Using modulation in radio communications is unavoidable. The simplest modulation technique is Amplitude Modulation (AM), where the amplitude of a carrier is varied according to the message that is to be transmitted. A carrier is…
This article is on a new method for detecting meteor reflections in radio signals for the BRAMS network. As shown below, these reflections are typically viewed as spectrograms. Hence, a straightforward way to approach the detection problem is to…
![Figure 1. The Wow! signal [image: Big Ear Radio Observatory and North American AstroPhysical Observatory].](https://tomroelandts.com/sites/tomroelandts.com/files/styles/thumbnail/public/field/image/the-wow-signal.jpg "Figure 1. The Wow! signal [image: Big Ear Radio Observatory and North American AstroPhysical Observatory].")
The famous “Wow!” signal is a radio signal that was received on 15 August 1977 as part of the SETI program. After all these years, it is still the most tantalizing candidate for being a true interstellar signal. Its name comes from the manually written word “Wow!” on…
This is the second of a two-part article on the PDART algorithm. It explains most of the nitty-gritty details. The PDART algorithm needs two extra input parameters to do its magic, a threshold and a gray level. After each SIRT iteration, each pixel of…
This article is a bit of an experiment. In it, I’ll try to explain PDART, an example of current algorithm research in computed tomography (PDART was published in 2011). What the algorithm does is, in a nutshell, a SIRT reconstruction with intermediate…
At first sight, this image has nothing to do with my site. I have not posted it or mentioned it. The picture is real, by the way, it is not “Photoshopped”. It is from TV coverage of the Scottish Open golf tournament in Aberdeen, and the effect is caused by atmospheric refraction. But the details of…
As a practical example of an iterative reconstruction algorithm, as introduced in “Tomography, Part 4: Algebra!”, I present the SIRT (Simultaneous Iterative Reconstruction Technique) algorithm. As in the mentioned article, I start from the system of linear equations…
![Figure 1. Rosetta and Philae at comet [image: ESA–J. Huart].](https://tomroelandts.com/sites/tomroelandts.com/files/styles/thumbnail/public/field/image/rosetta-and-philae-at-comet.jpg "Figure 1. Rosetta and Philae at comet [image: ESA–J. Huart].")
There’s a truly cool deep space mission that I need to bring to your attention: Rosetta. Visit ESA’s Rosetta page for details. Rosetta is an ESA (European Space Agency) mission. It will be the first spacecraft that…
Compressed sensing (or compressive sensing) is a relatively new technique that is becoming more and more important in image and signal acquisition. The term originates from image compression, where, in the classical workflow, images are first…
How to create a simple band-pass or band-reject filter, given two cutoff frequencies? These filters can be created by combining low-pass and high-pass filters. To do that, you need…