Condition of your dish
The first step in evaluating your current dish condition is to see if the dish reflector is bent or sagging. One method is to stretch two pieces of string, separated by 90 degree angles, across the diameter of the dish. Make sure the strings are tight and intersect near the center of the dish. If the dish is not bent the strings should touch at the intersection point. Another method is to site across the diameter of the dish with your naked eye. Look from the lower edge to the upper edge, and again from the side edge to the opposing side edge. In each case the edges should be parallel to each other, appearing in the same plane. If the dish appears to have sagged it should be adjusted, repaired or replaced to achieve maximum signal reflection. Next check to see if the dish is dented. Mesh dishes are easily subject to denting or ending. A dish damaged in this manner will suffer from poor signal gathering ability while also becoming more susceptible to interference from adjacent satellites. Consider buying a new dish if the damage cannot be repaired. Finally look to see that the feed horn is positioned correctly above the reflector. If it is not designed to be “offset”, the horn should be positioned above the center of the dish reflector. Check any connecting hardware for the feed assembly support poles, making sure there is a tight fit to eliminate any potential movement.
Alignment (Azimuth and Elevation)
The most effective way to check the alignment (“aiming”) of your satellite dish is to re-align it slightly to see if an improvement can be made in the signal quality and strength. Proceed by moving your satellite receiver outside with the dish so it can be monitored by those adjusting the alignment. Before any adjustments are made it is best to mark the current position of the dish by placing pencil marks on the pole and elevation guide. Loosen any hardware securing the dish in its current position. Most antennas use a crank or screw type adjustment for setting the azimuth (side-to-side) and elevation settings. Start with the azimuth angle and move the dish in one direction until the receiver begins to lose the signal. Mark this point on your dish and now turn it in the opposite direction. Turn past the starting point and stop where the signal again becomes marginal. Mark this point. Setting the dish halfway between the marks should be the point where the signal strength is greatest. Tighten the dish hardware at this point. Use the same technique for adjusting the elevation setting. To find the coordinates needed for the proper azimuth and elevation settings for your dish, refer to the azimuth and elevation chart. Polarization Once you have peaked the elevation and azimuth you can use the same type of procedure for setting the polarization of the LNB or LNA.
Mark the current position of the assembly, loosen the hardware and turn in both directions to find the points where you lose the signal. Halfway between these two positions should be the spot where signal strength is the greatest.
When installing a new satellite dish the first step is to conduct a site survey to select the location for the install. You can either hire someone to do this, or you can do it yourself. Satellites used in the broadcast industry are in a Geostationary orbit and thus reside on an arc in the sky, positioned above the equator. Your future dish site needs to be able to “see” this arc, or at least the portion of the arc that holds the satellite you want to receive programming from. By using a compass and inclinometer you can check the arc from your proposed site. Inclinometers are available at most hardware stores and are sometimes called an “angle finder”. Determining the site’s ability to see the arc should be the first step in your site survey. Refer to the azimuth and elevation chart to find out where your dish will need to “look” for the satellite you wish to tune to. A check of local ordinances and zoning laws should also be conducted. Be sure there are no regulations on land use such as historic district rulings. The next consideration should be the distance from the future dish location to where the satellite receiver will be located. As the distance increases so does the amount of cabling needed between the two points. The more cable you have the more it costs. More importantly as the distance increases the amount of signal to the receiver decreases. Also be sure the dish and any cable routing will be entirely on property you own or lease. Terrestial interference is also a concern for satellite downlink points. Interference can come from telephone company microwave links, cellular phone towers and even airport radar sites. Roof locations for a dish installation are not uncommon but present unique concerns. These include access to the dish location, ability to properly anchor the dish mount, and terrestrial interference that may not be a concern at a ground level location.
Selecting a dish
As with anything else purchasing a new dish will provide you with many choices, some more suitable than others. Your first decision is between a solid or mesh dish design. Solid dishes offer many advantages over a mesh dish and should be the choice for nearly every situation. Solid dishes hold up better against wind stress, retain their shape better and have a much longer life expectancy than a mesh dish. While being more expensive, you can expect better performance and longer life with a solid dish compared to a mesh design. Mesh dishes are more flexible due to their design and thus more subject to wind stress and more likely to lose shape. At the beginning of their life expect less signal reflection with a mesh dish, compound this with a greater tendency to lose shape and you can expect poor performance at some point down the road. Mesh dishes also tend to have poor side lobe rejection subjecting the desired signal to unnecessary interference. The next decision regard the size of the dishes diameter. Buy the biggest dish your budget can afford. Bigger dishes have higher gain and also look at a narrower “beam” from the satellite, providing better rejection of side lobe and terrestrial interference. Though good results can sometimes be obtained on 3 meter dishes, Learfield recommends that a dish of not less than 3.7 meters be used.
