Tagged: radio astronomy

SDRA2021 Talks: Electrosense, Neural Network Signal Classification, gr-rpitx, Radio Astronomy and More

The 2021 Software Defined Radio Academy conference was held online this year on June 26/27 and the talks have been recently uploaded to YouTube. There are some interesting talks this year including a presentation on various SDR related topics including Electrosense, gr-rpitx, 21cm radio astronomy with low cost SDR hardware, and using deep learning neural networks for automatic signal identification. Our favorite talks and blurbs are collected below for easy access, and the full set of talks can be found on their YouTube channel.

Dr. Henning Paul: Building a flexible Multi-Antenna-capable SDR using open Source

The availability of Open Source software components enables the ambitious hardware hacker to design their own powerful SDR. This talk is the follow-up to the talk on Scientific SDR and recapitulates the steps towards the current design of a Homebrew SDR based on a Xilinx Zynq SoC using the Linux kernel and other Open Source components. Furthermore, one of its applications, receiving shortwave radio with antenna diversity is presented.

SDRA2021 - 04 - Dr. Henning Paul: Building a flexible Multi-Antenna-capable SDR using open Source

Jean-Michel Friedt: GNURadio compatible gen. purpose SDR emitter using RasPi4 PLL

GNU Radio, the Raspberry Pi single board computer and Digital Video Broadcast Terrestrial receivers make an awesome combination for educational purposes of Software Defined Radio. gr-rpitx aims at complementing these tools with emitting capabilities, combined with the flexibility of GNU Radio.

SDRA2021 - 08 - Jean-Michel Friedt: GNURadio compatible gen. purpose SDR emitter using RasPi4 PLL

Sreeraj Radjendran: Knowledge extraction from wireless spectrum data

In this half-hour talk, the need for large scale wireless spectrum monitoring will be discussed. A short introduction to a large scale wireless spectrum monitoring framework, Electrosense, will be given. Furthermore, how anomaly detection and signal classification can be performed using the collected data will also be discussed. Insights to the major problems with state-of-the-art machine learning models will also be discussed in this context.

SDRA2021 -11- Sreeraj Radjendran: Knowledge extraction from wireless spectrum data

Stefan Scholl, DC9ST: Classification of shortwave radio signals with deep learning

Automatic mode classification of radio signals in the HF band is a valueable tool for band monitoring, operation of rare transmission modes and future applications of cognitive radio. In recent years, machine learning has established as a general and very powerful approach to classification problems. The presentation first provides an introduction to neural networks and deep learning. Then neural nets are applied to the task of radio signal classification. The result is an experimental deep convolutional neural net (CNN), that can distinguish between 18 different transmission modes occurring in the HF band, such as AM, SSB, Morse, RTTY, Olivia, etc.

Additional Links: Stefan Scholl's post on this topic 

SDRA2021 -12- Stefan Scholl, DC9ST: Classification of shortwave radio signals with deep learning

Marcus Leech: Mapping the sky at 21cm: Gnuradio and Radio Astronomy

We show the results of a year-long sky survey at the 21cm hydrogen line, producing an intensity map of the sky covering a declination range from -35 to +75DEG. We discuss the software tools used, Gnu Radio signal flows, and the hardware aspects of the instrument.

SDRA2021 -14- Marcus Leech: Mapping the sky at 21cm: Gnuradio and Radio Astronomy

GPU Accelerated RTL-SDR Radio Interferometer Code For Radio Astronomy

Evan Mayer (@millijanskys) has recently released some code called “effex” that allows you to use two RTL-SDR dongles as an interferometer for radio astronomy and other experiments.

The hardware used is two RTL-SDR Blog V3 dongles with synchronized oscillators via the selectable clock headers, two 1420 MHz filtered LNAs, a splitter and noise source consisting of a 50 Ohm load and wideband LNA, and a NVIDIA Jetson Nano GPU single board computer. We note that Evans code should also run on our KerberosSDR with some modifications to enable the built in noise source during calibration.

To add to this Evan wrote to us explaining how this code might be used:

You could start to do some basic interferometric imaging by adding more coherent channels. This is exactly what Daniel Estévez just did with USRPs and GNU Radio at the Allen Telescope Array.

Did you see the “picture” of the supermassive black hole shadow released by the Event Horizon Telescope collaboration in 2019? The “ring of fire” or “donut” image? Daniel’s image and that image were created by “aperture synthesis.”

In aperture synthesis, the signals from each pair of antennas distributed across an area can be cross-correlated to measure one component of the 2D Fourier transform of the radio brightness distribution on the sky. But, you need coherent receivers (or REALLY good time stamps) to cross-correlate the signals from the antennas. Get enough pairs of antennas, and you can start to more fully sample the 2D Fourier space of the sky brightness distribution, which you can then use to reconstruct a real image.

This is how distributed radio arrays like the EHT work, as well as localized ones like ALMA or LOFAR.

Building an 11.2 GHz Radio Telescope with an Airspy and 1.2m TV Satellite Dish

In the past we've posted several times about how 1.42 GHz Hydrogen Line amateur radio telescopes used with RTL-SDRs or other SDRs for Hydrogen line observations of the galaxy. Recently Hackaday ran a post highlighting a project from "PhysicsOpenLab" describing an 11.2 GHz radio telescope that uses an Airspy SDR as the receiver.

Celestial bodies emit radio waves all across the radio spectrum and typically observations can be made anywhere between 20 MHz to 20 GHz. Choosing an optimal frequency it is a tradeoff between antenna size, directivity and avoiding man made noise. For these reasons, observations at 10-12 GHz are most suitable for amateur radio telescopes.

