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Comment by mcguire | Hacker News Reader

There is no way to build a perfect filter. 5G equipment will emit outside of its assigned spectrum and radar altimeters will receive signals from outside their spectrum. The next important variables are the power of the transmitters and the effectiveness of the receiver's filters (and the sensitivity of the receiver). Radar altimeters have been doing their thing for decades because the previous uses of that band had much lower power.

Your analogy is a great demonstration why reasoning-by-analogy fails, by the way.

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Sure, but radar altimeter allocation is 200MHz wide and the gap between 5G and the altimeters is 220MHz. The problem isn't that the filters are insufficiently perfect, the problem is that the filters are hot garbage.

If Boeing needs 3.7GHz-5GHz in order to safely operate their aircraft, then Boeing needs to purchase and own the 3.7GHz-5GHz band. If they only want to pay for 4.2GHz-4.4GHz and nothing but 4.2GHz-4.4GHz, but squat on 3.7GHz-3.98GHz they can pound sand.

This isn't a Boeing-specific issue. Boeing doesn't even make the avionics in question. Some of the manufacturers don't even exist anymore. It's not clear who would pay, or how you'd enforce it.

At the time these units were built, the filtering was sufficient to guard against the known adjacent users of the band (low-power satellite signals). Neither the FCC or the FAA set performance standards to suggest otherwise. Nobody expected at the time we'd be blasting high-power omnidirectional signals everywhere at 4 GHz - outside a few specialized uses, it's a terrible band for wide-area communication unless somebody is motivated enough to build tons of towers...which the cell companies suddenly are.

We can agree that the filters are garbage by modern standards, but they were considered adequate at the time the units were built based on the circumstances.

It seems to me then the owners of the offending equipment are responsible for the bill. I don't see how you can come to any other logical conclusion.

At least I know why cell service at the airport is awful.

Nah, it's like healthy Western US forests need regular fires, but people moved into the woods, built flammable homes, and demanded all fires be stopped. Now we want to restart taking care of forests but they whine their house will burn. If avionics don't stick to their band, they are at fault.

> It seems to me then the owners of the offending equipment are responsible for the bill. I don't see how you can come to any other logical conclusion.

Because at the time the equipment was bought, it met every applicable federal standard. This would be unfair to the owners who had no way of knowing about the issue.

Also, in nearly every other case I can think of when spectrum changes, the FCC grandfathers in owners of legacy equipment.

> At least I know why cell service at the airport is awful.

I don't think that's at all related, given that we just started rolling out 5G. Plus the bands in question don't travel through walls very well. :/

At the time many buildings were sold, asbestos insulation met every applicable federal standard. The owners are still responsible for mitigating it.

> Because at the time the equipment was bought, it met every applicable federal standard. This would be unfair to the owners who had no way of knowing about the issue.

At least in Europe, there is precedent that modern use of frequency assignments make older equipment illegal to operate. 4G and 5G have heavily eaten into the frequencies used on stage for event equipment - microphones, IEM, that sort of thing. Many, many pieces can‘t be legally operated anymore, and it‘ll probably be the same in a few years time with the current-gen devices (although I hope I can swap crystals if needed and keep using my stuff).

Radio bandwidth is a scarce resource. If the radio altimeter is transmitting well outside of its boundaries and it creates problems (for any of the parties requirements), it’s the radio altimeters that need fixing. Even if it is expensive to do so.

No it did not meet every applicable law because it is using part of the spectrum it’s not supposed to be using. The only reason wireless communication in general isn’t pure jamming hell is because we abide by these simple rules.

I live 6 miles from an airport. I get less than 100kbps from Verizon on my iPhone 12. Thanks Boeing.

Boeing would pay and the FAA as the enforcement agency would enforce it...

As mentioned, this isn't a Boeing-specific issue. This affects every major aircraft manufacturer, as well as a lot of smaller aircraft with aftermarket avionics. Surely Boeing isn't going to pay for the entire industry.

Also, the FAA has no way of knowing if a particular aircraft operator is using a radio altimeter or not. Even if I have one installed, maybe I chose to switch it off. It's also possible I'm using it for situational awareness only (which is still allowed) and not using it to descend below legal approach minimums.

Boeing pays for their upgrades. Airbus can pay for their upgrades. Douglas Aircraft pays for their upgrades after we revive the company.

