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Comment by ajmurmann | Hacker News Reader

AFAIK it's not the power level, but 5G in the US has a sightly higher spectrum range that's closer to that of the radio altimeters. Finland apparently even uses power levels that are do high that they'd be illegal in the US without any problems.

Source: https://www.lightreading.com/5g/why-does-5g-only-pose-a-prob...?

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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)

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

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.

C-Band in the US is rolling out in 2 phases, the first uses spectrum from 3.7 to 3.8 GHz. The second - in roughly two years - adds the remaining 3.8 to 3.98 GHz. So for the first two years the spectrum used by C-Band 5G in the US is essentially the same as in most of the rest of the world.

https://www.commscope.com/blog/2021/maximizing-c-band-deploy...

I've read it's multiple concerns: https://www.faa.gov/5g

https://www.airlines.org/5g-frequently-asked-questions/

In Europe, the power output seems to be ~2.5 time lower, there's a bigger frequency separation in Europe, the 5G towers are placed further away from approaches, and the antennas have to point downwards.

Doesnt this show that some country's dont plan ahead that much or different elements of Govt are too disconnected to work cohesively?

Still, this chatter will no doubt give some loon some ideas on how to bring down a plane or mess around with the flight patterns at busy airports.

Radio spectrum was decided somewhere in the 1950s and as I understand it the US military owns most of it. It's difficult to plan ahead for future technology.

Oh I dont know, I think other countries seem to be making less of a hash of it, compared to the US.

And does it really matter if the US Mil own the spectrum? Thats like me saying the UK Govt owns the spectrum, they should still both be subjected to the court of law, if the laws are fit for purpose in the first place!

> Doesnt this show that some country's dont plan ahead that much or different elements of Govt are too disconnected to work cohesively?

This can be a feature, not necessarily a bug.

There are plenty of examples of government central planning and cohesion going very wrong.

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