4 ms·

"Don't interfere with defective radar altimeters" is not the way the law works. The law says don't emit more power than you are allowed to within your assigned

"Don't interfere with defective radar altimeters" is not the way the law works. The law says don't emit more power than you are allowed to within your assigned frequency band, and much less outside it. The basic problem here is that way too many radar altimeters are fundamentally defective in terms of being sensitive to emissions they should have been designed from the beginning to ignore. The FCC doesn't make any promises that listening to the wrong frequencies won't produce harmful interference. That is the receiver's job to avoid listening to signals on those frequencies. And if somehow radar altimeters can't or couldn't be designed to ignore radio emissions outside their assigned frequency range, the FAA should have demanded a far larger frequency band from the beginning instead of implying the one that was assigned was adequate for the purpose and then later attempting to squat all over frequency bands they were never assigned.

upofadown 5y ago
The root problem here is that this used to be a satellite downlink band. So virtually no guard bands were required. It is like if someone bought a house in a residential area, knocked it down, and built a steel mill.
bunnie 5y ago
The filter mask is reasonable for broadband radar, especially considering that we have to consider equipment older than 5G (I am plagued by FCC rules that protect AM radios, so why should radar altimeters be considered defective and not AM radios?). If you have to make a guess as to which is wrong, the legislation, or the laws of physics, I'd put my bets on the legislation being wrong. Furthermore, things could be much worse because the filters that are used to prevent leakage into radar altimeter frequencies can fail on a 5G device, but the 5G device would continue to operate just fine without anyone noticing (except for the plane that ended up in pieces on the runway). In other words, 5G transmitters would normally emit sidebands that jam altimeters, if not for a handful of components that prevent it from happening. But if one of these components were to fail -- say, a user dropped their phone and one of the filter elements cracked or de-tuned -- it'd just straight up jam an airplane's altimeter. I'd like to think that regulatory bodies exist because they are supposed to consider public safety as part of their mandate. We don't want to lose our children in an airplane crash and have the best answer be "whelp, that radar designed 20 years ago should have anticipated 5G jamming. Therefore that altimeter was defective. Anyways, no actual laws were broken, so those lives lost is just the price of progress". I think an alternative view would be that the FCC should have spectrum auctions not just "because valuable things should go to the highest bidder", but in part to raise funds to upgrade things like airplane radars so they could tolerate the interference caused by the new equipment that was going to be installed in an adjacent band. Government does this all the time: you want to move your business into the neighborhood? You have to upgrade the infrastructure to support the burdens of your new business. We didn't run megawatt-scale power lines to every suburban block just in case someone wants to setup a datacenter there, and if the power goes out because of the datacenter's loads we don't blame the residents of the town for not having anticipated the Internet. And with over $80 billion raised in spectrum auctions, you'd think that'd be within the realm of possibility - one could replace 100,000 radar altimeters at $10k a pop for "just" a billion dollars, or about 1% of the auction proceeds.

upofadown 5y ago

The root problem here is that this used to be a satellite downlink band. So virtually no guard bands were required. It is like if someone bought a house in a residential area, knocked it down, and built a steel mill.

bunnie 5y ago

The filter mask is reasonable for broadband radar, especially considering that we have to consider equipment older than 5G (I am plagued by FCC rules that protect AM radios, so why should radar altimeters be considered defective and not AM radios?). If you have to make a guess as to which is wrong, the legislation, or the laws of physics, I'd put my bets on the legislation being wrong. Furthermore, things could be much worse because the filters that are used to prevent leakage into radar altimeter frequencies can fail on a 5G device, but the 5G device would continue to operate just fine without anyone noticing (except for the plane that ended up in pieces on the runway). In other words, 5G transmitters would normally emit sidebands that jam altimeters, if not for a handful of components that prevent it from happening. But if one of these components were to fail -- say, a user dropped their phone and one of the filter elements cracked or de-tuned -- it'd just straight up jam an airplane's altimeter. I'd like to think that regulatory bodies exist because they are supposed to consider public safety as part of their mandate. We don't want to lose our children in an airplane crash and have the best answer be "whelp, that radar designed 20 years ago should have anticipated 5G jamming. Therefore that altimeter was defective. Anyways, no actual laws were broken, so those lives lost is just the price of progress". I think an alternative view would be that the FCC should have spectrum auctions not just "because valuable things should go to the highest bidder", but in part to raise funds to upgrade things like airplane radars so they could tolerate the interference caused by the new equipment that was going to be installed in an adjacent band. Government does this all the time: you want to move your business into the neighborhood? You have to upgrade the infrastructure to support the burdens of your new business. We didn't run megawatt-scale power lines to every suburban block just in case someone wants to setup a datacenter there, and if the power goes out because of the datacenter's loads we don't blame the residents of the town for not having anticipated the Internet. And with over $80 billion raised in spectrum auctions, you'd think that'd be within the realm of possibility - one could replace 100,000 radar altimeters at $10k a pop for "just" a billion dollars, or about 1% of the auction proceeds.