Distance between dishes??

[esteveW]

I just obtained a second BUD and want to place this one on the same north south line in my side yard. The first dish is now 4 ft from my true N/S property line. (easy to find true south, if you believe the property plot map.)

I have already surveyed the satelitte horizon and have noticed only one tree that could cause a problem and right now there is no bird at that azimuth.

Now my question is how far back from the first dish should I place the second, if I stay the same distance from the property line. I'll try and have the post height the same, right now the first dish is a 10' and the top rim is 13' off the ground. However. if I do a switch and put the new 9' dish on that post and that would put it 12' to the top of the dish rim. Trying to keep the space between to a minimum to consoladate the cable run to the house.

I could figure this by trial and error but run the risk of missing something in the process.

Can someone "do the Math" on this. (I'm located at 47 north.)

Steve

 

[pendragon]

The elevation of your true south bird is around 36 degrees. You want the bottom of the dish on the north to see over the top of the dish on the south. So first you need the difference in the vertical.

If your current 10' dish is pointed at true south and the height to the top is 13' above the ground, I'm going to estimate the bottom rim is about 5' above the ground. If the size of your new BUD is 9' and you put it on the same height pole north of the original, then its bottom rim should be about 5.4'. Next we subtract 'top rim height' - 'bottom rim height' = 13 - 5.4 = 7.6.

What ever you get, multiply it by 1.4 (the reciprocal of the tangent of 36 degrees) to get the distance behind the top of the front dish to the bottom of the rear dish. For this example 7.6 x 1.4 = 10.64' or about 10' 8". But the north dish sticks out south on the bottom and the south dish sticks out north on the top. Add 6' to the 10' 8" = 16' 8" to get the pole to pole distance (10 x sin 36). This is the absolute minimum spacing. I would add 2-4' in case the height changes some time in the future and to accommodate some second order effects that aren't worth calculating.