5 ms·

The international allocation of 2.4GHz spectrum for microwaves happened at lobbying of USA, but is global - and exists in order for airplane galleys to be equip

by p_l 3y ago

The international allocation of 2.4GHz spectrum for microwaves happened at lobbying of USA, but is global - and exists in order for airplane galleys to be equipped with microwave heaters and be allowed to travel internationally.

ThePowerOfFuet 3y ago
Are they actually microwave instead of convection?
- p_l 3y ago
  Depends on equipment of the plane - the original reasoning for making 2.4GHz the international dumpster spectrum was to install microwaves
  - jbverschoor 3y ago
    But we need to switch off WiFi and Bluetooth
    - p_l 3y ago
      That's because the equipment installed in the galley is going to be tested for operation with the specific aircraft. Meanwhile phone radios (not WiFi, not Bluetooth) used to have interference issues with various aviation systems (with some 5G bands still causing issues). Additionally, outside of interference issues from phone systems (and various other non-ISM band radios), the order helps preventing people from doing stupid things with electronics during takeoff and landing, where sudden deceleration can cause things to go awry.
      - nucleardog 3y ago
        The restriction on cellular phone use on a plane comes from the FCC not FAA. As far as the FAA is concerned as long as you can demonstrate (through standard tests) that a class of aircraft is tolerant of electronic devices (which the manufacturers can do), it’s up to the airline if they want to allow it. They’ve even greatly simplified the process due to the explosion of different electronic devices over the last couple decades. This covers your cell phone in the same way it does an e reader or anything else. [0] There are basically no substantiated instances of portable electronics interfering with aircraft. Certainly not the number you’d expect given the massive number of devices that transit on a massive number of planes every day at this point. The restriction on usage comes from the FCC, applies specifically to using land mobile frequencies from aircraft, and is not out of concern for safety of the aircraft. Things getting up into VHF, UHF and above are “line of sight” propagation. If you can draw a straight line between two points without hitting anything that will attenuate the signal… it’ll pretty much go anywhere. Voyager 1 is transmitting 15 billion miles to us on 8GHz with a 23 watt radio. Your cell phone can put out around 3 watts. People called in to ham radio nets in Vancouver, BC from Seattle, WA on a 5W handheld radio just by going to the top of the Space Needle. People regularly make contact with the ISS or satellites on similar power. A large limiting factor to the distance is the height of the transmitter. Thanks to the curvature of the Earth, over enough distance, that straight line between the two points will begin to intersect the Earth which works great to attenuate the signals to nothing. Getting higher up lets you "shout" further out. Your cell phone transmitting at 3 watts from that kind of altitude is potentially hitting dozens or hundreds of cell towers. Frequencies which are intended to be shared among inhabitatants in a maybe dozen mile radius now need to be shared across hundreds of miles, reducing the bandwidth available for everyone. And the weak signal will cause interference substantially further. The FCC limited transmissions while on an aircraft to prevent interference with ground communications, and continues to because there isn’t enough evidence that they won’t. [0] https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_91.21-1D.pdf https://www.faa.gov/documentLibrary/media/Advisory_Circular/...
        engcoach 3y ago
        This is incorrect. The Federal Aviation Regulations (FARs) expressly forbid operating in IFR conditions (or an IFR flight) with cell phones on.
        p_l 3y ago
        It's a bit of both. Aviation cares not just about specific plane, but also interaction with other systems - which in this case in USA are in purview of FCC. That said, both reasons are involved, though usually mobile networks tend to optimize for signal in horizontal plane in a way that makes them reduce receiving capability from outside of it.
jjtheblunt 3y ago
it's kind of funny because water resonates in that band, international consensus or not?
- Hello71 3y ago
  https://en.wikipedia.org/wiki/List_of_common_misconceptions https://en.wikipedia.org/wiki/List_of_common_misconceptions: > Microwave ovens are not tuned to any specific resonance frequency for water molecules in the food, but rather produce a broad spectrum of frequencies, cooking food via dielectric heating of polar molecules, including water. Several absorption peaks for water lie within the microwave range, and while it is true that these peaks are caused by quantization of molecular energy levels corresponding to a single frequency, water absorbs radiation across the entire microwave spectrum.
  - jcrawfordor 3y ago
    I would contest Wikipedia's description here a bit because I think it confuses the issue of microwave emissions. A number of ISM bands were allocated for RF heating applications originally, 6.78MHz, 13.560MHz, 27.12MHz, 40.68MHz, 915MHz (commonly referred to as 900MHz), 2.45GHz (commonly referred to as 2.4GHz), 61.25GHz, 122.5GHz. These are just examples taken from my NTIA chart which doesn't call all of them out. The lower ones are largely historic, the very first RF heating experiments used HF and VHF low band which were easier to produce with the radio transmitter technology of the time, but not very efficient at all. The invention of the magnetron changed that, suddenly it was much easier to produce microwave radiation at high power levels, and so the inefficient HF/VHF RF heating devices have all but faded away (there are some specific technical applications that remain exceptions, as usual). The low frequencies are inefficient and difficult to produce with compact electronics, the high frequencies aren't very attractive for food heating applications because of the limited skin depth. So every microwave oven you're likely to run into operates at 2.4GHz, which is pretty much the sweet spot for food heating among the allocated ISM bands. That band is defined as 2.4GHz through 2.5GHz. So I quibble with describing microwaves as "broad spectrum." Magnetrons do not produce very narrow output, one of the reasons they aren't often used for radio transmitters today, but microwave ovens are required to constrain their meaningful output to within 50MHz of 2.45GHz. 100MHz is a lot of bandwidth from a modern radio communications perspective, but isn't really that wide from a perspective of physical effects. 2.45GHz was chosen as an ISM band in part because it had good properties for heating, but it wasn't put exactly on a resonance frequency for water or anything like that. The exact details of the selection process are obscure but 2.45GHz was already being used for experimental microwave heating before the ISM band was allocated, and I would imagine came out of some combination of ease of magnetron construction and reasonably good heating properties. It is documented, for example, that the EHF bands were never popular for consumer microwave heating because of poor efficacy with food, although they do have industrial applications (especially in welding). Given the history of the topic there's a decent chance that 2.45GHz came about because it was being used by experimental radar at the time, the main thing that magnetrons were being built for. Microwave heating was basically a byproduct of radar development during its early days of development.

