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RFI Food for Thought

KD0RC Member, Super Elmer Moderator

Tonight I found a new source of RFI. The symptom is hitting the tune button with the 500 W amplifier engaged caused SmartSDR to become non-responsive, and therefore locked the tune button in the ON state. Keying my Flex 6400 with the keyline at the back of the radio caused no issues.

My hypothesis was that either the computer or the network was getting RFI, as the radio itself had no issues keying and unkeying 500 W.

On a whim, I unplugged an unused 10 ft. Cat 5 cable from my NetGear switch. Instant success! With the same cable plugged in to a Raspberry Pi, I had no issues. Unplugged from the Pi end, it apparently acts like an antenna, even with a mix 31 ferrite bead at the network switch end.

I hope this is useful for anyone else having a similar issue.



  • ka9ees
    ka9ees Member ✭✭✭


    Thanks Len!

    I think that might be causing me some trouble.

  • Randy KN4YBA
    Randy KN4YBA Member ✭✭


    With me living in an HOA and all HF antennas in my attic, the only resolution that stopped all RFI back to my radio was running 10gb fiber from my network back to my radios and computers.

    I fought this issue until running the fiber.

    Best of luck!



  • Mike VE3CKO
    Mike VE3CKO Member ✭✭✭

    You can assume the same for USB cables plugged into the computer but nothing at the other end. Any unused cables including audio, should be unplugged to prevent possible RFI.

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