This glossary is provided to help explain some of the terms used in this part of my website, as well as some of the digital-satellite jargon in general.
Please feel free to submit terms/phrases/words that you feel should be in this glossary, as well as letting me know if you think something could be explained 'better'.



The metal construction, usually up on your roof, designed to receive television signals and sometimes also radio signals.
Note that a satellite receiver doesn't have an aerial, it has a dish (or, technically, a dish and an LNB)...



This is the 'old' method of broadcasting, in which a 'varying voltage' signal was sent. This signal contained the TV picture and the sound, and scanned across the screen in a way similar to normal TV broadcasts.



I tend to use this to mean an 'aerial' because I can never remember how to spell 'aerial'!
Properly, an antenna is one of the touchy-feely things on a bug's head, or antennæ if plural.
According to my dictionary - 'antennas' and 'antennæ' can be used to refer to "an aerial". So if you think my incorrect use of antenna is strange, consider the use of a plural word to refer to a singular object! :-)



This is not the metal thing that picks up TV and radio signals - it is the name of a font family used predominantly with 'Windows' computers; it being a sans-serif font that is widely used due to people having an inability to figure out how to select a nicer-looking font.
Arial itself is a poor imitation of the likes of Homerton and Helvetica (in my opinion)...
(if you are using a Windows computer, this line should appear in Arial...)


Astra 19.2°E

This is the older Astra satellites, where Sky lived for over a decade. If you tune there now using an analogue receiver, you'll see about 30 channels - mostly German language. The satellite isn't dead, however, as there are loads of digital channels; in Spanish, German, English, and even an Italian one.


Satellite; GIF 3K


Astra 28.2°E

This is where SkyDigital lives. If you want your Digibox to receive 'English' TV (BBC, ITV, Sky, etc) then you'll need to point your dish in this direction...


boutique / bouquet

Because digital services offer multiple channels on a given frequency, they are offered to you in a 'boutique'. If you follow the setup example, you'll see a boutique offering CNN, Travel, Bloomberg, TVBS, TCM...
I think this is more commonly referred to as a 'bouquet' in English, but I've seen it called a 'boutique' in French, so that's what I am calling it (as I live in France, you see!).



The main way that digital can offer more channels is by compressing the signal. A lame example, but say you have a row of pixels that are all blue... You can either say:
a blue pixel, a blue pixel, a blue pixel, a blue pixel, a blue pixel (etc...635 times more!)
which is wasteful (and how analogue works), or you can say:
a blue pixel - repeat six hundred and forty times
Real life compression cannot offer compression as good as that, as television signals are rarely flat colour, however given the (lossy) MPEG compression, you can easily expect the compressed data to be a fifth of the uncompressed signal (and, hence, you could fit five such signals into the space of one uncompressed signal).
Another way to save space is to send a key frame every so often. This is an entire screen as you would see if you paused a video or a DVD. Between key frames, the broadcaster sends out a series of 'changes'. For example, Fionnula Sweeney reading the highlights on CNN will be a fairly static image of a woman sitting at a desk. That is the key frame. Then, little head movements, a blink or two, and moving lips will be sent as the changes between key frames...
Fionnula Sweeney; JPEG 13K
Fionnula Sweeney...
...and it looks like CNN has tried to 'sex' her up!



You are using a computer to read this. In some cases, you'll be using Internet Explorer on a Windows PC, and you'll know (with varying degrees of complexity) what a computer is capable of.
Or... you might be viewing this on some sort of dedicated 'box' (an STB) which provides you with the internet on your TV with minimal fuss. This too is a computer. In some cases, such as the Bush Internet box, you can gain access to the operating system and use it like a real computer.
What you might not know is the Digibox is also a computer. It contains firmware (a kind of software that isn't forgotten when the device is switched off) and memory (the stuff that is forgotten when you switch off) and a processor (the bit that co-ordinates everything and makes it work) and the MPEG decoder (it is too complicated to be done efficiently with software, so a special type of processor does this task).
The upside? It is a highly flexible system that can be upgraded from off-air signals.
The downside? Sometimes it crashes (usually after such an upgrade) requiring you to 'reboot' it by unplugging it for a minute and then plugging it back in.



