[Elecraft] Origin of Signal-Fine Structures in SSB Pass Band Waterfall, mainly 80/40m
Dave New, N8SBE
n8sbe at densbe.com
Sun Jan 7 13:42:43 EST 2024
Andy,
You may wish to subscribe to this Google group:
hamsci at googlegroups.com
and pose your questions there. There are a lot of folks on that list
that are interested in scientific investigations into radio propagation
anomalies.
73,
-- Dave, N8SBE
On 2024-01-06 14:29, Andy via Elecraft wrote:
> 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-bounces at mailman.qth.net
> <elecraft-bounces at mailman.qth.net> On Behalf Of Chris
> Sent: Saturday, January 6, 2024 6:54 PM
> To: elecraft at 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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