Satellite TV Reception Basics

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Satellite Dish Installation Guide for a C Band Dish

Selecting a site to install your dish

Surveying the site is the first step in a good installation. This is the same as for the KU band dish but may encompass a wider arc of view depending on the amount of Satellites to see.

Is there an unobstructed view to all of the satellite positions?
Will seasonal foliage cause problems?
Is the area that the dish is to be anchored into solid?
Are there sources of terrestrial interference that need to be considered?

Make sure that there is nothing that will obstruct the dish as it moves the full span of the sky. You must verify that there are no transmissions in the 3.7 to 4.2 GHz frequency band that will cause problems with reception. An easy way to verify this is to use a good LNB connected to a signal strength meter. Move the LNB around the target area in a full circle. If you notice any spikes of signal it is safe to assume those same spikes may cause interference after the installation is finished.

Planting The Dish

A properly installed dish requires a perfectly plumb pole and a well-anchored solid base. It is a good idea to fill the pole with concrete as well as pouring a concrete base; this will strengthen the installation and allow for more accurate reception of C Band signals.

A good "rule of thumb" is to use one bag of concrete for each full foot of dish size. A seven and one half-foot dish needs a minimum of seven bags of concrete as an anchor. If you are in a region where strong storms are common, then more Satellite Dish Footing concrete is recommended.

Check for plumb in three directions.
Allow the concrete to harden for at least 24 hours before dish mounting.
Use braces that are welded or drilled through the pole to prevent turning in the concrete under load conditions.

Dish Assembly

Every dish sold comes with directions for assembly. Make sure you read the instructions before attempting to assemble the dish! Some important things to remember:

The dish needs to be perfectly shaped. Use a measuring tape and measure across the diameter of the dish in three directions. All measurements should be identical.
Tie a piece of string across the diameter of the dish in two directions. The strings should just barely touch at the centre of the dish. If the strings are pushed hard against each other or fail to touch, then the dish is not properly assembled.
Don't over tighten the dish-mounting hardware. You do not want the ribs to be deformed by pressure, as this will prevent proper alignment. Allow the lock washers to perform the job of securing the bolts.

Mounting the Feedhorn

The dish is a reflector that focuses the energy into a small golf-ball sized orb at the mouth of the feedhorn. Inside the feedhorn are two small antennas that are selected by voltage from the receiver for vertical or horizontal polarity. Knowing this will allow you to see how important it is to properly mount the feedhorn.

Do not assume that because all the supports holding the scalar ring are the same length that centering is automatic. Make sure that all the supports are the same distance from the edge of the dish to the scalar ring. Each measurement should be within 1/32 of each other. You need to assure that the scalar ring (the supporting ring for the feedhorn) is parallel to the bottom of the dish and that it is perfectly centered in the dish. If all this isn’t done, then you will have imperfect reception. Having the focal point off by as little as one-half of one inch can cause a fifty percent loss in signal strength!

A Word About Focal Depth

The f/D ratio is the focal distance of the dish (f), divided by the diameter (D). When dealing with most prime focus antennas, the number should come out between .28 and .42. If you notice, most of those numbers are also on scale on the side of the feedhorn. You simply set the top edge of the scalar ring even with the line that corresponds to your correct f/D setting. What this adjustment actually does is determines how wide of an angle the feedhorn can "see".

To calculate the focal distance, you need to measure the diameter (D) and the depth (d) of the dish. Measurements should be in like units (you can't use feet for the diameter and inches for depth). For this example, let's say we have a dish that is 120 inches in diameter (D) and 18 inches deep (d). Focal distance (f) equals the diameter squared (D x D) divided by 16 times the depth (16 x d) or:

D x D = 120 x 120 = 14400

16 x d = 16 x 18 = 288

D x D/16 x d = 14400/288 = 50

Therefore focal distance f = 50 inches

After you have calculated the focal distance (f), you can use that figure to calculate the f/D ratio of your dish. In this case, using the same diameter of (D) = 120; and the calculated focal distance (f) = 50

f / D = 50 / 120 = .416

f /D = .416

And round up to give a setting of .42

All of this information will be provided in the dish manufacturer’s instructions. It is important to read the directions and understand the type of equipment you are working with. Often times you will be working on a system that was previously installed.

Feedhorn Issues

Moisture is the enemy of microwave reception. Making sure the feedhorn and LNB's are protected and properly installed is very important to long-term, service-free performance of a C-Band TV system.

Make sure that all coaxial cable connections are crimped with a proper tool and treated to prevent moisture from entering the cable. Make sure you use the gaskets supplied with the LNB's to prevent moisture from entering the throat of the feedhorn. Also, check to be sure the plastic covering for the throat of the feedhorn is attached firmly to prevent both moisture and pests from entering the waveguide.

Low Noise Block Amplifiers - The LNB

The LNB is the electronic device that mounts on the feedhorn and converts that golf-ball-sized globe of RF energy into an electrical signal the IRD (receiver) can understand and use. There are several kinds of LNB. There are LNBF’s that use voltage on the coaxial cable to switch from vertical to horizontal polarity. There are consumer grade LNB's that use an external servo motor to turn the probe and select polarity. And finally there are Digital or PLL (Phase Locked Loop) LNB's that are normally used on commercial installations. It is highly recommended that a PLL LNB be used on any high-quality TVRO installation, whether consumer or commercial.

The biggest difference between a normal LNB and a PLL LNB is the amount of frequency drift. No matter the type of LNB, don't get caught up in a numbers war. Many beginning installers think that a lower temperature LNB will always be better than a higher temperature LNB. This is not necessarily true. A PLL 25 degree LNB will almost always outperform a 17 degree consumer (standard grade) LNB.

Also, you cannot make up for poor dish alignment or installation with a better LNB or line amplifier. The dish needs to collect the signal and send it cleanly to the throat of the feedhorn. All the electronics in the world cannot help the picture if you are losing half your signal and sending loads of noise into the feedhorn. Use a good LNB, preferably a PLL LNB If it is to be commercial standard- but spend your time making sure the mechanics of the dish are up to snuff first.