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If I understand this correctly, the FCC has allocated the 4.2GHz-4.4GHz band for radar altimeters. The FCC has also allocated the 3.7GHz-3.98GHz band to 5G. It

If I understand this correctly, the FCC has allocated the 4.2GHz-4.4GHz band for radar altimeters. The FCC has also allocated the 3.7GHz-3.98GHz band to 5G. It turns out that the radar altimeters, as manufactured, use spectrum outside their allocated band, down to and including part of the 3.7GHz-3.98GHz 5G band. Am I missing something? If a rancher buys a plot of land from 34.42°N to 34.44°N to graze his cattle on, but in actual fact grazes his cattle all the way from 34.37°N to 34.47°N. Then a farmer buys a plot of land from 34.37°N to 34.398°N to grow wheat on. Does the rancher still get to herd his cattle down to 34.39°N to feed his cattle? The cattle have to eat, after all, and cutting down the grazing land by 30% could cause some cattle to starve to death. And the rancher has a vested financial interest in ensuring his cattle are well fed, and that wheat is good eating. And the rancher has always been grazing his cattle there, what right does the farmer have to till the soil on the racher's grazing land? And we, the American public, have the right to buy beef. Why should the farmer purchasing 34.37°N to 34.398°N interfere with my ability to buy a steak? Does any of this make any sense to anyone? Unless there's additional information I'm unaware of, it seems as if the design and/or manufacture of the radar altimeter is not fit for purpose. Using 3.7GHz to 3.98GHz for 5G doesn't break the radar altimeters; the radar altimeters are already broken and must be fixed or grounded, because the equipment is broken and unsafe. If 5G equipment is emitting outside of its allocated 3.7-3.98GHz spectrum then the FCC needs to drop a brick on that of course.

