Satellite Downlink: Check Dish
Check the Condition of Your Current Dish
1. Check to see if your main reflector is sagging, squinting or bent: With your naked eye, sight across the diameter of the dish from the lower edge to the upper edge. The two edges should be parallel to each other and should appear to be in the same plane. Do two sightings across two different diameters about 90 degrees apart. Another method is to take two pieces of string and stretch them across two different diameters of the main reflector, about 90 degrees apart. They don't need to pass through the exact center of the dish. Make sure the strings are taut. The two strings should intersect near the middle of the dish. Ideally, they should touch each other. Using either method, if the dish appears to have sagged you will need to see what hardware can be adjusted to bring the dish into alignment. You may need to contact the antenna's manufacturer for advice.
2. Check for a dented dish: Perforated metal dishes or mesh dishes are easy to bend or dent. This not only reduces the signal gathering ability of the dish from the intended satellite, but also increases the interference which will be received from adjacent satellites. If the dent cannot be corrected, it may be time to buy a new satellite dish.
3. Check the feed element: To see that it is centered. If it is not centered, and it's not an "offset" dish, you will need to adjust the hardware to bring it into alignment. If the pole or spar which holds up the feed element sways or moves and cannot be fixed in a central location, it may be damaged beyond economical repair. You may need to purchase new parts from the antenna manufacturer. If a new spar is unavailable, you may need to buy a new dish antenna.
4. Check the Aiming of Your Satellite Dish: The only way you can tell if your dish is pointed correctly at the desired satellite is to re-aim the dish slightly to see if the signal can be improved. You will need to temporarily relocate the satellite receiver outdoors, where those adjusting the antenna can view it. Loosen any hardware that holds the dish at its fixed elevation and azimuth angles. If your antenna uses a crank or screw mechanism for setting the azimuth and elevation angles, pick one direction of the azimuth axis, and turn the crank or screw mechanism. Keep turning the azimuth slowly in one direction until the receiver indicates a marginal condition. Stop turning the mechanism.
Reverse the direction of cranking, this time counting the number of turns of the crank or screw. The antenna will move into an area of better signal and then, once you pass the desired satellite, reception will become marginal again. Stop here. Note how many turns you cranked between when you started at the marginal signal on one side, and when you stopped with the signal turning marginal on the other side. Divide that number in half, and set the azimuth halfway between the two points. Tighten the hardware.
Repeat this exercise for the elevation axis.
5. Check for Correct Polarization: Make sure you peaked the elevation and azimuth as outlined above. Then use the same basic method you used in aiming your dish in the section above. Loosen the polarization hardware and twist the polarization slowly to find the two positions where the receiver indicates a marginal signal. Mark the two points and set the polarization halfway between those points. Tighten the hardware.
6. Check the Feed Element Focal Distance: On some antennas, there is an adjustment of what is called the "F/D ratio" or "focal length", which is the distance of the feed element from the main reflector. Once again, there is hardware to loosen and through trial and error you can see if the signal can be improved.
7. Is Your Antenna Purposely Mis-aimed? Some satellite users have deliberately mis-aimed their satellite dishes to minimize interference from an adjacent satellite on one side of the intended satellite. You may need to repoint your dish antennas to maximize reception of your desired satellite.