Satellite TV Reception Basics

  • Satellite TV Reception Basics


    A satellite is an object that orbits around another object in space. The satellites that concern us transmit television directly to the consumer. These satellites require a special orbit, so a little information about orbits is a good place to start in understanding satellite television basics.
    The time it takes for a satellite to complete an orbit depends upon its distance from the object that it orbits. The moon is a natural satellite that is 383,551 Kilometres from Earth. It takes 27.32 days for the moon to complete one orbit of the Earth. The space shuttle operates in a low Earth orbit. The shuttle orbits less than 322 Km to about 563 Km above the Earth. The average time for the space shuttle to complete an orbit around the Earth is about 90 minutes. The moon takes longer to complete an orbit of the Earth because it is much further from the Earth than is the space shuttle. The type of orbit that is required of the satellites that transmit television signals to the Earth lies between these two extremes.
    In order for a satellite to be used for television transmission, it must "hang" over one spot above the Earth. The types of orbits described so far would require a receiving dish that is constantly moving, in order to keep up with the transmitting satellite. Satellite television satellites are in a geosynchronous orbit that exactly matches the speed that the Earth spins. When a satellite is in a geosynchronous orbit, the satellite appears to be stationary when viewed from the ground. In order to accomplish a geosynchronous orbit, a satellite must be directly over the equator and about 35888 Km from the Earth. This area around the Earth is often called the Clarke Belt. Satellites maintain proper positioning in the Clarke Belt with onboard fuel. Ground stations constantly monitor these satellites and make any adjustments that are necessary.
    The television signals transmitted by a satellite are quite different from the television or radio signals that are broadcast over the air. The particulars of a satellite TV signal are beyond the scope of this small article, but there are some basics that you should know. Satellite TV is transmitted by microwaves. Microwaves don't behave like the lower frequency radio waves of off-air television or radio, which can bounce off obstructions, clouds, and the ground. Microwaves are strictly line of sight. In order for a satellite dish to receive a signal, there can be no obstruction between the transmitting satellite and the receiving satellite dish. The very first thing that a prospective dish owner should do is perform a site survey in order to ensure that there are no obstructions blocking the satellite(s) of interest. Because microwaves are highly directional, the satellite dish and associated components must be properly aligned.
    Satellite television in Australia is divided into two major types. The first major type is TVRO (Television Receive Only ). TVRO satellite systems have a large dish which is normally movable. This movable dish enables a TVRO system to view programs on the many satellites that are positioned in the Clarke Belt. TVRO satellite systems are also called C-Band. Just remember that if the dish is large (usually 2 to 4 metres across) and it can be moving, it is a TVRO satellite system.
    The second major type of satellite TV is DBS. DBS systems have a small dish (60 Cm to 90 Cm across generally) that does not move. In the Australia there are Four main users of DBS satellite systems, these are all pay TV operators ( Foxtel, Austar, Select TV & Aurora out back services) while there are more smaller services as well some encrypted . Each DBS system requires it's own special receiving equipment and has it's own programming line up.
    TVRO ( Television Receive Only )

    The first satellite television systems for the consumer were TVRO (Television Receive Only) satellite systems. TVRO started sprouting up all over the U.S. in the late 1970s and early 1980s. TVRO satellite systems are characterized by big dishes that are usually 2 to 4 metres across. TVRO systems receive television signals from C-Band satellites. A C-Band satellite has 24 channels (transponders) on each satellite. There are more than six C-Band satellites that may be received on the Australian mainland. A TVRO satellite system must have a movable dish in order to access the signals from so many satellites. Even though most of the press and most of the advertising that you now see involves the small dish DBS systems, TVRO is still alive and well.
    Other words are often used to describe a TVRO system such as C Band Satellite TV.
    There is a variety of programming on satellite television that is available through TVRO.
    The first type of TVRO satellite channels are called scrambled or subscription services. In order to view these scrambled channels you will need a decoder and a smartcard and buy a subscription to the channels of your choice. A subscription maybe just a phone call away. There are many companies that handle satellite TV subscriptions. Each company will have a variety of program packages designed for your viewing preferences. You can find out about the channels available by looking at the available programming on LYNGSAT web site. When you have the right equipment and call the programming company to subscribe the picture will usually pop on the screen while you are talking. It's easy!
    In addition to scrambled satellite TV channels, TVRO has a big variety of free channels available. The variety of channels includes news, educational, foreign language programming, music, old movies, and many other unusual programs. These free channels are called in the clear or unscrambled channels. Some of these free channels are regularly scheduled programs, other free channels are known as feeds. Feeds can be scheduled or unscheduled programs. Feeds are used by networks or other programming providers to beam shows, events, or news to their affiliates. When these programs are at times beamed unscrambled, TVRO viewers can pick them up. For instance, if a game is being played in Perth and a TV station in Sydney is carrying that game, a TVRO system can pick the game up, provided the signal is not scrambled. There is a huge wealth of programs, available to TVRO owners, which are sometimes broadcast unscrambled. News feeds are a favourite. News feeds may be used by network or other program providers to beam reports out in the field to their central location. Some news feeds are used by their program providers live, others are fed to their central location where they are edited for a later program. Unedited news feeds can be very interesting.
    The TVRO owner can not usually upgrade a regular C band TVRO system in order to add the capability of picking up Ku band signals. The Ku band signal is much higher in frequency and the mesh dish is not ideal for this signal. There are also scrambled signals on Ku band, Ku band satellite signals are at a higher frequency than C-band, typically 12 GHz apposed to 4 GHz on C band. Most modern satellite receivers have the ability to receive Ku band signals. The only upgrade that is required if this would be possible is in the modification of some of the outside electronics at the dish. The upgrade involves the feed and LNB, which are above the centre of the dish, usually under a plastic cover.
    DBS Basics