ddod 5y ago
I can't say if it's right or wrong, but in relation to your specific example, there are "adverse possession" laws that grant legal rights to the occupier of land in the US.[1] [1] https://www.nolo.com/legal-encyclopedia/neighbor-built-fence-over-the-property-line-does-own-land.html https://www.nolo.com/legal-encyclopedia/neighbor-built-fence...
- buescher 5y ago
  It's the receiver, so it's more like, you're asserting your right to leave your door wide open on a street that is suddenly much more busy. De facto possession of spectrum was heavily litigated in the early days of radio. There basically is none (not legal advice!), essentially no one has a claim on spectrum in the USA that is not assigned or regulated by the FCC. You have to sign away any claim to spectrum from before the establishment of the FCC to get a ham license or similar radiotelephone licenses. Nobody is around anymore that was operating then anyway. The language is blandly bureaucratic but in context that is what it means: "The Applicant/Licensee waives any claim to the use of any particular frequency or of the electromagnetic spectrum as against the regulatory power of the United States because of the previous use of the same, whether by license or otherwise, and requests an authorization in accordance with this application." There is probably some similar language in the applications for other licensed bands.
mcguire 5y ago
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.
- deleted 5y ago
  [deleted]
- 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.
pinephoneguy 5y ago
It's probably not good to nitpick but with the land analogy you have zoning (the lack of zoning that led to the West Texas disaster comes to mind) and animals (bees etc) tend to cross land boundaries so it's not quite that clear cut. It all does sound a bit silly though. I will say I wish the FCC was as happy handing spectrum/power to unlicensed users as it is to what are nearly exclusively Qualcomm customers.
- syncsynchalt 5y ago
  Note for clarity that that's West, Texas (which is not in West Texas, it's in the east). Assuming you mean https://en.wikipedia.org/wiki/West_Fertilizer_Company_explosion https://en.wikipedia.org/wiki/West_Fertilizer_Company_explos...
notatoad 5y ago
I think what you're missing is that assigning blame isn't especially helpful. those altimeters are already in the airplanes. those planes are serving an important purpose, and grounding them until they can be fitted with altimeters that only operate in their allowed spectrum would be more harmful than disallowing 5G equipment from operating in that spectrum. a rancher allowing his cattle to graze outside of his allowed land doesn't result in a fiery crash that kills hundreds of people. you're right, the planes are in the wrong and they should be fixed. but that's kind of not the point.
- gentryb 5y ago
  I'm curious as to why you think the planes should be fixed, but "that's kind of not the point"? It seems to me that it's pretty far out of the frequency boundaries.
- Swenrekcah 5y ago
  If this is the case the solution is simple. Postpone the 5G allocation, make the altimeter manufacturers/users pay market price for the spectrum to those that would have gotten it allocated until they can return the spectrum, and also pay a fine to the government for using spectrum not allocated to them (in the past, current and future breach covered with the rent mentioned before). And give some timeframe by which spectrum must be returned.
  - tjohns 5y ago
    The radar altimeters aren't "using" (in the FCC sense) any of the 5G spectrum. This is an issue on the receive side. The FCC primarily regulates transmission, and the transmitters themselves are compliant. The FAA's TSO-C87 doesn't have any requirements for rx filtering either. So there's no legal grounds to fine anyone.
    - ummonk 5y ago
      > The FAA's TSO-C87 doesn't have any requirements for rx filtering either. So there's no legal grounds to fine anyone. Then the FCC should proceed with the rollout of this allocation and let the clowns at Boeing and the FAA handle the fallout.
joshmlewis 5y ago
> It turns out that the radar altimeters, as manufactured, use spectrum outside their allocated band, down to and including part of the 3.7GHz-3.98GHz 5G band. Did the FAA say this is what's happening for sure? If so that answers a lot of questions I've had because like you said they are on different parts of the spectrum so it should not be an issue unless something is operating out of spec.
- tjohns 5y ago
  So, here's what's actually happening in a nutshell... The FCC allocated a specific band for radar altimeters to transmit in. The FCC only specified rules on transmission, and the radar altimeters are 100% compliant with the FCC rules and only transmit within their assigned band. The FAA published TSO-87C, which is the technical spec for the radar altimeters. But this also just covers transmission and performance. There's nothing in this spec about rejecting external interference. The radar altimeters are compliant with this spec as well. The problem is on the unregulated receive side. All radio signals have some amount of bleed-over into adjacent bands due to harmonic interference. Historically, the adjacent frequencies were used for low-power satellite communication, and the manufacturers added enough filtering to protect against the harmonic interference from these low-power stations. They did not anticipate a high-power (5G) signal in those adjacent bands, and nothing in the FAA/FCC specifications protected against it either. So it's not that the radio altimeters are "using" the adjacent bands, but the receive filtering is (in some cases) insufficient to account for the new (louder) users of the adjacent bands.
  - dataflow 5y ago
    What I'm confused about is, why are the FCC and FAA suddenly running into this problem now? Hasn't 5G been coming for a long time? What did they expect would happen instead?
    - labcomputer 5y ago
      "5G" doesn't refer to one specific set of bands. Radar has been operating this way for decades, and only last year did the FAA decide to allocate the nearby spectrum to high power transmitters.
Spooky23 5y ago
The difference is that cows don’t fall from the sky and kill hundreds of humans in the process. “Fix the thing” is the correct answer, but managing risk in the meantime in this regulatory environment is a shade of grey. Doing nothing puts people at risk. Grounding aircraft cripples a critical industry. Delaying 5G costs two network operators a lot of cash.
peteradio 5y ago
