An HF Ham Radio SSB/AM/FM/CW Transmitter made from a Raspberry Pi Pico and not much more
Over on Hackaday we've seen a story about a Raspberry Pi Pico based software defined radio transmitter that is capable of transmitting SSB, AM, FM and CW anywhere between 0.5 - 30 MHz.
The design generates an oscillator signal using the Pico's Programmable IO. For AM/SSB it uses the PWM output pins to generate an RF envelope which gets mixed together with the oscillator using an analog multiplexor. A small microphone is also connected to the Pico for voice transmissions. The designer notes that the output power is far too low to be used on the air, but adding an output amplifier would help.
The software is all open source and provided on GitHub, and more information about the design can be found on the designer's '101things' website.
The Raspberry Pi Pico is a low cost microcontroller board, and we note it cannot run Linux like standard Raspberry Pi boards. This means that software like RpiTX cannot be used.
Would a non-pico version be better?
Not at all: this is just bit-banging a signal just like you would on a regular Pi but less overhead. Really, this is going back to the good ol’ days in the 70’s-80’s when your cassette, serial, etc ports would all be bit-banged–if an old 8-bit processor can do this, it’s trivial for something like a Pico.
The CATCH is that it’s a square wave with all the harmonics: it needs heavy filtering to be legal. Fortunately the power is very low without some kind of amp.