LNA or LNB?
An LNA or LNB is the antenna element of your satellite dish. It is located in the feed horn. LNA stands for Low Noise Amplifier, while LNB stands for Low Noise amplifier Block downconverter. It is a combination LNA and block downconverter. An LNA receives the reflected satellite signal, amplifies it and passes it through coaxial cable to the satellite receiver. The signal remains in the C band range, 3,700 to 4,200 Mhz. It can be identified by it’s N connector output. An LNB converts the reflected signal of the satellite dish to a more manageable range of 950 to 1,450 Mhz. This L-Band signal can be more reliable when passing through coaxial cable than the higher C-Band. Virtually all new receivers today use L-Band inputs. An LNB can be identified by it’s F connector output. LNA’s are still commonly found, and in some cases required, in use with certain receivers. Learfield’s new Digiceiver system requires the use of an L-Band input signal. Other receivers in use by Learfield’s networks require a C-Band input that can only be received from an LNA.
Selecting an LNB
In certain situations where the L-Band signal is needed, a specific type LNB (or combination LNA & block downconverter) is required. SCPC receivers will only work properly with a Phase Lock Loop (PLL) LNB or L-Band block downconverter. The PLL contains an oscillator that stabilizes the frequency output. All other types of LNB will not operate properly, and ultimately result in lost time and money. Learfield’s new Digiceiver system does not require a Phase Lock Loop LNB for proper operation. One term which can cause confusion for purchasers of LNB’s is the “noise temperature” of the device. “Noise temperature” of an LNB is a measurement of the vibration of the atoms of the LNB. More vibration = more noise. Thus, a low “noise temperature” amplifier is the most desirable.
Adjusting the antenna
In order to align your new dish to the satellite you need to know where to point it. Click here for a chart that can help you find the correct coordinates for aligning your dish. In actually setting the dish alignment first set the elevation angle. Once the elevations is set you can sweep the sky in the expected azimuth area until you acquire the signal. Be sure you know the receivers signal acquisition time. Some digital receivers may take 20 seconds or more to lock onto the signal once they “see” it. If your first elevation setting is unsuccessful lower or raise the dish by about a half degree and try again, continue doing this until the signal is successfully locked in. Once you have found the signal move the dish several degrees to either side to ensure you are not tuned to a side lobe. A side lobe signal will appear to work but ultimately be subject to interference from adjacent satellites. If the signal is acquired at three points choose the middle one. If no sidelobes are detected then use the one point you have found. To determine the best polarization setting for the LNA/LNB rotate the feed element until you have the best signal level and least amount of interference from the opposing polarization. Learfield networks on AMC-8 are vertically polarized. Networks on Galaxy 4R are horizontally polarized.
Picking coax cable for your dish is an important decision. The distance from your dish to receiver and the type of cable you use will directly affect the amount of signal that is delivered to your receiver. Typical cable choice for an LNB is RG-59, RG-6 or RG-11. Cost vs. performance is a major factor in choosing which type to use. RG-59 is typically the cheapest but also suffers the most loss over a given distance. RG-11 is usually the most expensive but has much less loss.
Cable type Loss per 100′ at 1000 MHz
- RG-59 12 dB
- RG-6 9.8 dB
- RG-11 7.8 dB
For an LNA, cable choice would be RG-8 or RG-213. For long runs a “hardline” foam-dielectric coax is the best choice. Again cost vs. performance determines the choice you will make.
Cable Type Loss per 100′ at 3000 MHz
- RG-8 16 dB
- RG-213 16 dB
- Hardline 6 dB
Attention should be paid to the installation of the cable. Connectors not crimped and weatherproofed properly are certain to cause future problems. If routing the cable underground be sure to use conduit. If you use a splitter be sure it is of the correct type. A splitter from the hardware store will not work. These “consumer” splitters are designed for TV frequencies and will not pass the higher satellite range. Purchase a splitter designed specifically for your situation.