Category: Radio Astronomy

Imaging the Milky Way in Neutral Hydrogen with an RTL-SDR Part 2

Last month we shared information about Job Geheniau's success with using an RTL-SDR dongle to image our galaxy in neutral Hydrogen. Our galaxy is full of neutral Hydrogen, and lots of neutral Hydrogen together results in a detectable radio peak at 1.42 GHz. This peak is called the Hydrogen line. By scanning the galaxy at the Hydrogen line frequency with a 1.5 meter dish on a motorized mount, an RTL-SDR, and a few filters and LNAs, Job is able to create a radio image of our galaxy.

In Job's previous attempt he created an image by pointing the dish antenna at 168 predefined grids calculated to cover the Milky Way, resulting in 168 points of exposure data. In his latest work Job has created an even higher resolution image by taking 903 points of exposure data. Each exposure took 150s and the total 903 exposures took 8 nights to record. Once all data was collected he uses the same process as before, which is to input all the Hydrogen line data into a standard 2D excel sheet, then use conditional formatting to create a heatmap which reveals the image. He then applies a blur and stretches the image into the Mollweide Cartographic which can represent the entire Universe in one image.

Job has shared with us his PDF where he documented his process and shares his images (note 16 MB PDF file). We also share his full resolution images below, just click to open. We think that these images are quite amazing and an excellent achievement for a backyard radio astronomer.

If you're interested in Hydrogen line radio astronomy we have a tutorial that will help you observe the Hydrogen line peak on a budget. The tutorial could be improved upon by motorizing the dish, allowing you to create images like the ones above. You might also be interested in a similar project by Marcus Leech who took 5 months of hydrogen line observations with an RTL-SDR in order to create an even higher resolution image.

A Talk on 21cm Hydrogen Line Amateur Radio Astronomy

The Amateur Radio Experimenters Group (AREG) recently held an online talk with guest speakers Phil Lock and Bill Cowley, talking about amateur radio astronomy. In the talk they note how they use an RTL-SDR as their radio.

Cheaper electronics has created great possibilities for Amateur Radio Astronomy. This talk will describe a local project to receive and map the distribution of 1420 MHz signals from neutral hydrogen in our galaxy. We briefly describe the history of 21cm RA and why it’s still of great interest to astronomers. We outline some challenges over the last few years in assembling a 2m dish with custom feed, electronics and signal processing, then show recent results from our project.

The image in the thumbnail shows recent signals (May 17th) recorded over a 24 hour period for dish elevation of 53 degrees. The signal changes as the antenna points to different parts of the Milky Way.

https://www.areg.org.au

21cm (1420MHz) Amateur Radio Astronomy

Imaging the Milky Way in Neutral Hydrogen with an RTL-SDR

Over on Facebook Job Geheniau has recently been sharing how he's taken an image of our galaxy (the Milky Way) with a radio telescope consisting of a 1.5 meter dish, RTL-SDR and a few filters and LNAs. In the past we've posted several times about others observing the Hydrogen line with an RTL-SDR, and we have a tutorial here showing how to observe it on a budget.

In this case, Job went a step further than just a single measurement. He used a used a motorized dish and RTL-SDR to scan the entire Milky Way over one month, resulting in a full radio image of the galaxy. As his posts and pdf document are on Facebook and not visible to those without Facebook accounts, we asked for permission to reproduce some of them here for all to see. We have also mirrored his PDF file here, which contains more information about his radio telescope, results and setup.

To make a very long story short. After a month of angel patience (and that says something to me) I managed to take a 'picture' of our entire galaxy (galaxy) in neutral hydrogen! I attach some pictures. If you are more interested, please come after this and PDF with explanation. It was a hell of a job I can tell you. But here's the ' picture s' of the house (230 million light years wide) in which we live and in which we all have a big mouth......

