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by anfractuosity 1845 days ago
Are different frequencies attenuated differently then out of interest in water?
2 comments
kajecounterhack 1845 days ago
Different frequencies are attenuated differently, yes. So like, green laser vs red laser will have different max distances under water.

Fun fact, salinity of water also affects transmission. So rate of transmission in a lake vs ocean is also going to be different.

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xhrpost 1845 days ago
Yes, generally the smaller the wavelength, the worse the attenuation. Quick googling: 4g is 600Mhz to 2.5Ghz or 0.5m to 12.5cm wavelength. For comparison, the US Navy uses 80Hz or 3750km wavelength to talk to submerged submarines.[1]

[1] https://en.wikipedia.org/wiki/Ground_dipole

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zepearl 1845 days ago
From https://en.wikipedia.org/wiki/Ground_dipole :

> After initially considering several larger systems (Project Sanguine), the U.S. Navy constructed two ELF transmitter facilities...

> Both transmitters were shut down in 2004. The official Navy explanation was that advances in VLF communication systems had made them unnecessary.

I then started reading about VLF https://en.wikipedia.org/wiki/Very_low_frequency and on that page I see this sentence:

> VLF waves used to communicate with submarines have created an artificial bubble around the Earth that can protect it from solar flares and coronal mass ejections; this occurred through interaction with high-energy radiation particles.

That sounds absolutely weird - how should that "...that can protect it from solar flares..." be interpreted?

EDIT: didn't notice Wikipedia's linked article - https://www.theatlantic.com/science/archive/2017/05/wow-guys...

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