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4. Benefits of larger antennas:

In on-line news groups or blogs, periodically someone asks if installing a larger antenna will overcome some of the outages caused by rainfall attenuation during summer downpours.

The design of a DBS system is complex so there is not really a simple yes-no answer — but the antenna that comes with a standard DBS system is well optimized to serve most locations, most of the time.

With a standard basic system, the circular receive antenna is looking not at one, but at several satellites together in orbit. The standard receive antenna has a half-power (3 dB) beam width of about 3.5 degrees, permitting a fixed antenna to simultaneously see all satellites more or less equally. The beam can be compared to the beam from a searchlight, circular and tightly focussed.

As the diameter of an antenna is increased, its beam width becomes narrower, making pointing the antenna more critical. The standard antenna's half-power beamwidth angle is halved with a 3-foot (0.91-meter) diameter antenna while at the same time, the antenna gain is increased by about 6 dB.

With a 10-foot (3-meter) diameter antenna, the half-power beam width is only about 0.55 degrees with an increase in gain of about 16 dB over the standard antenna. With such a large antenna and forward error correction, there will still be outages during periods of heavy rain, but the outages will be somewhat shorter. Also, accurate pointing or aiming of the dish becomes very difficult with a 10-foot (3-meter) diameter antenna, an important consideration.

A problem with large antennas is caused by our planet's daily wobble about its axis. A geostationary satellite viewed from the earth over a 24-hour period describes a small figure 8 in the sky. Aiming a large dish will need to be done when the satellite is in the middle of the 8. (Professional satellite systems with large-diameter antennas use a steerable sub-reflector to compensate for the earth's wobble).

Wind loading becomes a problem as the antenna size is increased, as a satellite antenna acts like a sail. In a 50 mile-per-hour wind (80 Km/hour), the standard DBS antenna wind loading or maximum thrust is about 35 pounds (16 Kg). With a ten-foot, 3-meter diameter antenna, the thrust increases to a huge 850 pounds (386 Kg)! Unless you have mounted your large antenna on a concrete-secured mast with lots of steel bracing, the twist and tilt of the antenna during high winds will cause additional outages because of loss of aiming accuracy.

In summary, for most of us, be happy with the great signals received most of the time from your DBS system. The receiver package that you purchased was well designed and does a good job, far more reliably than many alternative solutions.

But there is one exception. If you are not directly located within the spot beam providing local station signals to a city, a larger antenna (up to a meter in size), pointed at the appropriate local-signal satellite, will often allow good reception for those outside the intended primary area. DirecTV and others employ frequency re-use, with individual antennas on the satellite providing different signals to different cities, sharing the same frequencies.

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