Tagged: radio astronomy

Searching for giga-Jansky fast radio bursts from the Milky Way with a global array of low-cost radio receivers (RTL-SDRs)

A few days ago a University research paper titled “Searching for giga-Jansky fast radio bursts from the Milky Way with a global array of low-cost radio receivers” was uploaded to the Cornell University Library. In this paper authors Dan Maoz of Tel-Aviv University and Abraham Loeb of Harvard suggest that citizen science enabled mobile phones and RTL-SDR dongles placed around the world could be used to detect fast radio bursts (FRBs) originating from within our own galaxy. The abstract reads:

If fast radio bursts (FRBs) originate from galaxies at cosmological distances, then their all-sky rate implies that the Milky Way may host an FRB on average once every 30-1500 years. If FRBs repeat for decades or centuies, a local FRB could be active now. A typical Galactic FRB would produce a millisecond radio pulse with ~1 GHz flux density of ~3E10 Jy, comparable to the radio flux levels and frequencies of cellular communication devices (cell phones, Wi-Fi, GPS). We propose to search for Galactic FRBs using a global array of low-cost radio receivers. One possibility is to use the ~1GHz communication channel in cellular phones through a Citizens-Science downloadable application. Participating phones would continuously listen for and record candidate FRBs and would periodically upload information to a central data processing website, which correlates the incoming data from all participants, to identify the signature of a real, globe-encompassing, FRB from an astronomical distance. Triangulation of the GPS-based pulse arrival times reported from different locations will provide the FRB sky position, potentially to arc-second accuracy. Pulse arrival times from phones operating at diverse frequencies, or from an on-device de-dispersion search, will yield the dispersion measure (DM) which will indicate the FRB source distance within the Galaxy. A variant of this approach would be to use the built-in ~100 MHz FM-radio receivers present in cell phones for an FRB search at lower frequencies. Alternatively, numerous “software-defined radio” (SDR) devices, costing ~$10 US each, could be plugged into USB ports of personal computers around the world (particularly in radio quiet regions) to establish the global network of receivers.

‘Fast radio bursts’ or FRBs are very brief pulses of extremely strong radio waves which have the transmit power of 500 million suns, though by the time they reach the earth they can only be picked up by radio telescopes. Radio astronomers have so far been mystified by the cause of these FRBs, and research has been hampered by the fact that the source of FRBs is notoriously difficult to pinpoint because they are unpredictable, and their energy appears to originate from all over the sky and not from a single point. Many scientists think that most FRBs must originate from outside of our galaxy, and in 2016 one was finally pinpointed as coming from a dwarf galaxy 2.5 billion light years away from earth. But the authors of the paper speculate from the rate of how often FRBs are seen, that our Milky Way galaxy could host its own local FRB event once every 30 – 1500 years.

If an FRB occurs within our own galaxy then they speculate that the received power could be strong enough to be detected by consumer level mobile phones or RTL-SDR radios, meaning that no large radio telescope dish is required for detection. By continuously monitoring for FRBs on mobile phones and/or RTL-SDRs spread around the world, a local FRB source could one day be pinpointed thanks to the high resolving power of multiple detectors spread apart.

[Also discussed at cfa.harvard.edu/news/2017-07]
The Very Large Array in Mexico was used to pinpoint an FRB in 2016.
The Very Large Array in Mexico was used to pinpoint an FRB in 2016.
Illustration of an FRB. Certain frequencies arrive faster than others.
Illustration of an FRB. Certain frequencies arrive faster than others.

Helping to Raise Funds for the Canadian Centre for Experimental Radio Astronomy (CCERA)

Patchvonbraun (aka Marcus Leech) is one of the pioneers in using low cost SDR dongles for amateur radio astronomy experiments. In the past he’s shown us how to receive things like the hydrogen line,  detect meteors and observe solar transits using an RTL-SDR. He’s also given a good overview and introduction to amateur radio astronomy in this slide show.

Now Marcus and others are starting up a new project called the “Canadian Centre for Experimental Radio Astronomy (CCERA)”. They write that this will be an amateur radio astronomy research facility that will produce open source software and hardware designs for small scale amateur radio astronomers. Currently they also already have a hydrogen line telescope set up, which is producing live graphs and data. From their recent posts it also looks like they’re working on building antennas for pulsar detection. They also have a GitHub available for any software they produce at https://github.com/ccera-astro.

