I have not seen this type of spectrum in the wild, Alex,
but the stepped frequency dithering of each 'carrier'
component in the spectrum suggests an SMPS
which is inadvertently modulating an RF carrier
in the affected band. The SMPS nominal switching
frequency is varied over time to reduce EMI. The
dither pattern may be a pseudo-random sequence,
but the deviation is clearly limited in frequency extent.
The RF carrier need not be at a remote transmitter,
but could be the LO of the receiver. That possibility
could be ruled out by attaching the RSP2Pro antenna
input (or the IC9700 antenna input) to a shielded 50 ohm
dummy load a moderate distance away from your host
computer for SDR Console. If you're using an external
clock reference for the RSP2Pro, it may be modulated
by any power supply noise on the reference source
output.
Fun puzzle!
73,
Mike, K8CN
________________________________
From: RFI <rfi-bounces+mike.carter=unh.edu@contesting.com> on behalf of
alex@kr1st.com <alex@kr1st.com>
Sent: Monday, December 19, 2022 2:57 PM
To: rfi@contesting.com <rfi@contesting.com>
Subject: [RFI] Dancing Carriers
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.
Hi there,
I'm trying to figure out what is generating these "dancing carriers" on 2m:
https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fyoutu.be%2FgKA0P2c-034&data=05%7C01%7Cmike.carter%40unh.edu%7C18de7069f2f44b70269f08dae1fb5bb6%7Cd6241893512d46dc8d2bbe47e25f5666%7C0%7C0%7C638070766934075514%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=lH0lmxzH9d4jXaDvzhoq5nBeQucq1g%2Fl5XVWaH6HdhQ%3D&reserved=0
I see them om on 6m and 1.25m as well. Has anyone come across this before
and can share a hint at what may be causing this? Since the signature looks
to be easily recognizable to someone who ran across this before I thought
I'd ask on this list.
I recorded this a few minutes ago using a RSP2Pro using SDR Console and a
CX-333 antenna at just 20ft or so. I have the gain on the RSP2 very low as
to rule out any overloading. The beacon you are hearing is W3CCX/b on
144.300 MHz. The carriers are not modulated and are there 24/7. They are
118.5 kHz apart. I also see it on the IC-9700 with a DCI-146-4H bandpass
filter so I don't think it's some mixing product caused by a strong out of
band signal.
73,
--Alex KR1ST
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