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Guest Message by DevFuse

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Using a pole to get over trees?


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23 replies to this topic

#1 OFFLINE   igator99

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Posted 27 July 2006 - 10:15 PM

Hi
I was wondering how do you calculate the length of pole needed to get over trees that are in the way? I already have a very long pole attached to my house ( about 18 feet ) and I wanted to move the dish back about 24 feet. About how long would the new pole have to be. I was hoping it could be much shorter or would that distance not matter much? Any help would be greatly appreciated. :)

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#2 OFFLINE   Earl Bonovich

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Posted 27 July 2006 - 10:27 PM

I would only be hazarding a guess... BUT...

You a simply 3-4-5 right triangle trig:

If the 18ft was the 3ft side of the triangle, then the mulitplier is 6
So the 4ft side would be 24ft away..

So according to math... you should be able to put the dish ON THE GROUND, if you move it back 24ft.

That would have to be 24ft straight back in line with the angle of your dish though.... (or perpendicular to your tree line)

If you are going to go back 24ft parallell to the line of sight for the dish... it will probably still have to be 18ft high..
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#3 OFFLINE   igator99

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Posted 27 July 2006 - 11:32 PM

I would only be hazarding a guess... BUT...

You a simply 3-4-5 right triangle trig:

If the 18ft was the 3ft side of the triangle, then the mulitplier is 6
So the 4ft side would be 24ft away..

So according to math... you should be able to put the dish ON THE GROUND, if you move it back 24ft.

That would have to be 24ft straight back in line with the angle of your dish though.... (or perpendicular to your tree line)

If you are going to go back 24ft parallell to the line of sight for the dish... it will probably still have to be 18ft high..



I knew I shouldn't have slept through math class. When I tuned the dish on a much shorter many years a go I was able to hit the sats on a six foot pole. I had to add another 12 foot pole to attach it to the house so I was guessing a 12 foot pole 24 feet away should do the trick. Thanks for the input however.:hurah:

#4 OFFLINE   walters

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Posted 28 July 2006 - 07:10 AM

I would only be hazarding a guess... BUT...

You a simply 3-4-5 right triangle trig:

If the 18ft was the 3ft side of the triangle, then the mulitplier is 6
So the 4ft side would be 24ft away..

So according to math... you should be able to put the dish ON THE GROUND, if you move it back 24ft.

That would have to be 24ft straight back in line with the angle of your dish though.... (or perpendicular to your tree line)

If you are going to go back 24ft parallell to the line of sight for the dish... it will probably still have to be 18ft high..


That takes no account for his dish elevation. In fact it assumes about a 37 degree elevation. But it's OK in this case since his is much higher. Someone in Seattle, though, might need to back up a little more to clear that tree. Or they could use the correct triangle for their latitude.

#5 OFFLINE   Earl Bonovich

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Posted 28 July 2006 - 07:38 AM

Well no.. it doesn't.

If you had a theoretical level platform at the top of that 18ft pole... and the dish mounted to it... The platform has no baring to what direction or elevation the dish needs to be pointed to... So that math part was to move that "platform" .... Kinda like two triangles connected at that one point

:D
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#6 OFFLINE   walters

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Posted 28 July 2006 - 07:56 AM

Are you saying the dish elevation doesn't matter? Do I need to draw a picture?

#7 OFFLINE   Earl Bonovich

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Posted 28 July 2006 - 08:00 AM

I know dish elevation does matter.

In a picture... place a flat piece of wood on top of that "right" triangle.
Take the dish out of the picture....

I am moving that platform around, not the dish.

Ahh well... not a big deal... the math probably won't even pan out correctly in the real life scenerio... as we need to account for the curvature of the earth, the level ground, other objects in the way, trees... and Murphy's law.
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#8 OFFLINE   walters

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Posted 28 July 2006 - 08:20 AM

I still can't figure out if we're arguing or not. :confused:

Suppose someone in Seattle has their DirecTV dish mounted on an 18 foot pole, and mounted there the signal just barely clears a tree. Do you agree that they would have to back up more than 24 feet to clear the tree at ground level, while someone in Louisianna would be just fine at 24 feet?

Those two triangles connected at the point of Dish installation you mentioned earlier: they have to be similar triangles.

Curvature of the earth is only about 8 inches per mile (about 4 hundredths of an inch at the scale we're talking about) and can be safely ignored in this case.

