the tool used by astronomers to study this region of the radio spectrum. Generally the larger the dish the better, but more novel approaches have been used to create a virtual dish by creating a large array of radio dishes like those at the VLA in Socorro New Mexico. Even radio dishes from other countries are tied together creating the Very Long Baseline Array - or VLBI. The image on the right is a dish called a Cassegrain, just like the telescope. The radio wave bounces off the big dish, to the secondary dish at the top, then through the center to the radio gear at the base of the tower.

So what does a radio image look like? Just a bunch of numbers really. Astronomers apply their collected data and plot them based on intensity and assigning them a color. These images of spiral galaxy NGC253 are a good example:

 This is an optical image. This is the radio "image."

The red on the radio image indicates higher levels of 21cm emission while the violet indicates the lowest levels. Strange really since the opposite holds true for stars - red stars are cooler than blue stars, so be careful with the details.

## How big a dish do I need for radio astronomy? - Astronomy

In much the same way that you tune your radio to listen to your favourite music, radio astronomers can tune their telescopes to pick up the radio waves that come from quasars, other distant galaxies and the cosmic microwave background that are millions of light years from the Earth.

Radio astronomers don’t often listen to these radio signals with their ears, but rather use computers to make sense of it.

They can unravel signals from pulsars, quasars, masers, distant galaxies and other mysterious objects in the universe. They use the information to study the birth and death of stars, the violent lives of galaxies and sometimes even to hunt for extraterrestrial life.

Radio waves are the same sort of waves as light. The difference is the length of the waves is much longer than it is for light. For example, the radio waves your FM radio receives have a wavelength of 3 metres, and your microwave oven produces radio waves with a wavelength of about 10 centimetres.

### How does a radio telescope work?

A radio telescope is a very sensitive receiver of radio waves. It has two basic components to help us to decipher the meaning of the radio waves that it detects:

1. A dish-shaped antenna is pointed to the sky to collect the radio waves. Because the strength of the radio waves that reaches the earth is very weak – they have come from a long way away! – the collecting area should be large. The curved surface of the antenna then reflects the radiation to the focus point of the dish, where it is received by a metal horn and fed to a sensitive radio receiver.
2. The receiver then amplifies the radio signal and digitises it – turns it into numbers – so that it can be stored in a computer.

This information is then processed with the help of computers. To help make sense of the strings of numbers, astronomers turn the numbers into pictures. Each of these numbers represents information from a specific point in space. Astronomers often assign specific colours to these numbers according to the amount of information they represent. They then combine the colours to make a picture so that they information can then be “seen”. These pictures tell us about many characteristics of the objects in the universe.

Radio telescopes usually study what is invisible to optical telescopes, and optical telescopes usually study what is invisible to radio telescopes.

### What kinds of work are related to radio astronomy?

There are many exciting things you can do if you are interested to work with radio astronomers, or perhaps be involved in designing one of the telescopes of the future.

• Astronomers and astrophysicists study physics for several years and then go on to advanced training in astrophysics. They are the people who decipher the meaning of the signals. It’s a bit like rocket science, but just think of having the universe as the lab where you work! They write the computer programs to run the telescopes and to get information from the data coming from the telescopes.
• Engineers help to design and build components for existing and new telescopes. They also develop the sophisticated software and computer systems needed to operate the telescope.
• Technicians are important members of a telescope team. They help to make new components and make sure everything on the telescope is working well.

### What’s happening with radio astronomy in South Africa?

People cause a lot of radio wave interference with their cell phones, radio and television broadcasts, air traffic, and many other radio devices. Therefore, radio telescopes must be built as far away as possible from big cities.

South Africa has a 26-m diameter radio telescope (that’s a huge dish!) at the Hartebeesthoek Radio Astronomy Observatory in a valley west of Krugersdorp. Hills around this site help to shield the radio telescope from radio signals from Tshwane and Johannesburg, for example from microwave ovens and cellphones.

South Africa is currently building the Karoo Array Telescope, or MeerKAT, a mid-frequency ‘pathfinder’ or demonstrator radio telescope, near Carnarvon in the Northern Cape. It will be the largest and most sensitive radio telescope in the southern hemisphere until the SKA is completed.

