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
Over on Facebook Job Geheniau has recently described his success in detecting interstellar high-velocity clouds with his telescope consisting of a 1.8 meter dish, amplifiers, band pass filters, and an RTL-SDR.
High-velocity clouds or HVC's are areas of interstellar gas that are moving at very high velocities relative to that of the galactic rotation.
His latest post about detecting high velocity clouds reads:
CIII High Velocity Cloud detected with 1.8 meter JRT.
The receiver was a RTLSDR connected to some amplifiers, band pass filter and a 1.8 meter dish.
HIGH VELOCITY CLOUD CIII with JRT (Job’s Radio Telescope)
Wikipedia: “High-velocity clouds (HVCs) are large collections of gas found throughout the galactic halo of the Milky Way. These clouds of gas can be massive in size, some on the order of millions of times the mass of the Sun and cover large portions of the sky. They have been observed in the Milky Way's halo and within other nearby galaxies.
HVCs are important to the understanding of galactic evolution because they account for a large amount of baryonic matter in the galactic halo. In addition, as these clouds fall into the disk of the galaxy, they add material that can form stars in addition to the dilute star forming material already present in the disk. This new material aids in maintaining the star formation rate (SFR) of the galaxy.
The origins of the HVCs are still in question. No one theory explains all of the HVCs in the galaxy. However, it is known that some HVCs are probably spawned by interactions between the Milky Way and satellite galaxies, such as the Large and Small Magellanic Clouds (LMC and SMC, respectively) which produce a well-known complex of HVCs called the Magellanic Stream. Because of the various possible mechanisms that could potentially produce HVCs, there are still many questions surrounding HVCs for researchers to study.”
For JRT the High Velocity Clouds are pretty hard to detect.
The Anti Center Complex is the easiest which I detected earlier last year.
This week I tried C III. It’s at Galactic Coordinates 120 50 and has a Vlsr of -140 km/s. You can find it on the chart:
In the simulation it looks like this:
Pay attention the low Brightness Temperature (0.3 Kelvin) compared for instance with Deneb (80 Kelvin)! Pretty hard to detect with my dish.
With JRT I did a 4 hour exposure (also 4 hours of Darks in the neighborhood) at 1420.405 MHz.
The new Feed I built is very good and has a perfect ‘pitch’ at gain 25 dB.
The final result for High Velocity Cloud CIII with my 1.8 meter dish:
SDRAngel is a general purpose software defined radio program that is compatible with most SDRs including the RTL-SDR. We've posted about it several times before on the blog, however we did not realize how much progress has occurred with developing various built in plugins and decoders for it.
Thanks to Jon for writing in and sharing with us a demonstration video that the SDRAngel team have released on their YouTube channel. From the video we can see that SDRAngel now comes stock with a whole host of built in decoders and apps for various radio applications making it close to an all-in-one SDR platform. The built in applications include:
ADS-B Decoder: Decodes aircraft ADS-B data and plots aircraft positions on a map
NOAA APT Decoder: Decodes NOAA weather satellite images (in black and white only)
DVB-S: Decodes and plays Digital TV DVB-S and DVB-S2 video
AIS: Decodes marine AIS data and plots vessel positions on a map
VOR: Decodes VOR aircraft navigational beacons, and plots bearing lines on a map, allowing you to determine your receivers position.
DAB+: Decodes and plays DAB digital audio signals
Radio Astronomy Hydrogen Line: With an appropriate radio telescope connected to the SDR, integrates and displays the Hydrogen Line FFT with various settings, and a map of the galaxy showing where your dish is pointing. Can also control a dish rotator.
Radio Astronomy Solar Observations: Similar to the Hydrogen line app, allows you to make solar measurements.
Broadcast FM: Decoding and playback. Includes RDS decoding.
Noise Figure Measurements: Together with a noise source you can measure the noise figure of a SDR.
Just a few days ago we posted about Job Geheniau's success at radio imaging the Cygnus-X star forming region at 1424 MHz with a 1.9m radio telescope, an RTL-SDR and some additional filtering and LNAs.
Now in his latest post on Facebook Geneniau has also shown that he has successfully imaged Cassiopeia A with the same equipment. Cassiopeia A is a supernova remnant known for being the "brightest extrasolar radio source in the sky at frequencies above 1 GHz" [Wikipedia]. Geheniau writes:
A new observation from JRT. These are driftscans of Cassiopeia A to make a radio plot. Several driftscans are made last week and combined. Always nice to see whats possible with a 1.5-1.9 meter dish. 2 LNA's and a bandpass filter, connected to a RTL-SDR at 1424 MHz. Happy that I got Cygnus complex and now Cassiopeia A which is the second radio source which is possible to receive with this dish.
