Tagged: pulsar

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

Astrophiz Podcast Interviews Steve Olney: Capturing the 2019 Vela Pulsar Glitch with an RTL-SDR

Back in May 2019 we posted about Steve Olney's HawkRAO amateur radio astronomy station which was the only station in the world to capture the 2019 Vela Pulsar "glitch" which he did so using his RTL-SDR as the radio. The astronomy focused podcast "Astrophiz" recently interviewed Steve in episode 95 where he talks about his amateur radio background, his home made radio telescope, his RTL-SDR and software processing setup, and the Vela glitch.

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 radio, like the RTL-SDR. The Vela pulsar is the strongest one in our sky, making it one of the easiest for amateur radio astronomers to receive.

Pulsars are known to have very accurate rotational periods which can be measured by the radio pulse period. However, every now and then some pulsars can "glitch", resulting in the rotational period suddenly decreasing. Glitches can't be predicted, but Vela is one of the most commonly observed glitching pulsars.

The HawkRAO amateur radio telescope run by Steve Olney is based in NSW, Australia and consists of a 2 x 2 array of 42-element cross Yagi antennas. The antennas feed into three LNAs and then an RTL-SDR radio receiver. 

Astrophiz 95: Steve Olney: From Ham Radio to Radio Astronomy - "The 2019 Vela Glitch" 

Feature Interview: This amazing interview features Steve Olney who has established the Hawkesbury Radio Astronomy Observatory in his backyard. Steve has constructed a Yagi antenna array, coupled it with a receiver and observed a pulsar 900 LY away and generated data that has enabled him to be the only person on the planet to observe Vela’s 2019 glitch in radio waves as it happened.

If you're interested in learning more about Vela, Astrophiz podcast episode 93 with Dr. Jim Palfreyman discusses more about the previous 2016 Vela glitch and why it's important from a scientific point of view.

Vela Pulsar Glitch Detected with RTL-SDR Based Radio Telescope

On February 1st 2019 the HawkRAO amateur radio telescope detected a "glitch" during it's observations of the Vela Pulsar. 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 radio, like the RTL-SDR. The Vela pulsar is the strongest one in our sky, making it one of the easiest for amateur radio astronomers to receive.

Pulsars are known to have very accurate rotational periods which can be measured by the radio pulse period. However, every now and then some pulsars can "glitch", resulting in the rotational period suddenly increasing. Glitches can't be predicted, but Vela is one of the most commonly observed glitching pulsars.

The HawkRAO amateur radio telescope run by Steve Olney is based in NSW, Australia and consists of a 2 x 2 array of 42-element cross Yagi antennas. The antennas feed into three LNAs and then an RTL-SDR radio receiver. He has been observing the Vela pulsar for 20 months.

His observations indicate that Vela glitched and spun up by 2.5PPM at 14:09 UTC on Feb 1, 2019. He claims that this glitch detection is a first for amateur radio astronomy as far as he is aware.

If you're interested in Pulsar detection, check out a few of our previous posts on the topic.

The HawkRAO Amateur Radio Telescope Vela Glitch Detection
The HawkRAO Amateur Radio Telescope Vela Glitch Detection (Blue graph on the right indicates the glitch detection)

Building A Giant $200 3D Corner Reflector Antenna for GOES, Moon Bounce and Pulsar Detection

A corner reflector antenna is basically a monopole antenna with a metallic 'corner' reflector placed behind it. The reflector helps the monopole collect signals over a wider aperture resulting in signals coming in stronger from the direction that the corner is pointing at. In past posts we've seen a homemade tinfoil corner reflector used to improve reception of the generic stock RTL-SDR monopole antenna, and a larger one was used in a radio astronomy experiment to detect a pulsar with an RTL-SDR.

Recently The Thought Emporium YouTube channel has uploaded a video showing how to build a large 2 meter 3D corner reflector out of readily available metal conduit pipes and chicken wire. While the antenna has not been tested yet, they hope to be able to use it to receive weather satellite images from GOES-16, to receive moon bounce signals, to map the Hydrogen line and to detect pulsars. 

Building a Giant 2m Corner Reflector Antenna For Less than $200 (For Goes-16, Pulsars and More!)

