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Re: Trees and S-band signals



Chris, Mark,

Pretty much echo Chris' remarks.  

I was a TV-satellite dealer in the mid 1980's-early 90's and have lots of
c-band experience with tree blockage.  Up here in Alaska the sats are
pretty weak and require a 10 foot dish at minimum for a clear picture.
Trees are either birch or spruce up here.  A tree on line with a satellite
would normally either block totally or reduce the signal to unacceptable
quality.  The conifers usually fell into the "total blockage"  category.
Satellite surveys to find a proper location for the dish on the propety
owners property was critical to having a "happy customer"!  I had to tell a
couple that they either cut down a lot of trees or move.

Here at home I used my 8 foot dish for c-band TV for awhile on Galaxy-V
with very seasonal variation in the poor signal due to birch tree foliage.
I now have an Echostar "Dish-Network" ku-band system: 33 inch dish on my
roof pointed at azimuth ~145, elevation ~15.  I cut down several birch
trees on my south property line to clear the signal.

So for ham microwave operation, I recommend you get the antenna up in the
clear for best use.  My 432 and 2.4G sat antennas are going up on the roof
near the sat-TV dish.  Some directions there will be tree blockage
[SW-West], and below 10 degree elev. in many directions.

Ed  

>From: "nn0v" <nn0v@home.com>
>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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