The dish is a reflector that focuses the energy into a small golf-ball sized orb at the mouth of the feedhorn. Inside the feedhorn is a small antenna that is turned by the servo motor to select vertical or horizontal polarity. Knowing this will allow you to see how important it is to properly mount the feedhorn.

Do not assume that because all the supports holding the scalar ring are the same length that centering is automatic. Make sure that all the supports are the same distance from the edge of the dish to the scalar ring. Each measurement should be within 1/32 of each other. You need to assure that the scalar ring (the supporting ring for the feedhorn) is parallel to the bottom of the dish and that it is perfectly centered in the dish. If all this isn’t done, then you will have imperfect reception. Having the focal point off by as little as one-half of one inch can cause a fifty percent loss in signal strength!

The f/D ratio is the focal distance of the dish (f), divided by the diameter (D). When dealing with most prime focus antennas, the number should come out between .28 and .42. If you notice, most of those numbers are also on scale on the side of the feedhorn. You simply set the top edge of the scalar ring even with the line that corresponds to your correct f/D setting. What this adjustment actually does is determines how wide of an angle the feedhorn can "see".

To calculate the focal distance, you need to measure the diameter (D) and the depth (d) of the dish. Measurements should be in like units (you can't use feet for the diameter and inches for depth). For this example, let's say we have a dish that is 120 inches in diameter (D) and 18 inches deep (d). Focal distance (f) equals the diameter squared (D x D) divided by 16 times the depth (16 x d) or:

D x D = 120 x 120 = 14400

16 x d = 16 x 18 = 288

D x D/16 x d = 14400/288 = 50

Therefore focal distance f = 50 inches

After you have calculated the focal distance (f), you can use that figure to calculate the f/D ratio of your dish. In this case, using the same diameter of (D) = 120; and the calculated focal distance (f) = 50

f / D = 50 / 120 = .416

f /D = .416

And round up to give a setting of .42.

Make sure that all coaxial cable connections are crimped with a proper tool and treated to prevent moisture from entering the cable. Make sure you use the gaskets supplied with the LNB's to prevent moisture from entering the throat of the feedhorn. Also, check to be sure the plastic covering for the throat of the feedhorn is attached firmly to prevent both moisture and pests from entering the waveguide.

The diagram below will point out some sensitive areas you need to check to assure best performance.

The biggest difference between a normal LNB and a PLL LNB is the amount of frequency drift. No matter the type of LNB, don't get caught up in a numbers war. Many beginning installers think that a lower temperature LNB will always be better than a higher temperature LNB. This is not necessarily true. A PLL 25 degree LNB will almost always outperform a 17 degree consumer (standard grade) LNB.

Also, you cannot make up for poor dish alignment or installation with a better LNB or line amplifier. The dish needs to collect the signal and send it cleanly to the throat of the feedhorn. All the electronics in the world cannot help the picture if you are losing half your signal and sending loads of noise into the feedhorn. Use a good LNB, preferably a PLL LNB - but spend your time making sure the mechanics of the dish are up to snuff first.

The Actuator Arm (The Dish Mover)

Now that we have the proper LNB mounted on the feedhorn, the feedhorn mounted on the dish and centered exactly, and the dish mounted on a plumb and properly secured pole, we are ready to connect the actuator arm. Make sure you use an actuator that is properly rated for the dish it is attached to. You should never use an 18" actuator arm to try and move a solid 12-foot dish! It may work for a while but the chances are good that you will be replacing it in short order. Try to get the best heavy-duty actuator arm you can - it will pay for itself many times over in years of trouble free service.

There are two types of actuators: the horizon-to-horizon mount that allows 180 degrees of uninterrupted travel; and the linear actuator. The linear arm is far and away the most common and will work just fine in almost all-domestic installations. If you have a desire to view some of the programming on the AOR (Atlantic Ocean Region) international satellites or the corresponding Pacific Region birds, then by all means try to get a horizon-to-horizon mount.

A common error made by both new installers and old-timers alike is in attaching the linear actuator arm. East of the Mississippi a Linear West setting is used. This seems counter-intuitive at first but closer examination will reveal the sense of this set-up. We want the actuator arm to push the dish into position and let gravity help to return it. From the eastern part of the country the lowest satellites will be on the western side of the arc. Therefore position the actuator arm on the west side of the dish (on the right when looking at the dish from behind). From the western part of the country the situation is reversed and the lowest satellites will be the eastern birds. West of the Mississippi, the actuator arm is attached to the left of the dish and called a Linear East Mount.

Correct choice of linear east or west will increase the useful life of the actuator arm. More importantly, on very sophisticated IRD's the receiver actually uses the pulses from the reed sensor switch to predict where a satellite should be. Misidentifying the type of actuator (calling it linear east when it is, in fact, linear west) is the most common problem in using an auto-installation feature.

Now we come to the hardest part of the installation. If you pay close attention to the following procedures it will pay off in the long run with better reception on Ku-Band and weaker C-Band satellites.

Three adjustments are required to ensure proper tracking of the arc: Azimuth (north/south heading), declination offset angle and polar axis angle (inclination angle). These parameters should be set while the dish is aimed toward its highest position, namely towards the southern-most satellite.

The azimuth must be set right in order to detect all the satellites in the viewable arc. Most dishes have a flat plate on the mount that can be used as a sighting reference. A hand-held compass is the most effective type for lining up the mount. Remember that a correction for magnetic variation is necessary. Add magnetic variation to the compass heading for west magnetic variation; subtract for east.

The polar axis angle or inclination angle is within fractions of the site latitude. Most mounts have one or two long threaded rods that are used to adjust the polar axis angle. An inclinometer resting on the axis bar or back part of the mount is used to set this angle.

The declination offset adjustment lowers the sight of a dish to the arc of the satellites. Declination is greater in locations farther away from the equator. Just like the offset angle, it is measured with an inclinometer. The difference between the two readings, one on the main bar, and one on a flat spot on the back of the dish, should be equal to the declination offset. The easiest way to set the declination offset is with an inclinometer placed on the back surface that is parallel with the face of the dish. Or via a flat board placed in a vertical direction spanning the rims. This reading should be equal to the sum of the polar axis and declination angles.

Determine the latitude of your installation by using a map. Below is a table where you can look up the polar axis, and declination angle as well the apex elevation for your latitude.

When the declination is properly set, the procedure is to set the dish to true south (not magnetic south). You need to compensate and use the polar axis adjustment to capture the southernmost satellite visible from your location. This is called the zenith satellite. Once you are peaked at the southernmost satellite you can use the actuator control on your receiver to move the dish to the lowest satellite off the horizon you can see. This is called the extreme satellite.

Once you have located the extreme satellite, gently push up and down on the edge of the dish to see which direction helps clear up the picture. If pushing down on the lip of the dish clears up the picture, then you need to rotate the polar mount counterclockwise. If pushing up on the lip of the dish clears up the picture, then you need to rotate the polar mount clockwise on the pole.