Surveying the site is the first step in a good installation. The purpose of the site survey is to assure that several conditions are met that will ensure the proper operation of the C-Band TV system. The conditions you are examining are:
Is there an unobstructed view to all of the satellite positions?
Will seasonal foliage cause problems?
Is the area that the dish is to be anchored into solid?
Are there sources of terrestrial interference that need to be considered?
Make sure that there is nothing that will obstruct the dish as it moves the full span of the sky. You must verify that there are no transmissions in the 3.7 to 4.2 GHz frequency band that will cause problems with reception. An easy way to verify this is to use a good LNB connected to a signal strength meter. Move the LNB around the target area in a full circle. If you notice any spikes of signal it is safe to assume those same spikes may cause interference after the installation is finished.
A properly installed dish requires a perfectly plumb pole and a well-anchored solid base. It is a good idea to fill the pole with concrete as well as pouring a concrete base; this will stabilize the dish pole and allow for more accurate reception of both C and Ku-Band signals.
A good "rule of thumb" is to use one bag of concrete for each full foot of dish size. A seven and one half-foot dish needs a minimum of seven bags of concrete as an anchor. If you are in a region where strong storms are common, then more concrete is recommended.
Every dish sold comes with directions for assembly. Make sure you read the instructions before attempting to assemble the dish! Some important things to remember:
The dish is a reflector that focuses the energy into a small golf-ball sized orb at the mouth of the feed horn. Inside the feed horn 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 feed horn.
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 feed horn) is parallel to the bottom of the dish and that it is aimed at perfect center of the dish. If all this isn’t done, then you will have degraded reception. Having the focal point off by as little as one-half 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 a scale at 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 feed horn 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.
All of this information will be provided in the dish and feedhorn manufacturer’s instructions. It is important to read the directions and understand the type of equipment you are working with. Often times you will be working on a system that was previously installed.
Moisture is the enemy of microwave reception. Making sure the feedhorn and LNB's are protected and properly installed is very important to long-term, service-free performance of a C-Band TV system.
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 LNB is the electronic device that mounts on the feedhorn and converts that golf-ball-sized globe of RF energy into an electrical signal the IRD (receiver) can understand and use. There are several kinds of LNB. There are LNBF’s that use voltage on the coaxial cable to switch from vertical to horizontal polarity. There are consumer grade LNB's that use an external servo motor to turn the probe and select polarity. And finally there are Digital or PLL (Phase Locked Loop) LNB's that are normally used on commercial installations. It is highly recommended that a PLL LNB be used on any high-quality TVRO installation, whether consumer or commercial.
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.
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 and the dish is pointing straight with the mount, the procedure is to set the dish to true south (not magnetic south). You need to compensate and use the polar axis (elevation) adjustment to capture the highest, southernmost satellite visible from your location. This is called the zenith satellite. Once you are peaked at the southernmost satellite using elevation and rotating the dish on the pole, 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 mount slightly towards the high side. If pushing up on the lip of the dish clears up the picture, then you need to rotate the mount towards the low side on the pole.
After you have made the azimuth adjustment, return to the extreme satellite and check that no up or down pushing improves or degrades the picture. Rotate the mount as necessary until you home in on the satellite exactly using only the actuator motion. Go back to the zenith satellite and check it. Also check the last satellite on the opposite end and adjust the polar tracking as necessary. After the dish is tracking the Zenith and two end satellites, The rest are automatically in line.