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Comment by fancyfredbot | Hacker News Reader

In Europe there are Boeing 737s and 5G C band radio masts. I'm guessing the laws of physics are the same in Europe. So I'm confused. What are they doing differently there? Why don't the US do the same thing?

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EU C-band rollouts are 200Mhz lower than in the US, making for almost twice as much gap between them. That said, EU is still starting to get worried [0] after some tests showed malfunctioning equipment can cause interference.

[0] https://strandconsult.dk/blog/5g-is-suddenly-a-flight-safety...

EU 5G uses 3.4 to 3.8 GHz

US 5G uses 3.7 to 3.98 GHz

Thank you! I'm now wondering why the US didn't stop at 3.8GHz and limit power levels too?

Issues with previously allocated spectrum and shoddy setup of mobile telephone spectrum in general leading to them needing more spectrum in 3-4GHz bands

See page 3 second half. https://ecfsapi.fcc.gov/file/101041916430138/GN%20Docket%20N...

We (Europeans) use other frequency bands for 5G: 700 MHz, 1.8, 2.1 and 2.7 GHz. That's comfortably far away from the 4.2 GHz band radio altimeters use.

Why the US decided to use 3.8 GHz for their 5G, only God knows.

It is a poor design on the part of the altimeter designers. 200MHz should be plenty far away.

Or poor design on the part of 5G transmitter designers?

The problem is the altimeters listening outside of their band, not the transmitters speaking outside of theirs.

200Mhz is an eternity away. You can fit all of the 2.4GHz WiFi/Bluetooth/whatever unlicensed band in that.

If the transmitters weren't leaking outside the assigned band, there wouldn't be a problem, right? Those transmitters are the best new tech, right?

No the idea is the transmitters are transmitting properly, and the receivers are “listening” outside of where they should be.

The transmitters aren't leaking out of their assigned band

The transmitters have FCC specs on how much power can leak outside of the band (It's called the band edge requirement). If the radar can't handle this out of band power transmission, then the FCC is on the line for writing a spec that isn't protecting the bands that they operate. It is unlikely this is the case given how far out of band this is.

No, the 5G transmitters are in their designated spec, and 200Mhz away from the altimeter frequencies. The problem is that the radio altimeters might not have proper filtering, which wasn't a problem in the past because the spectrum now allocated to 5G was not seeing much powerful transmissions.

The radio altimeters are fully up to spec, but the spec does not say enough about filtering out signals outside of the required band. This oversight in the spec was never much of an issue because of the aforementioned lack of usage in the spectrum before 5G.

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