Hydrogen Line Image of the Milky Way produced by Job Geheniau
Hydrogen Line Image of the Milky Way produced by Job Geheniau

For the Scientists among us... a beautiful plot of the Milky Way Graphically explained in neutral hydrogen....... In short, summarized... if you look up on a beautiful summer evening you will see a beautiful galaxy, this is graphically the same but then on a different frequency than the eye can perceive. own dates of course.....

A composite of Hydrogen Line readings at different points of the Milky Way
A composite of Hydrogen Line readings at different points of the Milky Way produced by Job Geheniau
An image of the Galactic Plane (longitude 20 to 240 steps of 5 degrees and latitude 0)
An image of the Galactic Plane (longitude 20 to 240 steps of 5 degrees and latitude 0)

His setup consists of a 1.5m dish, extended to 1.9m with some mesh. A 1420 MHz tuned feed, Mini Circuits ZX6-P33ULN LNA, Bandpass Filter, NooElec SAWBird LNA, Bias-T, RTL-SDR V3, PST Rotator Dish Software, VIRGO software, SDR#, Cartes due Ciel sky chart and a home made netfilter.

He uses a modified version of the VIRGO software to read sky coordinates from a text file, and this points the telescope at each predefined coordinate. He then uses VIRGO to record data for 180 seconds before moving on to the next coordinate. The data is then plotted in Excel, and the highest peak is taken at each coordinate and put back into an 8x21 matrix in excel. Conditional formatting is then used to generate a color gradient resulting in a rough map. Then a Gaussian blur is applied, and it is projected over the Galaxy, resulting in the images above.

Job Geheniau's Radio Telescope Setup
Job Geheniau's Radio Telescope Setup

In the past we've seen a very similar project performed by Marcus Leech from ccera.ca. However, his measurements use 5 months of observations resulting in much higher resolution data.

The Hydrogen Line is an observable increase in RF power at 1420.4058 MHz created by Hydrogen atoms. It is most easily detected by pointing a directional antenna towards the Milky Way as there are many more hydrogen atoms in our own galaxy. This effect can be used to measure the shape and other properties of our own galaxy.

Building a Motorized Hydrogen Line Radio Telescope with a DIY Horn Antenna, Drill Motor and RTL-SDR

Just on the back of yesterday's post about a helical antenna Hydrogen line radio telescope, we have another submission. This telescope is a bit more advanced as it consists of a large motorized horn antenna, with a custom made LNA and filter board connected to an RTL-SDR with GNU Radio DSP processing.

Over on Instructables "diyguypt" has posted a full overview of his creation. The horn antenna is first created out of aluminum sheets, and then the waveguide is cut out of copper wire and installed into the can part of the horn. He then notes that he created two custom LNA+filter boards with the Minicircuits PMA2-43LN+ LNA and the Minicircuits BFCN-1445+ filter. This then connects to the RTL-SDR that is accessed via GNU Radio which creates a visualization spectrograph.

He then shows how he made the rotation system out of a salvaged drill motor and two relays, and how he made the Z-Axis control with a stepper motor. The motors are controlled with an Arduino and a gyroscope module.

"diyguypt"'s Hydrogen Line Horn Antenna connected to an RTL-SDR
"diyguypt"'s Hydrogen Line Horn Antenna connected to an RTL-SDR

A Hydrogen Line Radio Telescope made from a Homemade Helical Antenna and RTL-SDR

Thank you to Geoff for submitting his experience with creating a hydrogen line radio telescope out of an easy to build helical antenna, Raspberry Pi, LNA and an RTL-SDR. The Hydrogen Line is an observable increase in RF power at 1420.4058 MHz created by Hydrogen atoms. It is most easily detected by pointing a directional antenna towards the Milky Way as there are many more hydrogen atoms in our own galaxy. This effect can be used to measure the shape and other properties of our own galaxy.

Earlier in the year we uploaded a tutorial showing how to observe the Hydrogen line with a 2.4 GHz WiFi antenna. In Geoff's setup he used a home made Helical antenna instead. This antenna is basically a long tube with a spiral wire element wrapped around the tube. He also shows how he needed to impedance match the antenna with a triangular piece of copper tape. The result is a directional antenna with about 13 dBi gain. To complete his setup he used a NooElec SAWBird H1+ LNA/Filter, an RTL-SDR Blog V3 dongle and a Raspberry Pi.

