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.
Over on the saveitforparts YouTube channel the creator has uploaded a video showing how he was able to image geosynchronous satellites with his modified motorized RV satellite dish. The idea is to scan the sky using the motorized dish, taking Ku-band RF power readings at each point in the sky. The result forms a heatmap image of satellite transmissions in the sky. For the most part, the satellites detected are TV satellites and they are at known positions in the sky.
However, in one of his recent scans saveitforparts appears to have detected an unknown satellite just outside of the geostationary plane. He goes on to discuss what it could have been, noting that it is most likely to be the AMSC 1 telecommunications satellite.
Recently I spotted a strange "UFO" with my homemade radio telescope / microwave imager. I've used this imager before to spot television satellites in geostationary orbit, but this unknown object was something new to me.
Spoiler Alert: I was able to determine that I'm probably seeing a geosynchronous (but not geostationary) satellite in an inclined / elliptical orbit. Specifically, I think this is the AMSC-1 telecom satellite, which is in a type of orbit designed to cover high latitudes like Northern Canada.
These types of satellites don't seem to show up too often on my telescope / imager setup, since they're not as common and aren't usually aimed directly at my location. This is the first time I've managed to spot one (if that's what I'm seeing), so it seems kind of rare to catch it with this particular equipment!
Folks might also ask if this "UFO" could be the sun or moon producing microwave signals, but those were both off to the left of the scan, not where the mystery signal showed up. It's also probably not a reflection / side lobe / "lens flare", I do get those, but they show up as rings around the main signals, and in fact this mystery signal has its own faint ring around it. Since my dish takes 3-4hrs to do a full scan, this also isn't something fast like a plane or low-orbit satellite as those don't show up on my imager (I'm essentially taking a very long time exposure).
I'm still planning to upgrade / rebuild this mini radiotelescope device in the future, hopefully with more flexibility to pick up different frequencies. That should let me see even more satellites (and maybe other space stuff!).
Mysterious Space Object Detected With DIY Radio Telescope
The Arecibo Radio Telescope has collapsed. Once the largest single dish radio telescope in the world at 305m, Arecibo was mostly used for radio astronomy research. However, the dish was made famous in 1974 for deliberating beaming a message into space as part of a search for extraterrestrial intelligence (SETI) experiment. It also played a part in popular culture, being a part of several famous films such as Golden Eye and Contact.
As part of it's goodbye we thought we'd highlight a few old posts where Arecibo was used together with SDRs for some interesting applications.
The project required finding and researching the original spacecraft documentation, and implementing the modulators and demodulators in GNU Radio. Whilst being successful in communicating with the satellite, ultimately the project failed due to the satellite's nitrogen tanks which had long leaked empty. But the fact that they were even able to find and communicate with the spacecraft using Arecibo was a major achievement. If you're interested in that project, Balint's 2015 talk on YouTube is an interesting watch.
Later in 2017 we saw how Arecibo was used for an Ionospheric heating experiment which involved transmitting 600kW of net power into the Ionosphere. This resulted in SDR users around the world being able to receive the signal. Other posts involve u/moslers Reddit post where he toured Arecibo and showed how they used a familiar program, HDSDR, as part of their monitoring suite.
So goodbye to Arecibo. However, we can look forward to the 500 meter Chinese FAST (Five-hundred-meter Aperture Spherical Radio Telescope) giving us new opportunities for single dish radio observations in the future.
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.
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
A Geostationary Satellite Imaged with the RTL-SDR Based Mini Radio Telescope
Just a few days we posted an update on the PICTOR open source radio telescope project. That project makes use of an RTL-SDR and a small dish antenna to receive the Hydrogen line, and is able to measure properties of our galaxy such as determining the shape of our galaxy.
Now over on Hackaday another amateur radio telescope project has been posted, this one called the "Mini Radio Telescope" (MRT) which was made by Professor James Aguirre of the University of Pennsylvania. This project makes use of a spare Direct TV satellite dish and an RTL-SDR to make radio astronomy observations. What makes this project interesting in particular is the automatic pan and tilt rotor that is part of the design. Unlike other amateur radio telescopes, this motorized design can track the sky, and map it over time. This allows you to create actual radio images of the sky. The image on the right shows a geostationary satellite imaged with the dish.
In the past we saw a similar project by the Thought Emporium YouTube channel which used a tracking mount and a HackRF to generate images of the WiFi spectrum. This was to be a precursor to a motorized tracking mount for radio astronomy but it doesn't seem that they completed that project yet.
Professor James Aguirre 's project including designs for the rotor is fully open source and can be found over on GitHub.
Back in July we posted about PICTOR, an open source and RTL-SDR based radio telescope project. The owner of the project recently wrote in and wanted to share some updates. His text is below:
The goal of this effort is to introduce students, educators, astronomers and others to the majesty of the radio sky, promoting radio astronomy education, without the need of building a large and expensive radio telescope.
Since the initial launch, PICTOR has gotten lots of updates and improvements, particularly in the software backend, providing more data to the users, using advanced techniques to increase the signal-to-noise ratio by calibrating spectra and mitigating radio frequency interference (RFI) (if present).
Here is an example observation with PICTOR, clearly showing the detection of 3 hydrogen-dense regions corresponding to 3 unique spiral arms in the Milky Way!
Graphs from the PICTOR RTL-SDR Radio Telescope showing the 3 unique spiral arms in the Milky Way.
Hydrogen atoms randomly emit photons at a wavelength of 21cm (1420.4058 MHz). Normally a single hydrogen atom will only very rarely emit a photon, but since space and the galaxy is filled with many hydrogen atoms the average effect is an observable RF power spike at 1420.4058 MHz. By pointing a radio telescope at the night sky and integrating the RF power over time, a power spike indicating the hydrogen line can be observed in a frequency spectrum plot. This can be used for some interesting experiments, for example you could measure the size and shape of our galaxy. Thicker areas of the galaxy will have more hydrogen and thus a larger spike.
In his tutorial Adam discusses important technical points such as noise figure and filtering. Essentially, when trying to receive the hydrogen line you need a system with a low noise figure and good filtering. The RTL-SDR has a fairly poor noise figure of about 6dB at 1420MHz. But it turns out that the first amplifier element in the receive chain is the one that dominates the noise figure value. So by placing an LNA with a low noise figure right by the antenna, the system noise figure can be brought down to about 1dB, and losses in coax and filters become negligible as well. At the end of the tutorial he also discusses some supplementary points such as ESD protection, bias tees and IP3.
One note from us is that Adam writes that the RTL-SDR V3 bias tee can only provide 50mA, but it can actually provide up to 200mA continuously assuming the host can provide it (keep the dongle in a cool shaded area though). Most modern USB 2.0 and USB3.0 ports on PCs should have no problem providing up to 1A or more. We’ve also tested the LP5907 based Airspy bias tee at up to 150mA without trouble, so the 50mA rating is probably quite conservative. So these bias tee options should be okay for powering 2xLNA4ALL.
Finally Adam writes that in the future he will write a paper discussing homebrew hydrogen line antennas which should complete the tutorial allowing anyone to build a cheap hydrogen line radio telescope.
One configuration with 2xLNA4ALL, 1x interstage filter, and 1x recceiver side filter with bias tee.