More like the rancher keeps his beefs within the usual limit but one or two can escape from time to time.
Ansil849 5y ago
> The cattle have to eat, after all, and cutting down the grazing land by 30% could cause some cattle to starve to death. You lost me here at this point in the comparison. How is this analogous to the situation with altimeters?
- profile53 5y ago
  The planes have to fly and preventing them from doing so could cause financial harm/bankruptcy/transportation delays.
hasmanean 5y ago
It’s more like, you can fence off your cattle but you can’t fence off the birds and the bees. So even if the cattle stay within their limits, the grass relies on bees coming in from neighbouring farmland to stay healthy. If you pave the area outside a cattle ranch the grass inside will die on the borders. So you have to zone the land outside the fences to make sure it some other ranch or else left wild. The same with spectrum. Adjacent frequency bands have to allocated to uses which do not produce a lot of interference that travels very far or is used very much.
awb 5y ago
> If a rancher buys a plot of land from 34.42°N to 34.44°N to graze his cattle on, but in actual fact grazes his cattle all the way from 34.37°N to 34.47°N. Then a farmer buys a plot of land from 34.37°N to 34.398°N to grow wheat on. Does the rancher still get to herd his cattle down to 34.39°N to feed his cattle? If you're actually curious about this specific scenario, in the US it's typically referred to as "adverse possession": https://en.wikipedia.org/wiki/Adverse_possession https://en.wikipedia.org/wiki/Adverse_possession > in the English common law tradition, courts have long ruled that when someone occupies a piece of property without permission and the property's owner does not exercise their right to recover their property for a significant period of time, not only is the original owner prevented from exercising their right to exclude, but an entirely new title to the property "springs up" in the adverse possessor. In effect, the adverse possessor becomes the property's new owner.[2][b] Over time, legislatures have created statutes of limitations that specify the length of time that owners have to recover possession of their property from adverse possessors. In the United States, for example, these time limits vary widely between individual states, ranging from as low as three years to as long as 40 years. Also, in some states like California you have to pay taxes on the land for a certain period of time before you can claim ownership. But yes, in your specific case it is possible to raise cattle on someone else's land for long enough to be able to legally claim that land as your own.
LeifCarrotson 5y ago
Your analogy is slightly oversimplified because it assumes a fully functional fence (probably two, with a road between them) between the wheat fields and the cattle. The cows might gaze longingly across the road at the wheat fields and the wheat farmer might smell some manure while harvesting, but the fence is fully functional. In real life, a 2200 lbs steer might not think much of a mere barbed wire fence or high-voltage tickle separating it from the wheat field...but that's stretching the analogy a bit too far into the weeds. A better analogy needs to understand that the filter on both sides of the equipment is imperfect. Replace the altimeter with, say, Mount Rushmore National Monument, and replace the wheat farmer with, say, a putrid landfill, sewage processing operation, or CAFO chicken farm. Neither the monument nor the viewing areas extend beyond the surveyed boundaries of the monument. But part of the appeal is that it's a pleasant, quiet, natural place in the middle of a national forest: abutting it with something smelly, noisy, or ugly might be legal but would harm it even though it doesn't extend past the property markers. Personally, I do think they need to upgrade and phase out the altimeters to be more tolerant against interference. But they're not necessarily broken, just too slow to adapt past the scope and capabilities of the tech available in 1967.
- mulmen 5y ago
  Mt Rushmore is neither beautiful nor natural. It is the ugly thing ruining the shared resource. This is the problem with analogy.
NikolaNovak 5y ago
It is my limited understanding that no EM signal drops off as vertical wall at the exact edge of spectrum, and radar altimeters behave within actual defined requirements and regulations. The land analogy is useful exactly to the point where it is deceptive / misleading (no ill intent is assumed here! We are all just trying to figure it out :). Land behaves like land (nice and discrete and binary with a thick clear line) and waves, well, like waves :-)
tgsovlerkhgsel 5y ago
> Does any of this make any sense to anyone? Yes. In your example, the government may decide to temporarily allow the rancher to keep grazing his cattle until the rancher can reduce the size of his herd, because they don't want to force him to destroy good cattle, while requiring the rancher to pay the farmer for the use of his land and lost profit from the wheat he cannot grow. The alternative would be to force the rancher to cull half of his herd, which would not only be wasteful, but also cause a national beef shortage, while the world so far survived without the extra wheat. So the government does the pragmatic thing, even though it shouldn't, according to the permits it issued. Probably wouldn't happen with beef vs. wheat, but I could see it happen with beef vs. corn-for-ethanol, because food safety trumps ethanol production. The FCC might decide that existing aviation needs beat not-yet-established mobile phone needs. Whether the spectrum owners would actually be compensated fairly, or whether the government would the "you're getting screwed over because I like the rancher more, I've got the bigger guns, what'cha gonna do about it?", - that I don't know. But from the article, it sounds very much like the FCC isn't doing much except having told the farmer to wait a few months before plowing the greenest grazing land to keep the peace, and the FAA is telling the rancher "your not-your-own grazing land is gone so your cows might starve, deal with it".
IncRnd 5y ago
These bands are not like drawing two parallel lines that don't touch, then blaming the other person for coloring outside the lines. 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.
zw123456 5y ago
