5 ms·

What are you talking about "guard bands" ? Is there spectrum assigned alongside the radalt to ensure no crosstalk?

leoqa 5y ago
“Guard” is a common frequency for all pilots to listen/communicate. It’s very rarely used as intended and is mostly cat meows and fart noises.
- addaon 5y ago
  Guard frequency (121.5) is different than "guard bands" in this context. Guard bands are, as was guessed, a frequency range at the edge of an allocation where no energy is /intentionally/ transmitted, and where received signal /should be/ disregarded. Basically it allows the reality of some frequency spillage to be accommodated between what would otherwise be adjacent frequency allocations.
- mlindner 5y ago
  That is completely unrelated. https://en.wikipedia.org/wiki/Guard_band https://en.wikipedia.org/wiki/Guard_band
avianlyric 5y ago
Yes exactly that. The FCC allocated spectrum for radalts to use, then set aside an equivalent amount of spectrum (which is an insane amount of spectrum for a guard band, easily double what most uses get) above and below the radalts spectrum as guard bands that no one is allowed to use. The guard bands ensure that if there is a little spill over from 5G (which there won’t be because modern radios are better than that), or if the radalts have crappy filtering on their front ends (which it seems they do). Then nothing bad will happen, because the guard bands give everyone lots of space for sloppy engineering (which Boeing seems to be abusing)
- p_l 5y ago
  Boeing is not abusing anything - they just published a study on the models of altimeters that were sold with their planes, in specific configurations. Similar studies are performed by Airbus, Bombardier, Dassault, Cessna, etc. etc. And FCC rules only specified transmission frequency of radar altimeters, and radio is analog and perfect filtering is close to impossible (especially with the kind of chirping signal radar altimeters use, where whole 200MHz of spectrum is spanned in single chirp)

“Guard” is a common frequency for all pilots to listen/communicate. It’s very rarely used as intended and is mostly cat meows and fart noises.

addaon 5y ago
Guard frequency (121.5) is different than "guard bands" in this context. Guard bands are, as was guessed, a frequency range at the edge of an allocation where no energy is /intentionally/ transmitted, and where received signal /should be/ disregarded. Basically it allows the reality of some frequency spillage to be accommodated between what would otherwise be adjacent frequency allocations.
mlindner 5y ago
That is completely unrelated. https://en.wikipedia.org/wiki/Guard_band https://en.wikipedia.org/wiki/Guard_band

avianlyric 5y ago

Yes exactly that. The FCC allocated spectrum for radalts to use, then set aside an equivalent amount of spectrum (which is an insane amount of spectrum for a guard band, easily double what most uses get) above and below the radalts spectrum as guard bands that no one is allowed to use. The guard bands ensure that if there is a little spill over from 5G (which there won’t be because modern radios are better than that), or if the radalts have crappy filtering on their front ends (which it seems they do). Then nothing bad will happen, because the guard bands give everyone lots of space for sloppy engineering (which Boeing seems to be abusing)

p_l 5y ago
Boeing is not abusing anything - they just published a study on the models of altimeters that were sold with their planes, in specific configurations. Similar studies are performed by Airbus, Bombardier, Dassault, Cessna, etc. etc. And FCC rules only specified transmission frequency of radar altimeters, and radio is analog and perfect filtering is close to impossible (especially with the kind of chirping signal radar altimeters use, where whole 200MHz of spectrum is spanned in single chirp)