Back in 2020, we posted a tutorial on how to set up a low-cost Hydrogen Line radio telescope using an RTL-SDR, LNA, and WiFi grid antenna. Since then we have seen similar setups successfully replicated in the community many times.
In a recent Hackaday post, we discovered a paper by Jack Phelps who has written an in-depth technical and scientific description of his attempt at Hydrogen line radio astronomy with similar equipment. His paper goes into deeper scientific explanations and describes the experiment and hardware setup in detail including some signal processing, observation, and calibration equations that might be useful for those looking to understand the science more deeply.
Jack Phelps Radio Astronomy Setup and some Results
Last week we posted about Alex Petit Jr's 'Project H Line 3D' which is a collection of documents and programs designed to be a beginner's guide to antenna fabrication, reception, recording, software processing, and graphic display of the 21 cm Hydrogen line. The project makes use of an RTL-SDR and LNA as the radio front end.
This week Alex gave an online talk to the Society of Amateur Radio Astronomers (SARA) discussing the project and giving an overview.
Project H Line 3D' is a collection of documents and programs designed to be a beginner's guide to antenna fabrication, reception, recording, software processing, and graphic display of the 21 cm Hydrogen line. The project makes use of an RTL-SDR and LNA as the radio front end.
The Hydrogen Line is an observable increase in RF power at 1420.MHz that is created by natural hydrogen atoms. The Hydrogen line is most easily detected by pointing a directional antenna toward the Milky Way where neutral hydrogen is abundant. Properties of the hydrogen line curve such as its shape and Doppler shift can be used to measure the shape and properties of our galaxy.
Alex's project H Line build is designed to be inexpensive and easy for students to build and set up for drift scans which involve pointing the antenna towards the sky and letting the Earth's rotation drift the Milky Way into and through the view of the antenna.
The project includes a design for a 13-element circular patch feed Yagi that can be built using common materials available from a hardware store. The 13-element Yagi results in about 15dBi gain and a 30-degree 3dB bandwidth.
The software portion of the instructions uses the SDR# IF Average plugin, and uses that to record log files every few minutes. The log files are then converted by an included Java program by Jamison Adcock into a logarithmic dB scale and a format compatible with Rinearn 2D and 3D graphics packages.
Thank you to Alex Petit Jr who wanted to submit 'Project H Line 3D' which is a collection of documents and programs designed to be a beginners guide to antenna fabrication, reception, recording, software processing, and graphic display of the 21 cm Hydrogen line. The project makes use of an RTL-SDR and LNA as the radio front end.
If you were unaware, the Hydrogen Line is an observable increase in RF power at 1420.4058 MHz that is created by natural hydrogen atoms. The Hydrogen line is most easily detected by pointing a directional antenna toward the Milky Way where neutral hydrogen is abundant. Properties of the hydrogen line curve such as its shape and Doppler shift can be used to measure the shape and properties of our galaxy.
Alex's project H Line build is designed to be cheap and easy for students to build and set up for drift scans which involve pointing the antenna towards the sky and letting the Earth's rotation drift the Milky Way into view of the antenna.
The project includes a design for a 13-element circular path feed Yagi that can be built using common materials available from a hardware store. Alex started with a Yagi design using circular director elements but found these difficult to find and fabricate. However, through NEC antenna analysis software he found that replacing the circular elements with more commonly found and easier-to-fabricate square elements had a negligible effect on the antenna's performance, unlocking a cheaper build. The 13-element Yagi results in about 15dBi gain and a 30-degree 3dB bandwidth.
Plate Yagi gives an almost identical Hydrogen line detection as the Disk Yagi
The software portion of the instructions uses the SDR# IF Average plugin, and uses that to record log files every few minutes. The log files are then converted by an included Java program by Jamison Adcock into a logarithmic dB scale and a format compatible with Rinearn 2D and 3D graphics packages.
