27 MHz ISM Fish Hook Swisher Interference RFI EMI RF HF Sealers Heaters Welders

[Exo]

27 MHz ISM Fish Hook Swisher Interference RFI EMI RF HF Sealers Heaters Welders Worldwide 11 Meter Band



Strong ISM type signals with a fish hook signature on the waterfall spectrum are observed worldwide in the 25 MHz to 27 MHz range.

Fish hook swisher signals may originate from poorly shielded ISM devices.

The industrial, scientific, medical (ISM) band at 26.957 MHz to 27.283 MHz overlaps the 27 MHz CB band.

Many types of industrial RF plasma devices, such as RF welding, plasma chamber deposition, plasma torch, plastic sealing or welding, or RF cutting machines use 27 MHz.

Other types of RF ISM type equipment, power RF devices, or RFID equipment may also be a source of signals with a similar spectrum signature.

The frequency accuracy of ISM devices may vary widely, and some ISM signals have been monitored operating 1.5 MHz or more out-of-band.

This category of EMI, EMC, or RFI  (ElectroMagnetic Interference, ElectroMagnetic Compatibility, Radio Frequency Interference) is heard intermittently and commonly by CB radio users, and sounds similar to a VFO knob being turned as the transmitter is swished across the band.
The sounds are often described as: "swishing, swisher, spinner, swish, slider, slide, sweep, whoosh, wind, howling, whoop, razzer, whooping".
They can often be much stronger than 11 meter CB radio signals.

Duration of the fish hook swisher signals is approximately 2 seconds to 20 seconds, with most of them averaging around 5 seconds long.

The initial frequency typically sweeps abruptly downward about 30 kHz to 50 kHz, then ends the sweep with a slower frequency change, or a stable frequency, which gives it the distinctive fish hook signature on the spectrum waterfall.

Some fish hook swishers have also been observed with upward frequency sweep, but they are not as common.
Some fish hook swisher signals have been observed having as much as a 400 kHz total sweep range.
Modulated tones, digital dithered, unmodulated carriers, and noisy carriers have all been monitored.

This report includes detailed monitoring of some fish hook swisher signals which were monitored during a very strong Sporadic E (Es) propagation opening which widely covered western USA in mid-2019.
These are not local signals near the receiver, such as switching power supply, computers, or lights.
The signals shown in this report are being transmitted by ISM sources 250 miles to 1200 miles away (400 km to 2000 km).

Report 2019JUN03 1800UTC
ID: various ISM signals, unidentified.
Frequency: 26 MHz to 27.8 MHz.
Signal levels: various, ranging from -130dBm to -70dBm

PLAY AUDIO 27 MHz Fish Hook Swishers compilation recorded in IQ mode at 12 kHz total bandwidth on 2019 June 03 EMI RFI


Spectrum waterfall images showing ISM RFI fish hook swishers in the 27 MHz range:















End of report.

[ChrisSmolinski]

Looks like the "Sliders" we talked about a few years ago? https://www.hfunderground.com/board/index.php/topic,12565.0.html

I still notice them from time to time, mostly on the higher frequencies, very rarely on the lower bands.

[Exo]

Looks like the "Sliders" we talked about a few years ago? https://www.hfunderground.com/board/index.php/topic,12565.0.html

I still notice them from time to time, mostly on the higher frequencies, very rarely on the lower bands.

Yes, many of the same waterfall signatures shown here were also shown by the OP in that thread
There were several different types of other RFI source signals discussed in that thread.
These signals have been around for many years, but recently they have increased dramatically, especially in Asia.

Let's talk about the source of these signals.
There seems to be a design trend in the source equipment, toward targeting the HF ISM bands, such as 13 MHz and 27 MHz.
But, for the RF industrial devices which need to be designed around a lower fundamental work frequency such as 2 MHz or 10 MHz, they can produce very strong harmonics up the spectrum.
While the lower frequency fundamental power may be suppressed and only propagate locally, the higher harmonics are more difficult to shield and can propagate via the ionosphere, to be monitored thousands of miles away.

