Monday, September 30, 2019

Tiny KT0803K transmitter won't do ham bands

John, VK2ASU, tipped me off about these boards. It's a little FM broadcast transmitter that can be controlled via two wire interface from an Arduino (for example). The chip is a Monolithic, digital stereo FM Transmitter KT0803K.

I got mine for AU$4.87 via eBay.

Sample software to drive it comes from the manufacturer Elechouse, here.

The board will transmit from 58MHz to 134MHz. It seems to get a little unreliable at the edges, I guess a PLL isn't locking or something.

I had to slightly modify the library for it to compile on the latest Arduino IDE. It seems they'd defined some integer sizes that are already defined these days.

In the file FMTX.h, up the top add this line:

#define __TYPE_REDEFINE 1

This will stop the type defines from being processed. Here's my test code based on their example.

#include "FMTX.h"

float fm_freq = 134;  // Here set the frequency
void setup(void)
{
  fmtx_init(fm_freq, AUSTRALIA); 
}

Anyway, a bit of fun for $5 and it certainly puts out a decent signal on the FM broadcast band. Disappointed I couldn't have a QSO on a ham band with it.

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