FT-920 CAT interference

Discussion in 'General Technical Questions and Answers' started by DL1AD, Jan 2, 2020.

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  1. DL1AD

    DL1AD Ham Member QRZ Page

    I recently tried to connect my FT-920 to my computer to do some FT-8. It does work in general but I have major issues with (I think) interference somewhere on my cables.

    So this is my Setup: I have a decoupled audio interface I connect to the FT-920 (via the DATA-socket on the back). This is connected to my external audio interface, which is connected to my computer via USB.
    Since my computer has no serial port as such, I bought an external USB interface (this one: https://www.digitus.info/en/products/computer-components/computer-peripherals/serial-parallel-adapter/da-70156/ ).

    As long as the transceiver is not transmitting, everything works like charm. CAT control is working, FT8-decoding works as well. Once I start transmitting, my other usb devices such as mouse and keyboard stop working (they are not connected on the same port) and when I use my Laptop the touchpad stops working while in TX.
    My best guess: Something picks up some HF from the device or so and transports it into my pc.

    I tried putting a ferrite (I had one laying around) on the USB cable that connects the adapter to my pc. I tried putting the adapter into my pc directly and connecting it to the transceiver via serial cable (also with a ferrite or even two loops through the ferrite) with the same results. Sometimes even the CAT-connection itself gets interfered with, so the whole connection breaks.
    Is it a bad adapter or - even worse - the serial output itself? And how could I get it to work without disrupting my whole computer?

    Tnx and 73, Julian, DL1AD
  2. K7GQ

    K7GQ Subscriber QRZ Page

    Please describe your antenna system completely.
  3. DL1AD

    DL1AD Ham Member QRZ Page

    I had the same problem with two different antenna systems.
    One was a ZS6BKW (selfmade) that I fed directly into the radio.
    The other was a 10.1m monopole fed into an unun that I have measured for the 40m band (and that does also work on 20). When the problem first came up, I also turned a little coil into my coax cable (RG58, 10 turns, ca. 10cm diameter). Thats the current antenna system.
    Both Antenna systems showed the same problems only when connected to the computer. If I transmit SSB via the desktop microphone without the USB-connection, my laptop keeps working fine.
  4. DL1AD

    DL1AD Ham Member QRZ Page

    Edit: I tried connecting just the audio to my pc and using VOX control and that caused the same problems.
    Also: I don't know if this is normal but while feeding audio (FT-8) into the device I can hear the tones (though the monitor is shut off as well as the AF GAIN is set to 0).
  5. K7GQ

    K7GQ Subscriber QRZ Page

    I believe that this is a typical case of RFI disrupting the USB port. I had a very similar problem that I easily solved by adding two Mix 43 ferrite cores (bought at Ham Radio Friedrichshafen) to my feed line in the shack. I also used several smaller cores (unknown mix) to the USB cable coming from the radio. Problem eliminated!
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    If I have cat interference I throw a shoe at it.

    Hope this helps.:)
  7. WE4E

    WE4E Premium Subscriber QRZ Page

    I'd agree. I have to use ferrite chokes on the USB keyboard on my shack PC or it will sometimes barf. I wind the USB cable through a couple of snap-on ferrites and no more barf.
  8. DL1AD

    DL1AD Ham Member QRZ Page

    Tnx for all your help. I ordered some snap-ons online today and as they arrive I will report back. I already discovered that one of the USB hubs on my desk seems to react very heavily to rf so I have taken it out of the loop. Lets see what happens on monday.
  9. K7GQ

    K7GQ Subscriber QRZ Page

    If the snap=ons don't work, use this style instead. I wrapped as many turns of coax through the core as I could fit.

    Attached Files:

  10. DL1AD

    DL1AD Ham Member QRZ Page

    I will try, thanks a lot. I am only transmitting with up to 100W. Is it safe to randomly put ferrites on the feed line?

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