Hi Chris,
Many thanks for your interesting EMI focused response.
I had already some experts indicating this possibility of potential EMI
origin....but no...
Yes, I agree EMI is a tricky issue as per
standards/regulations/politics/ and technology.
In some areas it is not main stream interest of some industries to
avoid disturbance/interference in HF.-Spectrum.
I am an EMC professional since 40 years..
EMI/RFI/EMC I can rule out because:
1.) The effect was also seen recently by a German HAM in a very quiet
QTH
2.) I checked the radios (all RX ok on Dummy Load),. The effect it is
not only visible on K3S P3 , but also on FTDX101MP, and direct front
end sampling SDR RX Perseus.
3.) I took my mobile HF car setup and operated RX from separated
battery, in very quiet location , and I could once see this propagation
effect.
So the propagation questions remain.
Questions:
1. Is this an indication of Multi-Path Reception? May be with different
propagation modes at that time over certain distances possible?
2. Is this therefore, e.g., based on delay times (phase/arrival time
differences) of reflections from different ionospheric layers ( e.g.
f1, f2 etc.) ?
3. Is this based on quasi simultaneous occurrences of skywave, NVIS and
may be even groundwave mode ?
4.) I observed this “ shift effect” also sometimes for OTH-Radar (real
or faked, yes some are faked, see my qrz.com under DQRM) signals
recently on 40m, in EU late afternoon , night time here.
Tnx, Cu, vy 73 de Andy
HB9CVQ, DK2VQ, AK4IG
https://www.qrz.com/db/HB9CVQ
-----Original Message-----
From: elecraft-boun...@mailman.qth.net
<elecraft-boun...@mailman.qth.net> On Behalf Of Chris
Sent: Saturday, January 6, 2024 6:54 PM
To: elecraft@mailman.qth.net
Subject: Re: [Elecraft] Origin of Signal-Fine Structures in SSB Pass
Band Waterfall, mainly 80/40m
Hello Andy:
I will offer some experience and opinion....
Your note implies that the interference is coming from the ionosphere,
and you may be correct, but it is also worth considering that you may
be looking at digital-based interference from local devices (in
addition to possible distant signals coming from afar).
Digital signals (square waves, waveforms with sharp edges) have very
high spectral content (_many_ harmonics), so you may see many lines at
constant frequency spacing all over the HF spectrum and beyond.
Switching power supplies (inside electronic devices, wall-warts, etc),
and digital signals from monitors, computers, routers, coffee makers,
washing machines, (seems everything that plugs in these days has
microprocessors), LED lighting, etc. can all cause interference like
this.
These sources may also shift or drift (slowly shift) due to changes in
temperature or operating (power supply/load) conditions in the digital
devices.
In my experience the root causes of this kind of RFI are usually the
digital devices, and possibly poor design for attenuation of the
harmonics resulting from the oscillators generating the broadband
interference lines. Not all oscillators are crystal based BTW, so they
may have significant change in frequency over short or longer time
spans. L-C and R-C circuits are just drifty.
BTW, I would also try to see if the lines are from within the radio.
Put the radio on a dummy load and look at the spectrum. If it is clean,
then you can probably eliminate the problem as being internal (either
hardware or signal processing software). Knowing Elecraft, I suspect
that the problem will NOT be inside the radio, but it is a place to
start.
The solution to external RFI _should _be in the design phase of these
devices. Design should include "right at the source" shielding of high
frequency oscillators, power supplies and digital circuits which should
use circuit layout which shields clock and data circuits with ground
lines right in the PC board. If you let the signals escape the board,
you now have to add ferrites and shielding on the wires leading to
peripheral devices. It is far better to prevent the emissions at the
source. But it seems to be cheaper to some manufacturers to ignore the
problems and trust that your RFI generating device will escape scrutiny
of regulators.
Devices using high frequency signals are required by the FCC to be
inspected and to have limits on their emissions. In practice it seems
many devices, perhaps especially from overseas, have somehow eluded
these certifications and can become real "firestorms" of RFI. Here in
Colorado we have experience with grow-light power supplies that have
strong emissions for miles around some "greenhouses" nearly wiping out
the HF spectrum. In my own home, when I had ADSL/VDSL internet-phone
service, I was able to show service technician the spectrum emitted by
his cable coming into the house. He confirmed that those are the
frequencies his equipment used, and when I pointed out that those
signals become interference if they do not _stay_ inside his cable, he
replaced the feed cable from the pedestal to my house.
This should be of special interest to hams, who are still attempting to
communicate using the HF spectrum, though the emissions can still be
strong way up into VHF and even UHF bands. A local parking lot with
solar-powered lighting generates signals every 15 KHz right up to high
VHF. I suspect that the solar panels use MPPT switching chargers to
power their batteries.
