Two CAT ports in FT 991A - rfrht/FT-991A GitHub Wiki

In my quest investigating my FT-991A functionalities, I found something very interesting: The presence and the ability of two independent CAT interfaces.

As of now, I thought that you would control the FT-991/A using either the Serial port (the DB9 connector at the radio rear) or make use of the USB port that seamlessly exports the CAT serial interface to your computer via the USB port.

So, I thought it was a either selection: You would control the radio by either the USB or RS-232 ports.

To my awe, the radio is happily controlled via both interfaces at the same time. Independently, without any interaction between both interfaces.

So, if you have a FT-991A and have to resort to hacks such as Virtual Serial Port Splitters, Port Replicators etc., well, you can definitely use both interfaces, at the same time.

In order to be able to use the DB-9 Serial Port as a CAT controlling interface:

  1. Change the menu 028 - GPS/232 Select to RS232C;
  2. Define the port's baud rate in menu 029 - 232C Rate;
  3. Connect the radio to your computer serial port.

If you don't have a serial port (which is the case on modern computers) in your PC, just get a USB-to-serial converter, hook it to the DB-25 port in the radio and the USB port in your computer.

It is important to notice that the some serial cables flips the TX, RX and other pins - this is called Null Modem Cable. Most of the commercially available cables are the Null Modem type. If you hook up to the computer and it does not work:

  • First check the speed - The speed in the computer should match the menu 029 - 232C Rate;
  • If the speed is correctly matched, get a multimeter and test the Pin #2. If the signal appears in Pin #3 at the other side, it is a null modem cable. Rewire it or return to the seller. The pin #2 (and all the others) should appear at the same position at the other end.

Choose the USB port in one app, the Serial port in other app and let them both take advantage of the dual and native functionality of your 991A.