2018. január 26., péntek

Contacting the International Space Station

The International Space Station (ISS) is a huge (>400 tonnes mass, >900m3 pressurized volume) habitable satellite on low earth orbit. It orbits the Earth at about 400km high with a speed of 7.67km/s (27,600 km/h), and goes around it in about every 93 minutes.

It's permanently crewed, can support up to 6 astronauts, and provides a platform for many scientific experiments. Besides astrobiology, astronomy, materials science, and many other fields, it hosts experiments for the ARISS - "Amateur Radio on the International Space Station" project.

ARISS experiments give opportunities to observe or even contact the station with simple amateur radio equipment.

2016. október 27., csütörtök

Building WSJT-X 1.7.0-rc1 from sources on Ubuntu 16.04.1 Xenial

WSJT-X is a great desktop application for communicating via radio using various weak signal modes. I use it on the HF bands to contact amateur radio operators literally all over the world.

The new 1.7.0-rc1 alpha release features a new algorithm for decoding, and it is quite a bit more effective than the previous 1.6.x versions. One of the most important parts is decoding Reed-Solomon codes. The previous versions used a proprietary decoder, this one uses a new, open-source method.

Since I work a lot in JT65 and JT9 on short wave, building the new version definitely worth the struggle.

2016. október 14., péntek

Building a radiation detector from scratch 4 - a stabilized detector

In this chapter I'm going to show you how to build an atmospheric ion chamber for detecting radiation. The detector will have little drift, can be set to zero, and can be used to compare the radioactivity of samples, measure weak sources, or follow the decay of short half-life sources for hours or days even.

These features all require that the detector to be stable, and the readings don't drift around with temperature.

Temperature drift is very likely the worst offender to our previous ion chamber design, so we're going to deal with that one this time.

2016. július 11., hétfő

CUDA accelerated linear algebra with Python and Theano

Theano is a Python module that enables one to construct mathematical expressions with matrices and/or tensors (basically more than 2 dimensional "matrices").

These expressions are than can be evaluated using Python, but Theano can translate the expression into a C program and compile it to binary. This way it can achieve respectable performance.

But wait, there's more! Theano can build the program so certain - or all - parts of it run on a GPU. Yes, on your video card. Modern cards can do calculations in a way that makes them especially fit for doing linear algebra and similar operations. In "similar" I mean the execution of simple operation on lots of data in parallel. A GPU-s can be several (tens or hundreds of) times better, than your CPU.

I'm going to show you how to exploit an NVIDIA GPU, using Python.

Building a radiation detector from scratch 3 - the first detector

The detector will consist of a tin can, two transistors and a DVM. I will also show how to improve and stabilize the basic circuit by adding an extra transistor and an identical "dummy" circuit to cancel leakage current and temperature dependence.

Musings on the ADIF file format

The ADIF file format is a simple way to store and organize Amateur Radio (or HAM Radio) log data.

It is a way amateur radio operators most frequently store their records on the contacts they make (probably after paper).

(For fellow HAMs, my callsign is HA5FTL, see my QRZ.com page for a description of my station and yours truly, and for contact information, if you wish to express your objections and/or approval of one or several of my points made in this article.)

I have to start with a disclaimer.

2014. szeptember 15., hétfő

Building a radiation detector from scratch 2 - a radioactive collection

If you build anything you must test it somehow.

But how on Earth do you test a radiation detector? A successful test would mean that there's radioactivity around! Who would want to go near radioactivity on purpose? How hard does this radioactivity thing make our efforts in testing the detector?

Well I have good news, and bad news.

(Update: new items added: monazite, uranium glass, tritum glow-in-the-dark thingy)