Agreed, David (K1TTT) - the step frequency variation could
readily be due to the FFT computation interval while the
frequency wobble of the spectral lines occurs continuously
because of drift in the source.
Given that Alex hears this set of roughly uniformly spaced
'carriers' on 50 MHz, 144 MHz, and 220 MHz, one would
expect that direct harmonics of any switch-mode electronics
with a fundamental switching frequency around 100 kHz
would have fallen off in amplitude long before reaching VHF.
How is this line spectrum appearing in multiple widely
spaced bands?
The RSP2Pro presumably generates I/Q samples after
digital down-conversion at a clock rate sufficient for the
frequency span being monitored. I was wondering if
the I/Q data is directly tainted by switch-mode converter noise
and thus appears present in multiple VHF bands? However, Alex
reported hearing the same noise and seeing similar 2 meter
spectra on his IC-9700, which conflicts with that hypothesis.
Still a fun puzzle, and I second Jim's (K9YC) request for audio samples of
the band around one or more of those wobbly spectral lines.
73,
Mike, K8CN
________________________________
From: RFI <rfi-bounces+mike.carter=unh.edu@contesting.com> on behalf of
k1ttt.dave@gmail.com <k1ttt.dave@gmail.com>
Sent: Monday, December 19, 2022 4:04 PM
To: alex@kr1st.com <alex@kr1st.com>; rfi@contesting.com <rfi@contesting.com>
Subject: Re: [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.
Signals like that which move up and down are generally something like
harmonics of switching power supply or variable speed motor or some other
non locked frequency digital system, that is, something that doesn't rely on
a specific clock frequency like computers, tv's, modems, ethernet, etc
require. Power supplies drift with temperature, line voltage, or load. The
step functions you see may be because the sdr only processes the spectrum a
few times a second so they appear to stay the same for a short time then
jump a bit as the next set of samples is plotted and the signal has moved
into the next fft column range.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web:
https://nam12.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwiki.k1ttt.net%2F&data=05%7C01%7Cmike.carter%40unh.edu%7C515021a1b3e540655d0908dae204b948%7Cd6241893512d46dc8d2bbe47e25f5666%7C0%7C0%7C638070807160922056%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=5nVF1RrFflx5uKhmVAC3dEa6XHoXH2dZnJ55tdAKV3E%3D&reserved=0
AR-Cluster node: telnet://k1ttt.net:7373
-----Original Message-----
From: RFI <rfi-bounces+k1ttt=arrl.net@contesting.com> On Behalf Of
alex@kr1st.com
Sent: Monday, December 19, 2022 14:57
To: rfi@contesting.com
Subject: [RFI] Dancing Carriers
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%7C515021a1b3e540655d0908dae204b948%7Cd6241893512d46dc8d2bbe47e25f5666%7C0%7C0%7C638070807160922056%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=Qb4CnEM%2F%2BEqJdbCL2ews866Bf6YL3zMyk99uU1i5O0Q%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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