But, most exciting of all, the majority of the SKA – the full dish array and the dense aperture array – will be built in Africa. The core – i.e. the region with the highest concentration of receivers – will be constructed in the Northern Cape Province, about 80 km from the town of Carnarvon (the same site as where the MeerKAT is being constructed).

### How do I become a radio astronomer?

You can’t do it without mathematics and physical sciences! With a matric exemption in both of these subjects at higher grade, you’ll be off to a good start. Computer science will also help! At university you will study astronomy and physics, before going on to more specialised postgraduate studies.

## Dish antenna for the amateur radioastronomy

In the previous article, I describe a low noise amplifier for the 21cm band.

Today I want to show you a construction of the dish antenna where this amplifier was used.

Most optimal, efficient, and easy to build is a classic dish antenna that consists of an actual dish that acts like a mirror and some receiver at the focal point.
Unfortunately, a 21 cm band requires a quite massive receiver so you can’t use a small dish. Also, you need to use a bigger antenna to achieve some reasonable resolution.
My antenna is 3m in diameter and it was used for satellite communication by some ISP

Antenna at work

The maximum angular resolution of this single antenna can be calculated by this formula:

Where λ is a wavelength (0.21 meters) and D is the diameter of the mirror (3 meters).

My antenna came as just a dish without any receivers and even without stands to secure the receiver at the focal point.
I needed to create this stands from scratch. The ideal material is an aluminum tube of a good reasonable diameter. But before cutting tubes it’s a good idea to figure out where is the focal plane of this mirror.

The focal distance of this antenna was totally unknown. There are a few ways to find this distance.
The first way is the calculation. For the parabola mirror you can find focal distance using this formula:

Where D is the diameter of the mirror and h it’s the depth of this mirror. Don’t forget to use the same magnitudes in both parts of the formula!

So I found the focal distance of my antenna.
The diameter is 300 centimeters and the depth is 47 centimeters.

Focal distance = 300*300 / 16 * 47 = 9000/752 = 119.68 centimeters.

Another way is experimental. You can use a strong source of light (the Sun), direct antenna to this source, and manually find a point of the max intensity. Yeah, this can be very tricky for such a big antenna and for the light.

In early experiments, I’m using the Sun as a strong source of wideband radio noise. As control receiver was used cheap satellite tv LNB and analog satellite finder with an arrow indicator.

Early experiments

### Antenna construction

To achieve maximum performance of the whole antenna we need to place complex construction at the focal plane.
This construction consists of the waveguide which is actually a tube with length and diameter selected for the band and a choke ring.

The purpose of the choke ring is to use the maximum area of the dish without losing incoming signals and without acquiring terrestrial noise from the dish edges.

This how actual construction looks like:

Waveguide and ring are also made from aluminum and secured with rivets.

There are few formulas to calculate the length and diameter of the waveguide and diameter, depth, and placement of the choke ring.

Waveguide diameter has an impact on minimal and maximal wavelength, acts as a bandpass filter.
Please note that the length of the wave inside the waveguide is longer than in open air.
You can find the minimal cutoff frequency in GHz from diameter using this formula:

To find maximal frequency just multiply Flcut by 1.3065
I chose waveguide diam as 14.5 centimeters so my cutoff frequencies are 1.21 GHz and 1.59 GHz. This is very good, maximal resonance is somewhere in between which is optimal.

The wavelength inside the waveguide can be calculated using this formula:

Where λ1 is the wavelength in an open-air – 21 centimeter and λ2 is a minimum cutoff frequency which was calculated above (24.7 centimeters in my case). So with a waveguide diameter of 14.5 cm, the internal wavelength is 40.8 centimeters!

The total length of the waveguide can be set as a minimum two-quarter wavelength inside the waveguide, the optimal value is three quarters.

So the length of the waveguide 40,8÷4×3 = 30.6 centimeters.

Now let’s talk about the choke ring.

Depth (h) of the choke ring can be calculated easily:

Where λ is again our wavelength – 21 centimeter. So the depth of the choke ring is 10.5 centimeters.

