JUST THE RIGHT CURVE
behind a satellite dish are simple but can be mechanically difficult.
Dishes are typically RF reflecting parabolas that must be exactly shaped
so a satellite signal will arrive at the LNB from all parts
of the dish.
Think of a dish
as an optical mirror where light focuses on a single point. Radio waves
follow the same principles as light, except you can’t see them. A
satellite signal heads toward Earth as a wave front. The system works
correctly when a wave striking the satellite dish then bounces off to
arrive at the focal point (LNB) as a combined signal.
The dish shape
is a double-edged sword. Signals arriving straight in (on-axis) reflect
and add at
the focal point, while off-axis signals are reflected to a different
point, or are just scattered away from the LNB. As they say, the angle
of incidence equals the angle of reflection.
A parabolic dish
is good at focusing received energy at one point. That is why a dish
looks at just one satellite, not others nearby in orbit. A warped dish
might reflect signal to the wrong point, causing low dish gain. Ouch!
Placement of the
feed horn and LNB is critical, too. Misalignment at the focal point,
even by just a few centimeters (fractions of an inch), could mean the
difference between a reliable dish and one that is a marginal performer.
That usually happens when a dish is warped.
You’ve seen this
one, too. The satellite signal goes away, and you find a bee or hornet
hive in a feed horn. Those critters love a location like that. It is
away from animals and somewhat sheltered from rain.
transparent material can be used to cover the horn. A little plastic
sheet, or even plastic food wrap, will do. It’s a maintenance item.
Be sure to mark
the EbNo, a signal-to-noise performance number, on the front of every
satellite receiver. It is easy and quick to check on regular inspections
and will tell you when trouble is brewing.
entrepreneurs, how about developing a curved broom that will help clear
snow and debris from satellite dishes?
facts helps you be a better engineer. It makes perfect sense.