What is the true dish viewing angle?

[SouthernSky]

One of the posters indirectly brought up a good question.

When looking from behind the dish, how do you determine line of site being free of obstructions? What is the "rule of thumb", if you will?

While many consumers follow the LNB extension arm up to the sky, I've always heard that one should eyeball from the bottom of the feed extension arm to the top of the bubble cover on the LNB. This, of course, is a much steeper angle than just looking up the arm itself.

And how would you view a twin LNB (like DISH 500) or a triple LNB? Do we use the same guidelines? Anyone ever heard from a manufacturer if this is even possible? Skewing (turning) the dish doesn't make our job easier, either.

I know we have our meters and can always check the screen AFTER we've installed but most installers I know have learned to mount the dish first to determine if a line of site even exists. With 19-degree spacing and the Zip Code lists always a degree or two off, can this visual angle even be achieved?

Sure, an inclinometer helps immensely when picking potential aiming spots, and a couple extra degrees on each side give a window of safety, but tall trees in the yards don't always make this possible, especially on multiple LNB dishes. Not to mention, magnetic interference on the compass when next to a metal building or mobile home.

Anyone have rules of thumb?

[Mike500]

While sighting over the top of the lnb gives a more than realistic idea of the correct line of sight angle than sighting along the lnb arm, it does not give an accurate location. From the physics law of reflection, the angle of incidence is equal to the angle of reflection. The actual angle is a line twice the angle made between a perpendicular line at the center of the dish pan and the line from the center to the center of the lnb's aperature window cover.

The ideal site survey would be with a telescopic transit of theodolite, using the property's survey map. That way, you can locate true north with triangulation to the survey map's corner pins and locate each individual satellite's position by azmuth and altitude by dialing the coordinated into the theodolite. That way, you can see exactly if you have line of sight.

Lacking the theodolite, the property map, the skills and the time, a cruder method would be a laser theodolite, which projects a horozontal laser beam into the night sky. The skew or tilt could be made to tilt the horizontal beam to the same skew or tilt as the setting that are provided by the satellite provider. The azmuth and the elevation could be set with the same settings. In effect, if the beam hits leaves or a stationary object, there is no line of sight in that area. Using the laser as a pinpoint to project the beam into the sky, each satellite location such as 119 can be pointed to with the laser from the prospective mounting location. If the laser's spot can be seen on an object, you have no line of sight.

Another method would be to use any astronomical telescope with an equatorial mount. With the computerized telescopes, all you need to do is to set the mount to your latidude and point the telescope to Polaris or the North Star, zero out the computer, enter in the correct elevation and right ascention(azmuth) and the telescope will automatically move to the correct satellite position.

All the above are theoretical nighttime techniques. For the daytime, you can use either the sextant or gps method.

Using a sextant and a chronometer, you can locate true north to set the transit or theodolite. Then you can see if you got line of sight with the same night method noted above.

Using gps you can locate the actual position of the satellite, but due to 12-16 ft error, this can only be used on large lots. I have experimented with the Garmin eTrex Vista and found the electronic compass to be pretty accurate.

My preferred method is to use a portable single lnb dish for problem installs. You can run signal tests at various locations of any single satellite without mounting the dish. You only proceed to mount the dish, when you have located the best position.