Currently CCERA is looking for donations over at gofundme, and they are hoping to eventually raise $25k. They write:

About CCERA:

Radio astronomy is one of the most important ways to observe the cosmos. It is how we learned about the existence of the afterglow of the big bang (the cosmic microwave background), it is how we observe huge swaths of the universe that are otherwise obscured by dust. Most of what’s going on out there can’t be seen with visible light.

Astronomy has traditionally been one of the areas in science where dedicated non-professionals have continued to make an enormous contribution to the field. Optical astronomy requires little more than a telescope and knowledge.

Radio astronomy has, up until recently, required a lot more skill and resources. However, technology has advanced enough that small groups could be making serious contributions to radio astronomy. With the right sorts of software and information, many dedicated non-professionals could be doing good work in the area, and CCERA intends to help make that a reality.

CCERA will be producing open source software and hardware designs to help non-professional and professional radio astronomers alike, documenting them, and helping people get up to speed so that they can use these powerful tools themselves. Our GitHub repository is: https://github.com/ccera-astro

CCERA will also be operating its own radio astronomy facilities, initially in Ontario, Canada. These will serve as a test-bed for our own designs, as a place for us to train interested people in the operation of low cost radio astronomy equipment, and will also be used for real radio astronomy work. All our data will be publically-available.

About us:

Roughly 10 years ago, I and a number of others started a project to restore a large, historic, satellite earth station antenna at Shirleys Bay in Ottawa. Our goal was to bring the dish back on-line for use in amateur radio astronomy, research, and importantly, educational outreach about science, and radio astronomy.

The project came to a sudden end back in 2013/14 when the owner of the dish (The Canadian Space Agency) needed to dismantle it to make way for other occupants of the site.

However, during that period, we became fascinated with the possibilities that opening up radio astronomy to skilled non-professionals could bring.

Since then, our group has been working on another far lower cost project to build our own a specialized radio telescope somewhere in the Rideau Valley area. Many of our group live in the area, and Marcus lives in Smiths Falls. With good attention to the usability of our designs and open publication of our tools under appropriate open source licenses, our work should be replicable by others. We thus hope to kick off a new era in non-professional radio astronomy.

What we need the money for:

We’ve secured a small office in the Gallipeau Center outside of Smiths Falls, and will be able to erect our specialized antenna arrays over the coming year.

While we have a lot of the equipment we’ll need, we’ll have more equipment to buy, and on-going expenses to cover, including rent, insurance, miscellaneous mechanical construction materials (lumber, metal, etc). We also need to cover expenses relating to incorporation as a not-for-profit.

Our goal is to provide a test facility for small-scale radio astronomy research, and to develop techniques that allow small organizations and educational institutions to run their own small-scale radio astronomy observing programs.

If we are successful, in addition to making our designs and software available under open source licenses, we’ll be holding regular public lectures, host training seminars, host school groups, etc. We will also produce videos of our work for those who cannot visit us directly in Ottawa. We want to make some of the techniques of “big science” accessible and understandable.

We can’t do it without the help of the public, who, we hope, will become our students, collaborators, and ongoing supporters.

We will also make all of our data available to the public without fee or restrictions. We believe in openness in scientific endeavours, even small ones such as ours.

Marcus Leech
(tentative) Director
Canadian Centre for Experimental Radio Astronomy
www.ccera.ca

If you have even a passing interest in radio astronomy please consider donating, as CCERA’s work may open up exciting new possibilities for amateur radio astronomers with low cost SDR dongles.

The pulsar antenna being built at CCERA.
The pulsar antenna being built at CCERA.

New SDR# Plugin: Radio-Sky Spectrograph Data Stream

Edit: If you downloaded an older version of the plugin please note that it has now been updated. The update fixes some stability issues which would previously hang SDR#. The updated .dll file can be downloaded directly from https://goo.gl/VQlH9E.

Radio-Sky Spectrograph is a radio astronomy software program which is often used together with the RTL-SDR or other similar SDRs. It is best explained by the author:

Radio-Sky Spectrograph displays a waterfall spectrum. It is not so different from other programs that produce these displays except that it saves the spectra at a manageable data rate and provides channel widths that are consistent with many natural radio signal bandwidths. For terrestrial , solar flare, Jupiter decametric, or emission/absorption observations you might want to use RSS.

