What do you think about this airline vs 5G brouhaha?

Brandon Martin lists.nanog at monmotha.net
Tue Jan 18 22:36:41 UTC 2022

On 1/18/22 5:06 PM, Mel Beckman wrote:
> Incorrect. Owning spectrum also includes the right to 
> interference-free operation. And you imply that the FAA and airline 
> industry has done nothing, when in reality it’s the FCC who has done 
> nothing. the FAA sponsored extensive engineering tests that 
> demonstrate the interference is a concern, and they notified all the 
> parties well in advance. The fCC et al chose to do no research of 
> their own, and are basing all their assumptions on operation in other 
> countries, which even you must admit can’t really be congruent with 
> the US.
Owning spectrum includes the right to interference-free operations from 
IN BAND interference (or not, depending on how you "own" it).

The FAA and airlines are (presumably) correct that there is de-facto an 
interference issue.  The FCC is also (presumably) correct that it's "not 
their problem" as the interference is due to grossly out-of-band 
signals, and the FCC has provided what they believe to be (and, 
according to most RF engineering practices I know of, is) a more than 
sufficient guard band between the two users.

Interference from out-of-band sources is on the operator of the 
receiving equipment to correct EVEN IF they are a licensed, primary user 
of their spectrum since the interference is from outside their 
allocation. This is always true so long as the folks sourcing the 
interference are complying with the limits of their spectrum (there are 
some other wiggles for Part 15 unlicensed users) including power limits 
and applicable transmit spectrum masks.

The FCC's job is to make sure that they set the rules such that folks 
with licensed spectrum do not experience practical problems when 
presented with out-of-band signals. When doing this, they attempt to use 
established guidelines of good engineering practice as well as reports 
from "the field", but they can't possibly account for users with what is 
arguably simply (very) faulty equipment.

If my 1kW HAM FM radio transmitter on 145MHz causes receive problems on 
your aviation band AM receiver (108-137MHz), that is YOUR problem as 
long as I'm complying with all the rules and regs of part 97. That is, 
your receiver sucks, and you need to fix it - possibly by replacing it. 
Likewise, if I'm getting receiver desense issues on my 145MHz FM 
handheld near the airport because of ATC's AM transmitter a few dozen 
MHz down, it's on ME to fix it (or live with it).

The issue that cropped up appears to be that, since the C-band spectrum 
under discussion went unused for so long, a LOT of sucky receivers got 
deployed, and nobody really noticed or cared. Now, it's a big deal to 
try to replace them all, and it's made even worse by how difficult 
changing anything in aviation is and how comparatively old and hence 
simple (perhaps too simple) the radio altimeter RF physical layer 
apparently is.

Brandon Martin

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