Re: satellite tv reception

[Ken Olum <kdo cosmos phy tufts edu>]

I guess no one answered this, so I will give it a try.  I would expect
that since trees have sap, which is probably a fairly good conductor,
they are generally opaque to electromagnetic radiation.  Of course if
you only have one tree, as opposed to a forest of closely spaced ones,
then waves that are longer than the width of the tree will just go
around it.  This certainly applies to AM, FM and broadcast TV signals.

Some cellphones operate at 2.4Ghz, which means about 10cm, which is
smaller than a tree trunk.  I conjecture that if you put your
cellphone  right next to the tree on the opposite side from the tower,
that it will not work.  If you're not right next to the tree, then
probably diffraction is enough.  Of course if there are multiple
possible towers than you would need trees between you and each of them.

For several times 10GHz, we have waves of 1cm or so.  Then if the tree
is sufficiently much larger than the dish and sufficiently close to
it, you will not get a signal.

I don't think it matters here, but the argument that materials are
transparent to higher energy waves is certainly not true in general.
Ordinary glass, for example, is opaque to ultraviolet but not visible
light.

                                        Ken