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I see this qrm on my system and other but not all systems. Any clue what it is?


  • My active loops have this in varying degrees over a period of hours and days. It has gotten worse this winter. My dipole does not seem to have it to this amplitude, but it is there in the noise. Active loops & 8075 , dipole 8073. I think it is intermodulation distortion from MW broadcast stations which is enhanced by the loop amps and then further enhanced by the KiwiSDR, but this is speculation and I haven't made any sort of attempt to fix it, as it has not seriously affected the receiver, with certain exceptions above and below MW for several KHz. I believe it exists in the MW band as well, but the general noise is up there and so not as noticeable. In my case it could be noise generated from the community about 1/2 mile away from me too and it does come and go.
  • In listening to that on your Rochester receiver, it doesn't sound like an MW intermod or similar. I poked around at several other Kiwi systems back east - including one near Rochester - but didn't hear it anywhere else.

    When I first heard it I thought "That's failing switcher supply" - but it immediately struck me that the pitch of the embedded hum was wrong, sounding pretty close to 100Hz noise one hears on 50Hz mains system. so I imported a sample of the sound into Audacity and noted that it was closer to 104 Hz.

    It could still be a failing switcher (possibly a battery charger) - but with a there are usually sets of harmonics related to the switching frequency scattered about, but in a quick look 'round I couldn't find any other occurrence of that noise aside from those astride 2300 kHz - and again, there's the "not 60 Hz" hum. (I know that there were at one time some 16-2/3 and/or 25 Hz mains systems in that part of the U.S./Canada, but I think that those are long gone!)

    I suppose that it could also be emanating from the Kiwi itself, somehow coupling into the antenna - but that would be easily proven/disproven by finding the same noise on a non-Kiwi general coverage receiver at your shack and removing power from the Kiwis' power supply.

    If you find it, let us know!

  • There are no switchers on any of the RF related gear. The network switch may have one though. My next mission is to sniff with my "RF Explorer" spectrum analyzer. My trusty Sony 7600 has failed me!
  • edited February 2019
    FYI, i have traced the exact waveform that you displayed, at near the same frequency, to be the SMPS from my Samsung LCD TV.
    despite that my TV is located a good distance from the Kiwi and Loop antenna and despite that i have "choked" the AC mains input to the TV, the SMPS PCB in the TV appears to "radiate" this particular RF quite strong from the PCB itself, only when the TV is turned on, when its turned off, the RF disappears.
    the Kiwi is located about 10 feet from the TV.
    the Loop antenna is located +100 feet from the TV.
    the Loop antenna and Kiwi linear DC supplies are not plugged into the same AC mains circuit as the TV.
    TV is on L1, linear DC supplies are on L2.
    input linear DC supplies to both devices including the LAN cable are "choked".
    adding the ferrite "chokes" to all devices power inputs reduced the problem but did not eliminate it.
    not sure if this will help anyone but thought id put it out there.
  • checked my TV's, none of them
  • Prompted by this I decided to turn my Kiwi back on, it's been off for a while, due to some weird HF wide QRM.
    Long story short while checking QRM decided to check weak 10m activity on another vertical with an RTL dongle on a PI but had to reboot the PI, band wide QRM changed.
    I don't have that ~2MHz interfence here but now I also don't have the HF wide stuff that over time has come up from my PI (over about two months).
    I will try to find out how it was making that sort of QRM later but for now it will stay off.

    That QRM signal you are seeing has a very hard intermitent sound, I don't have any supplies here that break so regularly and cleanly, unless it is a battery charger in top-up mode or some super efficient mains device that runs in short bursts (?).

    Either way has unintentionally helped my quest, the switchmode QRM is bad here tonight but that's always the case over the weekend but at least that strange switchback junk is off.
    It's a PI with the official PSU, don't know what it has changed, wasn't like it when I first powered it up.

  • edited February 2019
    Pi supplied PSU is a SWM, so can be noisy.
  • It's something beyond switchmode here, fired up the PI in another spot (more direct coax earth, right beside Kiwi) all OK if small increase in noise low down.
    Ran rtl_433 and strange QRM pattern is back, stopped rtl_433 footprint changes (still chooping but narrow), shutdown PI after a while the pattern is gone.
    Something to do with RTL/USB but I'm dragging this off-topic.

    Partly posted to say recheck local sources (power it all off), pretty sure my PI/RTL was OK at first but something has changed here.
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