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A comment on Turn Raspberry Pi’s GPIO into an FM Transmitter. Parent comment

Re:Turn Raspberry Pi’s GPIO into an FM Transmitter by miegl on Saturday November 12, 2022 @07:44PM (#33578786)
> There are ways to do a full software defined radio from a pi by using the I2S hardware, and that can transmit GPS, 433 MHz garage door openers, and various other things.

Wait, we can do sine wave up to ~1.5 GHz using the built-in PCM/I2S peripheral?

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Re:Turn Raspberry Pi’s GPIO into an FM Transmitter by pifm_guy on Saturday November 12, 2022 @11:07PM (#33579930)
The built in peripheral works up to about 100 MHz. Beyond that you use the third/fifth/seventh harmonic.

Because the pi is notionally outputting a square wave, there are plenty of high powered harmonics to use, and from a signal-quality point of view, they are just as good as the fundamental frequency.

Most people view harmonics, spurs and sidebands as unwanted, but with a bit of careful thought they can be controlled to be the exact signal you want...

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