After some recent discussions with two friends Rich & Dave I have been playing with WebSDR, decoding all sorts of transmissions using MultiPSK. I have never been particularly interested in amateur or “ham” radio but receiving and decoding signals from around the world is a fun way to pass a cold evening.
There is lots to find: weather information, humorous IRC style chat, worldwide operators trying to reach as far as possible and even digitally coded pictures.
Today I received some prototyping boards from Mike at White Wing Logic. These are a little like stripboard/veroboard on steroids, they have footprints for a number of different surface mount parts and connectors with breakout pads. I have used breadboard or custom PCBs solely for a few years but increasingly packages are only available in surface mount.
I needed a sine wave carrier for a magnetic transponder system I am working on. Various types of crystal based oscillator are available such as the Pierce, but these can be tricky to design and ensure they work correctly.
Rich suggested using a square wave oscillator with a filter to turn it into a sine wave. The filter attenuates all frequencies except the fundamental frequency, which should remove much of the square wave. Over a couple of nights I tested this in ltspice then built it on a breadboard and checked the real life results.