This is about money, the airlines want money from the telcos. The telcos paid off the Incumbent Earth Station operators to vacate the spectrum, now the airlines have their hand out because they are cash strapped after a pandemic lock down. I have posted this a bunch of times 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... I have read this carefully, and run calcs myself, the issue they are raising is the phones on the plane. But even at full power, very unlikely, but read my other post on this for more details. The real issue is that they want the telcos to pay them to swap out their radar but are asking for a large amount beyond what would be needed to do that.
- zw123456 5y ago
  ok whoever downvoted, read the report, you could not have done that by now, I thought HN was better than that.. they are asking for money, come on. this is what is wrong with HN, you can downvote without talking, be standup. what are you arguing ?
baryphonic 5y ago
> Does any of this make any sense to anyone? Regardless of whether this makes sense, the hypothetical scenario you describe is called "adverse possession."[0] Now, it may be that spectrum doesn't count as property (especially since the FCC's existence derives from the fiction that "the public owns the airwaves"). This situation makes something of a mockery of that FCC narrative, since no one believes these airplane radars will all be replaced at the drop of a hat, but nevertheless it would probably hold up in court as a matter of law. I have no idea how the government could try to remedy this situation. Seems like admitting adverse possession with some sort of compensation and/or trade in spectrum might make sense. [0]https://www.law.cornell.edu/wex/adverse_possession https://www.law.cornell.edu/wex/adverse_possession
hilbert42 5y ago
"Unless there's additional information I'm unaware of, it seems as if the design and/or manufacture of the radar altimeter is not fit for purpose." Whether radar altimeters in their present form are fit for purpose or not I cannot answer as I have insufficient information to do so. However, I must point out that: 1. ALL radiocommunications have limitations in that they can suffer interference from other services even when those other services are operating correctly and according to license (i.e.: being in their correct allocated frequency bands and operating at their correct power levels, etc.). 2. The role of Spectrum Management falls to the FCC. It operates under the auspices of the ITU (International Telecommunications Union) to manage the spectrum through its international treaties and its job is to ensure that interference between services is kept to a minimum. In essence, the aim is to maximize spectrum usage whilst keeping interference to trivial levels (it should be noted however there's no such thing as 'no interference'). (International treaties are necessary as electromagnetic radiation doesn't honor a country's borders.) 3. The way this is achieved is complex but in essence transmitter frequencies, power levels and transmitter locations are optimized to provide optimal protection ratios to each service so they can operate efficiently. 4. If services are mobile, as with radar altimeters, one of the parameters used in optimizing protection from interference is lost. Signals from radar altimeters can interfere with other services and vice versa as they can get too close to one another (interference increases significantly when powerful transmitters are close to sensitive receivers). 5. How tightly services can be packed together depends on many factors but two principal matters stand out: the laws of physics and the state of the art of electronics design. The major culprit in causing interference is a well known form of distortion whereby several radio signals can interfere with one another to produce multiple other freqenies that are harmonically related to the original frequencies. This interfere is called intermodulation distortion and it's one of the perennial scourges of radiocommunications: https://en.m.wikipedia.org/wiki/Intermodulation https://en.m.wikipedia.org/wiki/Intermodulation. For example, a transmitter on f1 (service 1) and another say on f2 (servive 2) can produce other unwanted frequencies, f3, f4, f5, etc. that can interfere severely with unrelated services. Under some circumstances interference to the unrelated service can be so severe that it can be rendered useless (as mentioned, this can be very problematic when services are mobile as it's very difficult to take every contingency or location into account). 6. These matters become much more critical when the stakes are high - with emergency services, radar altimeters, etc. where lives can be at stake if things go wrong. 7. Critical communications services have always demanded very high protection ratios and have traditionally been given them by Spectrum Management agencies - the FCC, et al. The current argument is that the ubiquity of 5G threatens the high protection ratio previously afforded radar altimeters. 8. If I were in the aircraft industry and I was responsible for the reliability of safety devices such as radio altimeters then I'd want to be absolutely certain that any new radiocommunication service is not going to interfere with any of my critical services. Moreover, I would be overly concerned with the potential for mobile phone services to interfere with these safety services specifically because phone services are a never-ending moving target when it comes to location, density of phone traffic, etc., all of which have potential to cause interference. 9. Whether 5G has real potential to interfere with radar altimeters or any other aeronautical communications service can only be determined by proper independent engineering studies. The fact that we have this dispute at this late juncture shows that something has seriously gone wrong in the planning phase. (From my observations, it seems the mobile phone industry has had too much political power, especially so when it comes to buying spectrum - and it has lots of money to demand what it wants (and to date it's gotten the spectrum it wants). Whilst government eyes the millions to be made from the sale of spectrum, the trouble is that it's also the regulator of the spectrum hence it has a conflict of interest. Fundamentally, spectrum auctions run by governments have the potential to compromise good spectrum management. Whether it's happened in this instance I cannot say for certain. The only other point I'd stress is that the electromagnetic spectrum is a scarce nonrenewable environmental resource and should be respected and treated as such (like any other environmental issue).
2143 5y ago
The animal doesn't know or care about who owns what land. It sees grass. It eats.