Usually to interface an RTL-SDR with Radio-Sky Specrtograph a program called RTL-Bridge is used. However, now SDR# plugin programmer Alan Duffy has created a new plugin that allows SDR# to interface with Radio-Sky Spectrograph via a network stream. This allows it to work with any SDR that is supported by SDR# plugins. Alan Duffy writes:

I wrote the plugin after becoming interested in amateur radio astronomy. The plugin allows you to use any of the software defined radios supported by SDR# to feed the Radio-Sky Spectrograph program with wide-band data. The plugin shows the frequency, bandwidth, and FFT resolution and has a user selected “Number of Channels” that are sent to the spectrograph program with an allowable range of 100 to 500. This number can only be edited when the data stream is not enabled. Also if certain key parameters change, such as the frequency or decimation, the network stream will stop as the spectrograph would no longer be capturing the same data. If this happens, simply click the start button on client side software (i.e. Radio-Sky Spectrograph). As long as the Enable box is checked on the server side, the plugin will listen for a connection and start transmitting data after RSS makes a new request for data.

We note that the software might also be useful for simply capturing a long term waterfall for finding active frequencies or looking for meteor scatter or aircraft scatter echoes. 

The Radio-Sky Spectrograph SDR# Plugin
The Radio-Sky Spectrograph SDR# Plugin

Radio-Sky Spectrograph now supports the SDRPlay

Radio-Sky Spectrograph is a radio astronomy software program that integrates data over long periods of time and displays it as a waterfall. It is described by the author:

Radio-Sky Spectrograph displays a waterfall spectrum. It is not so different from other programs that produce these displays except that it saves the spectra at a manageable data rate and provides channel widths that are consistent with many natural radio signal bandwidths. For terrestrial , solar flare, Jupiter decametric, or emission/absorption observations you might want to use RSS.

Radio Sky Spectograph is compatible with the RTL-SDR via an intermediary program called RTL Bridge, and now it is also compatible with the SDRplay via another intermediary program written by Nathan Towne called SDRplay2RSS

In previous posts we showed how some amateur radio astronomers were able to capture noise bursts from the sun and from Jupiter with an RTL-SDR. In the SDRplay software release post and documentation that comes with the software Nathan shows how he was able to capture solar emissions and Jupiter bursts with the SDRplay.

SDRPlay2RSS
SDRPlay2RSS
Solar emissions received with the SDRplay and Radio-Sky Spectograph.
Solar emissions received with the SDRplay and Radio-Sky Spectograph.
Jupiter Noise Bursts with the SDRPlay and Radio-Sky Spectrograph.
Jupiter Noise Bursts with the SDRPlay and Radio-Sky Spectrograph.

Building a Quad RTL-SDR Receiver for Radio Astronomy

Amateur radio astronomer Peter W East has recently uploaded a new document to his website. The document details how he built a quad RTL-SDR based receiver for his radio astronomy experiments in interferometry and wide-band pulsar detection (pdf – NOTE: Link Removed. Please see his website for a direct link to the pdf “Quad RTL Receiver for Pulsar Detection”. High traffic from this post and elsewhere has made the document go offline several times). Interferometry is a technique which uses multiple smaller radio dishes spaced some distance apart to essentially get the same resolution a much larger dish. Pulsars are rapidly rotating neutron stars which emit radio waves, and the strongest ones can be observed by amateur radio telescopes and a receiver like the RTL-SDR.

The Quad receiver has four RTL-SDR’s all driven by a single TCXO, mounted inside an aluminum case with fans for air cooling. He also uses a 74HC04 hex inverter to act as a buffer for the 0.5 PPM TCXO that he uses. This ensures that the TCXO signal is strong enough to drive all four RTL-SDRs.

The Quad RTL-SDR with air cooling.
The Quad RTL-SDR with air cooling.

Whilst all the clocks are all synced to a single master clock, synchronisation between the RTL-SDR’s is still difficult to achieve because of jitter introduced by the operating system. To solve this he introduces a noise source and a switch. By switching the noise source on and off, correlation of the signal data can be achieved in post processing.

Noise Source and Switch Calibration Unit.
Noise Source and Switch Calibration Unit.
How correlation with the pulsed noise source works.
How correlation with the pulsed noise source works.

In the document Peter shows in detail how the system is constructed, and how it all works, as well as showing some interferometry results. The system uses custom software that he developed and this is all explained in the document as well.

Hydrogen Line Observation with an RTL-SDR

The RTL-SDR can be used for many interesting radio astronomy applications such as observing the Hydrogen line. Hydrogen atoms randomly emit photons at a wavelength of 21cm (1420.4058 MHz). Normally a single hydrogen atom will 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.