by p_l 3y ago

ThePowerOfFuet 3y ago

Are they actually microwave instead of convection?

p_l 3y ago
Depends on equipment of the plane - the original reasoning for making 2.4GHz the international dumpster spectrum was to install microwaves
- jbverschoor 3y ago
  But we need to switch off WiFi and Bluetooth
  - p_l 3y ago
    That's because the equipment installed in the galley is going to be tested for operation with the specific aircraft. Meanwhile phone radios (not WiFi, not Bluetooth) used to have interference issues with various aviation systems (with some 5G bands still causing issues). Additionally, outside of interference issues from phone systems (and various other non-ISM band radios), the order helps preventing people from doing stupid things with electronics during takeoff and landing, where sudden deceleration can cause things to go awry.
    - nucleardog 3y ago
      The restriction on cellular phone use on a plane comes from the FCC not FAA. As far as the FAA is concerned as long as you can demonstrate (through standard tests) that a class of aircraft is tolerant of electronic devices (which the manufacturers can do), it’s up to the airline if they want to allow it. They’ve even greatly simplified the process due to the explosion of different electronic devices over the last couple decades. This covers your cell phone in the same way it does an e reader or anything else. [0] There are basically no substantiated instances of portable electronics interfering with aircraft. Certainly not the number you’d expect given the massive number of devices that transit on a massive number of planes every day at this point. The restriction on usage comes from the FCC, applies specifically to using land mobile frequencies from aircraft, and is not out of concern for safety of the aircraft. Things getting up into VHF, UHF and above are “line of sight” propagation. If you can draw a straight line between two points without hitting anything that will attenuate the signal… it’ll pretty much go anywhere. Voyager 1 is transmitting 15 billion miles to us on 8GHz with a 23 watt radio. Your cell phone can put out around 3 watts. People called in to ham radio nets in Vancouver, BC from Seattle, WA on a 5W handheld radio just by going to the top of the Space Needle. People regularly make contact with the ISS or satellites on similar power. A large limiting factor to the distance is the height of the transmitter. Thanks to the curvature of the Earth, over enough distance, that straight line between the two points will begin to intersect the Earth which works great to attenuate the signals to nothing. Getting higher up lets you "shout" further out. Your cell phone transmitting at 3 watts from that kind of altitude is potentially hitting dozens or hundreds of cell towers. Frequencies which are intended to be shared among inhabitatants in a maybe dozen mile radius now need to be shared across hundreds of miles, reducing the bandwidth available for everyone. And the weak signal will cause interference substantially further. The FCC limited transmissions while on an aircraft to prevent interference with ground communications, and continues to because there isn’t enough evidence that they won’t. [0] https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_91.21-1D.pdf https://www.faa.gov/documentLibrary/media/Advisory_Circular/...
      - engcoach 3y ago
        This is incorrect. The Federal Aviation Regulations (FARs) expressly forbid operating in IFR conditions (or an IFR flight) with cell phones on.
      - p_l 3y ago
        It's a bit of both. Aviation cares not just about specific plane, but also interaction with other systems - which in this case in USA are in purview of FCC. That said, both reasons are involved, though usually mobile networks tend to optimize for signal in horizontal plane in a way that makes them reduce receiving capability from outside of it.