Where h is the depth of the choke ring and D is the diameter of the waveguide.

The position of the choke ring can be obtained experimentally. I believe that optimal is when the outer edge of the ring and the outer edge of the waveguide at the same level.

You can use this electronic table to easily calculate all the values above including the position of the choke ring:

The actual receiving element is a probe placed inside the waveguide. This is a copper rod of small diameter (thick wire can be used) which is soldered on an N-type RF connector. This probe should be placed in one of the maximum energy points inside the waveguide. See the picture below.

The optimal probe position is λ2/4 from the dead end

Probe placement in my case is 10.2 centimeters from the waveguide’s dead end.

Probe length should be 1/4 of the open-air wavelength or 21/4 = 5.25 cm.

Construction of the probe mounted on RF N-type connector and how it looks inside the waveguide:

External view and probe connection to the LNA using high quality and low loss 50-ohm cable:

All this construction requires some calibration. As you can find in the electronic table above – the focal plane is placed somewhere inside the waveguide. The position of the whole waveguide with the choke ring should be adjusted to achieve the maximum signal level. As a “reference” signal source you can use the Sun or artificial satellites, like INMARSAT.
As you can on the photo in the beginning my mounting system with the stands allows us to move and align this receiver with a few screw-nuts.

The first successful test was in August 2017.
In the video below you can wideband noise from the Sun and signals from the INMARSAT satellites.
I’m moving this antenna manually to slide on all these objects.

As the receiver can be used a wide range of the SDR, RTL-SDR with a few HW mods (cooling + power filtering), for example.

Hydrogen line 21 cm is extra weak so it’s really hard to get and collect the signal.
I spent some time scanning the narrow line on the night sky. All collected data were summarized and I’ve got this picture of the signal fluctuation. The picture was projected to the actual view of the sky at that time.

Few notes about polarization of the signal.
Polarization is actually relative thing and depends on the actual position of the transmitter and receiver and where is “up” and “down”. It’s very important for the artificial signals.
In case of space signals vertical or horizontal polarization doesn’t make sense so you can place you probe in the waveguide at the any angle you wish. All this natural signals can be even non-polarized or partially polarized or polarized by the some way.
Polarization factor is very important for astrophysics and if you wish to measure polarization you need to build polarimeter.
Polarimeter has the same construction but contains two probes in the waveguide. This probes is placed perpendicular to each other. Getting and comparing signal from the both probes you can estimate polarization factor and even type of the polarization

Another interesting experiment (with the new LNA) is acquisition signals from the Moon.
You can enable English subtitles in the video below.

## NSF says Arecibo telescope will be dismantled

The following is a statement from the U.S. National Science Foundation, issued November 19, 2020:

Following a review of engineering assessments that found damage to the Arecibo Observatory cannot be stabilized without risk to construction workers and staff at the facility, the U.S. National Science Foundation (NSF) will begin plans to decommission the 305-meter (1,000 foot) telescope, which for 57 years has served as a world-class resource for radio astronomy, planetary, solar system and geospace research.

The decision comes after NSF evaluated multiple assessments by independent engineering companies that found the telescope structure is in danger of a catastrophic failure and its cables may no longer be capable of carrying the loads they were designed to support. Furthermore, several assessments stated that any attempts at repairs could put workers in potentially life-threatening danger. Even in the event of repairs going forward, engineers found that the structure would likely present long-term stability issues.

‘NSF prioritizes the safety of workers, Arecibo Observatory’s staff and visitors, which makes this decision necessary, although unfortunate,’ said NSF Director Sethuraman Panchanathan. ‘For nearly six decades, the Arecibo Observatory has served as a beacon for breakthrough science and what a partnership with a community can look like. While this is a profound change, we will be looking for ways to assist the scientific community and maintain that strong relationship with the people of Puerto Rico.’

Engineers have been examining the Arecibo Observatory 305-meter telescope since August, when one of its support cables detached. NSF authorized the University of Central Florida, which manages Arecibo, to take all reasonable steps and use available funds to address the situation while ensuring safety remained the highest priority. UCF acted quickly, and the evaluation process was following its expected timeline, considering the age of the facility, the complexity of the design and the potential risk to workers.