Psst! Boeing isn't the only manufacturer affected.

"Airbus has issued Flight Operations Transmission 999.0002/22 (01/10/2022) which describes the currently understood effects of radar altimeter anomalies. Guidance is provided for A320 family, A330, and A340 aircraft for handing these anomalies.

"Embraer Flight Operations Letter 170-001/22 and Operational Bulletin 170-001/22 (01/02/2022): Describe the possible effects of C-Band 5G interference on its E170, E175, E190, and E195 aircraft.

"The FAA has developed a process by which better performing radar altimeters that are able to reject 5G interference can be approved to operate without regard to the AD and NOTAMs. These Alternate Methods of Compliance (AMOC) approvals will be specific to a combination of aircraft model and radar altimeter model. The method of approval will take into consideration the performance of the aircraft/radar altimeter combination, as well as the location and power of the 5G transmitter in the vicinity of the airport. Therefore, the AMOCs are being issued with a list of airports where they are effective. As of 1/25/2022, FAA has approved AMOCs for several models of radar altimeters, installed on Boeing 717, 737, 747, 757, 767, 777, 787, and MD-10/-11; Airbus A220, A300, A310, A319, A320, A321, A330, A340, A350, and A380, Embraer 120, 170, and 190, all Canadair CRJ aircraft, some DeHavilland Canada DHC-8, and some ATR aircraft. These AMOCs are limited to certain airports and specific models of radar altimeters. Pilots should ensure that they have AMOC documentation for their aircraft and airport (e.g. in a dispatch release) before operating at an airport without regard to the 5G AD/NOTAM."

https://www.alpa.org/resources/aircraft-operations-radar-alt...

So some altimeters, manufactured by companies supplying all OEMs way hefore 5g was thing, have trouble with 5G now. There seems to be a solution for this old equipment, civil aviation moves on. For once no need to pick on Boeing here. Or on anyone else.

I never said Boeing should pay for other companies upgrades. Maybe I could have said "the companies that own the airplanes"... but I'm not unaware that other companies are affected... that fact was even in the comment I replied too.

See my post about the ITU and international radio regulations.

> This isn't a Boeing-specific issue.

If Airbus has the same problem, then ground Airbus too.

> Boeing doesn't even make the avionics in question. Some of the manufacturers don't even exist anymore. It's not clear who would pay,

Surely when the parts break, they are fixed, and if they are not fixed, then the plane is either grounded or flies in conditions such that the equipment is not required. There is a somebody who repairs, services, or replaces broken parts. These parts are broken. So that somebody fixes it.

> or how you'd enforce it.

You'd enforce fixing this broken part the same way you'd enforce fixing any other broken part. When the FAA finally got around to deciding that MCAS was in fact broken, they grounded the 737 MAX until it was fixed.

Everybody's acting like it's not a big deal that this equipment can't handle a signal that is more than 220MHz away from their nominal operating frequency. Certainly if Hasbro wanted to sell Batman(TM) BatWalkie BatTalkies, but they were rendered inoperable by another signal that far from their operating frequency, the FCC would deny the device its operating license and it would be pulled from the market.

> Nobody expected at the time we'd be blasting high-power omnidirectional signals everywhere at 4 GHz

Infrastructure 5g antennas are directional. The mobile devices themselves are omnidirectional, but those are very low power devices.

"Nobody expected at the time we'd be blasting high-power omnidirectional signals everywhere at 4 GHz - outside a few specialized uses, it's a terrible band..."

As I've point out in my post, why on earth wasn't all this sorted out before 5G was allocated the frequencies.

It seems to me that the the powers behind mobile services have railroaded themselves into these frequencies and that the FCC etc. haven't had the gumption to sort it out beforehand.

If 5G deployments broadcast too close to the frequency assigned to radio altimeters then that's something the FCC should have sorted out, but it appears more like the radio altimeters just have bad filters that let too much outside their assigned frequency through. That makes it a problem of the FAA. The FCC isn't responsible for policing bad receivers.

> That makes it a problem of the FAA. The FCC isn't responsible for policing bad receivers.

Ah, yes. The best thing you can have is tribal mentality in your government departments. Where instead of cooperating to sort problems out you just say "fuck everyone else" and press onward.

See my post above (once, I was on several pre-WARC/WRC advisory committees).