jjtheblunt 3y ago

it's kind of funny because water resonates in that band, international consensus or not?

Hello71 3y ago
https://en.wikipedia.org/wiki/List_of_common_misconceptions https://en.wikipedia.org/wiki/List_of_common_misconceptions: > Microwave ovens are not tuned to any specific resonance frequency for water molecules in the food, but rather produce a broad spectrum of frequencies, cooking food via dielectric heating of polar molecules, including water. Several absorption peaks for water lie within the microwave range, and while it is true that these peaks are caused by quantization of molecular energy levels corresponding to a single frequency, water absorbs radiation across the entire microwave spectrum.
- jcrawfordor 3y ago
  I would contest Wikipedia's description here a bit because I think it confuses the issue of microwave emissions. A number of ISM bands were allocated for RF heating applications originally, 6.78MHz, 13.560MHz, 27.12MHz, 40.68MHz, 915MHz (commonly referred to as 900MHz), 2.45GHz (commonly referred to as 2.4GHz), 61.25GHz, 122.5GHz. These are just examples taken from my NTIA chart which doesn't call all of them out. The lower ones are largely historic, the very first RF heating experiments used HF and VHF low band which were easier to produce with the radio transmitter technology of the time, but not very efficient at all. The invention of the magnetron changed that, suddenly it was much easier to produce microwave radiation at high power levels, and so the inefficient HF/VHF RF heating devices have all but faded away (there are some specific technical applications that remain exceptions, as usual). The low frequencies are inefficient and difficult to produce with compact electronics, the high frequencies aren't very attractive for food heating applications because of the limited skin depth. So every microwave oven you're likely to run into operates at 2.4GHz, which is pretty much the sweet spot for food heating among the allocated ISM bands. That band is defined as 2.4GHz through 2.5GHz. So I quibble with describing microwaves as "broad spectrum." Magnetrons do not produce very narrow output, one of the reasons they aren't often used for radio transmitters today, but microwave ovens are required to constrain their meaningful output to within 50MHz of 2.45GHz. 100MHz is a lot of bandwidth from a modern radio communications perspective, but isn't really that wide from a perspective of physical effects. 2.45GHz was chosen as an ISM band in part because it had good properties for heating, but it wasn't put exactly on a resonance frequency for water or anything like that. The exact details of the selection process are obscure but 2.45GHz was already being used for experimental microwave heating before the ISM band was allocated, and I would imagine came out of some combination of ease of magnetron construction and reasonably good heating properties. It is documented, for example, that the EHF bands were never popular for consumer microwave heating because of poor efficacy with food, although they do have industrial applications (especially in welding). Given the history of the topic there's a decent chance that 2.45GHz came about because it was being used by experimental radar at the time, the main thing that magnetrons were being built for. Microwave heating was basically a byproduct of radar development during its early days of development.