For the transmitter, he turned an Arduino Pro Micro into a USB sound card which he could plug into his laptop. That outputs both the audio signal and a 40 kHz carrier signal, implemented using the ...

The transmitter was actually a pretty simple circuit, just a crystal-controlled oscillator and an RF amplifier really, but still managed about 1.5 Watts output on the 80-meter ham band.

Thu, Jul 23, 2015, 1:30 PM Keedox 2-in-1 Bluetooth 4.0 Audio Receiver and Transmitter (Amazon) Whether it's due to frugality or nostalgia, sometimes it can be tough to move on from your older tech.