The proliferation of low cost RF sealing machines for use in consumer product packaging materials can explain the worldwide rise of widespread RFI from these devices.

Estimated by the signal strength compared to similarly located CB radio signals, some of the industrial RF power devices appear to be transmitting 10 Watts to 500 Watts ERP (Effective Radiated Power) into the air.

RF sealing is utilized to make many types of items, the most common is "blister pack" or "clam shell" product packaging and medical disposables.
RF welding is utilized for all types of materials, mostly metal, polymers, or plastics.
RF cutting is utilized for metal or plastic.
RF plasma cutters are common in metal machining and processes.
RF heating, laminating, embossing, and curing for wood and wood glue is common.

Conjecture about the source devices of the signals:
The frequency determining system is not precisely fixed.
In some types of RF power industrial units it is comprised of an inductance coil or capacitance in the cutting/sealing work head which combines with a variable or fixed compensation capacitor or tank coil for tuning them to self-resonance in the power transmitting circuit.
Also, the frequency needs to follow the self-resonance of the work head, in order to be power efficient and effective.
In other types of digital frequency-determining circuits, there needs to be a phase feedback sensor which tracks the work head self-resonance to the generator frequency.
Basically, it is an L-C power oscillator.
Power levels: hundreds of watts up to multiple kilowatts of RF.
The support structure and cable wiring from the RF power generator to the work head forms an unintended antenna which can radiate quite well.

When transmit power is initiated in bursts, either through the operator's foot switch pulser or the automated pulse timer, the inductor or capacitor in the work head heats up or temporarily changes shape. 
As the welder/sealer/cutter task is processed, the thickness and capacitance in the dielectric material between the work head and the grounded work surface changes.
This causes the self-resonant frequency to drift or sweep momentarily.
It cools back down again as the next work item or work spot is put into place under the head.
The process repeats.



In automated factories, the pulse bursts can be at very regularly repeated intervals.
In human operated machines or hand-held machines, it is more random.
The duration for RF sealing machines ranges from 2 or 3 seconds for plastic items, to about 30 seconds for wood.
Continuous duration or multi-minute duration is utilized for metal or plastic pipe sealing machines.

Listening to some of the remote receivers located near industrial zones of the world (US, Asia, Europe), it is easy to see the fish hook swishers starting up in the work day morning and ending later in the evening, often with dormant activity on Sunday.

RF 75 kilowatt HF welding machine:


Videos of RF sealing machines in action:

https://youtu.be/OmcHcfkuS_8

https://youtu.be/kDubcBvzFxc

https://youtu.be/F1g-268m1f0

https://youtu.be/8aLAbRF8HGQ

https://youtu.be/_l1WRNOuL08

-
Basic information about how RF heaters and sealers work, and human RF exposure to the high fields produced by them (World Health Organization and International Labour Organization)

[ChrisSmolinski]

I am now (2120 UTC 4 Jun 2019) copying one on the 19 meter band, not sure if I have noticed one before on either 13560 or 27120 kHz, where they "should" be:



And some more higher up the band:



And more!

[ChrisSmolinski]

The 11m was open this morning, around 1150z I was hearing lots of stations from the midwest, such as the Chicago area. I noticed quite a few sliders:

[Exo]

I am now (2120 UTC 4 Jun 2019) copying one on the 19 meter band, not sure if I have noticed one before on either 13560 or 27120 kHz, where they "should" be:
-
And some more higher up the band:
-
And more!
-
The 11m was open this morning, around 1150z I was hearing lots of stations from the midwest, such as the Chicago area. I noticed quite a few sliders:

Those are excellent waterfall images of the 15 MHz fish hooks, Chris. 
The industrial RF processing machines are cluttering the entire HF spectrum, and extending up into low band VHF.

Judging by the number of CB AM carriers in that last image, that was quite an 11m opening you had to the midwest!

Today, in California, there was double-hop Sporadic E propagation which covered a lot of southern Canada, the midwest USA, and the Pacific Northwest.

