[Ground-station] 2 kHz modulated signals in the CBRS guard bands

[Michelle Thompson]

"Here's an image of the narrowband "mystery signals" in the CBRS band. The
vertical axis is time, about 20 minutes total. Horizontal axis is
frequency. The frequency range covers the guard band between two CBRS
signals, whose emissions start just below and just above the frequency
range of this plot. These signals are often present, and often appear in
more than one CBRS inter-channel guard band. I've seen them in both places
where I have monitoring systems (Reston VA and Va Beach, about 150 miles
apart). They are modulated in amplitude and seem to have sidebands ~2 kHz
offset from their carrier frequency. Their PSD can exceed the measured PSD
of some CBRS signals in the area. The signals are present on different
spectrum analyzer models connected to different antennas, so they aren't a
spectrum analyzer artifact.
Here's an image of the narrowband "mystery signals" in the CBRS band. The
vertical axis is time, about 20 minutes total. Horizontal axis is
frequency. The frequency range covers the guard band between two CBRS
signals, whose emissions start just below and just above the frequency
range of this plot. These signals are often present, and often appear in
more than one CBRS inter-channel guard band. I've seen them in both places
where I have monitoring systems (Reston VA and Va Beach, about 150 miles
apart). They are modulated in amplitude and seem to have sidebands ~2 kHz
offset from their carrier frequency. Their PSD can exceed the measured PSD
of some CBRS signals in the area. The signals are present on different
spectrum analyzer models connected to different antennas, so they aren't a
spectrum analyzer artifact."

Any ideas? Anyone closer to VA that can get more recordings, give it a try.

-Michelle Thompson



On Tue, Jul 18, 2023 at 12:08 PM Michelle Thompson <
mountain.michelle at gmail.com> wrote:

> Maybe someone on this list might know about this strange unknown signal
> popping up on the CBRS band.
>
> CW 2 kHz modulated signals, right in between CBRS channels, with multiple
> signals observed.
>
> Observed in Virginia. I'm supposed to get some recordings.
>
> Any ideas on what these are? Will share recordings when I get them.
>
> I know we have several spectrum experts and signal intelligence folks
> here. Several dynamic spectrum sharing experts have noticed this, can't
> figure out what it is, and have put the question out to a wider group,
> which includes ORI.
>
> -Michelle Thompson
>
>
>
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