The results show a clear increase in RF power at the Hydrogen line frequency when the antenna points at the Milky Way, indicating that the setup works as expected. It's good to see a Helical working for this, as it is fairly light weight and could easily be mounted on a motorized mount to scan the entire sky.

A Hydrogen Line Radio Telescope made with a Helical Antenna.
A Hydrogen Line Radio Telescope made with a Helical Antenna.

YouTube Video Replicates our Galactic Hydrogen Line Detection Tutorial

Earlier in the year we posted a tutorial showing how to detect the Galactic Hydrogen Line at home with less than $200 in components. All that is really needed is a 2.4 GHz WiFi dish, an RTL-SDR and an LNA. With this setup it's possible to do home science like determining the size, shape and rotational speed of our own galaxy. 

Over on YouTube user Nicks Tech Hobby has successfully replicated our tutorial with similar hardware, and has uploaded a time lapse video showing his results. His success confirms that this is a good way to get introduced into radio astronomy. What's also interesting is that it is possible to spot the Hydrogen line energy on the live waterfall even without averaging/integration. 

My first successful attempt to detect galactic hydrogen (Hydrogen line)

CygnusRFI: New RFI Analysis Tool for Ground Stations and Radio Telescopes

Thank you to Apostolos for submitting information about his new open source program called "CygnusRFI". CygnusRFI is a tool designed for analyzing radio frequency interference (RFI) with a focus on how it affects satellite ground stations and radio telescopes. We note that in the past we've posted several times about Apostolos' other project called PICTOR, which is an open source radio telescope platform that makes use of RTL-SDR dongles. 

Apostolos explains CygnusRFI in the following: 

CygnusRFI is an easy-to-use open-source Radio Frequency Interference (RFI) analysis tool, based on Python and GNU Radio Companion (GRC) that is conveniently applicable to any ground station/radio telescope working with a GRC-supported software-defined radio (SDR). In addition to data acquisition, CygnusRFI also carries out automated analysis of the recorded data, producing a series of averaged spectra covering a wide range of frequencies of interest. CygnusRFI is built for ground station operators, radio astronomers, amateur radio operators and anyone who wishes to get an idea of how "radio-quiet" their environment is, using inexpensive instruments like SDRs.

CygnusRFI Screenshots
CygnusRFI Screenshots

Radwave Updates: Browse SETI Spectrum Data on your Android Device

Back in February 2019 we first posted about Radwave, an Android SDR App for RTL-SDR dongles. It has some interesting features not found in other Apps like the ability to easily zoom, pause and rewind the spectrum at any time.

The author has decided to make use of these spectrum browsing enhancements by providing access to full SETI (Search for Extraterrestrial Intelligence) spectrum data sets which can be browsed via the app for a small fee. From a post on our forums the author of Radwave writes:

I've been developing Radwave, which is an RTL-SDR Android app for exploring the spectrum. I recently added some new functionality, allowing users to interactively explore full resolution SETI data hosted in the cloud - no SDR needed. You can see a preview of it here https://youtu.be/8ZJFzKcWejA and download it from https://play.google.com/store/apps/deta ... ve.android

This data comes from Breakthrough Listen. These datasets are quite large, and Radwave does all the bulk downloading, processing and hosting of the datasets, allowing you to easily navigate your way through the spectrum. If you find something cool, you can tag it and share it.

Currently there are three datasets available in the first bundle ($10 USD): Voyager 1 and two 'Oumuamua collections (surveys of the the first observed interstellar object in our solar system). The data is big, and is hosted in AWS. That gets pricey, so I'll be adding more collections to this first bundle as funding permits. If there are certain datasets you're interested in seeing, definitely let me know.

 

radwave intro 20200225