ddod 5y ago

I can't say if it's right or wrong, but in relation to your specific example, there are "adverse possession" laws that grant legal rights to the occupier of land in the US.[1] [1] https://www.nolo.com/legal-encyclopedia/neighbor-built-fence-over-the-property-line-does-own-land.html https://www.nolo.com/legal-encyclopedia/neighbor-built-fence...

buescher 5y ago
It's the receiver, so it's more like, you're asserting your right to leave your door wide open on a street that is suddenly much more busy. De facto possession of spectrum was heavily litigated in the early days of radio. There basically is none (not legal advice!), essentially no one has a claim on spectrum in the USA that is not assigned or regulated by the FCC. You have to sign away any claim to spectrum from before the establishment of the FCC to get a ham license or similar radiotelephone licenses. Nobody is around anymore that was operating then anyway. The language is blandly bureaucratic but in context that is what it means: "The Applicant/Licensee waives any claim to the use of any particular frequency or of the electromagnetic spectrum as against the regulatory power of the United States because of the previous use of the same, whether by license or otherwise, and requests an authorization in accordance with this application." There is probably some similar language in the applications for other licensed bands.

mcguire 5y ago

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.

deleted 5y ago
[deleted]
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.

pinephoneguy 5y ago

It's probably not good to nitpick but with the land analogy you have zoning (the lack of zoning that led to the West Texas disaster comes to mind) and animals (bees etc) tend to cross land boundaries so it's not quite that clear cut. It all does sound a bit silly though. I will say I wish the FCC was as happy handing spectrum/power to unlicensed users as it is to what are nearly exclusively Qualcomm customers.

syncsynchalt 5y ago
Note for clarity that that's West, Texas (which is not in West Texas, it's in the east). Assuming you mean https://en.wikipedia.org/wiki/West_Fertilizer_Company_explosion https://en.wikipedia.org/wiki/West_Fertilizer_Company_explos...

notatoad 5y ago

I think what you're missing is that assigning blame isn't especially helpful. those altimeters are already in the airplanes. those planes are serving an important purpose, and grounding them until they can be fitted with altimeters that only operate in their allowed spectrum would be more harmful than disallowing 5G equipment from operating in that spectrum. a rancher allowing his cattle to graze outside of his allowed land doesn't result in a fiery crash that kills hundreds of people. you're right, the planes are in the wrong and they should be fixed. but that's kind of not the point.

gentryb 5y ago
I'm curious as to why you think the planes should be fixed, but "that's kind of not the point"? It seems to me that it's pretty far out of the frequency boundaries.
Swenrekcah 5y ago
If this is the case the solution is simple. Postpone the 5G allocation, make the altimeter manufacturers/users pay market price for the spectrum to those that would have gotten it allocated until they can return the spectrum, and also pay a fine to the government for using spectrum not allocated to them (in the past, current and future breach covered with the rent mentioned before). And give some timeframe by which spectrum must be returned.
- tjohns 5y ago
  The radar altimeters aren't "using" (in the FCC sense) any of the 5G spectrum. This is an issue on the receive side. The FCC primarily regulates transmission, and the transmitters themselves are compliant. The FAA's TSO-C87 doesn't have any requirements for rx filtering either. So there's no legal grounds to fine anyone.
  - ummonk 5y ago
    > The FAA's TSO-C87 doesn't have any requirements for rx filtering either. So there's no legal grounds to fine anyone. Then the FCC should proceed with the rollout of this allocation and let the clowns at Boeing and the FAA handle the fallout.