During the unusual 27 MHz propagation, hundreds of fish hooks were seen on the waterfall.
Some of the longer duration ones, 20 to 30 seconds, may have been wood processing machines.

Video: How It's Made "Laminated Wood Beams" see the RF power wood glue curing machine at 1:50 in the video. "pressed between two plates" "about 20 seconds of heat cures the glue"
https://youtu.be/nU-2FiJVtC4?t=109

A few of the longer zig-zag drift patterns showed up on the waterfall today, probably RF wood processing machines:

[ChrisSmolinski]

Yes, it was a very good opening. Eventually we even got short skip, I heard stations from Buffalo and Massachusetts.  Now... the band is completely dead.

Based on the Wallops Island foF2 plots, looks like conditions were pretty good for a short time:

[R4002]

I wonder how many of these ISM users use the 40.680 MHz frequency vs. 13.56 MHz or 27.12 MHz.  I know these sporadic-E openings have included (sporadic) 6-meter/50 MHz band DX as well as 11-meter and 10-meter openings.  So perhaps 40 MHz (8 meters!) 40.66-40.70 MHz is another place to look for these ISM swooshers/swishers/heaters/fish hooks if/when the bands are open and 6 meters/VHF low band is active.

BTW, Exo and Chris, great waterfall images.  Always nice to see signals literally every 10 kHz from 26.7 MHz or so to 27.5 MHz or 27.6 MHz when the band is open enough for the ISM signals to be seen on the SDR waterfalls.

This is slightly off-topic but worthy of a mention as well:

Apparently the 40.66-40.70 MHz region is also used for R/C, datalink and remote control type purposes in Europe and elsewhere, much like the 26-27 MHz Part 95 R/C frequencies are used for datalink purposes in the USA (and everywhere else).  I know its a different part of the rules (ISM vs. Part 95) but the regulator agencies seem to have no problem with assigning these things to the same bands. 

Also, don't forget the US Government's SNOTEL snowfall/precipitation telemetry data link network on VHF low band 40.670 MHz.   https://wiki.radioreference.com/index.php/SNOTEL

I doubt they have issues with interference from ISM but when the band is open 40.67 MHz is quite lively. 

[Leonard]

That was great information. I have been hearing those sounds for years, I had recently posted a question on another forum, eham, about what those sounds could be. For me I hear them quite often although I only hear one cycle  5 to 15 minutes apart. After a while I began to think these sounds could be an indication of propagation.

[Exo]

I wonder how many of these ISM users use the 40.680 MHz frequency vs. 13.56 MHz or 27.12 MHz.  I know these sporadic-E openings have included (sporadic) 6-meter/50 MHz band DX as well as 11-meter and 10-meter openings.  So perhaps 40 MHz (8 meters!) 40.66-40.70 MHz is another place to look for these ISM swooshers/swishers/heaters/fish hooks if/when the bands are open and 6 meters/VHF low band is active.

BTW, Exo and Chris, great waterfall images.  Always nice to see signals literally every 10 kHz from 26.7 MHz or so to 27.5 MHz or 27.6 MHz when the band is open enough for the ISM signals to be seen on the SDR waterfalls.

You're right, R4002.
There are many ISMs on 40 MHz.

But, the big risk for the 40 MHz ISM transmitting equipment designers is the suppression of their 3rd harmonic, which falls right in the middle of the VHF aeronautical voice band!
ISM Band 40.680 MHz +/- 20 kHz = 40.66 MHz to 40.7 MHz band limits

40.660 MHz x 3 =121.980 MHz
40.680 MHz x 3 =122.040 MHz
40.700 MHz x 3 =122.100 MHz 

[Exo]

VIDEO 27 MHz hand operated wood welder



https://youtu.be/9bpX-qiELD4


VIDEO 27 MHz Wood Welder tank coil frequency adjustment.
"Making Turbo Encabulators since 1947"
"..it goes through a 13 foot coaxial cable.. " (1/2 wave at 27 MHz x 0.75 velocity factor for foam coax cable)




https://youtu.be/nFwGZhec3AI

[ChrisSmolinski]

High power RF generators, capable of lots of watts at 27 MHz, ending up on the surplus market. What could possibly go wrong? 