The engineering teams had designed and were ready to implement emergency structural stabilization of the auxiliary cable system. While the observatory was arranging for delivery of two replacement auxiliary cables, as well as two temporary cables, a main cable broke on the same tower Nov. 6. Based on the stresses on the second broken cable – which should have been well within its ability to function without breaking – engineers concluded that the remaining cables are likely weaker than originally projected.

‘Leadership at Arecibo Observatory and UCF did a commendable job addressing this situation, acting quickly and pursuing every possible option to save this incredible instrument,’ said Ralph Gaume, director of NSF’s Division of Astronomical Sciences. ‘Until these assessments came in, our question was not if the observatory should be repaired but how. But in the end, a preponderance of data showed that we simply could not do this safely. And that is a line we cannot cross.’

NSF’s first priority is safety. Multiple assessments by independent engineering companies found the telescope structure is in danger of a catastrophic failure and its cables may no longer be capable of carrying the loads they were designed to support. https://t.co/En0S7OOhY4

&mdash National Science Foundation (@NSF) November 19, 2020

The scope of NSF’s decommissioning plan would focus only on the 305-meter telescope and is intended to safely preserve other parts of the observatory that could be damaged or destroyed in the event of an unplanned, catastrophic collapse. The plan aims to retain as much as possible of the remaining infrastructure of Arecibo Observatory, so that it remains available for future research and educational missions.

The decommissioning process involves developing a technical execution plan and ensuring compliance with a series of legal, environmental, safety and cultural requirements over the coming weeks. NSF has authorized a high-resolution photographic survey using drones, and is considering options for forensic evaluation of the broken cable – if such action could be done safely – to see if any new evidence could inform the ongoing plans. This work has already begun and will continue throughout the decommissioning planning. Equipment and other materials will be temporarily moved to buildings outside the danger zone. When all necessary preparations have been made, the telescope would be subject to a controlled disassembly.

Scientists at Arecibo conducted Nobel Prize winning research on the potential of other habitable planets. Earlier this month one of the massive steel support cables snapped and damaged the 1,000- foot-wide reflector dish. pic.twitter.com/tjFQYlwakM

&mdash CGTN America (@cgtnamerica) November 19, 2020

After the telescope decommissioning, NSF would intend to restore operations at assets such as the Arecibo Observatory LIDAR facility – a valuable geospace research tool – as well as at the visitor center and offsite Culebra facility, which analyzes cloud cover and precipitation data. NSF would also seek to explore possibilities for expanding the educational capacities of the learning center. Safety precautions due to the COVID-19 pandemic will remain in place as appropriate.

Some Arecibo operations involving the analysis and cataloging of archived data collected by the telescope would continue. UCF secured enhanced cloud storage and analytics capabilities in 2019 through an agreement with Microsoft, and the observatory is working to migrate on-site data to servers outside of the affected area.

Areas of the observatory that could be affected by an uncontrolled collapse have been evacuated since the November cable break and will remain closed to unauthorized personnel during the decommissioning. NSF and UCF will work to minimize risk in the area in the event of an unexpected collapse. NSF has prioritized a swift, thorough process with the intent of avoiding such an event.

The first I heard about Arecibo, I was a kid. It was through this shot from the @thexfiles. @davidduchovny

&mdash Salvatore Vitale (@sasomao) November 19, 2020

NSF recognizes the cultural and economic significance of Arecibo Observatory to Puerto Rico, and how the telescope serves as an inspiration for Puerto Ricans considering education and employment in STEM. NSF’s goal is to work with the Puerto Rican government and other stakeholders and partners to explore the possibility of applying resources from Arecibo Observatory for educational purposes.

‘Over its lifetime, Arecibo Observatory has helped transform our understanding of the ionosphere, showing us how density, composition and other factors interact to shape this critical region where Earth’s atmosphere meets space,’ said Michael Wiltberger, head of NSF’s Geospace Section. ‘While I am disappointed by the loss of investigative capabilities, I believe this process is a necessary step to preserve the research community’s ability to use Arecibo Observatory’s other assets and hopefully ensure that important work can continue at the facility.’

