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A comment on U.S. FAA clears 45% of commercial plane fleet after 5G deployed. Parent comment

Re:U.S. FAA clears 45% of commercial plane fleet after 5G de... by mdasen on Monday January 17, 2022 @11:02PM (#29974936)
The FAA doesn't cite that concern on their page, but having a 200MHz buffer in the US rather than a 380MHz buffer is a difference.

As noted in the article you posted, Canada is requiring antenna down-tilting nationwide as well as exclusion zones around airports.

EDIT: "an exclusion band is allowed ±10% around the band, within which the HIRF levels are very low—for radar altimeters, this spans 3.78–4.84 GHz"

https://www.rtca.org/wp-content/uploads/2020/12/Slides-5G-In...

So, in Europe, their C-Band ends at 3.8GHz and barely enters the range. In the US where we're going to 3.98GHz, we're well into that range.

It looks like Korea's band ends at 3.7GHz which is outside the range (and definitely by 3.8GHz which is where band N78 ends; the US is using Band N77 which ends at 4.2GHz, but we've only licensed spectrum to 3.98GHz)

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Re:U.S. FAA clears 45% of commercial plane fleet after 5G de... by DannyBee on Tuesday January 18, 2022 @11:02AM (#29981113)
200 is already crazy large. Super crazy. The original request from Boeing was only 100

These altimeters are dangerously defective if they need a 400mhz guard band. That is nuts

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Re:U.S. FAA clears 45% of commercial plane fleet after 5G de... by indrora on Tuesday January 18, 2022 @06:06PM (#29987438)
you're actually looking at the intersection of three problems:

* LTE is very noisy (it has echos in its sidebands for up to 100Mhz)

* low-frequency LTE is *loud* -- punch through mountains loud.

* These altimiters are doing the RF equivalent of looking for a needle in a haystream

While FCC Part15 says "accept any/produce as little as possible", much of this comes down to the physics of RF.

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