The posts by PhysicsOpenLab are split into two. The first post highlights the hardware used which includes a 1.2m prime focus dish, and 11.2 GHz TV LNB, a wideband amplifier, a SAW filter, a bias tee, and the Airspy SDR. The LNB converts the 11.2 GHz signal down to 1.4 GHz which can be received by the Airspy. Once at 1.4 GHz it's possible then to use existing commercial filters and amplifiers designed for Hydrogen line observations.

The second post explains the GNU Radio based software implementation and the mathematical equations required to understand the gathered data. Finally in this post they also graph some results gathered during a solar and lunar transit.

Finally they note that even a 1.2m dish is quite small for a radio telescopic, but it may be possible to detect the emissions from the Milky Way and other celestial radio sources such as nebulae like Cassiopeia A, Taurus A and Cygnus A a radio galaxy.

A 11.2 GHz 1.2m Amateur Radio Telescope with GNU Radio and Airspy

Arecibo Radio Telescope Collapses: A look back at some SDR fun with Arecibo

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.

Back in 2014 we saw engineers hook up USRP software defined radios to Arecibo in order to contact the lost ISEE-3 NASA spacecraft (Wikipedia Article). The idea was to contact the solar orbiting spacecraft which was last heard from in 2008, and get it to fire it's thrusters in order to reuse it for a new mission. The idea was initially abandoned by NASA, however a crowdfunding campaign raised US$125,000 which funded the project.

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.

Arecibo Radio Observatory

Job’s Radio Telescope: Hydrogen Line Northern Sky Survey with RTL-SDR

We've posted about Job Geheniau's RTL-SDR radio telescope a few times in the past [1] [2] [3], 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.

JRT - Northern sky Hydrogen Line Survey with RTL-SDR

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.

Searching For Extraterrestrial Intelligence (SETI) with a HackRF

The Search for Extraterrestrial Intelligence (SETI) is an ongoing project that aims to detect radio signals originating from intelligent species somewhere in the universe. Recently Alberto Caballero, a SETI researcher has been proposing a distributed search (project pdf document) with amateur and/or professional radio telescopes. The idea is that multiple stations around the world would monitor a single star for a period of time in order to collect data 24/7. To participate the requirements are a dish 2.1 meters or larger, a motorized mount, and a feed, LNA and radio system able to receive 1 - 4.5 GHz.

An example of a SETI station can be found at SETI Net. Here the owner has a 3M dish on a rotor connected to a HackRF. An LNA and band pass filter are also used at the feed end. SDR Console or SDR# is used to monitor a specific frequency, and the audio is sent into a special automatic SETI analysis program as well as spectrum analysis software. If an interesting signal is detected the software notifies the user, then further analysis can be undertaken.

If you have a suitable radio telescope available and want to participate, you can contact the SETI project via their contact form.

SETI Net Block Diagram

Notes on Observing Pulsars with an SDR from CCERA

A pulsar is a rotating neutron star that emits a beam of electromagnetic radiation. If this beam points towards the earth, it can then be observed with a large dish or directional antenna and a software defined radio. In the past we've posted a few times about Pulsars, and how the HawkRAO amateur radio telescope run by Steve Olney in Australia has observed Pulsar "Glitches" with his RTL-SDR based radio telescope.

Over in Canada, Marcus Leech has also set up a Pulsar radio telescope at the Canadian Centre for Experimental Radio Astronomy (CCERA). Marcus has been featured several times on this blog for his various amateur radio experiments involving SDRs like the RTL-SDR. In one of his latest memos Marcus documents his Pulsar observing capabilities at CCERA (pdf). His memo describes what Pulsars are and how observations are performed, explaining important concepts for observation like de-dispersion and epoch folding.

The rest of the memo shows the antenna dish and feed, the SDR hardware which is a USRP B210 SDR, the reference clock which is a laboratory 0.01PPB rubidium atomic clock and the GNU Radio software created called "stupid_simple_pulsar". The software DSP process is then explained in greater detail. If you're thinking about getting involved in more advanced amateur radio astronomy this document is a good starting point.

Dish Antenna + Feed used for receiving Pulsars

Using an RTL-SDR to Measure the Basis for the Dark Matter Hypothesis

From calculations depending on the distribution of visible star mass in our galaxy, a certain galactic rotational velocity vs distance from center curve is expected. However, when scientists actually measure the galactic rotation, another curve is found - a curve which should result in the galaxy flying apart. This mismatch in expected vs measured data has given rise to the theory of "dark matter". The theory essentially states that in order to get the measured curve, the galaxy must have more mass, and that this mass must come from non-luminous matter scattered amongst the galaxy which is difficult or impossible to observe.

In the past we have posted about Job Geheniau's radio astronomy projects a few times on this blog. So far he has used an RTL-SDR and radio telescope dish to generate a full radio image of the galaxy at the Hydrogen Line frequency of 1.42 GHz. This project worked by pointing the telescope at one section of the galaxy, measuring the total Hydrogen line power with the RTL-SDR over a number of minutes, then moving the telescope to the next section.

Job's Radio Telescope + Laptop and RTL-SDR Setup

Using the same hardware and techniques to observe the Hydrogen Line frequency, he was now able to measure the rotational curve of our galaxy. When the telescope points to different arms of the galaxy, the Hydrogen line measurement will be doppler shifted differently. The measured doppler shift can be used to figure out the rotational velocity of that particular arm of the galaxy. By measuring the rotational velocity from the center of the galaxy to the outer edges, a curve is created. Job's measured curve matches that seen by professional radio astronomers, confirming the mismatch in expected vs measured data.

Job's document explaining his setup and measurement procedure can be found here (pdf file).

Job's Measured vs Expected Curve

If you'd like to get started with Hydrogen line radio astronomy with an RTL-SDR, we have a tutorial over here.