In college, I was fortunate to spend many months doing research at the Arecibo Observatory—a special place that inspired many young people (including me) to pursue careers in science.

It also led me to meet my wife, who also began her research career there. pic.twitter.com/ztgq2wnxle

&mdash Casey Dreier (@CaseyDreier) November 19, 2020

Engineering summary

Arecibo Observatory’s telescope consists of a radio dish 1,000 feet (305 meters) wide in diameter with a 900-ton instrument platform hanging 450 feet (137 meters) above. The platform is suspended by cables connected to three towers.

On August 10, 2020, an auxiliary cable failed, slipping from its socket in one of the towers and leaving a 100-foot (30 meter) gash in the dish below. NSF authorized Arecibo Observatory to take all reasonable steps and use available funds, which amounted to millions of dollars, to secure the analysis and equipment needed to address the situation. Engineers were working to determine how to repair the damage and determine the integrity of the structure when a main cable connected to the same tower broke Nov. 6.

The second broken cable was unexpected – engineering assessments following the auxiliary cable failure indicated the structure was stable and the planning process to restore the telescope to operation was underway. Engineers subsequently found this 3-inch (7.6 cm) main cable snapped at about 60% of what should have been its minimum breaking strength during a period of calm weather, raising the possibility of other cables being weaker than expected.

Inspections of the other cables revealed new wire breaks on some of the main cables, which were original to the structure, and evidence of significant slippage at several sockets holding the remaining auxiliary cables, which were added during a refit in the 1990s that added weight to the instrument platform.

RIP Arecibo :'( Good memories from this amazing telescope, which has been going strong for 57 years (photos from 2013)….

Posted by Theresa Vliegert on Thursday, November 19, 2020

Thornton Tomasetti, the engineering firm of record hired by UCF to assess the structure, found that given the likelihood of another cable failing, repair work on the telescope – including mitigation measures to stabilize it for additional work – would be unsafe. Stress tests to capture a more accurate measure of the remaining cables’ strength could collapse the structure, Thornton Tomasetti found. The firm recommended a controlled demolition to eliminate the danger of an unexpected collapse.

‘Although it saddens us to make this recommendation, we believe the structure should be demolished in a controlled way as soon as pragmatically possible,’ said the recommendation for action letter submitted by Thornton Tomasetti. ‘It is therefore our recommendation to expeditiously plan for decommissioning of the observatory and execute a controlled demolition of the telescope.’

UCF also hired two other engineering firms to provide assessments of the situation. One recommended immediate stabilization action. The other, after reviewing Thornton Tomasetti’s model, concurred that there is no course of action that could safely verify the structure’s stability and advised against allowing personnel on the telescope’s platforms or towers.

‘Critical work remains to be done in the area of atmospheric sciences, planetary sciences, radio astronomy and radar astronomy,’ UCF President Alexander N. Cartwright said. ‘UCF stands ready to utilize its experience with the observatory to join other stakeholders in pursuing the kind of commitment and funding needed to continue and build on Arecibo’s contributions to science.’

After receiving the contracted assessments, NSF brought in an independent engineering firm and the Army Corps of Engineers to review the findings. The firm NSF hired concurred with the recommendations of Thornton Tomasetti and expressed concern about significant danger from uncontrolled collapse. The Army Corps of Engineers recommended gathering additional photographic evidence of the facility and a complete forensic evaluation of the broken cable.

Given the fact that any stabilization or repair scenario would require workers to be on or near the telescope structure, the degree of uncertainty about the cables’ strength and the extreme forces at work, NSF accepted the recommendation to prepare for controlled decommissioning of the 305-meter telescope.

I'm really bummed about #Arecibo Closing. I understand why, but to me it was always an iconic space telescope that was immediately recognized and known about when people talked about Astronomy.
It helped that the movie Contact made it well known.
RIP old girl.
You did good.

&mdash Dee West (@DeeWestastro) November 19, 2020

Bottom line: The National Science Foundation announced on November 19, 2020, that the big-dish Arecibo telescope in Puerto Rico is to be dismantled, following engineering reports suggesting it is unsafe, due to damage from hurricanes and other factors.