"That makes it a problem of the FAA. The FCC isn't responsible for policing bad receivers."

What do you mean by 'bad' receivers?

Spectrum management, irrespective of country, sets the parameters of every radiocommunication service by notional equipment standards - here that would be the typical intermodulation figures for radar receivers, inter alia.

The FCC and ITU through WARC/WRC - World Radiocommunication Conferences would have been aware of notional equipment standards for radar altimeters at the time the spectrum was allocated (equipment must comply with the standard or it be deemed out of spec - non compliant).

Note: adjacent services must consider interference to their adjacent services, etc. The standards associated with any service can only be deemed old or 'changed' at WRC conferences specifically to avoid the situation we now have here. The real question is 'who fucked up' - i.e.: did not abide by WRC rules (the international treaty/agreement obligations).

Remember, here international rules are paramount BECAUSE aircraft licensed in other countries that land on US territory also have to meet the same international standards for their radar altimeters as those of the US fleet - it has nothing to do with receivers being 'bad').

FYI: https://en.m.wikipedia.org/wiki/World_Radiocommunication_Con.... Note: the ITU deems that the FCC IS responsible for radio regulations within the USA.

presumably that's why the two spectrums have a 0.2GHz gap between them, which btw is massive. based on 2020 mid-spectrum prices, this is worth a staggering $66B.

We are talking radar here though. Radar in general is more sensitive to noise. It's not a digitally encoded signal like communications. It's looking at the reflections of radio waves and their strength among other things. This is an analog process the sensor is using. Before digitally encoded broadcasting was the norm the gaps between frequencies tended be wider to limit noise. For communication even with analog encodings like AM, FM ect... The noise floor is quite a bit higher before it becomes unusable for communications compared to radar. Radar needs to look at a wider band of spectrum as things will get shifted more from reflection and such. Further it needs to read the much weaker reflected signals. The signal is weaker because lots of energy will be lost by the time it's reflected. So it's quite possible some higher order harmonics operating on the edge of the 5G spectrum could bleed into the frequency area the radar is using above the expected noise floor.

Keep in mind these sensors were designed and approved long before the FCC allocated this spectrum above this range to 5G. 200 Mhz may be massive for communications, but not that is not entirely true for radar.

If this were even remotely accurate, the s-band radars that are commonplace for weather radar and maritime radars would be rendered useless by high power telecom/TV BRS and EBS spectrum.

This is a pretty shallow dismissal that doesn't actually provide data to back up the claim. Why would the interference be substantial enough to make them useless? Which weather and maritime radar? There are many at many different bands. What is the meaningful impact of interference on those measurements, and how does it differ from the impact of interference on radio altimeters used in planes during take-off and landing? These are just a few of the reasonable questions that should be answered in such a strong dismissal. Instead, you called it inaccurate without providing any real analysis.

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...

I already said s-band (which is 2-4ghz) specifically. BRS/EBS (2.5-2.7ghz) has no meaningful guard band to protect s-band radar, and the radars, at least when used on military vessels, are actually dramatically more sensitive than aviation radar altimeters. And not only has EBS/BRS been operating for decades without any problems, but a) the maritime radar emission/detection patterns are horizontal, just like telecom/television, which should produce more interference than the perpendicular patterns of radar altimeters, and b) EBS has operated for 3 decades using television broadcast power levels...1000s of watts as opposed to the 100s of watts that telecom uses. If interference was actually a problem, the DoD would have shut down those two bands back in the 80s.

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.

> Frankly …

This whole discussion has a really low SNR

I did not say it was impossible to design a radar system to work with a higher noise floor. Also, if you have looked some of the concerns the FCC has in the S-Band range is radar. If you have looked at the frequency allocation rules and such. Quite often around certain frequencies you will see your not to cause interference with radar. However, a lot of radar in the S-Band pulse power tend be quite strong because of atmospheric attenuation, and also noise.

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.

"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).

The FAA and FCC need to figure out what to do, but the above comment isn't the consideration they need to be worried about.

> 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.

In support of this comment, as a radio astronomer I used to think I understood radar. Then I sat in a presentation by some smart people from MIT, and it turns out that I was really wrong, but the things actual radars do are built on top of things that I know from astronomy.

