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Author Topic: 27 MHz ISM Fish Hook Swisher Interference RFI EMI RF HF Sealers Heaters Welders  (Read 623 times)

Offline Exo

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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.

Some possible speculation for the prevalence of ISM fish hook swishers below the 27 MHz ISM and CB bands:

1. Natural downward frequency drift of the ISM work head resonant L-C tank when in use.

2. Initial calibration at 27.12 MHz is done with the heating work head in free air, rather than in contact with the dielectric work piece, which increases capacitance and causes resonant frequency to shift lower.

3. Factory calibrators may intentionally tune each ISM device toward the low end of the ISM band ~26.96 MHz (rather than 27.12 MHz center) to avoid the wrath of:
_ a. Amateur radio 28 MHz fox hunt vigilantes, frequency cops, or intruder monitors.
_ b. CB radio operators who might get angry.

4. After the ISM device is purchased and goes into service, it is probably never frequency calibrated again because nobody cares.
« Last Edit: June 14, 2019, 2043 UTC by Exo »
Exo
HF aficionado. On the coast of northern California.
Various receivers, transceivers, and broadband antennas.
kiwiSDR receiver on private LAN for multi-freq HF monitoring.

Online Josh

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Also wouldn't be surprised to find the maintenance crew left rf enclosures off as well.
Conveniently located near Vincennes Indiana.

Offline R4002

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Some possible speculation for the prevalence of ISM fish hook swishers below the 27 MHz ISM and CB bands:

1. Natural downward frequency drift of the ISM work head resonant L-C tank when in use.

2. Initial calibration at 27.12 MHz is done with the heating work head in free air, rather than in contact with the dielectric work piece, which increases capacitance and causes resonant frequency to shift lower.

3. Factory calibrators may intentionally tune each ISM device toward the low end of the ISM band ~26.96 MHz (rather than 27.12 MHz center) to avoid the wrath of:
_ a. Amateur radio 28 MHz fox hunt vigilantes, frequency cops, or intruder monitors.
_ b. CB radio operators who might get angry.

4. After the ISM device is purchased and goes into service, it is probably never frequency calibrated again because nobody cares.

Also wouldn't be surprised to find the maintenance crew left rf enclosures off as well.

Probably a combination of all of the above.  The lower end of the ISM band is 26.957 MHz, the swishers I saw during that band opening (and in band openings since) have gone down to closer to 26.5 MHz or even lower.  There are certainly some that are also active above channel 40, which is even further away from the legal ISM band.  I imagine you're both right about the heaters never being RF calibrated after they leave the factory (and maybe when they're installed) and metal RF enclosures left off, or installed incorrectly, etc. 

If there's one thing we need, its more RF signals in the 26-30 MHz range.  :D
U.S. East Coast, various HF/VHF/UHF radios/scanners/receivers

Offline Leonard

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Driving home last evening I have my radio set to 27.385 and as usual there is no activity, so I leave it at low volume. Just before 6:00 Los Angeles time, the swisher sound was so clear and very loud. I only heard one, it sounded like a local signal but chances are it came from some distance.

Offline Exo

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Driving home last evening I have my radio set to 27.385 and as usual there is no activity, so I leave it at low volume. Just before 6:00 Los Angeles time, the swisher sound was so clear and very loud. I only heard one, it sounded like a local signal but chances are it came from some distance.

That ISM you heard could have been anywhere within a 2000 km radius, since it was probably via "short skip".
Put a pin at your location and draw a 3500 km diameter circle around it.
The location of that ISM was probably on that line.
It's amazing how strong short skip can be, almost as if it is being amplified.
There's been a whole lot of short skip (Es) lately around California, the west coast, and around the rockies.
« Last Edit: July 11, 2019, 0907 UTC by Exo »
Exo
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Various receivers, transceivers, and broadband antennas.
kiwiSDR receiver on private LAN for multi-freq HF monitoring.

Offline Exo

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It is no wonder that these ISM signals can be propagated to very far distances.
The governmental regulations for these transmitting devices are very loose, allowing high power levels and high radiated signal strength.

For example, here are some of the US federal ISM transmitter regulations from about 10 years ago, at a time when many of the ISM devices presently in use were designed [emphasis added].

  • Operation on Particular Frequencies Designated for ISM Equipment

    The following frequencies are designated for use by ISM equipment, the emissions of which shall be confined within the frequency limits associated with each frequency:

    6780 kHz 15.0 kHz
    13560 kHz 17.0 kHz
    27120 kHz 163.0 kHz
    40.68 MHz 20.0 kHz
    915 MHz 13.0 MHz
    2450 MHz 50.0 MHz
    5800 MHz 75.0 MHz
    24.125 GHz 125.0 MHz
    61.25 GHz 250.0 MHz
    122.5 GHz 500.0 MHz
    245 GHz 1.0 GHz

    In the event harmful interference is caused by ISM operation to any authorized radio service outside the frequency limits specified,
    the operator of the ISM equipment shall promptly take necessary steps to eliminate such interference,
    except in those cases where the interference is due to direct intermediate frequency pickup by a receiver of the fundamental frequency emissions of ISM equipment operating on an ISM frequency, and the operator otherwise complies with this section.