joshmlewis 5y ago

> It turns out that the radar altimeters, as manufactured, use spectrum outside their allocated band, down to and including part of the 3.7GHz-3.98GHz 5G band. Did the FAA say this is what's happening for sure? If so that answers a lot of questions I've had because like you said they are on different parts of the spectrum so it should not be an issue unless something is operating out of spec.

tjohns 5y ago
So, here's what's actually happening in a nutshell... The FCC allocated a specific band for radar altimeters to transmit in. The FCC only specified rules on transmission, and the radar altimeters are 100% compliant with the FCC rules and only transmit within their assigned band. The FAA published TSO-87C, which is the technical spec for the radar altimeters. But this also just covers transmission and performance. There's nothing in this spec about rejecting external interference. The radar altimeters are compliant with this spec as well. The problem is on the unregulated receive side. All radio signals have some amount of bleed-over into adjacent bands due to harmonic interference. Historically, the adjacent frequencies were used for low-power satellite communication, and the manufacturers added enough filtering to protect against the harmonic interference from these low-power stations. They did not anticipate a high-power (5G) signal in those adjacent bands, and nothing in the FAA/FCC specifications protected against it either. So it's not that the radio altimeters are "using" the adjacent bands, but the receive filtering is (in some cases) insufficient to account for the new (louder) users of the adjacent bands.
- dataflow 5y ago
  What I'm confused about is, why are the FCC and FAA suddenly running into this problem now? Hasn't 5G been coming for a long time? What did they expect would happen instead?
  - labcomputer 5y ago
    "5G" doesn't refer to one specific set of bands. Radar has been operating this way for decades, and only last year did the FAA decide to allocate the nearby spectrum to high power transmitters.

Spooky23 5y ago

The difference is that cows don’t fall from the sky and kill hundreds of humans in the process. “Fix the thing” is the correct answer, but managing risk in the meantime in this regulatory environment is a shade of grey. Doing nothing puts people at risk. Grounding aircraft cripples a critical industry. Delaying 5G costs two network operators a lot of cash.

peteradio 5y ago

More like the rancher keeps his beefs within the usual limit but one or two can escape from time to time.

Ansil849 5y ago

> The cattle have to eat, after all, and cutting down the grazing land by 30% could cause some cattle to starve to death. You lost me here at this point in the comparison. How is this analogous to the situation with altimeters?

profile53 5y ago
The planes have to fly and preventing them from doing so could cause financial harm/bankruptcy/transportation delays.

hasmanean 5y ago

It’s more like, you can fence off your cattle but you can’t fence off the birds and the bees. So even if the cattle stay within their limits, the grass relies on bees coming in from neighbouring farmland to stay healthy. If you pave the area outside a cattle ranch the grass inside will die on the borders. So you have to zone the land outside the fences to make sure it some other ranch or else left wild. The same with spectrum. Adjacent frequency bands have to allocated to uses which do not produce a lot of interference that travels very far or is used very much.

awb 5y ago

> If a rancher buys a plot of land from 34.42°N to 34.44°N to graze his cattle on, but in actual fact grazes his cattle all the way from 34.37°N to 34.47°N. Then a farmer buys a plot of land from 34.37°N to 34.398°N to grow wheat on. Does the rancher still get to herd his cattle down to 34.39°N to feed his cattle? If you're actually curious about this specific scenario, in the US it's typically referred to as "adverse possession": https://en.wikipedia.org/wiki/Adverse_possession https://en.wikipedia.org/wiki/Adverse_possession > in the English common law tradition, courts have long ruled that when someone occupies a piece of property without permission and the property's owner does not exercise their right to recover their property for a significant period of time, not only is the original owner prevented from exercising their right to exclude, but an entirely new title to the property "springs up" in the adverse possessor. In effect, the adverse possessor becomes the property's new owner.[2][b] Over time, legislatures have created statutes of limitations that specify the length of time that owners have to recover possession of their property from adverse possessors. In the United States, for example, these time limits vary widely between individual states, ranging from as low as three years to as long as 40 years. Also, in some states like California you have to pay taxes on the land for a certain period of time before you can claim ownership. But yes, in your specific case it is possible to raise cattle on someone else's land for long enough to be able to legally claim that land as your own.

