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Comment by BugsJustFindMe | Hacker News Reader

It's been a very long time since I worked with directional radios, but it feels very weird to learn that a tree counts as a sky obstruction significant enough to kill the signal. It's just a tree, not a giant steel building or a mountain. Leaves are barely there, relatively speaking.

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For RF absorption, the rule of thumb is that the higher the frequency, the more the signal is attenuated. Once you get into the gigahertz range, things like leaves block (actually: absorb) a huge amount of the energy.

This is why if you have a wifi router with both 2.4 and 5 GHz bands, the 2.4 GHz band usually has much better range.

Visible light is in the THz spectrum which is blocked by anything solid that isn't clear or translucent.

I have a backup 4G modem here, and when the leaves come out on the trees in the summer, I see a signal drop. 4 bars to 2 bars.

The trees (forest) is line of sight between me and the only tower.

I presume it's all that water in the leaves.

I think that your observation of water is probably spot-on. When it comes which RF frequencies get absorbed, with water the answer is pretty much "yes". Combined with what I'd imagine is some really fun scattering math tossed in, tree cover is a pretty good bet for reducing signal quality, especially if it's more than one.

Is that a function of the wavelength it's using? A quick search suggests that starlink uses 10-12ghz, are trees opaque at those frequencies?

I had a digital TV antenna in Oshawa pointed direct at the CN Tower in Toronto, there was only one tree in my direct line of sight, come summer when the leaves were fully developed I lost a number of channels because the signals was not strong enough. The tree was not on my property so I could not cut it.

Leaves are mostly water, which does a good job of absorbing 10Ghz RF.

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