[RFI] Dancing Carriers

Tue Dec 20 07:24:00 EST 2022

Switchers generally exhibit a few characteristics:

o  They are generally somewhat unstable, with their free-running frequencies changing with temperature, load and supply voltage.
o They typically generate buzzy carriers ever N kHz, with N being the free-running frequency
o With that, they generally drift up or down when they are first turned on.
o They usually exhibit short-term frequency variation when there is a momentary power fluctuation
o They usually have a noticeable to very strong 60- or 120-Hz component (50- or 100-Hz in some countries).

It seems natural to ask, "What is it?,"  when looking for a device, but for many reasons, that is often the wrong question.

See this article I wrote to explain why:

http://www.arrl.org/files/file/RFI/WHAT%20IS%20IT.pdf

WHAT IS IT? By Ed Hare, W1RFI - American Radio Relay League<http://www.arrl.org/files/file/RFI/WHAT%20IS%20IT.pdf>
always drift. Stay parked on the frequency for a while, and keep listening. Switchers almost always exhibit little changes in frequency as voltage dips and surges occur,
www.arrl.org

________________________________
From: RFI <rfi-bounces+w1rfi=arrl.org at contesting.com> on behalf of alex at kr1st.com <alex at kr1st.com>
Sent: Monday, December 19, 2022 10:00 PM
To: rfi at contesting.com <rfi at contesting.com>
Subject: Re: [RFI] Dancing Carriers

Thanks everyone for taking an interest!

I know what a SMPS sounds and looks like. In fact, I have one in the shack
that I can hear if I take the common mode chokes off it. It will wander up
and down the bottom portion of 2 meters, where most of my interest is on
that band.

The carriers in the video sound just like that, carriers. There is no
detectable modulation on them. They just like a tone with no noise
whatsoever. I will make a recording of this.

At this time carriers have morphed into signals like that of a stuck keyer:

https://youtu.be/3o_cBp_YfpQ

The signals are 175 kHz apart. If I zoom in on one of those carries on 6m I
see there are two pulses. A second one is present at half the frequency
interval 50 Hz than the first pulse:

https://youtu.be/asuJHFRXBxQ

I'm starting to think it's some sort of sensing circuit causing this. I've
seen something similar to this latest recording many years ago when I lived
in SC. I noticed a similar signal that was caused by the sensing circuit of
an electric blanket a neighbor just purchased. The power supply would
continuously send pulses through the wiring of the blanket in order to
detect if a person was present. If it detected a person it would turn on the
power supply. I forgot what happened to the signal when the power supply
turned on. I wonder if I have a recording from back then (15 or so years
ago). I seem to remember it was on 10 meters, but maybe it was 2 meters
also. That signal was way more invasive though and made the band pretty much
unusable. Now the lady using it had cancer and the blanket offered pain
relief, so I wasn't going to suggest not to use the blanket of course. She
did contact the manufacturer on her own accord, however, and got a new power
supply that solved the problem.

The signal does seem to come from the direction of a neighbor's house, but
my 10 element 222 beam indicates a 30 degree different heading than the 9
element 2m beam. I will see if I can find some correlation with time of day,
etc. I'm fixing my mobile installation and will drive around and see what I
find.

Thanks for your help and suggestions!

73,

--Alex KR1ST

From: Michael Carter <Mike.Carter at unh.edu>
Sent: Monday, December 19, 2022 8:18 PM
To: rfi at contesting.com
Cc: alex at kr1st.com; k1ttt at arrl.net
Subject: Re: [RFI] Dancing Carriers

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 at contesting.com
<mailto:rfi-bounces+mike.carter=unh.edu at contesting.com> > on behalf of
k1ttt.dave at gmail.com <mailto:k1ttt.dave at gmail.com>  <k1ttt.dave at gmail.com
<mailto:k1ttt.dave at gmail.com> >
Sent: Monday, December 19, 2022 4:04 PM
To: alex at kr1st.com <mailto:alex at kr1st.com>  <alex at kr1st.com
<mailto:alex at kr1st.com> >; rfi at contesting.com <mailto:rfi at contesting.com>
<rfi at contesting.com <mailto:rfi at 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 at arrl.net
web:
https://nam12.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwiki.k1ttt.
net%2F
<https://nam12.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwiki.k1ttt
.net%2F&data=05%7C01%7Cmike.carter%40unh.edu%7C515021a1b3e540655d0908dae204b
948%7Cd6241893512d46dc8d2bbe47e25f5666%7C0%7C0%7C638070807160922056%7CUnknow
n%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6
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reserved=0>
&data=05%7C01%7Cmike.carter%40unh.edu%7C515021a1b3e540655d0908dae204b948%7Cd
6241893512d46dc8d2bbe47e25f5666%7C0%7C0%7C638070807160922056%7CUnknown%7CTWF
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d=0
AR-Cluster node: telnet://k1ttt.net:7373

-----Original Message-----
From: RFI <rfi-bounces+k1ttt=arrl.net at contesting.com
<mailto:rfi-bounces+k1ttt=arrl.net at contesting.com> > On Behalf Of
alex at kr1st.com <mailto:alex at kr1st.com>
Sent: Monday, December 19, 2022 14:57
To: rfi at contesting.com <mailto:rfi at 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%2
FgKA0P2c-034
<https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fyoutu.be%
2FgKA0P2c-034&data=05%7C01%7Cmike.carter%40unh.edu%7C515021a1b3e540655d0908d
ae204b948%7Cd6241893512d46dc8d2bbe47e25f5666%7C0%7C0%7C638070807160922056%7C
Unknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLC
JXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=Qb4CnEM%2F%2BEqJdbCL2ews866Bf6YL3zMyk99uU
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erved=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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