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://sdellington.us/hr/RFI/10m_RF_25.10.18.png
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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