Perhaps clubs should consider forming RFI committees to investigate
this interference and try to identify sources, maybe even by
manufacturer/model number. It is difficult to know when a device
exceeds the FCC limits for emission without a measurement lab. Maybe
the effort would include getting the ARRL to either build such a lab or
fund tests on apparently noisy consumer devices (?).
This has been a slowly growing problem for decades now, and in suburban
areas HF spectrum can become almost unusable, with so many houses with
computers, TVs, video cameras, and appliances emitting at low levels
and adding up to make noise well over S9 at locations of which I am
aware.
No wonder so many hams are using remote stations - perhaps their home
stations are almost unusable due to RFI.
To troubleshoot, I would recommend powering your radio on a battery and
then turning off all house power and looking again at the spectrum. If
it has significantly reduced interference, that source is in the house,
and if _not_ reduced, it is external (neighborhood or atmospheric).
Troubleshoot the house by turning on rooms one at a time to see where
it is coming from. Then plug/unplug devices one at a time to see if you
can find a single device as a major contributor. If you do this, be
aware that some appliances, notably refrigerators and A/C units may
need to be off for a minute or two to allow the pressurized system to
relax before power is again applied. Also note that some digital
devices like internet routers may take 2 minutes or so to become fully
operational after power is again applied.
RFI is a difficult problem to diagnose, and it seems to me that it is
receiving very little attention from regulators. Cheap appliances are
popular and convenient but some may have bad effects on our spectrum.
Cutting corners in design affects spectrum users, and having dozens of
devices in every home adds up...
73,
Chris K0PF
On 1/6/2024 6:33 AM, Andy via Elecraft wrote:
I have a general question to better understand analysis of SSB ( RX
Pass
Band) signals displayed as waterfall, mainly on RX of night
time/evening low bands (80m/40m) propagation.
(Sorry up to now no waterfall screenshots available yet. Anomality is
only sometimes occurring, but not very short lived.
Waterfall:
The horizontal axis is frequency , the vertical axis is time and the
brightness corresponds to signal amplitude received via any
propagation mode (Skywave/NVIS/Groundwave, or mixtures)
Modulation/ splatter become visible.
The propagation effect I try to understand does not always occur.
It is a "specially (modulated) signal pattern" , a vertical waterfall
signal fine structure with periodic signal amplitude (brightness)
minima and maxima lines.
These lines are sometimes in SSB just straight down vertically with
ca. 300 to ca. 400 Hz intervals (6 periods) .
Digital signals seem to have more lines in RX Pass Band on the
waterfall.
Sometimes in the RX Pass Band these minima/maxima (QSB) lines are
shifted right ( QRG >)
Or at later observation times also may be left shifted (QRG<).
I can rule out EMI of broad/narrow band nature. It must be due to
propagation of the very observed signal
Sometimes signature appears as " distributed cloud islands" in the
vertical SSB PB waterfall band
I observe for TX SSB Mode (e.g., 2.7kHz BW) in the RX waterfall
display :
1. About 6 Periodic, straight vertical lines (periodic signal
amplitude
minima, which are darker), --normal propagation
2. About 6 Periodic, right shifted ( staring low f to higher f)
vertical lines (signal amplitude minima) , --special propagation mode?
3. About 6 Periodic right shifted ( staring high f to lower f)
vertical
lines (signal amplitude minima) , -- special propagation mode?
4. The angle to the vertical axis seems to change often over time.
Probably according to HF Condx/Propagation?
5. It seems to be independent of TX LSB or USB mode.
6. Digital signals have often more vertical lines
7. The angle to the vertical axis seems to change often over time,
according to HF Condx/Propagation.
8. I have observed this effect also on day on 80m night time on a KIWI
SDR only 12km away in hilly HB9 ( combination of NVIS/ groundwave?)
Questions:
1. Is this an indication of Multi-Path Reception? May be with
different
propagation modes at that time over certain distances possible?
2. Is this therefore, e.g., based on delay times (phase/arrival time
differences) of reflections from different ionospheric layers ( e.g.
f1, f2
etc.) ?
3. Is this based on quasi simultaneous occurrences of skywave, NVIS
and
may be even groundwave mode ?
Any comments or reporting of similar observations are greatly
appreciated.
PS:
I observed this " shift effect" also sometimes for OTH-Radar (real or
faked, yes some are faked, see my qrz.com under DQRM) signals recently
on 40m, in EU late afternoon , night time here.
Tnx, Cu, vy 73 de Andy
HB9CVQ, DK2VQ, AK4IG
<https://www.qrz.com/db/HB9CVQ> https://www.qrz.com/db/HB9CVQ
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