#9 OFFLINE   Earl Bonovich

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Posted 28 July 2006 - 08:22 AM

What where we talking about ;) ?
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#10 OFFLINE   igator99

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Posted 28 July 2006 - 08:56 AM

I still can't figure out if we're arguing or not. :confused:

Suppose someone in Seattle has their DirecTV dish mounted on an 18 foot pole, and mounted there the signal just barely clears a tree. Do you agree that they would have to back up more than 24 feet to clear the tree at ground level, while someone in Louisianna would be just fine at 24 feet?

Those two triangles connected at the point of Dish installation you mentioned earlier: they have to be similar triangles.

Curvature of the earth is only about 8 inches per mile (about 4 hundredths of an inch at the scale we're talking about) and can be safely ignored in this case.



My goodness this is turning into a geometry class. Thanks for the input. I guess the question was more complicated than I thought. I plan on moving the pole when the new slimline dish comes out and I want the pole to be no more than ten feet in the air so I can get to it using a good ladder. I really appreciate the help. :)

#11 OFFLINE   TMullenJr

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Posted 28 July 2006 - 09:51 AM

Cut it out! My head is starting to hurt. :icon_dumm

#12 OFFLINE   Upstream

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Posted 28 July 2006 - 10:22 AM

See the picture below.

The original poster doesn't say how far the 18 ft pole is from the tree, or how high the tree is. So I have to assign some variables:

a = distance from tree to pole
t = height of tree
b = t - 18


The angle of sight to the satellite does not change by moving the dish back 24 feet. I don't know what the angle is, but it doesn't matter. I also assume that the ground is level (the curvature of the Earth is negligible at a distance of 24 feet), and I assume that there is nothing other than the tree blocking the line of sight to the satellite.

When you move the dish back 24 feet the height of the new pole is calculated as:

height = 18 - ( 24 b/a )

If the result is a negative number, it is not necessary to dig a hole. Just put the dish on or slightly above the ground.

Posted Image

#13 OFFLINE   walters

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Posted 28 July 2006 - 10:44 AM

Actually, you do know the angle, and it does matter. It's the arc tangent of b/a.

#14 OFFLINE   igator99

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Posted 28 July 2006 - 10:48 AM

Thank you thank you thank you. So in dummy terms (this is what I need) I should have no problem hitting the sats with a ten foot pole or less? BTW How in the heck did you get that picture done? Wait maybe I don't want to know I feel my head might explode. Sincerley thank you! :) Now I just have to wait for the slimline to come out.

#15 OFFLINE   Earl Bonovich

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Posted 28 July 2006 - 10:59 AM

Whats the phrase...

"I was told there would be no math"
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#16 OFFLINE   Upstream

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Posted 28 July 2006 - 11:06 AM

igator --

whether you can get away with a 10 ft or shorter pole depends on the ratio between b and a. If b/a is 1/3 or larger, then you are OK. But if b/a is less than 1/3, you need a pole taller than 10 ft.

For example, if your tree is 20 feet tall, and the pole is currently 10 feet from the tree, then b=2 and a=10. The ratio b/a is 0.2 (which is less than 0.33). You will need a pole which is 13.2 feet tall (18 - 24 x 0.2).

#17 OFFLINE   harsh

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Posted 28 July 2006 - 11:15 AM

Actually, you do know the angle, and it does matter. It's the arc tangent of b/a.

Better yet, we know the angle to be the relative elevation of the satellite.

Don't forget to take into account that most living trees are growing and what works this summer may be obscured by new growth next summer.

#18 OFFLINE   Earl Bonovich

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Posted 28 July 2006 - 11:21 AM

I think at this point it would be easier just to get a chainsaw (or bigger) and just take out the trees.
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#19 OFFLINE   Upstream

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Posted 28 July 2006 - 11:34 AM

Better yet, we know the angle to be the relative elevation of the satellite.



Good point. For New Orleans, the satellite elevation is approximately 53 degrees.

This means the ratio of b/a in my illustration above is TAN 53 = 1.3. So the height of the new pole would need to be 18 - (24 x 1.3) = -13 feet.

This is a negative number, so he could just put the dish on the ground (which is what Earl said 14 hours ago).

#20 OFFLINE   y0ud0ntkn0wjack

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Posted 28 July 2006 - 12:56 PM

I think at this point it would be easier just to get a chainsaw (or bigger) and just take out the trees.

I think that might be the best solution. Never thought there'd be so much math involved in moving a satellite dish. :lol:




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