    ISM equipment, other than industrial heating equipment, that is operated on the frequencies 915, 2450, 5800 MHz, and 24.125 GHz, is subject to the following conditions:
    1. The energy radiated and the bandwidth of emission shall be reduced to the maximum extent practicable.
    2. In the event harmful interference is caused to authorized radio services from spurious or harmonic radiation from ISM equipment, the operation of the ISM equipment shall be discontinued until necessary measures have been taken to eliminate such interference.

    Medical diathermy equipment may be operated on the designated ISM frequencies without regard to the type or power of emissions being radiated, except as specified above. However, any harmonic or other spurious radiation outside the frequency limits specified in this section shall be suppressed so as not to exceed a strength of 25 uV/m at a distance of 300 meters.
    Measurements to determine field intensity shall be made in accordance with standard engineering procedures.

    Industrial heating equipment and RF stabilized arc welders may be operated with unlimited radiation on any designated ISM frequency, but shall be adjusted to operate as close to that ISM frequency as practicable. Filtering between the industrial heating equipment and power lines must be provided to the extent necessary to prevent the radiation of energy from power lines on frequencies other than those designated for ISM, with a field strength in excess of 10 uV/m at a distance of 1600 meters from the industrial heating equipment, and at a distance of 15 meters from the power line.

    Miscellaneous ISM equipment may be operated on the designated ISM frequencies without regard to the type or power of emissions being radiated, provided any harmonic or other spurious radiation outside the frequency limits specified in this section is suppressed so as to not exceed:
    25 uV/m at a distance of 300 meters or,
    for equipment generating more than 500 watts of RF power on the fundamental frequency,
    25 uV/m times the square root of P/500 (where P is the actual RF power generated),
    but not to exceed 10 uV/m at 1600 meters,
    provided this increase is not permitted for equipment located in a predominantly residential area and operating on a frequency below 1000 MHz.

    Operation on Frequencies Other than Those Designated for ISM Equipment
    Operation of ISM equipment within the following safety, search and rescue frequency bands is prohibited: 490-510 kHz, 2170-2194 kHz, 8354-8374 kHz, 121.4-121.6 MHz, 156.7-156.9 MHz, and
    242.8-243.2 MHz.

    In the event harmful interference is caused to any authorized radio service outside the frequency limits specified in previous Section, by ISM operation conducted pursuant to this section, the operator of the ISM equipment shall promptly take the necessary steps to eliminate the interference.

    Medical diathermy equipment shall be provided with a rectified and filtered plate power supply, powerline filters, and shall be constructed so that any radiated radio frequency energy (including harmonic or other spurious emissions) on a frequency outside the frequency limits specified in the previous Section does not exceed a strength of 15 V/m at a distance of 300 meters.

    Measurements to determine field intensity shall be made in accordance with standard engineering procedures.

    Industrial heating equipment and RF stabilized arc welders may be operated provided all of the following conditions are met:

    1. Radiation on the fundamental carrier frequency, as well as spurious and harmonic radiations resulting from any source frequency, and falling outside the frequency limits specified in the previous Section, shall be suppressed so that:

    a) below 5725 MHz the field strength does not exceed 10 V/m at a distance of 1600 meters and;

    b) above 5725 MHz it is reduced to the greatest extent practicable.

    2. Filtering between the industrial heating equipment and power lines shall be provided to the extent necessary to prevent the radiation of energy from power lines on frequencies other than the designated ISM frequencies, with a field strength in excess of 10 V/m at a distance of 1600 meters from the industrial heating equipment and at a distance of 15 meters from the power line.

    Miscellaneous ISM equipment may be operated on frequencies other than those designated for ISM equipment provided all of the following conditions are met:

    1. The equipment shall be provided with a rectified and filtered plate power supply and power line filters.

    2. Any radiated radio frequency energy outside the frequency limits specified in previous Section (including harmonic or other spurious emissions) shall not exceed:
    15 V/m at a distance of 300 meters; or, for equipment generating more than 500 watts of RF power on the fundamental frequency, 15 uV/m times the square root of P/500 (where P is the actual RF power generated), but not to exceed 10 V/m at 1600 meters, provided this increase is not permitted for equipment located in a predominantly residential area and operating on a frequency below 1000 MHz.

    Operation of ultrasonic equipment shall not result in radiation exceeding the following limits:

    1. Below 490 kHz
    2400 V/m at 300 meters/Frequency (in kHz)

    Between 490 and 1600 kHz
    24000 V/m at 30 meters/Frequency (in kHz)

    Over 1600 kHz (excluding frequencies within the limits specified in previous Section)
    15 V/m at 30 meters

    2. For equipment operating below 490 kHz and generating more than 500 watts of RF power on the fundamental frequency.
    2400 V/m at 300 meters Frequency (in kHz) times the square root of P/500 (where P is the actual RF power generated), but not to exceed 10 V/m at 1600 meters, provided this increase is not permitted for equipment located in a predominantly residential area.

    3. On any frequency 490 kHz and above, the radio frequency voltage appearing on each power line shall not exceed 200 V; below 490 kHz it shall not exceed 1000 V.
Exo
HF aficionado. On the coast of northern California.
Various receivers, transceivers, and broadband antennas.
kiwiSDR receiver on private LAN for multi-freq HF monitoring.

Offline R4002

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As close to frequency as practicable

So basically, these aren't rules, they're more like guidelines.

U.S. East Coast, various HF/VHF/UHF radios/scanners/receivers