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Quite recently, a significant noise source has shown up on my HF radio - it is NOT from my property as I have turned off the main breaker to the house - completely NO power - and still observe it on my battery-operated receiver.

The noise is about 7 kHz wide and is spaced every 24 kHz from about 2.7 MHz all the way up to just below 5 MHz. There is no indication of the noise above 5 MHz. I have a video of it in addition to the screen shot. It can be seen here: Video of Noise

Any help or ideas - especially if you've encountered similar RFI would be greatly appreciated.

Kevin Reid AG6YO
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Raydeeoh
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    What radio, and what antenna are you receiving the noise with? Does it stop abruptly at 5 MHz, or fade away around there? Do the higher "harmonics" move around more than the lower ones (if they move). – tomnexus Jan 20 '23 at 05:41
  • On ALL my radios. Kenwood TS-940s, Icom IC-7100, Flex3K, Hermes-Lite 2. I was using the Hermes-Lite 2 on battery when I shut down house power. There was NO change in the noise.

    The antenna is a simple dipole at about 35' AGL.

    The noise moves slightly as you can see from the video. The main "hump" of the signals moves back and forth about 0.5 to 1 kHz. It shimmies back and forth, doesn't matter what freq.

    It is strongest from 3.3kHz - 3.4 kHz. It is quite a bit stronger there. It does taper off at both the lower end of the range (2.7 - 2.8 kHz) and the upper range (4.7 - 4.8 kHz).

     – Raydeeoh Jan 20 '23 at 17:00
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    I suspect something like powerline ethernet, or ADSL (though the details don't match). If it's strong, try building a sniffing antenna with 20 turns of wire around a plastic bowl or jug, or even just a coat hanger stuck in the antenna jack, and walk the house and neighbourhood around trying to find it. (key is that the antenna is small and insensitive so you can tell when you're getting closer) – tomnexus Jan 20 '23 at 17:23
  • The way it stops around 5 MHz will be a clue about the type of device. If it just vanishes after the last tone, it's being intentionally generated by something, for communication. If it fades away over several tones, it's probably accidental, like a faulty power supply. – tomnexus Jan 20 '23 at 17:25
  • Thanks. I have built two magnetic loop antennas and used in the past to find noise. Unfortunately, the Tecsun PL600 I was using with them died recently and I'm waiting on delivery of a newer portable radio. We don't have powerline ethernet here. – Raydeeoh Jan 20 '23 at 21:24
  • 25 kHz is a common switching frequency for solar voltaic DC to AC voltage inverters. Any solar power installations nearby? Just a thought. – Mike Waters Jan 20 '23 at 23:00
  • Can you hear this noise on the AM broadcast band or 160m? How about below the broadcast band? Try a random length of wire on the back of your radios, as the dipole and feedline may be attentuating it on lower frequencies. – Mike Waters Jan 20 '23 at 23:02
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    Nope. Cannot hear it below 2.7MHz or so with a random piece of wire (about 60' or so of 14ga wire). – Raydeeoh Jan 21 '23 at 02:42
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    Yes, there is a solar install nearby, but it has been there for over 3 years. That isn't to say something went "wrong" with it. Unfortunately, the neighbors who live there are away in Palm Springs until the end of January... – Raydeeoh Jan 21 '23 at 02:43

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Looks like LED Grow Lights using 24 KHz SMPS driver. What hours of the day do you observe the noise? After dark eliminates solar. Another possibility is an EV charging station. It is something using SMPS power supplies somewhere operating at 24 KHz, either a very large SMPS like commercial grow operations or EV charging stations or something smaller really close by in the neighborhood.

Good luck and 73's

AI5DH

Dereck
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    There are no commercial grow operations or commercial EV charging stations anywhere near me. I don't know of anyone near me with a LED grow light, but I'm waiting for my new portable SW receiver (my PL600 died) and then I'm going out with my mag loop for a little walk about.

    The noise is there 24/7 which makes me think it isn't a grow light and possibly not a solar set up, although, my understanding is it COULD be a solar system inverter or optimizer. My understanding is that solar system inverters are used to convert the solar power that is stored in batteries into AC via SM circuitry.

     – Raydeeoh Jan 23 '23 at 03:24
  • Try an experiment since your instruments are portable take them for a walk, and maybe you can figure what the source is, somewhat like a fox hunt. – Gil Jan 23 '23 at 14:19
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    That is my plan, as soon as my replacement radio comes... After doing so, I will post what, if anything, I discovered. – Raydeeoh Jan 23 '23 at 23:13
  • My MPPT solar controller also generates noise if it's connected to a battery at night, so it's not just during times of generating power that it is ... noisy – Scott Earle Feb 03 '23 at 08:05
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I have a solar MPPT controller that produces noise just like that.

Perhaps someone nearby has installed a solar system? You might be able to get them to disconnect the solar controller from the batteries during the evening, if it is a battery charging system. The problem is that an MPPT controller plugged into solar cells and a battery will take its power from either side (I tried disconnecting mine from one side, and from the other - and it only shuts down and stops producing the noise if I disconnect it from both sides. Or just disconnect it from the battery in the evening, as the solar cells generate no power at night).

Scott Earle
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  • Scott, yes the neighbors across the street have a solar install but they've had it for 3-4 years and, up until recently, I've not had this noise. That isn't to say that it's not their system. Unfortunately, they are away in Palm Springs until Feb so I will have to wait until they return to have them disconnect and test. Coincidentally, they left for Palm Springs in early November, just after we left for a 2 week cruise. Before I left, I had no noise but it was there on my return - which makes me think you are probably correct. – Raydeeoh Jan 29 '23 at 18:32
  • I was unable to do a walkabout with my mag-loop and portable RX as my PL-600 had a heart attack. I just received a new RX and hope to get out there in the next few days. – Raydeeoh Jan 29 '23 at 18:32
  • So I just had a long conversation with the chaps who installed the solar system across the street from where I live. They've told me they used Enphase IQ7+ microinverters which convert the solar DC to AC right at the panel. The system has NO batteries and obviously, no battery charger. Hence, when the panels aren't generating power (night), the noise would go away - it doesn't. I have it 24/7 which means their solar installation is highly unlikely to be the cause. – Raydeeoh Feb 17 '23 at 20:42