I have started on the tracking transmitter that I will use to send dummy date to the HABAT via dl-fldigi. I have ordered a few GPS boards to use in the project and since I already have a Radiometrix NTX2, I have started work on the transmitter.

Its a simple circuit that is in use on many HAB projects that works by changing the voltage on the TX Data pin. More details can be found here.

This is what I ended up with:

The EN pin needs to be pulled high in order to turn the NTX2 on. I have taken it to pin 6 on the Arduino so that I can control the NTX2 from my code.

TXD is the data input (our 1’s and 0’s) so I split the input into two pins on the Arduino via two different value resisters. Pin 4 creates the 0’s and pin 5 creates the 1’s.

I assembled the circuit on a breadboard to test and hooked it up to the Arduino.

The last thing I need is some simple code to test the transmitter which was provided by NigeyS from UKHAS. I won’t post it without permission but it basically takes the GPS data from the Arduino serial port, formats it into RTTY and send it out via pins 4 and 5.

Once I was happy with the results, I built the final circuit on a piece of strip board ready to be mounted on the Arduino.

The finished result is good. Here is a short clip of the transmitter sending some dummy text to dl-fldigi. The signal is very stable and dl-fldigi has no problem decoding the RTTY data.

Just need to wait for the GPS to arrive then I can get it sending GPS data.

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