## SETI Talks - Radio Astronomy: The End of Big Dishes?

Big-single dish radio astronomy observatories such as the 305-m Arecibo Observatory and the 500-m FAST (Five-hundred-meter Aperture Spherical Telescope) have made key breakthroughs in science, including the discovery of the first extrasolar planets. Recently, interferometric telescopes such as MeerKAT in South Africa, ASKAP (Australian Square Kilometre Array Pathfinder), and CHIME (Canadian Hydrogen Intensity Mapping Experiment) have opened up new observing windows. These experiments are all precursor to the SKA (Square Kilometer Array), whose construction will begin in 2021 and is expected to be the most sensitive radio telescope ever built.

Why this explosion of radio telescope projects?
What’s the scientific reasoning for building arrays separated across continents?
What challenges do astronomers and engineers face?
Finally, what kind of science are these arrays useful for and will SETI benefit from their capabilities?

To answer these questions, we invited two astronomers who have worked for years in the field of radio astronomy. Cherry Ng is a researcher at the Dunlap Institute of Astronomy & Astrophysics in Canada. She has used the single-dish Parkes Radio Telescope in Australia and the CHIME (Canadian Hydrogen Intensity Mapping Experiment) radio telescope for her research on neutron star and fast radio bursts. Evan Keane, an award-winning astrophysicist, works in time-domain radio astronomy and has been the Square Kilometer Array project scientist since 2015.

Cherry Ng and Evan Keane will describe their past, current and future work with radio telescopes, the potential of future facilities for their research and the SETI search.

Cherry Ng is a post-doctoral researcher at the Dunlap Institute for Astronomy & Astrophysics. During her PhD study, she has discovered 60 rapidly spinning neutron stars with the Parkes Radio Telescope in Australia. Her hunting effort continues, now with the Canadian CHIME telescope. Together with the team, she uses CHIME to detect and study “fast radio bursts,” a new astrophysical mystery that involves short bursts of radio waves that have come from far outside our Milky Way galaxy.

Evan Keane is an award-winning astrophysicist working in the area of time-domain radio astronomy. Time variable astrophysical signals arise from extreme physical environments, impossible to create in an Earth-bound laboratory, and so offer unique insights into laws of nature. His work involves searching for pulsars and fast radio bursts and using these as tools to understand the Universe. Recently he has begun working on SETI search systems. Since 2015 he has been Project Scientist for the Square Kilometre Array, which commences construction in 2021. Evan's role has been to ensure that the telescope designs can deliver scientifically in time-domain science.

## A change in radio astronomy

This huge surge in humankind’s knowledge of the radio sky has several consequences.

First, we expect to answer some of the major questions in astrophysics, such as understanding why super-massive black holes seem so common in the universe, how that regulates the growth and evolution of galaxies and how galaxies swarm together to form clusters.

Second, it will change the way we do radio astronomy. At the moment, if I want to know what a galaxy looks like at radio wavelengths, chances are I’ll have to win time competitively on a major radio telescope to study my galaxy.

But I’ll soon be able to go to the web and observe my galaxy in data already collected by EMU or one of the other mega-projects. So most radio astronomy will be done by a web search rather than by a new observation. The role of major radio telescopes will change from finding new objects to studying known objects in exquisite detail.

Third, it will change the way that astronomers do their astronomy at other wavelengths. At the moment, only a small minority of galaxies have been studied at radio wavelengths.

From now on, most galaxies being studied by the average astronomer will have excellent radio data. This adds a new tool that can routinely be used to uncover the physics of galaxies, opening wide the radio window on the universe.

Fourth, having such large volumes of data changes the way we do science. For example, if I want to understand how the gravitational field of nearby galaxies bends light from distant galaxies, I currently find the best single example I can, and spend night after night on the telescope to study the process in detail.

In future, I will be able to correlate the millions of background galaxies with the millions of foreground galaxies, using data downloaded from the web to understand the process in even greater detail.

Fifth, and probably most importantly, history tells us that when we observe the universe in a new way, we tend to stumble across new objects or new phenomena that we didn’t even suspect were there. Pulsars, quasars, dark energy and dark matter were all found in this way.

