Question: Why RLB-232 must install an external to drive the device ?
ANS: The RS-232 output of the early computer was designed with standard +-12V, so you can take electricity from the signal line for any use.
But, now the newly designed RS-232 port’s output voltage has fallen to +- 6.5V~9V. If you want to extract power from the signal line to drive the Repeater, it will not be enough, and even affect the signal transmission speed.
At present, there is no RS-232 port equipped for most computers and tablets, and many of them are turned out with USB. This will cause the quality of the output voltage to be different. If used in two-way asynchronous transmission with only two TX-RX signals, there is no other foot of the DB-9 can supply electricity.
So SUNBOX uses a standard external power supply design (external 5V voltage). With this, you don't have to worry about the transmission speed and power shortage when using it.