Over on Facebook Job Geheniau has posted results from his latest radio astronomy experiment which involves imaging the Cygnus-X star forming region at 1424 MHz with a 1.9m radio telescope, an RTL-SDR and some additional filtering and LNAs. In the past we've posted about Geheniau's previous work which involved imaging the entire Milky Way at 1420 MHz, and measuring the basis for the dark matter hypothesis with a similar process and the same equipment. His latest post reads:
Cygnus-X is a massive star-forming region in the constellation Cygnus at a distance of 1.4 kiloparsecs (4600 light-years) from the Sun.
Cygnus-X has a size of 200 parsecs and contains the largest number of massive protostars and the largest stellar association within 2 kiloparsecs of the Sun. Cyg X is also associated with one of the largest molecular clouds known, with a mass of 3 million solar masses. [Wikipedia]
The idea: To take a radio picture of the Cygnus complex (Cygnus A + Cygnus X) with my 1.9 meter radio telescope. Equipment: 1.5 - 1.9 meter radio telescope Mini Circuits LNA ZX60-ULN33+ Bandpass filter 1200-1700 MHz 2nd LNA RTL-SDR VirgoSoft
Implementation: Multiple 4-hour drift scans of the Cygnus complex and beyond. In order not to be affected by HI at 1420 MHz, measurements were made at 1424 MHz. At this frequency there is Synchrotron radiation and no neutral hydrogen emission. To be sure that no Milky Way synchrotron radiation is measured there would be no or hardly any measurable power change outside the Cygnus complex during the drift scan. This was also observed in these measurements and also confirmed earlier in test measurements.
A total of 7 drift scans of 4 hours were made at 1424 MHz. Because the start of the driftscan generates a lot of wrong data (the 'cooling down/warming up' of the RTL-SDR), this has been removed in the measurements. The measurement starts at 2000 seconds and is always aborted at 12000 seconds in post-processing.
7 shots from RA 19 to RA 22. The declination varied each observation from DEC 36 to 43 degrees.
Because not every driftscan was perfect (heavy clouds gave worse results anyway as well as wind/rain or rfi) a total of 15 measurements were done, of which 7 were thus acceptable enough for editing.
In the end JRT performed measurements from 24 September to 9 October. Patience is a good thing.
Results: By editing the driftscan data in Excel with Conditional Format (giving color to the data) the final result is a 'radio photo' of the complex.
Of course, in view of the dish diameter, the beam is 8 degrees and thus a somewhat rough image of the Cygnus complex is sketched here.
While these WiFi grids are relatively cheap, Marcus tests an order of magnitude cheaper solution based on a tall metal "Maple-Sap" bucket which are commonly found in Canada. A horn antenna is constructed out of the 24cm diameter bucket simply by attaching a feed (wire) connected to a type-N connector, fitted ~8.8cm from the bottom of the bucket. This results in a signal almost as strong as the 60cm WiFi grid. A second test with a larger 30cm bucket fitted onto an existing 24cm horn antenna yielded results on par with the WiFi grid. A third test was done with a 6-turn Helix antenna, however it resulted in poor performance.
Marcus notes that almost anything that is shaped like cone could be modified into a horn antenna with a little DIY construction. He mentions that one alternative to the maple-sap bucket which could be hard to find outside of Canada might be a "French Style" steel floral bucket.
We've posted about Job Geheniau's RTL-SDR radio telescope a few times in the past   , and every time his results improve. This time is no exception as he's created his highest resolution radio image of the Milky Way to date. We have uploaded his PDF file explaining the project here.
Job used the same hardware as his previous measurements, a 1.5 meter dish, with 2x LNA's, a band pass filter and an RTL-SDR. Over 72 days he used the drift scan technique to collect data in 5 degree increments. The result is a map of our Milky Way galaxy at the neutral Hydrogen frequency of 1420.405 MHz.
This image is quite comparable to an image shown in a previous post which was created by Marcus Leech from CCERA who used a 1.8m dish and Airspy.
If you're interested in exploring our Galaxy with an RTL-SDR via Hydrogen Line reception, we have a simple tutorial available here. The ideas presented in the tutorial could be adapted to create an image similar to the above, although with lower resolution.
At this years FOSDEM 2020 conference Apostolos Spanakis-Misirlis has presented a talk on his PICTOR open source radio telescope project. We have posted about PICTOR in the past [1, 2] as it makes use of an RTL-SDR dongle for the radio observations. The PICTOR website and GitHub page provide all the information you need to build your own Hydrogen line radio telescope, and you can also access their free to use observation platform, where you can make an observation using Apostolos' own 3.2m dish radio telescope in Greece.
The PICTOR radio telescope allows a user to measure hydrogen line emissions from our galaxy. Neutral Hydrogen atoms randomly emit photons at a wavelength of 21cm (1420.4058 MHz). The emissions themselves are very rare, but since our galaxy is full of hydrogen atoms the aggregate effect is that a radio telescope can detect a power spike at 21cm. If the telescope points to within the plane of our galaxy (the milky way), the spike becomes significantly more powerful since our galaxy contains more hydrogen than the space between galaxies. Radio astronomers are able to use this information to determine the shape and rotational speed of our own galaxy.