From the linked repo:

> rpitx is a general radio frequency transmitter for Raspberry Pi which doesn't require any other hardware unless filter to avoid intererence. It can handle frequencies from 5 KHz up to 1500 MHz.

Wait, how does that work?

1.5GHz is a _lot_, I can't imagine this is done with bit-banging an I/O line, nor do I expect the Pi will have a DAC with anything close to a 3GHz+ sample rate.

> Plug a wire on GPIO 4, means Pin 7 of the GPIO header (header P1). This acts as the antenna.

A bit of Googling shows me that on the later Pi board GPIO4 (pin 7) has a bunch of alternative modes, amongst which is a general purpose clock output (GPCLK0), a DPI output bit (DPI_D0) and what I recon is composite analog video in/out (AVEOUT_VID0, AVEIN_VID0), and the TDI JTAG pin. But none of these would get close to 1.5Ghz TRX capabilities, no?

What's the magic here?

RF is basically black magic but here it’s the harmonics of lower frequencies that are in GHz range (and very noisy and weak)

This did come up when I was researching this but it’s incredibly dangerous as you’ll be spewing all over the spectrum due to harmonics, I considered it too much of a hack for my liking