It is more sensitive noise. I did not say it was impossible though to design radar with a higher noise floor in mind. Like the main reason this is problem is not really Boeing's or Airbus's fault. It's only now the FAA went wait a minute when they could have been looking at this years ago since the FCC did announce this quite a bit ago now. The allocation here in the US is closer than to other countries so spurious emissions from 5G equipment and higher order harmonics could possibly be larger issue.

"A radar that can't handle noise is poorly designed..."

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.).

> 200 Mhz may be massive for communications, but not that is not entirely true for radar.

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?

Radar for an altimeter since by it's very nature it needs to measure distance and not just speed is going to be frequency modulated. Unmodulated/continuous frequency radar can only measure speed. When you start processing the small amount of doppler frequency shift from reflections with a changing frequency things get tricky especially when one has have multi-path return (aka it's reflecting off multiple objects) This will lead two or more reflections with roughly the same frequency, but they have a phase shift. That's the kind of shift I am talking about here. The more noise you have the more difficult it is to separate these reflections when processing these signals.

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.

Okay, sure, you frequency modulate your output. But the frequencies you get back should be almost identical, right? That doesn't explain why something 200MHz away would interfere.

Yes, they will be very close in frequency. If you have multi-path return you will have two more or more frequencies with different phases. The problem is not so much this alone. All transmitters will have spurious emissions of some level and also your going to have higher order harmonics of the root frequency that will be outside the allocated spectrum. The higher the transmit power of a transmitter the more higher order harmonics you will see above the noise floor. At least for low power transmitters you don't have to worry about more than 2nd order harmonic. Although if you have a powerful enough transmitter like a cell tower 3rd order harmonics can be a problem. Spurious noise is going to depend a lot the design of the transmitter and amplifiers and filters. So how much noise leaks into this bad used for aircraft altimeters is gonna depend alot on the quality of the equipment cellar providers use. Noise can effect radar more easily than normal communication transmissions.

It was not considered massive enough everywhere else, though - even when frequencies up to 4GHz were allocated to 5G, the usage came with special regulations related to use near airports.

I don't think that the physics of the situation is affected by the financial aspects of the situation.

The distance between the transmitter and receiver is quite important. Signal strength is inversely proportional to the square of the distance. At some distance you are going to have problems no matter how good the filters are. The problem here is that the receiver is mobile.

Aircraft flying over C band satellite dishes (what used to use the current 5G band) used to cause interference to those dishes. In that case the problem was that the transmitter was mobile. Now the C band satellite people will have to fight interference from 5G transmitters in what remains of their band.

With radar, it's actually worse! Received signal strength is proportional to the fourth power of distance (1/r^2 on the way to the target, then 1/r^2 on the way back to the radar).

That's part of the reason 5G is such an issue, despite the ostensibly-large guard band. You need really good filters on the cellular 5G equipment to make sure it doesn't leak into the radar band.

Let's not also forget about drift on these filters. Those components will experience drift from age. That drift can also be accelerated from quiet a few factors such as heat ect...

And many hundreds of emitters. All those towers and phones pumping out 1s and 0s will occasionally line up in a way thay looks like a higher/lower frquency. The aircraft looking down sees across multiple cells. All sorts of strange combinations might occur. Thats what guard bands are for.

> With radar, it's actually worse! Received signal strength is proportional to the fourth power of distance (1/r^2 on the way to the target, then 1/r^2 on the way back to the radar).

I think that's specifically true when you're pointing a radar at an aircraft, but is not true for radar altimeters.

When you're pointing a radar at an aircraft, the angular size of the aircraft is 1/r^2, so 1/r^2 of the emitted radiation hits the aircraft. Once emitted from the aircraft, the angular size of radar receiving dish is 1/r^2, so 1/r^2 of that radiation is detected.

With a radar altimeter, you're pointing the radar at the ground. The angular size of the ground is 50% of the sphere, whether you're one foot above the ground or 100,000 feet. (...ok, maybe it's like 49.5% of the sphere...) As long as you're pointing it down-ish, 100% of the emitted radiation hits the ground. There is only one 1/r^2 relationship, on the return leg.

Well, 100% of the emitted radiation hits the ground in terms of total power, but the radar is looking for the _closest_ reflection, which is some relatively small solid angle straight down. It doesn't change your conclusion though, that solid angle is independent of the distance to the ground.

