Microwave filters for dummies

For a recent project I needed a bandpass filter in the microwave range, made from non-magnetic materials. Remembering this very nice article from Paul Wade, I decided to give it a shot and roll my own. As the results turned out to be spectacular, I had to share this experience.

The green flatscreen

Well, what to do with a perfectly fine flatscreen, found in the trash with a blown backlight?

Convert it to solar power of course!

It works surprisingly well as a secondary monitor. Provided there is enough sunlight, the image is quite crisp and colourful. And the best thing is: The brighter the sun, the better it looks -- while the picture on an ordinary monitors becomes unrecognisable.

Some nice "Hidden Sector Photon" fieldplots

Some 3D plots I have done recently for a presentation. They were done with Python and Mayavi. They show how a hypothetical hidden photon field would look like. The emitting structure is a microwave cavity, with a strong electromagnetic field inside. This field is the driving force for the hidden photon field which can penetrate the cavity walls and propagate into space. Unfortunately you can not see the cavity geometry itself in these pictures.

You don't need to understand any of this, just enjoy the visuals...

A power amplifier for the serious garage door opener

While my serious garage door opener works nicely and reliably, it's output power is "only" 10 dBm (10 mW). It is able to open the garage door from about 100 m -- this is clearly not enough.

So I thought an impressive looking garage door opener needs an impressive amount of RF output power as well. And I found a wonderful solution to that problem, the SKY65116 chip module.

It provides up to 2 W of output power from 390 - 500 MHz, 30 dB of gain and its input and outputs are matched to 50 Ohm. In fact it contains a third matching circuit between the internal pre- and power-amplifier  It can be put into standby mode drawing only a few uA and thus can be left connected to the battery. When running at full blast it draws 1.2 A at 3.6 V, so its efficiency is about 50 %. Not bad at all!

The serious garage door opener

Garage door openers are handy little gadgets. Most of them are cheap chinese plastic crap though. This one definitely isn't. It started by collecting parts from my favorite electronics shop: the dumpster.

An old emergency shutdown switch makes the perfect case with a seriously big red button.

PyAudio with 24 bit under windows

Here are the results, proofing that with the WASAPI architecture I got true audio 24 bit samples under Windows 7:

PyAudio: How to get 24 bit support under windows

PyAudio is a really useful and user-friendly python extension for accessing the soundcard from python.

Pyaudio uses the portaudio bindings between some windows sound architecture and python. Only the WASAPI and the ASIO APIs on windows 7 support real 24 bit resolution. The standard version that comes shipped with pyaudio is compiled for WMME which is old and emulates win xp sound. It converts the 24 bit data to 16 bit and calculates with this precission internally. It returns 24 bit numbers but this is zero-padded16 bit data (can be seen as there is no change in the quantizing noise floor)

So pyaudio and portaudio needs to be rebuilt from source to support WASAPI. (or ASIO but you have to register at steinberg as a developer to get the SDK from there)

This is how I managed to build it: