A number of satellites have been launched into orbit around the earth. They sit in a circle above the equator at a distance of 36,000km. This position allows them to remain in the same relative position in the sky.
To a viewer on Earth, they do not move.
Each satellite has the ability to receive signals transmitted from Earth and to re-transmit them back to Earth. The satellite on-board equipment which does this is called a Transponder. A satellite can have several transponders. On the ground, large transmitting dishes are used to "uplink" the programmes to each satellite. Each transponder of each satellite beams the programme back down so that it reaches an area designated the "footprint". This is the area where the signal is strongest. The signal becomes weaker towards the edges of the footprint.
To receive a signal you need a dish. This acts as a curved mirror and focusses (concentrates) the weak signal at a point in front of the dish.

What is an LNB?
What is a satellite receiver?
What is a decoder?
Do I need a decoder?
How do I decide what to buy?
What is Digital?
What is Astra?
What is Hot Bird?
Can I install my own system?
What is Polarisation?
How to receive Right circular and Left circular polarisation?
What are Sparklies?
Can I receive even more programmes?
Should I buy the cheapest?
Adding a second LNB to my system?

LNB - Low Noise Block Downconverter

At this point is mounted an "LNB" which stands for Low Noise Block Downconverter. This LNB often has a horn which collects the focussed signal and feeds it to a tiny aerial inside the LNB. The job of the LNB is to convert the weak microwave signal into a stronger signal at a lower frequency. This lower frequency signal can then be fed down a coaxial cable to the satellite receiver.

Satellite receiver

The satellite receiver is able to separate the mess of signal coming from the LNB into several recognisable TV picture channels and soundtrack channels. Normally you will be able to "tune" the receiver so that you get your desired programmes at particular channel numbers.

Decoder

Many of the programmes are scrambled before they are uplinked to the satellite. In order to descramble them you need a decoder. For most scrambled channels you will also need a Smartcard to allow the decoder to work. Smartcards are generally available by subscription in specific countries. This is because the programme providers are licensed to broadcast films etc. only to certain countries for which they pay a fee. This is not really a decoder but simply a means of translating a different transmission standard.

If your receiver does not have a suitable internal decoder you will usually be able to connect one externally. You should consider this point before you buy because some combinations of receiver and decoder will not work. Always get the whole bunch of equipment demonstrated before you buy and make sure that the connecting leads used to demonstrate are the ones you take home (these can give problems as well).

Do I need a decoder?

You can watch a lot of "free" programmes with only a receiver. However, only a few of these are English. But do remember that you can receive dozens of Radio programmes from satellite and you don't need a decoder for these! Some broadcast in stereo and some in mono.

What to buy?

Ask several satellite-owning neighbours to demonstrate their systems. Usually they will be pleased to do this. See if you can find somebody with a big motorised dish who will show you the vast choice you can receive from different satellites. Apart from looking at picture quality, performance and price, consider reliability, too. About ten percent of satellite receivers fail within two years.

Digital

Astra expected to transmit mostly digitally compressed signals. This method is more efficient because it allows one transponder to transmit up to fourteen different programmes at the same time! However, you will need to buy a Digital Satellite Receiver in the future in order to receive these new programmes. Such receivers are already in use in parts of Europe, South Africa, Australia, Indonesia and the USA (and other places). They may be more than four times as expensive as current "analogue" receivers.

Astra

Astra is the name given to a group of satellites which are located at the same place above the Earth (around 19 degrees east of south). As far as your dish is concerned, this group of satellites looks like one large satellite because they are so far away and so close together. At present there are six satellites in the group, labelled 1A to 1F. Satellite 1A to 1D transmit mostly ordinary "analogue" signals.

Hot Bird

Hot Bird is the name of a satellite that is located at 13 degrees east of south. You can point your dish in that direction and receive signals from Hot Bird just the same as you can from Astra. There are a few English programmes which are not scrambled but most programmes are foreign language (sometimes English with foreign subtitles).

Installing my own system

Yes. You don't need any special equipment, although you can not guarantee perfect pictures without the use of a meter. There are lots of books on this subject
The dish has to point towards the desired satellite(s). It can be mounted almost anywhere, provided that it has "line-of-sight". Make sure that there are no trees or buildings blocking this line.

Polarisation

Polarisation is a way to give transmission signals a specific direction. It makes the beam more concentrated. Signals transmitted by satellite can be polarised in one of four different ways: linear (horizontal or vertical) or circular (left-hand or right-hand). FSS satellites use horizontal and vertical polarisation, whereas DBS satellites use left- and right-hand circular polarisation. To use the channels that are available for satellite broadcast as efficiently as possible, both horizontal and vertical polarisation (and left- and right-hand circular polarisation) can be applied simultaneously per channel or frequency. In such cases the frequency of one of the two is slightly altered, to prevent possible interference. Horizontal and vertical transmissions will therefore not interfere with each another because they are differently polarised. This means twice as many programs can be transmitted per satellite. Consequently, via one and (almost) the same frequency the satellite can broadcast both a horizontal and a vertical polarised signal (H and V), or a left- and right-hand circular polarised signal (LC and RC).