[Exo]

High power RF generators, capable of lots of watts at 27 MHz, ending up on the surplus market. What could possibly go wrong? 

Back in the 1960s, there were many surplussed 13 MHz medical diathermy units that got turned into 20 meter CW and AM amplifiers by hams.

27 MHz diathermy "therapy" units were also produced.

They required adding bigger capacitors in their power supplies, because the diathermy designers didn't care how much awful AC hum they were transmitting.

You can see plenty of power supply ripple in the fish hook signals of present-day industrial RF power devices, too.

The shortwave diathermy units started appearing at junk yards... after the medical establishment discovered... that purposely RF burning their patients to relax their muscles wasn't such a great idea after all 

These are known as quack machines now.

VIDEO: Old Spark Gap Shortwave Diathermy really lights you up



https://youtu.be/dez2UU3kUIc






This is reminiscent of the early "radium is good for you" craze.

Radium The Undark.



Radium Water. Yummm.



Radium lipstick, for glowing approval 

[R4002]

You're right, R4002.
There are many ISMs on 40 MHz.

But, the big risk for the 40 MHz ISM transmitting equipment designers is the suppression of their 3rd harmonic, which falls right in the middle of the VHF aeronautical voice band!
ISM Band 40.680 MHz +/- 20 kHz = 40.66 MHz to 40.7 MHz band limits

40.660 MHz x 3 =121.980 MHz
40.680 MHz x 3 =122.040 MHz
40.700 MHz x 3 =122.100 MHz 

Very true.  Interference on the VHF airband is bad news.  Having said that, the 11 meter CB band produces harmonics on the VHF aeronautical band too (albeit at the 4th and 5th harmonics, not the 3rd harmonic for 40 MHz ISM).  CB channel 2, for example at 26.975 MHz, 4th harmonic is right on 107.900 MHz (at the very top end of the FM broadcast band, another bad place to cause QRM), 5th harmonic is on 134.875 MHz, in the voice (comm) portion of the airband. 

CB channel 6 (everyone's favorite unfiltered splatterbox amplifier producing all the harmonics/spurs channel) 27.025 MHz 4th harmonic is 108.100 MHz (in the nav portion of the airband) and 5th harmonic is on 135.125 MHz, also in the voice (comm) portion of the airband.  I'm sure ISM devices are filtered enough to not really have to worry about 4th/5th harmonics, but CB equipment is another story.  Some of the amplifiers used by guys on 27.025 MHz and other 11m frequencies have no harmonic filtering whatsoever and the possibility of throwing a several-watt signal on an aircraft frequency is very real. 

I suppose the potential interference on the 3rd harmonic as well as interference considerations for the 40.67 MHz SNOTEL system and military/government users in the United States (the military and some agencies of the US government - see here: https://wiki.radioreference.com/index.php/Tennessee_Valley_Authority#Transmission_and_Customer_Service_.28TCS.29 makes heavy use of the 40-42 MHz band) means 40.68 MHz ISM isn't as popular as 13.56 MHz ISM or 27.12 MHz ISM. 

Hmmm...diathermy equipment.  I remember reading somewhere about the origins of the CB service in the United States back in the 1950s and an issue with QRM from short wave diathermy machines on the original 23 channel CB allocation.

Also note:

https://www.hfunderground.com/wiki/Remote_Control#United_Kingdom

The use of the 26 MHz, 27 MHz, 34 MHz, 35 MHz and 40 MHz bands (40 MHz R/C band in the UK goes from 40.665 MHz to 40.995 MHz in 10 kHz steps, despite the 40 MHz band being an EU-standardized FM military band). 

[R4002]

Noticing a large number of swooshes on the lower freeband frequencies - roughly 26.500 MHz to 26.900 MHz, with some in-band as well.  All 40 CB channels are busy at 1613 UTC.