Which of the following connectors would be a good choice for a serial data port? [G6B12]
B. Type N
C. Type SMA
The answer is D. DE-9. Now, wait a minute! I thought those were DB-9 connectors! Well, technically no. The “B” refers to the size of the shell, so the older style 25-pin DB-25 connectors could be called that. The DB designator just followed along, because they’re used so often for serial ports also. The connector in the above image is an example of the DE-9 connector.
The remaining three connectors in the question, PL-259, N-Type, and SMA are all center-pin/outer-shield 2 conductor style connectors, specifically made for coaxial cables, like your radio-antenna feed line. A serial port requires at minimum four conductors, two for transmit, and two for receive.