LeifCarrotson 5y ago

Your analogy is slightly oversimplified because it assumes a fully functional fence (probably two, with a road between them) between the wheat fields and the cattle. The cows might gaze longingly across the road at the wheat fields and the wheat farmer might smell some manure while harvesting, but the fence is fully functional. In real life, a 2200 lbs steer might not think much of a mere barbed wire fence or high-voltage tickle separating it from the wheat field...but that's stretching the analogy a bit too far into the weeds. A better analogy needs to understand that the filter on both sides of the equipment is imperfect. Replace the altimeter with, say, Mount Rushmore National Monument, and replace the wheat farmer with, say, a putrid landfill, sewage processing operation, or CAFO chicken farm. Neither the monument nor the viewing areas extend beyond the surveyed boundaries of the monument. But part of the appeal is that it's a pleasant, quiet, natural place in the middle of a national forest: abutting it with something smelly, noisy, or ugly might be legal but would harm it even though it doesn't extend past the property markers. Personally, I do think they need to upgrade and phase out the altimeters to be more tolerant against interference. But they're not necessarily broken, just too slow to adapt past the scope and capabilities of the tech available in 1967.

mulmen 5y ago
Mt Rushmore is neither beautiful nor natural. It is the ugly thing ruining the shared resource. This is the problem with analogy.

NikolaNovak 5y ago

It is my limited understanding that no EM signal drops off as vertical wall at the exact edge of spectrum, and radar altimeters behave within actual defined requirements and regulations. The land analogy is useful exactly to the point where it is deceptive / misleading (no ill intent is assumed here! We are all just trying to figure it out :). Land behaves like land (nice and discrete and binary with a thick clear line) and waves, well, like waves :-)

tgsovlerkhgsel 5y ago

> Does any of this make any sense to anyone? Yes. In your example, the government may decide to temporarily allow the rancher to keep grazing his cattle until the rancher can reduce the size of his herd, because they don't want to force him to destroy good cattle, while requiring the rancher to pay the farmer for the use of his land and lost profit from the wheat he cannot grow. The alternative would be to force the rancher to cull half of his herd, which would not only be wasteful, but also cause a national beef shortage, while the world so far survived without the extra wheat. So the government does the pragmatic thing, even though it shouldn't, according to the permits it issued. Probably wouldn't happen with beef vs. wheat, but I could see it happen with beef vs. corn-for-ethanol, because food safety trumps ethanol production. The FCC might decide that existing aviation needs beat not-yet-established mobile phone needs. Whether the spectrum owners would actually be compensated fairly, or whether the government would the "you're getting screwed over because I like the rancher more, I've got the bigger guns, what'cha gonna do about it?", - that I don't know. But from the article, it sounds very much like the FCC isn't doing much except having told the farmer to wait a few months before plowing the greenest grazing land to keep the peace, and the FAA is telling the rancher "your not-your-own grazing land is gone so your cows might starve, deal with it".

IncRnd 5y ago

These bands are not like drawing two parallel lines that don't touch, then blaming the other person for coloring outside the lines. 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.

zw123456 5y ago

This is about money, the airlines want money from the telcos. The telcos paid off the Incumbent Earth Station operators to vacate the spectrum, now the airlines have their hand out because they are cash strapped after a pandemic lock down. I have posted this a bunch of times 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... I have read this carefully, and run calcs myself, the issue they are raising is the phones on the plane. But even at full power, very unlikely, but read my other post on this for more details. The real issue is that they want the telcos to pay them to swap out their radar but are asking for a large amount beyond what would be needed to do that.

zw123456 5y ago
ok whoever downvoted, read the report, you could not have done that by now, I thought HN was better than that.. they are asking for money, come on. this is what is wrong with HN, you can downvote without talking, be standup. what are you arguing ?