Job Geheniau was someone whose amateur radio astronomy projects were often featured on RTL-SDR Blog (often referred to as Job's Radio Telescope). It with great sadness that we have recently learned that Job Geheniau passed away from cancer in late December 2023. We would like to take the time share this post to highlight some of his achievements in the amateur radio astronomy field.
Back in 2020 Job first surprised us with one of his first radio astronomy results (Part 1, Part 2) where he was able to image the Milky Way in neutral hydrogen by using a 150cm dish, RTL-SDR, LNA and motorized mount. Over eight nights he recorded hydrogen line readings throughout the Milky Way and ended up creating a 2D Excel sheet that showed an image of the Milky Way at the 1420 MHz hydrogen line frequency.
Job would go on, rapidly evolving and each time showing us that low cost hardware set up in a backyard could be used to unlock many of the secrets of the universe. Using a satellite dishes less than two meters in diameter, RTL-SDRs, LNAs and filters he was able to:
Job's Radio Astronomy website remains up at https://jgeheniau.wixsite.com/radio-astronomy, and many results and writeups of his other experiments can be found there. We will sorely miss posting about Job's achievements, but we hope that his life has inspired you to take a closer look at the amateur radio astronomy hobby.
Thank you to Mario A. Natali (I0NAA) who wrote in an wanted to share his Windows software called TotalPower which is designed for mapping the galactic Hydrogen line and works with RTL-SDR dongles.
The Hydrogen Line is an observable increase in RF power at 1420.4058 MHz which is created by Hydrogen atoms. It is most easily detected by pointing a directional antenna towards the Milky Way as there are many hydrogen atoms in our own galaxy. This effect can be used to measure the shape and other properties of our own galaxy.
Mario writes:
[TotalPower] was originally designed to measure total power of received spectrum and that, thanks to the input of many users, is now able to perform many other tasks including the 3D mapping of selected sky areas and HLine detection with the ability to estimate the speed of rotation of galaxy arms ( respect to our position )
In addition to the last Hydrogen Line radio astronomy post from a few minutes ago, we've also recently seen a post on Hackaday about a research paper (PDF) that describes a Hydrogen Line Radio Telescope made from a cooking Wok, LNA and RTL-SDR dongle.
In the paper Leo W.H. Fung et al of Hong Kong University of Science and Technology uses a 61cm cooking Wok with a custom made dipole feed at the calculated focal point. A filtered LNA sits after the feed, and is connected to an RTL-SDR Blog V3 dongle enclosed within a metal cookie box for additional shielding.
The results show that the Hydrogen Line was indeed detected, and measurements of the galactic rotational velocity were possible.
Again we note that we will soon by crowdfunding for a product called the 'Discovery Dish' that will be fairly similar in size and shape. It is designed for receiving L-band weather satellites, but can also be used as a Hydrogen Line telescope too.
Back in 2020 we released a tutorial about how to use a 2.4 GHz WiFi Grid Dish antenna as a radio telescope which can detect and measure the Hydrogen line emissions in our Milky Way galaxy.
Recently matt from the TechMinds channel has uploaded a video showing this same project but using the NooElec mesh antenna that has been slightly modified for improved performance on 1.7G and 1.4G.
In his video Matt sets up a drift sky scan, where the rotation of the earth drifts the Milky Way through the beamwidth of the dish. Matt uses Stellarium to virtually visualize the live sky map, SDR# and the IF average plugin to average the spectrum, and an Airspy software defined radio.
Back in January 2020 we posted a tutorial showing how it's possible to detect and measure the galactic Hydrogen line using a simple 2.4 GHz WiFi dish, RTL-SDR Blog V3 and a filtered LNA. Since then many people have used the same setup with great results.
Over on YouTube user stoppi who is one such person who is using the same steps from our tutorial, and he has uploaded a video showing his setup and results. If you're thinking of getting started with Hydrogen Line reception, his video slide show tutorial would be a good complimentary overview to go along with our text tutorial.
Detection of the galactic hydrogen - the 21 cm radiation - Wasserstoffstrahlung der Milchstrasse
