> Radar in general is more sensitive to noise.... The noise floor is quite a bit higher before it becomes unusable for communications compared to radar

This is not true. A radar has the huge advantage of knowing what signal was sent and only looks for returns that are similar- the FMCW radars in question often mix the return with the originating signal, and outside interference just doesn't cohere and won't affect the result unless the interference is very high power. Radars do not need to look at a wider band of spectrum, reflections do not change the frequency and the Doppler shift a radar altimeter (looking straight down) needs to accommodate is minuscule. A radar that can't handle noise is poorly designed, not that they are inherently susceptible to noise. Radar does require "high" transmit power to easily detect returns, but they can be robust to noise. A radar (including RA) can integrate over a relatively large window if needed and detect with an SNR <1 if it's designed that way.

Whether the old 737 RA was properly designed and can handle the interference, or if they took shortcuts because saving a buck took precedence is a different discussion than the (incorrect) generalities about radar presented in the above comment. Whether the existing RAs can be retrofitted with better filters for cheaper than lobbying the FCC is also unclear, but we know what approach the airlines are attempting right now.

I agree with the general tenet of your post but do we know what the status of the radar's RX's front end is like in practice?

From my experience, many of the front ends of older radar receivers are primitive by comparison with today's state of the art in that they have very bad crossmoduation figures (basic diode mixers etc.).

The gap is the same size as the entire allocation, and the frequency difference is more than 4 percent. That's massive.

> Radar needs to look at a wider band of spectrum as things will get shifted more from reflection and such.

If you skew a radar signal by a thousand miles per hour, isn't that around 2 parts per million? Am I missing an effect here?

Edit: I will add the a fair amount of interference by multi path return can be mitigated by making the transmitter and receiver shielded from other directions and designed to be highly directional. This also is generally not to hard to do for an altimeter since the datatum one is measuring after all is just elevation over a small area, compared to something like radar for topography that wants to cover a large area.

RFI is a problem in these spaces [1]. It's been a problem for many years, and is an increasing one.

[1] https://www.researchgate.net/publication/283760070_The_Threa...

Franky speaking, everybody here is talking out of their asses, and just rehashing bullshit that they get told. I'll lowbrow dismissal that all day long because it doesn't deserve and inch more of effort.

This whole discussion has a really low SNR

Additionally, lot these weather radars are not trying to achieve same level of accuracy as an altimeter. If the weather formations ones monitoring is off by a little bit, but overall the data is close it's fine. Similar thing with a lot maritime radar, ships are not moving that fast so you also have a lot more time to average out the data. If an altimeter when landing is off by too much can cause a lot problems, especially when you factor in the speeds of an airplane it's you have less time to average out noise or doing other things to filter out spurious noise. Edit: Also one other thing about maritime radar there nowhere as much interference once you get outside ports or areas near land.

Also it's not just Boeing here having issues, airbus also along with Boeing has brought this to the attention the FAA. The frequency bands in other countries for 5G tend to be farther away as well from the frequencies used by altimeters so it's not been issue in other countries. It only seems to be handful of air-frames that effected.

Secondly, NOAA have been concerned about 5G, particularly near 24Ghz, again for possibly interfering with radar.

All I was saying is radar is a lot more sensitive to the noise floor and if suddenly that noise floor is higher I am not surprised some equipment will have issues depending on it's use case. Especially, when things were designed long before these new spectrum allocations.

See my post about international radio regulations, the 5G service should not have been allocated if it was going to interfere with radar altimeters as that was (and still is) a 'going' service and it takes precedence under international radio treaties.

Thus, an aircraft from a country that's not under US jurisdiction expects to be able to land in the US without its radar altimeter being jammed by some unexpected local service. (It stands to reason that the safety of an aircraft that travels across international borders should not be endangered because of inference to its navigation equipment.)

This is the precise reason why international radio regulations exist! Under the treaty the 'interference' rules apply to ALL radiocommunication services.

If such regulations (standards) are deemed 'old' then they have to be changed at an ITU WRC meeting in Geneva and the item must appear on the meeting's agenda some years before said meeting takes place to give all countries adequate time to respond (as I mentioned elsewhere, I was once involved in that process).