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> the one operating on 60 GHz so that it cannot be heard from the ground directly

Isn't that the same frequency for ground-based 5G mmWave?



Yes. It is absorbed by moisture in the atmosphere. That limits its range, which is great if you want to setup lots of cellular towers without them interfering with each other. If 5g used a frequency that wasn't absorbed, individual towers would have to be much further apart, increasing "cell" size and limiting available bandwidth.

https://en.wikipedia.org/wiki/Extremely_high_frequency


I read a paper about that. It said that 98% of the energy emitted at that frequency is absorbed by oxygen, and this was touted as a benefit, because it effectively “insulated” the towers, so they would not interfere with each other. But I am still surprised that any engineer would design a system that is only 2 percent efficient.


At scale all radio is absorbed by something... mostly not your recipient's antenna.


or continues propagating into the endless depths of space


Sure. Unlikely for 5G towers given frequencies and location.


In the US, the current licensed 5G millimeter bands are 24, 28, 37, 39 and 47 GHz. 60 GHz is an unlicensed band (actually 57 to 71 GHz) used for 802.11ad. Typical use is uncompressed HDMI extenders inside of a single room.




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