Every amateur astronomer’s dream: building their own radio telescope. Do you dare to try it? An astronomer tells us how to do it… it will take time and patience.
Imagine that you are like ET, the lovable alien who, lost on Earth, builds a homemade device to call home . With ingenuity and parts found around the house, he manages to create a machine that emits signals into space, trying to contact his people. Although this sounds like pure science fiction, today, amateur astronomers can do something similar from their own garden. With a few differences. Not to call a spaceship, of course, but to capture real signals from the universe .
Observing the universe doesn’t always require giant telescopes or expensive observatories. A little ingenuity, patience, and skill might just do the trick. In fact, amateurs and astronomy enthusiasts can investigate celestial phenomena from the comfort of their homes using a homemade radio telescope . This tool makes it possible to capture radio signals from space, specifically the famous 21 cm line, emitted by the neutral hydrogen atoms that abound in the Milky Way. The creation of these accessible instruments has gained popularity, allowing more people to contribute to the understanding of the structure and dynamics of our galaxy.
Phelps presents a detailed guide to building a home-made radio telescope. The paper describes an efficient and low-cost design that allows enthusiasts to detect neutral hydrogen emissions and analyze the dynamics of galactic clouds. The paper provides a step-by-step guide to the necessary components and data processing, as well as techniques to minimize interference, thus facilitating observation even in urban environments.
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The importance of the 21 cm line
Table of Contents
The 21 cm line is a radio emission produced by neutral hydrogen, the most abundant element in the universe. This spectral line comes from a very particular energy transition in the hydrogen atom, where the electron spin changes with respect to the proton spin. This emission has a wavelength of 21 cm and a frequency of 1420 MHz . Thanks to this property, astronomers can “see” through interstellar dust that blocks other forms of radiation, allowing them to map the distribution of hydrogen in the galaxy.
Neutral hydrogen is key to understanding the formation and evolution of galaxies. Studying it through the 21 cm line reveals the spiral structure of the Milky Way and allows us to observe the relative velocities of gas clouds, which often suggests the presence of dark matter. Thus, the analysis of these emissions helps to reconstruct the history of cosmic expansion and to refine models of the behaviour of the universe on large scales.
Basic components of a homemade radio telescope
To build a homemade radio telescope, several components are needed that are readily available to amateurs. According to Phelps’ study, the antenna is a central element and it is recommended to use a dish of about 1 meter in diameter, originally intended for receiving satellite data. This type of antenna is ideal due to its high gain and focusing, which facilitates the capture of weak signals coming from galactic hydrogen.
The next essential component is the low noise amplifier (LNA) , which boosts the signal picked up by the antenna before it is processed. Phelps’ design includes the use of a Nooelec H1 LNA , which offers up to +40dB gain, reducing interference and allowing for improved detection of the 21cm line. A software defined radio (SDR) device , such as the RTL-SDR, is used to convert the analog signal into digital data processable by a computer. This type of device allows for great flexibility , making it easy to analyze radio signals through open source programs such as GNU Radio.
Data processing and analysis
Picking up radio signals is just the first step. Data processing is essential to identify the 21 cm line among the noise and other interference. The study recommends using fast Fourier transforms (FFT) , a mathematical technique that allows signals to be converted from the time domain to the frequency domain. This makes it easier to identify the peak corresponding to the 1420 MHz frequency, where the emission from neutral hydrogen is found.
Additionally, the use of filtering and vector median techniques helps mitigate radio frequency interference (RFI) , common in urban environments. In his paper, Phelps details how removing these stray signals improves data clarity , allowing even the faintest emissions to be detected. Calibrating the telescope, using “hot load” and “cold load” sources (such as the ground and the night sky), is essential to convert measurements into physical units, such as brightness temperature, making them easier to interpret scientifically.
Problems and solutions in construction
One of the main challenges when building a homemade radio telescope is interference mitigation. Radio interference (RFI) pollution can come from multiple sources , from nearby electronic devices to radio and television broadcast signals. To reduce this interference, Phelps suggests wrapping the electronics in aluminum foil and grounding the entire system. This type of shielding acts like a Faraday cage, blocking unwanted external signals.
Another crucial aspect is the alignment and positioning of the antenna. According to the study, it is important to perform regular calibrations and adjust the angle of the antenna to maximize the capture of the hydrogen signal. Software tools such as Stellarium can be useful to verify the orientation of the telescope and ensure that it is pointed at a “dark” part of the sky, where interference is less likely to be encountered and observation of the 21 cm line is made easier.
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Benefits of the project
Building a homemade radio telescope is not only an affordable way to explore the cosmos, but also an excellent opportunity to learn about astronomy, physics, and technology. Data obtained through these devices can contribute to broader studies of galactic dynamics and the distribution of hydrogen in the Milky Way. Projects like the one described by Phelps foster interest in science and open the door to amateur participation in meaningful research.
Using low-cost components and accessible software, anyone with the right guidance can build their own telescope and observe signals that are billions of years old. Initiatives like this democratize astronomy and show how citizen science can contribute to understanding complex universal phenomena.
