RFI Help

Discussion in 'Ham Radio Discussions' started by KC3NHE, Jan 16, 2021.

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  1. KC3NHE

    KC3NHE Ham Member QRZ Page

    Not sure if I’m posting this in the right place. I need some assistance with quelling some RFI. I have a god awful consistent S9 on 40m and have tracked down a few culprits. I know what needs to be done to reduce the RFI but I’m having difficulty figuring out what exactly I need to do this. I’m guessing a Mix 31 is what I need but I’m lost beyond that. I have a TV and a cable modem that are the cause of a lot of noise when I did a test for RFI with my SW receiver.

    Should I be using toroids or snap beads? How many and what size, and where do I get them at a reasonable cost? Thanks in advance and 73!
  2. W1VT

    W1VT Ham Member QRZ Page

    The inductance is roughly proportional to the turns squared. You need 10 to 15 turns or 100 to 225 beads. You can run multiple cables through one large toroid. I recently bought some FT-240-43 toroids for winding choke baluns from Mouser. They were nicely packed in foam and cardboard.

    Zak W1VT
  3. KF5LJW

    KF5LJW Ham Member QRZ Page

    Tells me you coax and or CATV is improperly bonded. Better to address the cause rather than a band-aid treating the symptom.
    WE4B likes this.
  4. KP4SX

    KP4SX Premium Subscriber QRZ Page

    First suspect is a bad wall-wart for the modem.
    N0TZU and KC3NHE like this.
  5. KC3NHE

    KC3NHE Ham Member QRZ Page

    i have an OTA antenna that is attic mounted, so no CATV there. I only have the noise on 40, all other bands are quiet. Is there something more that I should be doing with my hardline that I’m not doing?
  6. KC3NHE

    KC3NHE Ham Member QRZ Page

    The wall wart is definitely a cause of, major interference when I get close to it with the receiver
  7. KC3NHE

    KC3NHE Ham Member QRZ Page

    Thank you, I’ll start there
  8. NK7Z

    NK7Z XML Subscriber QRZ Page

    N0TZU likes this.
  9. KC3NHE

    KC3NHE Ham Member QRZ Page

  10. K0RGR

    K0RGR Premium Subscriber QRZ Page

    Yes, I have one here that produces solid S9 noise on 20 meters and below. After checking the voltage and current specs for the beastie, I replaced it with a nice analog 12 V supply I happened to have in my collection.
    KC3NHE and N0TZU like this.

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