> Well, 100% of the emitted radiation hits the ground in terms of total power, but the radar is looking for the _closest_ reflection, which is some relatively small solid angle straight down.

This fixed angle paints a larger and larger circle as altitude increases. If you double your altitude, you quadruple the size of the surface that's reflecting radar back at you.

A bunch of stuff cancels out and you end up with 1/r^2 at the receiver, which is what we started with.

An alternative explanation is that you treat the ground as a flat mirror, and the radar detects the distance of your mirror image. The distance between you and your mirror image is (2r), so the signal strength you receive from your mirror image is ~1/(2r)^2, still follows 1/r^2 .

I’m not arguing with the idea most of the signal gets to the ground, but, I’m worried that you get specifics quite wrong. Planes don’t want a reflection from 50% of the sphere. They want it from directly below. Other land is further from the plane and obscures the measurement.

But they’re not broadcasting to the whole sphere either, because the radar instrument is not an isotropic radiator. That antenna has gain. It’s louder / more sensitive in a specific direction. Probably by a lot. You can’t make perfect antennas, but you don’t need any signal at all from most of the sphere, so you can gain many decibels.

The angle of the beam you do have is probably fixed, and being fixed would imply that the area swept by the core of the beam is indeed proportional to the square of the altitude. But I don’t think two trips through an n^2 distance is n^4 unless I’m missing some of the physics. Shouldn’t it be (2n)^2 and this still proportional to the square of the altitude not to the hypercube? (And affected by scattering and bad reflectivity from the terrain, which seems likely to be independent of altitude?) This is different for detecting random entities in free space where most of the first n^2 trip really is lost.

So it’s like you say but for different reasons??!?!

The altimeter does not want to know the average distance to the ground over a several square mile region. It wants to know the distance to the ground directly under the aircraft.

"That's part of the reason 5G is such an issue, despite the ostensibly-large guard band."

As I keep repeating here, if excessive or debilitating interference is being experienced between services under normal operating conditions then there has been a failure of Spectrum Management planning - absolutely no question about it.

OK, we know such interference has happened, so who was responsible for the planning fuck-up?

I've no argument about filters, RFI etc., what most are saying about the engineering issues makes sense.

My argument is that the spectrum planning has failed and that much of the reason can be put down to deregulation in the 1980s when many governments essentially washed their hands of Spectrum Management (succumbed to commercial pressures and overly loosened engineering standards and now we're paying the penalty).

It seems to me (given the international nature of the problem with non-US registered aircraft flying into US airspace, etc.) that we need to go back to the core of the problem and acknowledge these past 'regulations' errors before the problem can be fixed properly.

Perhaps all radar altimeters will have to be changed (respecified with much tighter filters, better intermod figures, etc.) but given the fuck-up who should pay? After all, it's not the FAA's fault nor that of the aircraft industry (see my comments in other posts about the ITU and WRC).

As I see it, this is a political issue, not a technical one.

Right, so, the issue is NOT the BTS that is being raised, it is the phone on the plane, which are a lot closer to the antenna on the plane, which is on the ass end of the plane which is the low point during take off and landing.

this is the white paper that the FAA bases their concerns on https://www.rtca.org/wp-content/uploads/2020/10/SC-239-5G-In...

that is the issue they are raising

I have run the numbers and there is no way even at phone full power that it can interfere unless it was less than 2m away even then it would have to be free space, etc.

the body losses, airframe, antenna back scatter all taken into account, very very unlikely unless the radar bandpass filters are from the 1960's

>...unless the radar bandpass filters are from the 1960's ...

Were filters particularly bad in the '60s? If you claim to have run the numbers you will have to reveal your assumptions.

yes, DSP's did not exist then :)

The numbers are in the doc i posted.

Thanks for sharing. I’m going to read this report now. Are you in Radar? Potentially looking for a job at a well-funded startup making very high powered phased arrays in c and x bands?