    DBS stands for Direct Broadcast Satellite. DBS is broadcast by medium and high powered satellites operating in the microwave Ku band. These high powered, high frequency satellites make it possible for the signals to be picked up on a small dish.
    Digital compression makes it possible to have many channels on a single satellite. The current DBS systems that are operating in the Australia are Foxtel, Austar, Select TV and Aurora. Commonly they all use a 60Cm offset satellite dish in the most powerful reception areas this can increase to one metre in some parts of the continent. One of the big advantages of DBS systems is that the small dish does not have to move.
    All current DBS systems in Australia have mainly scrambled channels and require descrambling with their own special receivers and smart card. The consumer can only receive programs intended for their subscribed of satellite TV system.
    Satellite Dish Installation Guide for a Offset KU Band Dish

    Satellite Dish InstallationSatellite TV is one of the growing forms of entertainment whether you are travelling on the road in your caravan or are a home user. The choice we have is constantly growing.
    The choice includes free to air programs such as Optus Aurora, which has ABC and SBS available to everyone along with a selection of regional commercial stations which are available to travellers, outback homesteads and locations which cannot receive TV by a regular antenna, known as black spots. Along with the free to air channels we have a choice of pay services such as Foxtel, Austar and the latest entrant in the market being Selectv.
    This guide will explain the steps involved in installing & aligning your satellite dish for TV reception.

  • Quick Start Guide

    Selecting a site to install your dish

    Find a Clear Line of Sight
    [Blocked Image: http://www.mobilesatellitetv.c…ges/satellite-dish_04.gif]To ensure you have trouble free reception from the satellite the first step to a successful installation is to perform a site survey.
    Before you do this you need to understand a few satellite basics.

    • [Blocked Image: http://www.mobilesatellitetv.c…ges/satellite-dish_03.gif]Go outside and locate at least one site on your property that has a clear view to the Satellite/s.
    • Do you have at least one clear view to the Satellite/s?
      Remember, no trees, leaves, buildings or any obstruction can be between the Dish and the Satellite/s
    • Imagine an arc 30 to 60 degrees above the horizon.

    [Blocked Image: http://www.mobilesatellitetv.c…ges/satellite-dish_02.gif]Obtain Dish Pointing Coordinates – Use our program to obtain your pointing direction and angles to your desired satellite. This will give you the exact coordinates (azimuth and elevation) for pointing the dish. You will need your site longitude and latitude which can be obtained from a GPS device or from the map in our program.
    Select the Precise Mounting Site – Use the dish pointing coordinates to
    conduct a precise site survey to determine the exact mounting site.

    Begin Dish Assembly – Attach the reflector to the support arm so that you can preset the correct elevation.
    Set the Elevation on Dish – This is an important step. Making sure that your
    elevation setting is correct will help you to more easily obtain the signal later
    Mounting the Mast

    Mount the Mast – Depending on your type of mounting, permanent or portable, the mount should be secure, as the slightest movement of the dish can affect the signal.
    Completing the Final Installation

    Level the Mast – The mast must be perfectly vertical to enable the elevation co-ordinates to be accurate.
    If the mast is not vertical you may have terrible trouble aligning the dish as the elevation and azimuth will be affected.
    Complete the Dish Assembly – Place the dish on the mast and connect the
    RG-6 coaxial cable to the LNB, and attach the LNB to the support arm.
    Run the Cables from the Satellite Dish into the House – Run the RG-6 cable
    to the receiver, using a wall plate outlet and fly lead if required.
    Make the Final Connections to the Receiver – Connect the RG-6 to the
    satellite input on the receiver and connect receiver to your TV.
    Acquire and Fine-Tune the Satellite Signal – Use Sat Finder tool or Satellite meter
    to check for a signal. Once the signal is obtained, adjust dish pointing to
    achieve maximum signal strength for your location.
    Adjust the Skew of the LNB – Use Sat Finder tool or Satellite meter or chart to adjust the Skew angle of the Lnb to get the correct polarity and best signal.
    Time to watch TV.

