Your
Satellite Downlink
Checking
Out Your Current Satellite 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.
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