The wireless video data link modem default is TTL. Which is the core module of TX900, which is a long-range wireless video transmitter and receiver.
If the client does not have a specific requirement, the default data port of TX900 is RS232.
The flight control, Pixhawk, and the data port need TTL.
So how do we change the RS232 to TTL of the long-range wireless video data transmitter and receiver?
Please open the metal of the TX900, you will find the board like the one below.
The left side is TTL, there are more 6pcs zero resistors and no two chipsets.
The right side is RS232, there are more two chipsets and no 6pca zero resistors.