FM audio transmitter using NTX2

Transmit FM audio on 434.65 Mhz. by substituting a Radiometrix NTX2  for a crystal oscillator in this circuit:

http://scitoys.com/scitoys/scitoys/radio/am_transmitter.html

Radiometrix: http://www.radiometrix.com/content/ntx2

NTX2 datasheet: http://www.radiometrix.com/files/additional/ntx2nrx2.pdf

On the NTX2, the connections are:

  • 5V to the NTX2 VCC pin 4
  • 5V to the NTX2 EN pin 5
  • GND to the NTX2 GND pin 6
  • Upper lead of audio transformer to the NTX2 TXD pin 7

A voltage divider input coupler will also work. See this post for a simple circuit: https://reactivemusic.net/?p=12263

notes

  • Audio modulation level is very low. This circuit would benefit from a preamp. For example, as in this circuit by Amanda Ghassaei: http://www.instructables.com/id/Arduino-Audio-Input/
  • Connect an antenna wire to NTX2 pin 2 (and 1 for RF ground)
  • The circuit worked with 3.3 volts and would probably be fine with less.
  • Used line out of an iPod touch for an audio source. Volume was up fairly high.
  • You can also receive using AM mode using ‘edge’ detection
  • In the US, you need a ham license to transmit on 434.65 Mhz.