RFI Mitigation

Discussion in 'General Technical Questions and Answers' started by KI4VVA, Mar 10, 2021.

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  1. KI4VVA

    KI4VVA Ham Member QRZ Page

    Hey everyone, how do you get rid of RFI?

    I think I see a lot of it on my HF and VHF rigs. On my HF rig (IC-7300) I see ripples, waves, and continuous peaks in a pattern on most bands. I know my switching power supply could be part of it. But I also see a lot of the same stuff on my AirSpy HF+ SDR. I have gone around and put clip on toroids on all the power cables in my home office, some I even managed to run through the toroid a couple times, granted they were cheap on Amazon.

    My tribander rig picks up all kinds of spurious transmissions and I rarely hear anyone speaking (could be because I live in North Idaho) and even the repeaters are quiet, but I hear them squawk and I can use them, so I know I can hear them.

    We have WiFi, we have cellphones, we have wireless reporting transformers in our remote neighborhood, and we use a point to point wireless local ISP (a dish on top of a 40 ft utility pole pointing at a tower a few miles away - way better than satellite was *puke*). Otherwise any devices I have added in the last couple of years didn't seem to make any difference (weather station and wifi gear).

    I know it will never be perfect, but I want to get the noise down as much as possible.

    Any suggestions, tips, or wisdom are appreciated.
  2. G8FXC

    G8FXC XML Subscriber QRZ Page

    I think the only thing that has a significant effect is diversity reception.

  3. W7HV

    W7HV Ham Member QRZ Page

    It's not necessarily easy or something that can be covered in a forum response. I recommend googling the topic and looking for good articles. ARRL has many good pubs. Study these to develop and understanding of the issues and methods by which they might be addressed and then go and do it.

    Are we not hams?
  4. W6KCS

    W6KCS Ham Member QRZ Page

    I'd start with shutting off your house main breaker and powering the radio(s) from a battery to see if any of it is still there. If it's gone, you can turn things on/off until you find the source.
    N1VAU, SM0GLD, KC2RGW and 1 other person like this.
  5. N9XV

    N9XV Ham Member QRZ Page

    Start with the easy stuff first - high quality feed lines like the LMR-### series for everything ham radio i.e. feeders, jumpers etc.

    Do the same for the non-ham radio related cables i.e. routers, modems, TV etc. High quality "Quad-Shield" cables etc. I'd even look at shielded twisted pair for the non-coaxial runs. Of course the shield of all those coaxial connections and/or boxes should be positively bonded to EGC (i.e. Romex bare conductor in the house wiring) of the 120-volt AC receptacles. There are a variety of IT/media rack-enclosures that would make this easier to do a look very "professional". If the enclosure is not metal, I'd even consider "caging" it with a screen material that's also bonded to EGC.

    On the outside, make sure all of the media cables are bonded to each other and then to the AC power service entrance ground rod connection.

    I doubt your getting any RFI from the switching supply in the shack. We hear that all the time, but those bugs have pretty much been worked out for most of the current supplies out there. You could always load test the supply in question - load up a transmitter 100 watts into a dummy load and check the supply with either an AM portable radio or wire connected to another HF radio etc.
  6. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    PU2OZT likes this.
  7. KH6AQ

    KH6AQ Ham Member QRZ Page

    As W6KCS says, shutting off AC power to your house (power the IC-7300) on a battery and see if the noise decreases.

    If it does the noise source is in your home. From there each room is shut ON/OFF one at a time while monitoring the noise. Once it is isolated to a room devices in that room are unplugged until the noisy one is found. In my home the ceiling fan lights are the offenders. Solution? We don't run the lights when I'm on the air.

    If the noise source is not in your home you can try to locate it.

    What is the noise level in S-units, by band, and with the IC-7300 set to SSB? Ambient noise levels in residential neighborhoods have crept up over the years and what you hear might be "normal." At my QTH S-7 on 40 meters is normal. At one QTH it ran S-9 on 80 meters and that made working Europe from Utah on CW a challenge. The dominant noise source seemed to be the McDonald's a mile away. An MFJ-1026 noise canceller nulled that, revealing the shopping center half a mile in another direction. The end result was 1 S-unit of noise reduction was had and it made the difference with frequency QSOs into Europe.
    K8XG likes this.
  8. K8XG

    K8XG XML Subscriber QRZ Page

    When Turning off your house, DO not forget about any battery backup items like Wifi or internet routers, cable modems, and if your standby charging any batteries, disconnect them from the charger. Many chargers will get back feed from the battery and still make their Hash noise many do.

    If you are getting Hash into any portable radios, HTs ; you can use them to hunt down the noise bringing them closers to things that might be causing it and noticing if things get worse approaching them. I have a Kenwood TH-74D HT with all band [0.500mhz - 525mhz] all mode receive (SSB, CW, AM,FM). It is great in hunting down RFI in SSB and/or AM modes.
    Last edited: Mar 11, 2021
  9. K8XG

    K8XG XML Subscriber QRZ Page

    What brand switching power supply do you have just out of curiosity.
  10. KC3PFR

    KC3PFR Ham Member QRZ Page

    I have a neighbor (somewhere) who I suspect has a television (based on pattern of use) that almost completely wipes out my station. It is a pulsating noise on most of the ham bands. Worse on some than others, but bad on all. I can attenuate and still receive, but it does significantly decrease my experience in operation and limit what I can do. Not much to be done but live with it until I can try and find which neighbor and approach them about a solution.

    I've worked through all of the in-home troubleshooting as described above. The random sweeps and crashes I just live with. Sometimes you get harmonics of strong signals nearby. The worst thing I have seen is when there is someone running the vacuum in the house. I hear refrigerators can also be problematic. I'm a big fan of the turn off circuit by circuit and see if your noise source goes away approach for your own stuff.

    You'll also want to make sure that your ferrites are the right mixture. Mix 31 is supposed to be best for HF. People have recommended Palomar Engineering to me as a reliable source.

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