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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

• deleted 5y ago
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• darksaints 5y ago
  • mcguire 5y ago
    https://www.rtca.org/wp-content/uploads/2020/10/SC-239-5G-Interference-Assessment-Report_274-20-PMC-2073_accepted_changes.pdf https://www.rtca.org/wp-content/uploads/2020/10/SC-239-5G-In...
  • upofadown 5y ago
    >High power radio bandpass filters allow for guard bands on the scale of a single mhz. Not at 4GHz. This stuff works in terms of percentages of the frequency in use. The higher the frequency the larger the guard bands required for any sort of practical filtering.
  • omegalulw 5y ago
    From FCCs doc that the other counter linked > Radar altimeters used in civil and commercial aviation operate using either unmodulated pulse radar or frequency-modulated continuous wave (FMCW) radar technology, with FMCW being far more common among models developed in the last few decades. In either case, the above ground level (AGL) altitude of the aircraft is measured in the radar altimeter by transmitting radio frequency (RF) energy down to the ground and receiving a portion of this energy back through reflection off of the terrain or other obstacles, and determining the round-trip propagation time of the RF energy. The radiated power levels are low, typically on the order of one watt, and thus highly sensitive receivers are required for radar altimeters to function properly. As such, radar altimeters are highly susceptible to RF interference entering the receiver, which can negatively impact their performance. The planes use the band to bounce signals off of the ground and that needs to be super sensitive. That's why they probably can't afford to properly filter within the 200 MHz guard band.
• ricw 5y ago
  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.
  • anfilt 5y ago
    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.
    • darksaints 5y ago
      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.
      • mirashii 5y ago
        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_Threat_to_Weather_Radars_by_Wireless_Technology https://www.researchgate.net/publication/283760070_The_Threa...
• LatteLazy 5y ago
  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...
  • p_l 5y ago
    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)
    • LatteLazy 5y ago
      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!?
      • p_l 5y ago
        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...
      • theYipster 5y ago
        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-Interference-Assessment-Report_274-20-PMC-2073_accepted_changes.pdf 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.
• lxe 5y ago
  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.
• deleted 5y ago
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• teawrecks 5y ago
  > Your analogy is a great demonstration why reasoning-by-analogy fails, by the way. Douglas Hofstadter would like a word with you.
• upofadown 5y ago
  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.
  • labcomputer 5y ago
    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.
    • anfilt 5y ago
      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...
    • sandworm101 5y ago
      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.
    • nwallin 5y ago
      > 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.
• Phylter 5y ago
  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.
• nwallin 5y ago
  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.
  • tjohns 5y ago
    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.
    • kcmastrpc 5y ago
      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.
      • coryrc 5y ago
        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.
      • 5y ago
• registeredcorn 5y ago
  >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?
• westoncb 5y ago
  > 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.
  • dotancohen 5y ago
    All analogies are wrong. Some analogies are useful.
    • rusk 5y ago
      All reasoning is by analogy. The map you have in your head, is not the territory my friend.
• helsinkiandrew 5y ago
  > 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.