The conclusions in the report are more severe than your comments are presenting. I don't think this is a good forum to discuss it further though. There is another comment suggesting a clash of two vastly different safety cultures that really hits the nail on the head, and I think that even the hypothesized/speculative risk to aviation needs addressing, though you are also probably right that the aircraft industry wants cash from the telcos for a retrofit that they should pay for themselves and were willing to drag their feet assuming FAA would trump the FCC in this matter (they will). Frankly if they want digital pulse-compression radar altimeters that are going to operate even with adversarial interference, I built/am-building the most advanced matched filter in the world though it will cost a bit more than a sub-$1K High Pass Filter plugged in line with the antennae which is probably sufficient (though avionics safety requirements will probably find a way to make it $100K anyway)

> Your analogy is a great demonstration why reasoning-by-analogy fails

It's a matter of understanding what the analogy is giving you. In many cases, as above, it's merely a foothold, a way of getting started understanding what something is through partial identification with something already known. From that point, the differences between the two can be clarified.

You can think of it in terms of compressing descriptions: let's say you need to describe an SUV to someone; you could start by saying "it's like a truck but [...]," and remove a lot of the redundancy you'd get by starting from scratch.

AFAICT people who think there's something wrong with reasoning-by-analogy are analyzing it with the false assumption that people are just doing "X is like Y" rather than "X is like Y EXCEPT [...]," while also having an understanding on some level of the imprecision/limits of the partial identification.

That people are out there reasoning with analogies thinking they form perfect, limitless mappings between the domains involved seems like an imaginary problem.

All analogies are wrong. Some analogies are useful.

All reasoning is by analogy. The map you have in your head, is not the territory my friend.

There's no perfect filter and no perfect transmitter... correct. But the devices are required to accept reasonable interference and I guarantee that the 5g transmitters don't produce unreasonable interference. This is an issue, like has been said, of poorly manufactured/broken altimeters.

I don't think this is true. There's plenty of ways to build a filter that won't meaningfully interfere across such large swaths of rf bands.

> Your analogy is a great demonstration why reasoning-by-analogy fails, by the way.

I hate reasoning-by-analogy in general but in this case it sounds fine to me. Boeing are grazing their cattle on someone else's land - they don't get squatters rights because no one else was using it at the time when they built their fences. Because it was contractors that built the fences and Boeing didn't perhaps know they were using someone else's land then they should get a little time to move the cattle - or the FAA/FCC can arrange a deal and give the telecom companies some new land - but it's Boeings problem.

>There is no way to build a perfect filter.

Fair, but if we are to expect a certain level of "drift" outside of designated bands, does that mean that the gap between allocated bands should increase?

That is to say, if precision is an issue, what the most effective solution to deal with that lack of precision? From the sounds of it, the technology is unable to comply with the bands allocated, so the regulations around how those bands are distributed should be far more strict, right?

Don't The FCC set maximum levels of noise a device can emit and minimum levels of noise other devices must tolerate. Unless the antennas are way above their limits this shouldn't be an excuse...

In a way, this is a case of disagreement on both accepted levels of noise generated by 5G equipment, and how big the noise is in reality, with FCC having very strong lobby to push through, while FAA having very strict safety requirements (and extra reason to avoid cutting corners after the MCAS fiasco)

But the FAA don't set the noise tolerance limit, the FCC do.

And so far, despite weeks of work, no one has shown anyone is breaking the noise generation limit.

What confuses me here is exactly the FAAs safety requirements: they've said there could be a problem. But they've also not done any research to assess it. And they're not grinding any planes. So they apparently aren't that bothered by safety!?

Noise tolerance limits for SOHO gear or telcos are completely different to requirements on FMCW radar transmitting a signal across all of 200MHz band...

There is ongoing body of work, done internationally, for several years now. They aren't grounding planes because there's no operational need to right now - worst case expect a lot of canceled flights and maybe Southwest going bust as their scheduling flaps too much (also, USA is a bit lucky in having lower need for Category II or worse approaches than some other countries).

And as someone else mentioned in comments, there are already issues cropping up with malfunctioning 5G transmitters despite 400MHz guard bands...

Your confused perhaps because your assertion about research done to assess the problem is wrong.

Here is the industry research, presented two years ago:

https://www.rtca.org/wp-content/uploads/2020/10/SC-239-5G-In...

Note the telco industry have attacked and politicized the research, but they have not offered up their own data to back up their claims. The aviation industry is on much stronger ground here.

And as another commenter put it so eloquently, the aviation industry assumes something is dangerous until proven safe, not that something is safe until proven dangerous.

> Your analogy is a great demonstration why reasoning-by-analogy fails, by the way.

Douglas Hofstadter would like a word with you.

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