[RFI] Broadband RFI on 10 meters

[Michael Carter]

Interesting story, and a good resolution, Scott - no need for embarrassment.  I am curious about the apparent directionality of the source given it's in your own house, and your antenna is elevated.  I would think that the antenna directivity at ground level would not be sufficient to resolve the source direction, but apparently it is.

Do you know a brand/model of the charger used for the eBike?  I am surprised that the manufacturer would go to the trouble of dithering the SMPS switching frequency.  In a wide spectrum view, are there any discrete spectral lumps you can see?  Your RF spectrum screenshot is remarkably uniform in power density.  I wonder if FM detection would reveal the frequency modulation rate if the switching frequency is being dithered?

73,
Mike, K8CN
________________________________
From: RFI <rfi-bounces+mike.carter=unh.edu at contesting.com> on behalf of K9MA <k9ma at sdellington.us>
Sent: Friday, October 17, 2025 11:35 PM
To: rfi at contesting.com <rfi at contesting.com>
Subject: Re: [RFI] Broadband RFI on 10 meters

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This is embarrassing, but I've found the source: My own ebike charger.
The important lesson here is that such devices can produce broadband
noise, without the spectral peaks one expects at harmonics of the
switching frequency. (I saw this kind of spectrum once before from a
different source, which I never identified.) I suspect the switching
frequency is deliberately "dithered".

  In any case, I'll know what to look for if this kind of RFI shows up
from the neighbors.  I shudder to think about how much RFI could come
from a 20 kW EV charger.

It's hard to believe this device comes even close to meeting FCC part
15. Naturally, it comes from a certain very large Asian country.

73,
Scott K9MA




On 10/17/2025 7:48 PM, K9MA wrote:
> Links to RF and AM audio spectra below. The noise level is about 30 dB
> above my usual noise floor at the same span.  It is definitely
> directional, so it's not internal to my station.  It's certainly
> local. I may have to see if any of my neighbors in that direction has
> recently gotten an EV.
>
> If anyone can find a clue as to the type of source from either
> spectrum, Please let me know.
>
> 73,
> Scott K9MA
>
> https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsdellington.us%2Fhr%2FRFI%2F10m_RF_25.10.18.png&data=05%7C02%7Cmike.carter%40unh.edu%7C682f1aa8a20f47a6863c08de0df76660%7Cd6241893512d46dc8d2bbe47e25f5666%7C0%7C0%7C638963553434628751%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=GBXDGnqQdl6lzkFZQsy10YzBZRaMqBeRzb%2BSumN7W2o%3D&reserved=0<https://sdellington.us/hr/RFI/10m_RF_25.10.18.png>
>
> https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsdellington.us%2Fhr%2FRFI%2F10m_AM_25.10.18.jpg&data=05%7C02%7Cmike.carter%40unh.edu%7C682f1aa8a20f47a6863c08de0df76660%7Cd6241893512d46dc8d2bbe47e25f5666%7C0%7C0%7C638963553434656610%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=12Nu%2FkznzrFwaK7PuucPlPJOYZf%2Ft30VrZm0rd698Tc%3D&reserved=0<https://sdellington.us/hr/RFI/10m_AM_25.10.18.jpg>
>
>
> On 10/16/2025 8:50 PM, Mike Fatchett W0MU wrote:
>> Take a picture with your phone............
>>
>> W0MU
>>
>> On 10/15/2025 10:11 PM, K9MA wrote:
>>> In fact, the audio DOES tell us something: That modulation is
>>> clearly audible. If I can hear that with a portable AM receiver, and
>>> it makes no difference what frequency it is tuned to over a wide
>>> range, I'm tracking the right source.
>>>
>>> As I've said, the RF spectrum is virtually flat over the widest span
>>> the K4 can display, 368 kHz.  There's just no point in posting an
>>> image, which really WILL tell us nothing. (And it's a pain to do
>>> with the K4, as it can only save to a USB drive, not directly to the
>>> computer.)
>>>
>>> BTW, as of 04Z, 11 PM local, it's gone, so it's likely one of my
>>> neighbors.
>>>
>>> 73,
>>> Scott K9MA
>>>
>>>
>>>
>
>


--
Scott  K9MA

k9ma at sdellington.us
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