Radio astronomy may reveal more about the supermassive black hole, typically found at the heart of many galaxies.

## How big a dish do I need for radio astronomy? - Astronomy

I'm in grade/middle/high school. What do I need to do to become an astronomer?

I advise you to take as much math as you can. Having high school calculus under your belt will make your first physics classes much easier. Physics and other sciences should be a priority, too, but don't neglect other classes. Astronomers still need to be good writers and communicators, and good grades across the board are necessary for college admission and scholarships.

Increasingly, computer programming skills are a key ingredient to success in astronomy -- and they open up other career paths, too. Working with robotics kits or doing free online coding projects, like those offered through CodeAcademy, can be a great introduction even if your school doesn't offer programming classes.

This page was last updated on June 19, 2015 by Ann Martin.

#### Britt Scharringhausen

Britt studies the rings of Saturn. She got her PhD from Cornell in 2006 and is now a Professor at Beloit College in Wisconson.

Radio astronomy is the sub-area of ​​astronomy that studies the universe between 30 MHz and 700 GHz with radio waves. Instead of expensive receivers you can create a good receiver for meteors with a simple piece of hardware and a laptop. In particular I concentrate on Neutral Hydrogen. 1420.405 Mhz with my 1.5-1.9 meter dish

You can't capture a meteor itself with radio, but you can record the so-called ionization track that a meteor leaves behind. In France there is the Graves transmitter that broadcasts a specific carrier. We can capture the reflected signal with SDR (Software Defined Radio). So you can detect meteors that you cannot see because of the distance.

For that you need an antenna. I use a 4 Elements 2 meter band Yagi antenna on a rotor.

Also I do have a 4 elements 6 meter Yagi and a remote controlled 1.9 meter dish on rotor for neutral Hydrogen detection with SDR# and VIRGO software

And software, One application to convert the signal to audio and one to make a spectrum using FFT (Fast Fourier Analysis).

While reading up on recent astro info, I was left wondering if amateur astros ever get into radio astronomy using radio dishes.

There are several points that would make radio astronomy very atractive to amateurs:

- daytime astronomy all day long is possible
- "low" reflector antenna tolerances about 1/10 those of optical telescopes
- no visual LP to worry about, though there's lots of radio sources to hide from
- moon phases don't interfere
- aperture fever could flare to big diameters

So how come you never see an amateur with a radio dish?

### #2 Bob W6PU

There is a multitude of Info. on this subject on the web, and I suggest that you "Google" this subject!

### #3 tatarjj

So how come you never see an amateur with a radio dish?

### #4 Dipole

I actually do a little radio astronomy!

And to reply to tatarjj (not picking on you but you posted the list!)

1. You can visualize your results with awesome graphs!
2. With a smallish baseline and two antenna you can do pretty high resolution interferometry. No big dish needed!
3. If you have a short wave radio you can make cheap antenna and listen to Jupiter and the Sun for pennies!
4. Think harder!

Seriously, I have an old shortwave radio receiver that I use with a small home made antenna to listen to Jupiter and the solar system at 30Mhz. I also have a down converter and pre-amp (about $150 worth) that's connected to a small quad yagi for listening around 150Mhz for galactic signals. All this feeds from the audio out to my sound card where it's recorded and graphed. Some people as so good at it that they can "see" solar storms coming and hear changes in Jupiter atmospheric storms. ### #5 tatarjj I actually do a little radio astronomy! And to reply to tatarjj (not picking on you but you posted the list!) 1. You can visualize your results with awesome graphs! 2. With a smallish baseline and two antenna you can do pretty high resolution interferometry. No big dish needed! 3. If you have a short wave radio you can make cheap antenna and listen to Jupiter and the Sun for pennies! 4. Think harder! Seriously, I have an old shortwave radio receiver that I use with a small home made antenna to listen to Jupiter and the solar system at 30Mhz. I also have a down converter and pre-amp (about$150 worth) that's connected to a small quad yagi for listening around 150Mhz for galactic signals.

All this feeds from the audio out to my sound card where it's recorded and graphed. Some people as so good at it that they can "see" solar storms coming and hear changes in Jupiter atmospheric storms.