The FAA has noted that in other countries there were mandates for lower power levels for 5G and that the antennas be pointed down toward the earth so that they interfered less.

https://www.faa.gov/5g

Lower power levels and a downward tilt on the antennas would mean less range for C-Band networks so carriers would rather not do that - especially in the US where the population is much more suburban and rural than Europe.

It's possible that C-Band won't interfere even at higher power levels and even without downward antenna tilts. However, other countries have mandated greater permanent restrictions on C-Band than the US's temporary 6-month measures.

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...?

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.

I thought that AT&t and Verizon offered to do lower power towers near airports. The story from November seems to say as much.

https://www.theverge.com/2021/11/24/22801008/verizon-att-mid...

All cell phone towers seem to be aimed toward the ground.

I've flown a GA aircraft all around the lower 48, and only get a cell phone signal briefly when flying directly over a cell tower.

Naturally. Why would a cell carrier want to expend energy beaming signal into space?

That said, you do get the occasional misaligned antenna or weird bounce off terrain that gets you signal midflight for a minute.

How easy is it to report those type of issues?

What do you like to report? That cell signal was available somewhere?

make a phone call, and let the big data folks raise eyebrows when they see the elevation the call was made.

It's really regional. I get 5 bars pretty much anywhere below 5000ft in the bay area.

Yep, I get signal up to about 3000' AGL where I am.

Well, given that the possible range to a cell tower is about 35 km / 20 mi (max, an absolute limitation of how the GSM/timing is done), it's very plausible that even if cell broadcast antennas are generally pointed down + flat with the horizon, you're gonna get some signal from some antenna in the distance.

The US seems stuck in a holding pattern of "two more weeks, two more weeks" without addressing any of the potential workarounds like power, directional antennas, or even blackout zones. From what I've read, the airlines and FAA haven't really put forward any proposals for compromise, like leaving towers off near airports. It's always no 5G anywhere until they've had more time, as if the planned 5G deployment came as a total surprise. Or why can't the towers be turned off in bad weather only?

My read is either the FAA or the airlines or both want money re-allocated from the FCC spectrum sales or the carriers (or both) to retrofit their dated equipment.

So the airlines are cheap bastards, got it

yeah as someone that isn't following this super closely it feels like the airlines are on their back foot and unprepared. These radios are days away from being turned on permanently and they haven't done any smoke testing? Why weren't they working with the telecoms 12 months ago to run trials?

I'm not sympathetic to the airlines right now.

This is not the airlines problem: the airlines have type certified transport/commuter category aircraft with all kinds of radios - include the radar altimeters that are the problem here - that are required to meet exact performance specifications - which they did.

The FAA waited until December to issue airworthiness directives that limit the ability of the airlines to rely on radar altimeters under certain circumstances. The background here appears to be some kind of pissing match between US government agencies including the FAA, the FCC and the NTIA.

What exactly do you think the airlines were supposed to do here? Go out and have all their radar altimeters replaced? Replaced with what? The required standards haven't changed, and it's the FAA that writes the standard (technical service orders).

This is also not a "smoke testing" problem. This is a "on the worst day, in the worst set of circumstances, what is the degree of compromise of the assumed safety margins" question.

>it feels like the airlines are on their back foot and unprepared.

maybe the airlines should temporarily reassign the teams that redesign seating arrangements to reduce spacing to allow more people onboard. they seem very efficient at their tasks, and there's really not much left for them to do

Shouldn't be surprising to hear that the FAA doesn't really do anything with this stuff. They appoint a corporate-filled board of avionics companies to do all of the work for them, and then rubber stamp what those companies want.

It’s not all 5g, just a new band. They can figure out the technical issues without putting airliners at risk.

Maybe key people are out with Covid?