Here is a neat, 30 minute hack for your Raduino to turn the Si5351 into a pretty stable, solid NBFM transmitter. The hack is to add a varactor diode in series with the reference crystal oscillator and drive it with audio. I used a very simple audio amplifier to boost up the audio. Here is the circuit:
Attach a small piece of wire to clock 2 to radiate the signal. Here is the sketch :
/**
* This source file is under General Public License version 3.
*/
#include <Wire.h>
#include <si5351.h>
Si5351 si5351;
void setup()
{
int32_t cal=0;
si5351.init(SI5351_CRYSTAL_LOAD_8PF,25000000l, cal);
si5351.set_correction(cal);
si5351.set_pll(SI5351_PLL_FIXED, SI5351_PLLA);
si5351.set_pll(SI5351_PLL_FIXED, SI5351_PLLB);
//si5351.drive_strength(SI5351_CLK2, SI5351_DRIVE_2MA);
si5351.output_enable(SI5351_CLK0, 0);
si5351.output_enable(SI5351_CLK1, 0);
si5351.output_enable(SI5351_CLK2, 1);
si5351.set_freq(14500000000l, SI5351_CLK2);
delay(10);
}
void loop(){
}
