Line of Sight experiments

[Corrado]

I've been thinking about where some of my fixed dishes are located in relation to the house. With the coming of autumn I've been tracking the sun approaching the Clarke belt in comparison to an opening in the line of sight between the trees.

In my site survey I'm going to setup a temporary test dish for a trial while the leaves are still on. But here's the question...

How much of a opening at a distance of 100' is required? Anyone ever experiment with how wide of an opening is necessary to get the beam through?

I have clear elevation at 35° and up, but only about 20' wide as viewed with the leaves in place.

 

[AcWxRadar]

Corrado,

It might amaze you how small of a "window" you really need, but the larger problem is going to be how much the trees sway with the wind. That will have to be factored in to the equation.

If we are referring to linear Ku band sats, then it is known that these sats may be spaced every two degrees without interfering with the neighboring satellite. Then is seems logical that a four degree "window" of LOS would be sufficient. i.e. two degrees to either side of the satellite desired.

When the solar transit occurs in the fall or the spring, I would say that if the sun is viewable through the opening in the trees so that you can see it, unobstructed, when it is aligned with the two sats adjacent to the one sat that you desire, then you should have no problems at all. This would be quite a large window (roughly 6 degrees or more), but it should factor in any swaying of the trees when the leaves are on. Beyond this, as long as you can view the entire sun through this "window" when it aligns with the desired satellite, then you are probably going to receive the full signal from it (if the trees don't sway in the wind or grow).

Does this sound like a logical method for determining what you are after?

RADAR

 

[pendragon]

The size of the window is angular, and the linear dimensions will depend on how far away the possible blocking object is from the dish as noted. Obviously one does not want the object to obscure a portion of the dish, but there will also be the issue of how much thermal noise impinges on the dish from the object even if it is not blocking line-of-sight. It can be a bit sobering when considering how the earth's thermal noise creeps into a large BUD even when you're say 25 degrees above the horizon.

In terms of solar testing, it would be good to note where the shadows fall on the ground relative to the test dish or where it might be. That would help estimating the angular clearance. A 20' window at 100' is about 11 degrees. Determining where the edges of the dish fall with respect to this window is the crux move.

 

[AcWxRadar]

In terms of solar testing, it would be good to note where the shadows fall on the ground relative to the test dish or where it might be. That would help estimating the angular clearance. A 20' window at 100' is about 11 degrees. Determining where the edges of the dish fall with respect to this window is the crux move.

Pendragon has a really good point here. If the dish antenna (the entire reflecting area) is not shaded from the sun by any of the obstructions during the solar transit, when the sun is aligned with the desired satellite, then the transmission from the satellite will have a clear LOS to the dish.

Therefore, if the sun's rays are not blocked from illuminating the dish, then the satellite's signal will certainly not be blocked. So you could judge by the shadows on the dish itself (assuming of course that the dish is properly aligned).

This will obviously not be able to be determined on an overcast day and only at the proper time during the solar transit.

This solar transit is an exceptional tool for us to use. In case anyone else reading this thread does not have the URL to the calculator... I will provide it here:

Sun Outage Calculator

RADAR

 

[B.J.]

The sun outages in the fall are not when the sun is approaching the Clarke belt, but instead about a bit more than a week AFTER the sun has passed the Clarke belt.
The size of the opening is not an angular effect, because the rays from the sun are effectively parallel. Basically the opening has to be at least as big as the dish, which as mentioned above is when the dish will be in full sunlight with no shadows at the time of the outage.

 

[Corrado]

I was using the sun for a rough estimate and I realize that it's still several degrees higher than the belt presently.Currently it's at the top of the gap. The opening casts little shadow in the areas behind for at least an hour between 1:00-2M. The sun illuminates the area several times wider than the opening. I was thinking about that too.

With that in mind, I have some room to spare as far as what satellite might be available there. I'll try it out for something to do.

Thanks for the brainstorming guys.

 

[AcWxRadar]

Corrado,

Don't forget that the solar transit doesn't occur until the first week of October (roughly) and the date and time vary depending upon your location. Be sure to reference the solar outage calculator to determine the exact information.

The solar outage calculator will list the precise time and day when the sun will be directly behind the satellite. This is when you will want to be looking for the satellites position.

RADAR

 

[Dale_Gribble]

If you have an inclinometer and a small piece of pipe(roughly 1/2 inch by 6 inches) attached to something that you could stick in the ground, this can be usefull for seeing just how clear your path to the satellite is. It's not dead-on-balls accurate, but close enough to be usefull. For me hispasat at 30 deg. west is difficult because of trees, with 1 meter dish, I could get all channels as long as there were no thick clouds or rain. I gave that dish to a friend a few miles away, and he has a clear view of 30 west and a much stronger signal than I had. I attached some pics that show what my view of 30 deg west is. The tree with the lighter color trees is about 100 feet away.