When choosing a new antenna, diameter and gain may no longer be the most important parameters. Side-lobe rejection is also now important. Many antennas were sold with a “two degree compliant” sales pitch. This indicates that the side-lobe rejection curve for this antenna meets section 29.205 of the FCC’s Rules. This specification alone may not be good enough for reliable operation in a real-world two degree spaced environment.
Solid dishes offer many advantages over mesh or perforated dishes. Solid dishes are sturdier, they hold their shape better and they flex less in the wind. They are more expensive, but have a better value for the dollar. Expect solid dishes to have a useful life of 7 to 15 years. Westwood One recommends using only solid dishes.
Mesh or perforated dishes are more flexible than solid dishes. They move more in the wind and are less durable. Mesh dishes are less expensive, but need more frequent replacement. Expect mesh or perforated dishes to have a useful life of 4 to 6 years. Other disadvantages of mesh or perforated dishes include poor side lobe rejection of adjacent satellites and the rejection is not consistent from year to year.
Offset dishes are another type of dish seen on the market. “Offset” means the feed element is purposely kept outside of the “main beam” between the dish and satellite. Offset dishes reduce terrestrial interference and improves the beam shape slightly, but they are more complex to set up and adjust.
Diameter choices come down to one statement: “Bigger is better”. Bigger dishes offer higher gain, they have a narrower “beam” that has better side lobe rejection of adjacent satellites and better rejection of terrestrial interference. Westwood One recommends a minimum dish diameter of 3.7 meters. A dish as large as 4.5 meters virtually guarantees headache-free operation for 15 years or more.
Mounting choices are several and you must select very carefully. An improperly mounted dish will move in the wind. Inexpensive mounts, often sold separately, may be less durable than the dish manufacturer’s own mounting structure. Single pole mounts work best when braced with diagonal members also anchored to the foundation. Purchase a high-wind brace kit if it is available for your dish. What follows is a listing of mounting choices.
- Will require digging and concrete pouring.
- Will give the best stability while enjoying the advantages of a ground location.
Roof structure add on:
- An architect or structural engineer will need to design an “adapter”, usually of steel members, to “mate” the structure of the building to the mounting legs of the antenna.
- Suggest designing for 125 mph wind survival.
- Will require a steel contractor to install.
- Will be very stable but very expensive.
- It’s custom made for the building. If you move the dish to another building, the investment will be lost.
- Can rarely be used on wood frame buildings.
Roof non-penetrating mounts:
- Uses “dead weight” (usually concrete blocks) to hold the dish in place.
- Rarely stable enough for antennas large enough to receive C-band signals.
- Will creep (move) in gusty wind.
Pole mount at side of building:
- Pole is mounted in a concrete foundation on the ground.
- Pole is taller than the building and is attached to the building near the roof line.
- Only workable for one or two story buildings.
- More expensive than ground foundation, but uses less land area.
- Harder to change out a faulty feed system.