FT-991 - Dual CAT port operation

Discussion in 'Radio Circuits, Repair & Performance' started by PY2RAF, Sep 3, 2019.

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  1. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Hi there, QRZers.

    In my quest abusing investigating my FT-991A functionalities, I found something very interesting.

    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 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.

    Well, after doing some tests with the serial port I just went curious and connected both USB and Serial to the computer. It is not a OR, but a... AND!

    To my amazement, the radio was happily controlled via both interfaces at the same time. And the noteworthy news is, when you send a command through a CAT interface, this command is not echoed on the other interface, which is great, the radio providing separation of both interfaces.

    So, if you have a FT-991A and have to resort to hacks such as Virtual Serial Port Splitters, etc., well, you can definitely use both interfaces, at the same time. Just change the menu 028 - GPS/232 Select to 'RS232C', set the proper baud rate and connect it to your computer serial port. If you don't have a serial port (which is the case on modern computers), just get a USB-to-serial converter, hook it to the DB-25 port in the radio and the USB port in your computer.

    Choose the USB port in one app, the Serial port in other app and let them both take advantage of CAT. At the same time.

    Hope that helps, 73,

    - Rodrigo.
    Last edited: Sep 3, 2019
    YT4EW likes this.
  2. K3DDT

    K3DDT Ham Member QRZ Page


    It seems appropriate to respond to this post here. This discovery is going to save me quite a bit of time. I was about to explore ways to enable PTT through the 6 pin DIN RTTY/DATA port. I never considered that both interfaces would be active at the same time.

    PY2RAF likes this.
  3. DL9GZ

    DL9GZ Ham Member QRZ Page

    Dear Rodrigo,

    Regarding my problem Your post was the only one that I found in google.
    Hopefully, after that long time since Your post my response will be read and will be likely to yield the very result getting my rig Yaesu FT-991A connected with my Laptop via RS-232/DB-25 port.
    Trying the wanted connection by hooking up a USB-to-serial converter equipped with FTDI chip, e.g. for usage of Log4OM logbook software, there won't come out any connection success, no matter what data/box/values are ticked/checked out.
    Converter, rig and PC ok, according driver properly installed, everything`s fine but connection via serial port fails consequently. Btw, connection by USB port works ufb.
    Thus my request: Can You or any other kind person give me a friendly clue how to solve this inconvenience? Support is very welcome!

    Thanks a lot in advance!
    73, Günther
  4. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Hallo herr Zimmer!

    It is probably because of your cable. Some cables crosses the TX and RX pins - and this will not work. It is very easy to check if it is the case. Take a multimeter, check if from one side your pin 3 gets the signal on the other connector in pin 3. My hunch is that you will see the signal in pin 2. Check every other pin.

    The relevant ones are 2, 3, 5, 7 and 8.

    This is how I have wired here:


    For pictures of the actual thing, check the below links:
    - Radio side
    - USB adapter side

    Don't forget a clip-on ferrite; spare yourself the hassle of having the radio or computer playing fun when in transmit mode.

    Good luck; tschüs!

    - RF.
    Last edited: Feb 12, 2020
  5. DL9GZ

    DL9GZ Ham Member QRZ Page

    Olá, dear OM Rodrigo,

    Obrigado and thanks a lot for this really particular depiction as an absolutely content-related representation by text, drawing and attached photographs, awesome!

    Yes, I also assumed that my cable had a pin crossing by comparing the port pin drawings of FT-991 manual and the manual of the USB to RS-232 converter cable, but I didn't probe that by a measuring device, because the log4om software that I intended to connect rig and PC via RS-232 port suddenly worked fine by usage of USB to USB connection.
    Thus I waived further attempts regarding the converter cable and returned it to the shop.
    This is ok, especially since I am going to use the RS-232 port now for connection with the control device of my magnetic loop antenna.

    Thanks again, 73 and tchau!

  6. KA9JLM

    KA9JLM Ham Member QRZ Page

    Normally the DB25 on a laptop is a LPT parallel port, Not a 232 serial port.
  7. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Oh. Wow. *thank you very much* for your incredible, amazing and infinite wisdom on spotting that DB-25 belongs to parallel/LPT port, even if the picture clearly depicts a DB-9 connector.

    Without your post, I am positive that everyone else in this thread would be at a complete and total loss.

    Thank God you are here, observing, posting, and providing incredible and high quality posts in the threads that you participate.
  8. W0KDT

    W0KDT Ham Member QRZ Page

    Just FWIW, I have an FT-991a and have been controlling in from a PC via the USB port. Works like a dream with several different programs.

    I recently bought an LDG AT200ProII antenna tuner. When I discovered that it, too, needed a serial connection I was a little worried. But as it turned out, the tuner wanted the DB-9 and it was zero effort plug & play. Control programs are happy, tuner is happy, owner is very happy.
    PY2RAF likes this.
  9. PY2RAF

    PY2RAF XML Subscriber QRZ Page

  10. AK4R

    AK4R Ham Member QRZ Page

    Can the usb ports & the gps ports be set to different baud rates?

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