Stuff I do

What is amateur radio? Amateur radio (or HAM radio) is a great hobby, or sport - it depends on how seriously do you take it, and what activities you choose to engage in precisely. Basically HAM radio is a pastime where people around the world buy and/or build radio transceivers, antennas and lots of other gear, and make contacts with each other using the frequencies and modes that complies with rather strict regulations. Amateur radio operators also participate in emergency communication, since no infrastructure is required, and with the proper tools, they can talk over thousands of kilometres. Despite the aforementioned strictness of radio regulations, there are multitude of ways you can "do HAM radio". If you enjoy chatting, you can buy a cheap hand-held device and check into a "net" on a local repeater. If you like "hunting DX" - making long-distance contacts on different continents (or covering an unusually large distance at the given circums...

Why? A digital 90° phase shift filter is an important building block of the so-called Software Defined Radios (SDRs). And SDR is a radio that has (relatively) minimal hardware, and most of the features are implemented in software. There are no fancy buttons and displays, but there is a UI application that controls the box. The box is a direct conversion receiver. It just converts part of the radio frequency spectrum to the audio spectrum (the reality is a bit more complicated, but you got the idea). An SDR usually provides two signals that are almost the same, except one signal's frequency components are shifted 90 degrees in one direction. Given these two audio signals, the software can do anything a conventional receiver can achieve with bulky components or expensive integrated circuits. Plus, the software can be changed easily. Actually this is the greatest thing in SDRs. The software can demodulate AM signals by LW-MW-SW broadcast stations, or FM usually encountered ...

How to write fast programs with numpy and python At first, I wanted to write a post about "how to write fast programs with python and numpy". After writing a few test cases it quickly turned out that the fast, numpy versions of tests are not only fast because of numpy, but because they use numpy "the right way". Let's see what does it mean.

Python is a great language but it's far from being a complete tool. It do have got a lot of libraries, many of them already built into the standard distribution. However as you do more and more work with it, chances are that you'll have to do something that does not have a canned solution ala Python. This usually means that you have to interface with C libraries or you even have to write the C code yourself. It's possible and even not too hard to write C libraries that can be loaded by Python and expose Python objects and functions. If you want to rewrite existing Python code to be faster, it's probably the way to go. (I strongly advise you to think twice before you act, such work won't be an easy thing to do.) So if you have to write your own Python things in C, read this . If you haven't done much C before, this gonna hurt. Fortunately there is one particular case when you don't have to write C code at all, even it smells like low-level coding: the case ...