An Overview of Neutron Star Group Pulsar Detection Projects with the RTL-SDR

Earlier in April we posted about Hannes Fasching (OE5JFL)’s work in detecting pulsars with an RTL-SDR. Thanks to Steve Olney (VK2XV), administrator of the Neutron Star Group for pointing out that there are actually several amateur radio astronomers who are using RTL-SDR dongles for pulsar detection. 

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. Pulsars create weakly detectable noise bursts across a wide frequency range. They create these noise bursts at precise intervals (milliseconds to seconds depending on the pulsar), so they can be detected from within the natural noise by performing some mathematical analysis on the data. Typically a few hours of data needs to be received to be able to analyze it, with more time needed for smaller dishes.

 

One problem is that pulsar signals can suffer from ‘dispersion’ due to many light years of travel through the interstellar medium. This simply means that higher frequencies of the noise burst tend to arrive before the lower frequencies. Mathematical de-dispersion techniques can be used to eliminate this problem enabling one to take advantage of wideband receivers like the RTL-SDR and other SDRs. The more bandwidth collected and de-dispersed, the smaller the dish required for detection.

Over on the Neutron Star Group several amateur pulsar detection projects are listed, and entries denoted with the “^” symbol make use of the RTL-SDR. Below we show a brief overview of those projects:

Andrea Dell’Immagine (IW5BHY) – Based in Italy Andrea often uses a 3D corner reflector antenna which is equivalent to a 2.5 meter diameter dish to observe pulsars in the 70cm band (~420 MHz). The antenna is in a fixed position so he can only detect pulsars that drift into the beam width of the antenna. With this antenna, a 0.3dB NF LNA, an RTL-SDR and de-dispersion techniques he’s been able to detect the Pulsar B0329+54 which is 2,643 light years away with an integration time of about 3 hours.

Andrea (IW5BHY)'s 3D Corner Reflector Pulsar Detection Antenna.
Andrea (IW5BHY)’s 3D Corner Reflector Pulsar Detection Antenna.

Andrea has also used a 4M dish to detect Pulsar B0329+54 also at 70cm with an RTL-SDR. With the larger dish he’s able to detect it within about 40 minutes of integration time.

Andrea (IW5BHY)'s 4M dish.
Andrea (IW5BHY)’s 4M dish.

Hannes Fasching (OE5JFL) – Based in Austria Hannes has a 7.3M dish that he uses for pulsar detection with his RTL-SDR. With this large dish he’s been able to receive 22 pulsars at both 70cm (424 MHz), and 23cm (1294 MHz) frequencies. With such a large dish, detecting a strong pulsar like B0329+54 only needs less than a minute of integration time.

Mario Natali (I0NAA) – Based in Italy Mario uses a 5M dish to observer pulsars at both 409 MHz and 1297 MHz. Combined with a low noise figure LNA and his RTL-SDR he’s been able to receive the B0329+54 pulsar with an integration time of about 2 – 2.5 hours.

Mario Natali (I0NAA)’s 5M Dish

Michiel Klaassen – From the Dwingeloo Radio Observatory in the Netherlands Michiel has used their large 25M dish and an RTL-SDR to detect B0329+54 at 419 MHz.

Peter East & Guillermo Gancio  Peter and Guillermo have used the large 30M dish at El Instituto Argentino de Radioastronomía (IAR) in Argentina and an RTL-SDR to detect the Vela pulsar (B0833-45) at 1420 MHz.

In terms of hardware required, from the above projects we see that you’ll need an RTL-SDR dongle (other more costly SDR’s could also be used), a dish as large as you can get (along with some sort of dish pointing system), a low noise figure amplifier (0.5dB or less is desired) to be placed right by the dish, a few line amps if the cable run is long and perhaps a filter if you are seeing interference from terrestrial signals.

An overview of software for detecting pulsars with the RTL-SDR can be found over on the Neutron Star Groups software page. Essentially what you need is an analysis program which can work on the raw IQ data that is collected by the RTL-SDR and dish antenna. This software ‘folds’ the data, looking for the regular noise bursts from the pulsars. The output is data that can be used to create a graph indicating the spin period of the pulsar, and thus confirming the detection.

