Saturday, October 28, 2017

Raduino as NBFM TX

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_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);   

void loop(){



  1. wah , Farhan Jee.
    Wish you the best for developing 6m /2m nbfm T/Rx cheap anough. You are known to break the cost barriers.

  2. A coat effective transceiver kit for 6 meters and 2 meters will not only be popular in India but also abroad.

  3. I can see a new 2m Fox Hunt transmitter in my near future

  4. Ashan is that Clock 2 signal at TTL drive levels or less. If at TTL level say +-5V or even 2.5v adn 400uA source then I can provide a weakware power chain to drive say 5W out, based on hacking ideas from Dave Benson's work. Are we talking about a Bitx40 which would have a hack applied using a DPST relay so it coulld be kept as an SSB transmitter but also with a lot of extra hardware ie an add in board be turned in to a 6m Transmitter ? THe Rx bit is easy; you use a Moto 3362 part. It has been proved to be fine for ham work on 6 m NBFM with an adequate filter. There is no way to hack about an HF rx chain to get equivalent performance without seriously compromising what the user already has. A hint. The LT1252 is your friend in terms of driving a mixer . BTW am registered with the BitX site.

  5. Excuse me intended to say Ashar non n.