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Re: Trees and S-band signals



Hello, Chris here......using a 9 foot tvro dish with an s converter.
Yes trees are bad for adding noise, if they are leafed out.
If you have a receiver that has AGC or power reading, you see noise power
increase when you steer thru a tree. Thus things are much nicer in the
winter
than in the summer. One branch can noise up a broadcast satellite, at 4 GHz
in a 36 MHz bw it will raise 6-10 db at occlusion. . At s band it is not as
bad but
the thermal energy can still be seen. The wider the bandwidth the more
noticable the effect. Precip seems to also affect things, while I was
checking
the TDRSS S band signals I noticed bad weather at lower angles can knock
 a few db off the c/n of these, but with AO40 there are too many other
variables that change the equation like offpoint, range, mispoint.
On my setup beamwidth is 3 degrees so its tougher to find the satellite but
more possible to hear it once it is found, I have 3k, 15k and 200 k on this
reciever. One can calculate the expected noise in that bandwidth,
sky is 4k, sun is 4000k but only 1/2 degree of the beam included,
and a tree would be 300K with a big nearby tree this would include 100% of
the
beam plus attenuation through the tree, and the leaves are like resistive
loads at
2-6 GHz. I think trees get pretty bad at 800 MHz and above depending
on frequency and the number of them you have to penetrate, for cellular
it may be 3000 feet of trees and for a satellite it may be one tree.
AO 40's orbit is pretty close to that of a geosync satellite so it will have
a
pretty good compatability if you can use TVRO at your house.
At narrow bandwidths attenuation is more a factor, at wide bandwidths
the thermal noise begins to predominate even at low attenuations, such as
one layer of leaves. Also big maple leafs do differently than small elm
leaves.
Elm trees are really noisy at C band. In the summer low elevation effects
begin to weaken the low to the horizon satellites.

While I was tracking the C band 4 GHz satellites the soviets used to run,
I found I had to eat most of a tree to keep it out of my beam to that
satellite,
which one would point north to use. I use lasers to determine if any of a
tree
is in my beam and eitehr move the dish or trim the tree. AO40 has not been
degraded much by looking through dormant leafless trees, but at its
offpointed
signal level there is less than no margin there to begin with.........

I downloaded the audio files from the 40 foot dish and noted evven they had
bad CRC errors, but maybe reprocessing the audio for flat dynamics would
help.



> I've been curious about the effect of trees, branches, and leaves on
> S-band.  I have MANY trees all around my house, and it's never a clear
shot
> (okay, maybe a little one) to a bird.
>
> For 2M and 70cm, I know it hurts the signals, but it's workable.  For my
> Dishnetwork setup, it can't tolerate anything in the way.
>
> Can anybody comment about working S-band through the trees?
>
> Mark L. Hammond  [N8MH]
>
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