On his website Steve Olney has been writing about his experiments and results with using an RTL-SDR to observe the hydrogen line. On his website he writes that he uses a 3M dish, with an LNA at the antenna to reduce the system NF, a hydrogen line tuned bandpass filter to remove out of band noise, 2 line amps to overcome coax loss, and finally a second LNA just before the RTL-SDR dongle to optimize the signal strength for the ADC. The dongle he uses has been modified to use a TCXO, and is aircooled via a PC fan. He also uses a modified version of the rtlsdr.exe IQ file recorder and his own custom GUI for controlling the RTL-SDR and antenna tracking mechanism.

His results show that he was able to detect the Hydrogen in the Large and Small Magellanic clouds. He also shows a method for converting the 8-bit IQ data down to 1-bit to save disk space, and shows that while some noise is added, the overall result is preserved.

See the related posts for other hydrogen line experiments with the RTL-SDR.

The 3M dish used for hydrogen line detection.
The 3M dish used for hydrogen line detection.
The fan cooled RTL-SDR used to detect the Hydrogen line.
The fan cooled RTL-SDR used to detect the Hydrogen line.

Software De-Dispersion of RTL-SDR Pulsar Data

Back in September 2015 we posted about how radio astronomers Peter W East and GM Gancio were able to use an RTL-SDR dongle for the radio astronomy task of detecting pulsars. 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 antenna and a radio, like the RTL-SDR. 

More recently they published a new paper titled “Software De-Dispersion of RTL-SDR Pulsar Data” (pdf).  De-dispersion is a technique that allows very weak signals to be extracted from the background noise. The introduction to the paper reads:

Data files produced by RTL SDR dongles can be folded directly for pulsar detection using software such as rapulsar.exe. Using simple I/Q vector averaging software, the data can be down-sampled by factors of more than 100 prior to folding and/or period search processing to speed up useful data extraction. Ideally, wide band RF data should be de-dispersed to optimise later search and folding processing. De-dispersion is normally carried out by time adjusting data sampled from RF filter banks before combination. This note describes how data already digitised from the RTL SDR can be spectrum analysed or filtered using the FFT algorithm. Two methods are discussed, one summing power with some down-sampling; the second, a ‘coherent’ method that de-disperses the rtlsdr.exe .bin data file and outputs a .bin-compatible file. Both accurately de-disperses the data offering an improved folded data SNR.

More information about radio astronomy with the RTL-SDR, pulsars and the associated software links can be found at Peter W East’s webpage http://y1pwe.co.uk/RAProgs/index.html.

The de-dispersion principle
The de-dispersion principle

Radio Astronomy Tool rtl_power_fftw Updated

The rtl_power program allows you to use the RTL-SDR to perform a power scan over an arbitrarily large portion of the frequency spectrum (within the RTL-SDR’s supported frequency range) by hopping over ~2 MHz swaths of bandwidth. The updated rtl_power_fftw software was originally written by Klemen Blokar and Andrej Lajovic and is an update over the regular rtl_power program. It uses a faster FFT processing algorithm and has several other enhancements that make it more useful for radio astronomy purposes.

Recently Mario Cannistrà has released a new version of rtl_power_fftw which has several additional improvements applied. He intends to use it in his RTL-SDR based radio astronomy IoT project which is presented on his Hackster.io blog. He writes:

I added the following command line parameters:

  • -e param for session duration
    this allows to specify the recording duration in sec, mins… etc just like it was possible with rtl-power
  • -q flag to limit verbosity
    this will allow the various printouts to happen only the first time and not on every scan
  • -m param to produce binary matrix output and separate metadata file
    this will get a file name (no extension) and use it to store the power values in binary format within a .bin file + a metadata text file with .met extension

Summary of my requirements:

  • I wanted to leverage the ability of rtl-power-fftw to specify N average values to integrate for less than 1 second when needed. Plus running multi-MHz scans and storing for several minutes.
  • I wanted to use a binary format instead of the .csv one in order to obtain the smallest possible size since I’m logging all the night long (CSV’s blank delimiters and decimal dots were wasting my precious microSD space)
  • keep high the precision on decimal digits saving float values (could be important for other usages)
  • obtain a complete stream of binary values representing all the bins for each scan, one scan after the other, in a matrix like organization
  • …that would allow me to plot the waterfall extremely fast with gnuplot
  • …and then add specific annotations and file properties/metadata in a more convenient way using python
Example rtl_power_fftw output: A scan of Jupiter's radio emissions.
Example rtl_power_fftw output: A scan of Jupiter’s radio emissions.