  • 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 [Blocked Image:]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.

  • Satellite Dish Installation Guide for a C Band Dish (Continued)

    The Actuator Arm (The Dish Mover)

    Rear view of a typical Linear Actuator Arm. This arm is set up for Linear East / West Use[Blocked Image: http://www.mobilesatellitetv.c…ite-dish-actuator-arm.gif]
    Now that we have the proper LNB mounted on the feedhorn, the feedhorn mounted on the dish and centered exactly, and the dish mounted on a plumb and properly secured pole, we are ready to connect the actuator arm. Make sure you use an actuator that is properly rated for the dish it is attached to. You should never use an 18" actuator arm to try and move a solid 12-foot dish! It may work for a while but the chances are good that you will be replacing it in short order. Try to get the best heavy-duty actuator arm you can - it will pay for itself many times over in years of trouble free service.
    Aligning The Dish

    Now we come to the hardest part of the installation. If you pay close attention to the following procedures it will pay off in the long run with better reception on weaker C-Band satellites.
    Three adjustments are required to ensure proper tracking of the arc: Azimuth (east/west heading), declination offset angle and polar axis angle (inclination angle). These parameters should be set while the dish is aimed toward its highest position, namely towards the Northern most satellite.
    Setting the Polar Axis Angle - The polar axis angle is set by placing an inclinometer on the polar bar and then raising or lowering the dish to that angle.[Blocked Image: http://www.mobilesatellitetv.c…lite-polar-axis-angle.gif]
    The azimuth must be set right in order to detect all the satellites in the viewable arc. Most dishes have a flat plate on the mount that can be used as a sighting reference. A hand-held compass is the most effective type for lining up the mount. Remember that a correction for magnetic variation is necessary. Add magnetic variation to the compass heading for west magnetic variation; subtract for east.
    The polar axis angle or inclination angle is within fractions of the site latitude. Most mounts have one or two long threaded rods that are used to adjust the polar axis angle. An inclinometer resting on the axis bar or back part of the mount is used to set this angle.
    The declination offset adjustment lowers the sight of a dish to the arc of the satellites. Declination is greater in locations farther away from the equator. Just like the offset angle, it is measured with an inclinometer. The difference between the two readings, one on the main bar, and one on a flat spot on the back of the dish, should be equal to the declination offset.

    The easiest way to set the declination offset is with an inclinometer placed on the back surface that is parallel with the face of the dish. Or via a flat board placed in a vertical direction spanning the rims. This reading should be equal to the sum of the polar axis and declination angles.
    [Blocked Image: http://www.mobilesatellitetv.c…lite-polar-axis-angle.jpg] Setting the Declination Angle - The declination angle is set by placing an inclinometer on a flat service of the dish that is parallel to the line between the rims and adjusting the declination bolts until the reading equals the sum of the polar axis and destination angles. Using the Dish Face to Set A Declination Angle - If a flat surface cannot be found on the rear of the dish or on the hardware that supports the declination adjustment, the declination angle can be set by placing an inclinometer on a flat board that rests on the face of the dish. [Blocked Image: http://www.mobilesatellitetv.c…-declination-angle_02.gif] Determine the latitude & Longitude of your installation by using our program.
    When the declination is properly set, the procedure is to set the dish to true North (not magnetic North. You need to compensate and use the polar axis adjustment to capture the northernmost satellite visible from your location. This is called the zenith satellite. Once you are peaked at the northernmost satellite you can use the actuator control on your receiver to move the dish to the lowest satellite off the horizon you can see. This is called the extreme satellite.
    Once you have located the extreme satellite, gently push up and down on the edge of the dish to see which direction helps clear up the picture. If pushing down on the lip of the dish clears up the picture, then you need to rotate the polar mount counter clockwise. If pushing up on the lip of the dish clears up the picture, then you need to rotate the polar mount clockwise on the pole.
    After you have made the azimuth adjustment, return the dish to the northern most satellite and use the elevation adjustment to clear the picture up. Keep moving back and forth between the extreme satellite and the zenith satellite using the polar adjustment and the elevation adjustment respectively until the dish tracks the arc.
    You are now ready to run your cabling as in the KU setup and install the decoder and start viewing!

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