Graph showing the half-period of B0329+54. 350 * 2 = 700 ms which is about what matches on the B0329+54 Wikipedia page.
Graph showing the half-period of B0329+54. 350 * 2 = 700 ms which is about what matches on the B0329+54 Wikipedia page.

Amateur Pulsar Observations with an RTL-SDR

Back in September 2015 we made a posted that discussed how some amateur radio astronomers have been using RTL-SDR’s for 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.

In their work they showed how they were able to detect and measure the rotational period of the Vela pulsar, one of the strongest and easiest to receive pulsars. They also noted how using several RTL-SDR dongles could reduce the required satellite dish size.

Recently we came across Hannes Fasching (OE5JFL)’s work where he shows that he has detected 15 pulsars so far using RTL-SDR dongles. His detection system specs include:

Antenna: 7.3m homemade offset dish, OE5JFL tracking system
Feeds: 70cm (424 MHz) dual-dipole with solid reflector, 23cm (1294 MHz) RA3AQ horn
Preamplifiers: 23cm cavity MGF4919, 70cm 2SK571 (30 years old!)
Line Amplifier: PGA103+
Interdigital filter: designed with VK3UM software, 70cm 4-pole, 23cm 3-pole
Receiver: RTL-SDR (error <1ppm), 2 MHz bandwidth
Software: IW5BHY, Presto, Tempo, Murmur

Furthermore, from looking at the Neutron Star Group website, it seems that the majority of amateur radio astronomers interested in pulsar detection are currently using RTL-SDR dongles as the receiver. Some of them have access to very large 25m dishes, but some like IW5BHY, IK5VLS and I0NAA use smaller 2.5m – 5m dishes which can fit into a backyard.

If you are interested in getting into amateur pulsar detection, check out the Neutron Star Group website as they have several resources available for learning.

OE5JFL's 7.3m pulsar detection dish with an RTL-SDR receiver.
OE5JFL’s 7.3m pulsar detection dish with an RTL-SDR receiver.

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

Detecting Pulsars (Rotating Neutron Stars) with an RTL-SDR

The RTL-SDR has been used for some time now as an amateur radio astronomy tool. Radio astronomers Peter W East and GM Gancio have recently uploaded a paper that details their experiments with detecting Pulsars with an RTL-SDR (doc file).

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. The abstract of the paper reads: 

This project sought to determine the minimum useful antenna aperture for amateur radio astronomers to successfully detect pulsars around the Hydrogen line frequency of 1420MHz. The technique relied on the collaboration with GM Gancio, who provided RTL SDR data of the Vela pulsar (B0833-45, J0835-4510) and others, collected with a 30m radio telescope. This data was processed to determine the achievable signal-to-noise ratio from which, the minimum useful dish size necessary for some effective amateur work, could be calculated. Two software packages were developed to do synchronous integration, a third to provide a power detection function and a fourth for spectrum analysis to recover pulsar rotation rate.

With their system the authors were able to detect and measure the rotation period of the Vela pulsar. Also, from their data they were able to estimate that the minimum dish aperture required to observe the Vela pulsar would be 6m, noting that the Vela pulsar is probably the strongest pulsar ever detected. They also write that by utilizing 5 RTL-SDRs to gather 10 MHz of bandwidth together with some processing that the minimum required dish aperture could be reduced to 3.5m.

The Vela pulsar pulse power integrated over a 50 second 100MB file, combining some 560 pulsar pulses
The Vela pulsar pulse power integrated over a 50 second 100MB file, combining some 560 pulsar pulses.

In addition to these Pulsar experiments, Peter has also uploaded new papers about improving his Hydrogen Line RTL-SDR Telescope (pdf), and has updated his paper on improving the frequency stability of RTL-SDR’s with air cooling (doc file). Peter found that the frequency stability of the RTL-SDR (with standard oscillator) could be significantly improved by adding heat sinks and aircooling them. The graph from his paper below summarizes his results.

Results from air cooling the RTL-SDR.
Results from air cooling the RTL-SDR.
The air cooled and heatsinked RTL-SDRs
The air cooled and heat sinked RTL-SDRs

All of Peters papers can be found on his website at y1pwe.co.uk/RAProgs/index.html. He has many RTL-SDR radio astronomy related resources there, so check it out if you are interested.