Eventually we may build an amateur radio transceiver based on an arduino.
But for the moment we’ll just collect useful snippets and libraries that might come in handy.
I2C communication is used all over the place in digital radios to set the frequency of oscillators, read power sensors, and select digital switches. But it’s really annoying when the I2C clock becomes audible on the radio receiver. But I2C doesn’t require a fast regular clock to operate, it can use a totally random clock, that operates as slowly as you like, and probably becomes totally invisible to the radio circuits.
The SlowJitteredI2C sketch implements I2C in software with a slow jittered I2C clock so you can test whether the peripherals still work and whether the the I2C can be made non-interfering.
Building a radio receiver, hooking it up to antenna, and hearing nothing means that there’s nothing to hear or that your radio is broken. It’s hard to distinguish the two without a second receiver or a signal generator.
The MarkerGenerator sketch uses an Arduino timer to generate a variety of frequencies and their harmonics. Bring a wire plugged into the Arduino output close to your antenna and you should be able to see or hear the harmonics on your receiver.