Distance to Clear Obstacle

[HDTVFanAtic]

This came up a few months ago.....and someone posted a url that calculated the distance needed to clear an obstacle with a dish (such as a fence, roof line or house next door). I bookmarked the url:

http://www.bjupress.com/services/bjhomesat/tech_support/obstacle.html

So I need it today and since I know I have the bookmark, I don't think much of it...until I read the page.

It says Enter your elevation. (Please consult the table below if you do not know your elevation.)

For Florida it lists:

Miami 54.5
Tampa 53.7

Those seem a little high in elevation to me, but whatever.

But then I start examining the list and note that according to this list San Antonio Texas is the highest point in the nation with an elevation of 55.7 feet beating Denver (the mile high city) which is lower than Florida at 43.3 feet??????

If I put in I am at 5 feet above sea level and trying to clear an 8 foot object, I need to be 91 feet back from the 8 foot object??????

wtf......even my dog knows that isn't right.

Does anyone have a site that isn't on crack?

 

[damaged]

Maybe because it is elevation of your dish pointing at the sky (as in Elevation/Azimuth/Tilt), not the elevation of ground level.

 

[voomvoom]

I just tried that and I don't know my elevation and my town isn't listed. The 2 in my state listed, one on the coast @ 48.8 and the other closer to the mountains @ 48.5, can't be right. I took a guess and used 321 (elevation) trying to go over a 38 (height) tree, it gave me a "-47" from the object I'm trying to clear. How would it know what you're trying to get (as which sat), and I can't help but wonder what degree it's supposed to be angling at.
I noticed that homepage belongs to a service that's usually scrambled, but is currently in the clear on IA5. At least it was last night. Now, I don't know if I want to learn anything from them.

Al

 

[voomvoom]

Maybe because it is elevation of your dish pointing at the sky (as in Elevation/Azimuth/Tilt), not the elevation of ground level.

I suppose then that your dish needs to be 91 feet from an 8 foot object to get the lowest possible satellite in the arc. That almost makes sense. I still wonder what degree angle that would be on the horizon.

Al

 

[Pepper]

Those elevations are that of a dish pointed at the specific satellite BJ Homesat uses, IA5 at 97W, not feet above sea level or any other such thing. San Antonio is closer than Denver to 97W, plus it's further south, thus a higher look angle.

At a 45 degree angle, the height of an object is equal to the distance from it you must be to clear it at that angle. If the angle is > 45, you can be closer, further away at <45.

There's a simple geometry formula that with the length of one side of a right triangle (height of object) and an angle (elevation) you can calculate the other side (distance from object). Maybe somebody who was in geometry class less than 20 years ago can remember.

 

[voomvoom]

Thanks for that explanation Pepper, about "Those elevations are that of a dish pointed at the specific satellite BJ Homesat uses, IA5 at 97W, not feet above sea level or any other such thing.", never would have figured that or anything like it.
hope the rest of your explination can help HDTVFanAtic.

Al

 

[PSB]

The satellite table is only for IA-5

This calculator will work for any satellite SIMPLY enter the ELEVATION to the satellite you are aiming for (38º for IA-6 here in MN. for example) Enter the hieght of the tree/building you are trying to clear...........

Click on CALCULATE and it gives you the distance that you would have to be away from the object to clear it!

The formula is built into the tool!

(So for IA-6 @ 38º (Here in MN.) with a 100' tall building in front of me, I would have to be 128' away to clear it!)

 

[voomvoom]

Thanks Pete, that's even more helpful. So, what I thought should be feet are actually degrees, and it should be from me to whichever sat I'm interested in. And the height of an object would still be whatever it is. I'm slow, but I'm getting there.

Al

 

[PSB]

Iceberg STILL has trouble with that one too (I think?)

Its a handy tool I have used for a few years now!

 

[HDTVFanAtic]

The satellite table is only for IA-5

This calculator will work for any satellite SIMPLY enter the ELEVATION to the satellite you are aiming for (38º for IA-6 here in MN. for example) Enter the hieght of the tree/building you are trying to clear...........

Click on CALCULATE and it gives you the distance that you would have to be away from the object to clear it!

The formula is built into the tool!

(So for IA-6 @ 38º (Here in MN.) with a 100' tall building in front of me, I would have to be 128' away to clear it!)

Ok, I am clearly missing something again

What calculator is "this calculator"? The BJ calculator page?

 

[Pepper]

yes, the BJ calculator page

This page has some pictures that can help you to visualize the process. http://www.bjupress.com/services/bjhomesat/tech_support/site_survey/site_survey2.html

 

[voomvoom]

Ok, I am clearly missing something again

What calculator is "this calculator"? The BJ calculator page?

OK, let's see if I got it right? Think of the Elevetion (angle of your dish) that you enter as being the LOS from your dish to whatever satellite you want to get. Of course you will need to know what that is first. Then put the Height of your obstruction in the other box and Calculate.

Al

 

[BKP]

Of course you will need to know what that is first.

I got that part now.. But, how do you know the angle of the sat you want..

 

[PSB]

I use the Satfinder program, enter your zip code and it gives you all the angles needed for all satellites from your area!

http://www.satelliteguys.us/showthread.php?t=50258

 

[vj9999]

I have used this calculator for figuring out distance to clear the obstacle for a while now. It is european and in metric, but it serves the purpose.

http://www.satlex.de/en/elobst_calc.html

 

[HDTVFanAtic]

I have used this calculator for figuring out distance to clear the obstacle for a while now. It is european and in metric, but it serves the purpose.

http://www.satlex.de/en/elobst_calc.html

Actually if you put keep the measurement unit consistent, whether metric, inches, feet or yards, it doesn't mater what you use as you can see if you put in 1 Meter in both boxes or 3.1 (as in feet) or 39 (as in inches) as the formula is still the same.

But thanks for the link!

 

[BKP]

I use the Satfinder program, enter your zip code and it gives you all the angles needed for all satellites from your area!

http://www.satelliteguys.us/showthread.php?t=50258

Yes, I thought of that this morning..