Receiving right and left circular polarised channels

Probably nothing whatsoever. You need to read up on how a depolarizer works. Then you'll see that the latter will take the H & V rotating components of a circularly polarized signal, and reinforce them by combining them into one of two linear planes (depending upon whether LC or RC). The LNB can then discriminate between each orientation, and also benefit from a 3dB increase in signal. However, the depolarizer also has an effect on linearly polarized signals. If the dielectric material is positioned so as to minimize this, then the circularly polarized signals will be received at +/- 45 degrees to the H & V, and hence cannot be picked up by the (fixed) H or V probes of a Universal LNB. OTOH, if the material is positioned so as to present the circularly polarized signals AT H or V, then it will affect the linearly-polarized signals by creating an effective circulalry polarized signal, which will present at +/- 45 deg (and moreover be reduced by 3dB (= fifty percent!). Thus applying a depolarizer to a Universal LNB is a non-starter; it is ONLY applicable to an LNB with a separate polarizer (magentic or mechanical) which can select other angles apart from strictly horizontal or vertical.

Sparklies

Signal Too Weak

A weak signal can have many different causes. The most common are:

Heavy rainfall
Obstruction such as trees
Buckled or rusty dish
Cable fault (water inside, kinked or bad connection at LNB or a joint or connection in the cable)
Faulty LNB or water inside
very infrequently, a faulty tuner module inside receiver

The effects of rainfall and trees are all too obvious but they fool some people! If the picture is bad when it rains then a sparkly picture can result directly from the rain itself (because it reduces the signal coming from the satellite) or from water getting into the LNB or cable. The effect of trees is more obvious in summer when the leaves are present. The interference will vary as the branches move in the wind.

Dish faults are quite common. Even a brand new dish straight from the box can be twisted, bent or buckled. Even a slight amount of distortion is sufficient to move the focal point away from the LNB feed horn. You may be able to correct the distortion but the best answer is to change the dish.

To determine the exact cause of your problem, it's best to change each element, one by one. Try a different receiver first. The next, simplest step is to run a new length of cable alongside the old one. Connect it at each end and test the system. While you are there, check the old cable and LNB for corrosion at the connectors - a sure sign that water has crept inside. Occasionally an LNB can be dried out and will work perfectly again but, if it's difficult to reach the dish, my advice would be to renew the LNB. Be sure to use self-amalgamation tape to make a waterproof connection. It's also a good idea to fasten a polythene bag over the LNB, although this looks unsightly.

If you fit the new cable permanently, do not kink it by bending it tightly around a corner or by hammering a clip too hard.

Receiving more programmes

You can install a larger dish on a "polar mount". This is a special swivel mounting which allows the dish to move in such a way that it tracks the satellite arc above the equator. There are several variations on this theme: another is the "Horizon to Horizon" mount which gives a longer arc of travel. For most purposes, an ordinary polar mount with a linear actuator (motor) is the most cost-effective solution. You will also need a "positioner" (power supply and control unit) to drive the actuator which moves the dish.

Buying cheapest

This is the question which nobody likes to answer. The cheapest systems are fine if you don't need the best picture and sound quality. Even the lowest price systems can be expected to give better pictures than ordinary terrestrial TV. If not, there is something wrong so don't accept it. However the price tends to reflect the build quality and, therefore, the reliability. The installation cost also tends to reflect the quality of materials and workmanship.
How can an installer save money? Easy: by using a low-quality cable which does not carry the signal as well as good cable (but you won't see a problem till it rains) and which does not last as long outdoors (ultraviolet light from the sun cracks the plastic and water gets in). By skimping on the length of cable and on brackets and clips (eg. install it on the front of the house instead of round the back out of sight). By skimping on other items (connectors, LNB noise-figure, Dish quality). By joining lengths of short cable (never!)
For the best quality equipment and workmanship it pays to find out about specialist installers. There are some but they take a lot of finding. They won't do a low-cost job but they'll be happier to come back to sort out any problems because this cost will be built-in to the price. You get what you pay for.

Adding second LNB to the system

If you add a 2nd LNB you will need to put it on a 2nd dish! Much easier is to swap the existing LNB for a "twin output" type which will feed two receivers. This could lead to problems however because the new LNB will probably be an "Enhanced" type which will not directly match your existing receiver in terms of frequency range.
If, however, you are adding a second LNB to watch programmes from a second satellite then you may be able to fit it to the same dish by using a special bracket (but you will probably need a larger dish).

DISCLAIMER: Information is given in good faith. No responsibility will be accepted for any loss, damage or injury which occurs directly, or indirectly, as a result of your use of this information. It is your responsibility to check the facts.

Questions & Comments are welcome to

E-mail
knight@knightsat.cjb.net

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