Next job was to get the transmitter running and prove it was transmitting correctly by hooking up a receiver to decode the radio signal. The program waggles a single output pin which is then reduced in amplitude and offset a little to match the transmitter’s requirements. Here’s the resulting signal fed to the transmitter:
This signal alters the transmitter’s frequency a little, and when picked up on a ham radio has a distinctive “Teleprinter” warble. I don’t yet have such a radio, so instead I generated that warble by using a tiny receiver (Radiometrix NRX2, matching the NTX2 transmitter) and fed its output into the sweep input of an audio signal generator. The result is the same as the radio ham setup, except that the two tones of the warble will be different. That doesn’t matter since the decoding software can easily be configured to match the tones received. So, here is a screen-shot from that decoder, showing the message that was transmitter over the airwaves, and picked up by my receiver about 20cm away!
This may look similar to an earlier post, but that time there was no radio signal involved – this time it’s much closer to what the balloon payload will be doing. Next step here is to change the test message to be real balloon data (GPS, temperatures etc.).