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Can someone with insight into radio technology explain this? > The 5G network deployment in the U.S. starting on December 5 is in the 3700 to 3800-MHz bands th

Can someone with insight into radio technology explain this? > The 5G network deployment in the U.S. starting on December 5 is in the 3700 to 3800-MHz bands then later in the 3700 to 3980-MHz bands. Radio altimeters use the 4200 to 4400-MHz band. [1]. Are these not sufficiently separated? Can this not be tested easily, by blasting 5G frequencies at a bunch of different planes in test flights? They've had like a decade to do this; I'd expect something more concrete then "concerns about potential interference" at this point. [1] https://www.ainonline.com/aviation-news/air-transport/2021-11-02/faa-issues-saib-5g-radio-altimeter-interferenc https://www.ainonline.com/aviation-news/air-transport/2021-1...

onphonenow 5y ago
There is something weird going on at FAA / NTSB etc. In most radio applications a guard band of 220Mhz is absolutely unheard of. You would do a guard at 10% of bandwidth lets say. On one side you'd have 5%. So we are talking 1-2 Mhz? My understanding was planes already had 2-3 altimeters, with guard band spacing of maybe 5Mhz (ie, planes already have devices blasting signals at frequencies much closer than 200Mhz).
- p_l 5y ago
  There will be usually only one active radio altimeter, with center frequency around 4.3GHz.
  - onphonenow 5y ago
    So a guard band of 300Mhz then? What's weird is that I'd expect an altimeter to be on the order of .1 to 2MHz bandwidth max. There's just something wrong in the math here.
    - drmpeg 5y ago
      Radar altimeters use frequency modulated continuous wave (FMCW) and the bandwidth is 20 to 170 MHz (the larger the chirp, the more accurate it can be). It's extremely difficult to have a 170 MHz wide filter at 4.3 GHz with a brick wall response out of band. https://www.ntia.doc.gov/files/ntia/publications/compendium/4200.00-4400.00_01MAR14.pdf https://www.ntia.doc.gov/files/ntia/publications/compendium/...
jltsiren 5y ago
It's probably more about the safety culture than the technology. This is the same industry that grounded the 737 MAX worldwide for almost two years due to some rare issues that would have been tolerated in almost every other field. Because radio altimeters have not been required to tolerate interference above a certain threshold within ~10% of their frequency band, the assumption is that they cannot tolerate it until there is something like a decade or two of production-scale experience without any serious issues. Or until all passenger planes have radio altimeters certified for the new stricter requirements. And because the latter costs money, the industry won't do it as long as other options remain.
- formerly_proven 5y ago
  Those "rare issues that would have been tolerated in almost every other field" are the root cause that killed hundreds of people.
  - jorvi 5y ago
    Not only that, the issue was caused by Boeing cheaping out on quantity of sensors, and then the ‘there is an issue’ light was sold as a safety upgrade. And the reason this was all needed was because Boeing wanted to escape having to recertify pilots for a new type rating.
  - jltsiren 5y ago
    Road traffic kills over a million people every year, many of them due to various technical and design flaws. People just tolerate those deaths far better than deaths from plane crashes.
    - jacquesm 5y ago
      If the MAX had continued to fly without getting to the root cause it would have been a completely different story than the one that we have today, which is bad enough as it is with both Boeing and the FAA owning what they broke.
    - sofixa 5y ago

onphonenow 5y ago

There is something weird going on at FAA / NTSB etc. In most radio applications a guard band of 220Mhz is absolutely unheard of. You would do a guard at 10% of bandwidth lets say. On one side you'd have 5%. So we are talking 1-2 Mhz? My understanding was planes already had 2-3 altimeters, with guard band spacing of maybe 5Mhz (ie, planes already have devices blasting signals at frequencies much closer than 200Mhz).

p_l 5y ago
There will be usually only one active radio altimeter, with center frequency around 4.3GHz.
- onphonenow 5y ago
  So a guard band of 300Mhz then? What's weird is that I'd expect an altimeter to be on the order of .1 to 2MHz bandwidth max. There's just something wrong in the math here.
  - drmpeg 5y ago
    Radar altimeters use frequency modulated continuous wave (FMCW) and the bandwidth is 20 to 170 MHz (the larger the chirp, the more accurate it can be). It's extremely difficult to have a 170 MHz wide filter at 4.3 GHz with a brick wall response out of band. https://www.ntia.doc.gov/files/ntia/publications/compendium/4200.00-4400.00_01MAR14.pdf https://www.ntia.doc.gov/files/ntia/publications/compendium/...

jltsiren 5y ago

It's probably more about the safety culture than the technology. This is the same industry that grounded the 737 MAX worldwide for almost two years due to some rare issues that would have been tolerated in almost every other field. Because radio altimeters have not been required to tolerate interference above a certain threshold within ~10% of their frequency band, the assumption is that they cannot tolerate it until there is something like a decade or two of production-scale experience without any serious issues. Or until all passenger planes have radio altimeters certified for the new stricter requirements. And because the latter costs money, the industry won't do it as long as other options remain.

formerly_proven 5y ago
Those "rare issues that would have been tolerated in almost every other field" are the root cause that killed hundreds of people.
- jorvi 5y ago
  Not only that, the issue was caused by Boeing cheaping out on quantity of sensors, and then the ‘there is an issue’ light was sold as a safety upgrade. And the reason this was all needed was because Boeing wanted to escape having to recertify pilots for a new type rating.
- jltsiren 5y ago
  Road traffic kills over a million people every year, many of them due to various technical and design flaws. People just tolerate those deaths far better than deaths from plane crashes.
  - jacquesm 5y ago
    If the MAX had continued to fly without getting to the root cause it would have been a completely different story than the one that we have today, which is bad enough as it is with both Boeing and the FAA owning what they broke.
  - sofixa 5y ago