baryphonic 5y ago

> Does any of this make any sense to anyone? Regardless of whether this makes sense, the hypothetical scenario you describe is called "adverse possession."[0] Now, it may be that spectrum doesn't count as property (especially since the FCC's existence derives from the fiction that "the public owns the airwaves"). This situation makes something of a mockery of that FCC narrative, since no one believes these airplane radars will all be replaced at the drop of a hat, but nevertheless it would probably hold up in court as a matter of law. I have no idea how the government could try to remedy this situation. Seems like admitting adverse possession with some sort of compensation and/or trade in spectrum might make sense. [0]https://www.law.cornell.edu/wex/adverse_possession https://www.law.cornell.edu/wex/adverse_possession

hilbert42 5y ago

"Unless there's additional information I'm unaware of, it seems as if the design and/or manufacture of the radar altimeter is not fit for purpose." Whether radar altimeters in their present form are fit for purpose or not I cannot answer as I have insufficient information to do so. However, I must point out that: 1. ALL radiocommunications have limitations in that they can suffer interference from other services even when those other services are operating correctly and according to license (i.e.: being in their correct allocated frequency bands and operating at their correct power levels, etc.). 2. The role of Spectrum Management falls to the FCC. It operates under the auspices of the ITU (International Telecommunications Union) to manage the spectrum through its international treaties and its job is to ensure that interference between services is kept to a minimum. In essence, the aim is to maximize spectrum usage whilst keeping interference to trivial levels (it should be noted however there's no such thing as 'no interference'). (International treaties are necessary as electromagnetic radiation doesn't honor a country's borders.) 3. The way this is achieved is complex but in essence transmitter frequencies, power levels and transmitter locations are optimized to provide optimal protection ratios to each service so they can operate efficiently. 4. If services are mobile, as with radar altimeters, one of the parameters used in optimizing protection from interference is lost. Signals from radar altimeters can interfere with other services and vice versa as they can get too close to one another (interference increases significantly when powerful transmitters are close to sensitive receivers). 5. How tightly services can be packed together depends on many factors but two principal matters stand out: the laws of physics and the state of the art of electronics design. The major culprit in causing interference is a well known form of distortion whereby several radio signals can interfere with one another to produce multiple other freqenies that are harmonically related to the original frequencies. This interfere is called intermodulation distortion and it's one of the perennial scourges of radiocommunications: https://en.m.wikipedia.org/wiki/Intermodulation https://en.m.wikipedia.org/wiki/Intermodulation. For example, a transmitter on f1 (service 1) and another say on f2 (servive 2) can produce other unwanted frequencies, f3, f4, f5, etc. that can interfere severely with unrelated services. Under some circumstances interference to the unrelated service can be so severe that it can be rendered useless (as mentioned, this can be very problematic when services are mobile as it's very difficult to take every contingency or location into account). 6. These matters become much more critical when the stakes are high - with emergency services, radar altimeters, etc. where lives can be at stake if things go wrong. 7. Critical communications services have always demanded very high protection ratios and have traditionally been given them by Spectrum Management agencies - the FCC, et al. The current argument is that the ubiquity of 5G threatens the high protection ratio previously afforded radar altimeters. 8. If I were in the aircraft industry and I was responsible for the reliability of safety devices such as radio altimeters then I'd want to be absolutely certain that any new radiocommunication service is not going to interfere with any of my critical services. Moreover, I would be overly concerned with the potential for mobile phone services to interfere with these safety services specifically because phone services are a never-ending moving target when it comes to location, density of phone traffic, etc., all of which have potential to cause interference. 9. Whether 5G has real potential to interfere with radar altimeters or any other aeronautical communications service can only be determined by proper independent engineering studies. The fact that we have this dispute at this late juncture shows that something has seriously gone wrong in the planning phase. (From my observations, it seems the mobile phone industry has had too much political power, especially so when it comes to buying spectrum - and it has lots of money to demand what it wants (and to date it's gotten the spectrum it wants). Whilst government eyes the millions to be made from the sale of spectrum, the trouble is that it's also the regulator of the spectrum hence it has a conflict of interest. Fundamentally, spectrum auctions run by governments have the potential to compromise good spectrum management. Whether it's happened in this instance I cannot say for certain. The only other point I'd stress is that the electromagnetic spectrum is a scarce nonrenewable environmental resource and should be respected and treated as such (like any other environmental issue).

2143 5y ago

The animal doesn't know or care about who owns what land. It sees grass. It eats.