Local oscillator leakage from an RTL-SDR dongle can be used as a very low power FSK transmitter. This program transmits RTTY and also makes it easy to use the same dongle to receive RTTY in between transmissions. The goal is to make it possible to have a two-way QSO between two dongles.
Over on YouTube oh2ftg has also uploaded a video that demonstrates the software in action by doing a 1270 MHz RTTY QSO between two modified RTL-SDR dongles. He uses fldigi to decode the RTTY signal and the signal is sent with the following settings: 425 Carrier shift, 45.45 Baud rate, 5 Bits per character, none Parity, 2 Stop bits.
La suite est à lire An RTL-SDR to RTL-SDR QSO with RTL-TRX: Transmit RTTY with the RTL-SDR de : RTL SDR