The antenna is at 70 feet, about 50 feet south of where the charger was
located in the garage, so the heading was about right. That may have had
more to do with polarization.
The charger is one of these:
https://www.amazon.com/dp/B0DSPSQKX9?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1
<https://www.amazon.com/dp/B0DSPSQKX9?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1>
It was specified by Bafang/Varstrom, the source of the ebike conversion
kit. Model DZLS4830-01. No manufacturer is specified on the label, but
it's made in China. I suspect most of the RFI comes from the short DC
leads, since it was strongest on 10m, and considerably weaker on 15 and
20. So it could possible meet part 15 which, as you know, applies only
to the AC leads. I suspect ferrite cores would fix it, but in this case
it's easier just to unplug it.
I did test the charger to make sure it was terminating the charge
properly, so at least it's not likely to start a fire.
I saw another case of such broadband RFI, from an aquarium heater, I
think. It also had an AM component to the broadband noise, which was
clearly audible and allowed me to track it down. This charger only
showed the audible AM component after charging was complete, but that
allowed me to quickly track it down with a receiver in AM mode.
This got me wondering how the spectrum of amplitude modulated broadband
noise differs from the unmodulated. I didn't try FM detection. It
certainly didn't show up in the spectrum magnitude, but maybe phase.
Maybe a good question for a communications theory exam.
73,
Scott K9MA
On 10/18/2025 7:12 AM, Michael Carter wrote:
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@contesting.com> on behalf
of K9MA <k9ma@sdellington.us>
*Sent:* Friday, October 17, 2025 11:35 PM
*To:* rfi@contesting.com <rfi@contesting.com>
*Subject:* Re: [RFI] Broadband RFI on 10 meters
CAUTION: This email originated from outside of the University System.
Do not click links or open attachments unless you recognize the sender
and know the content is safe.
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@sdellington.us
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--
Scott K9MA
k9ma@sdellington.us
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