Tagged: pulsar detection

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

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.

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

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.

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.