Picture and/or sound faults, often due to a weak signal or damaged LNB or cable.



I include this as a useful note if you plan to have somebody repair any equipment. Typically, what people often say is 'dead' is something very much alive. I know of a person who gave me a 'dead' video recorder. What he meant it is it wouldn't play tapes. It 'appeared' to work fine, but on inserting a tape, you saw crap on the screen that looked like an untuned TV.
The problem? Dirty video heads. I fixed the problem using a piece of manilla envelope (I'm not going to say how as if you mess it up you risk ripping the video heads out of their mountings and then your video will be a piece of scrap - use a cleaning tape if you don't know the brown-paper method).
Is your <thing> really dead? When you plug it in, nothing should happen. Not a single thing. If the red light, say, on the front of a Digibox lights up, it cannot be called 'dead' even if it refuses to do anything else.
When sending stuff to be repaired, please note this kind of thing down. The red light comes on but it is not responsive to the controller or the front-panel buttons (you did try the buttons didn't you - in case the controller batteries are flat!).
Of course, you could always omit this detail in which case the service engineer will go through the various tests himself. The only difference? He'll be charging you for the time spend doing what you could have told him you've already done...
Oh, and don't forget to provide suitable descriptions. Don't just write "the controller didn't work". Do you have access to another controller, say at a friend's house? Did you try that one? If the on/off button doesn't work, pressing 'Services' (or whatever) will switch the Digibox to 'on' (from standby) and take you straight to the services menu. Maybe you have a 'sticky' button?
If the Digibox (or whatever) actually does something when you plug it in, it is not dead.



A device used with the older analogue systems. Originally, it was a separate box about the size of an Amstrad receiver. It sat on top of the receiver and decoded the 'Videocrypt' video signal. Later receivers (that accept the Sky card directly) have this facility built into them.
There were a number of different encryption types, though most typical Sky users are unlikely to have come across any of them - other than the weird-sync-pulse used for that Scandinavian soft-porn channel.
In these digital days, the decoder is either built into the receiver itself (as is the case with the Digibox, or receivers built for the likes of Canal and TPS) or available via a plug-in module which is not unlike the PCMCIA system used to 'expand' laptop computers.



The 'generic' name for the digital receivers supplied by Sky. The Digibox actually says 'skydigibox' on it (at least, my Pace does) but it is hard to consider it as a specific brand name given that a number of companies (Pace, Grundig, Panasonic, Sony) have built receivers to the BSkyB specification; so it is better to consider a Digibox to be a digital receiver designed for the Sky service.
Some people may use the term 'Digibox' to refer to any generic digital satellite receiver, and while this isn't technically wrong (after all, it is a digital receiving box), it is unusual. Most associate 'Digibox' with the Sky-specification box, and not the likes of the Aston Xena which does loads of things. My magazine rates the Xena highly, but for a price around 750 euros, I'd expect it to do a lot!



Instead of sending the picture dot-by-dot, it is sent as a 'binary data-stream' which can include the entire picture every second or so, and a sequence of 'changes' in the interval, all of which is compressed. Additionally, sound and ancillary information (teletext, programme/station ID, date and time, software updates, the-red-button-stuff, etc) can be included.
The difference? Analogue sends the picture dot by dot as you see it on the TV screen. Digital sends it in a computerised form in which the picture needs to be 'rebuilt' by the receiver. This sounds like a load of hassle; however it allows interactive services, better picture quality, more channels...



"Digital Satellite Equipment Control"
This is a method of modulating the 22kHz signal to control equipment such as multi-LNB switches, rotators, etc.
The Digibox doesn't support DiSEqC.



The big thing that is probably perched somewhere like your chimney...
The dish does not receive the signal. The LNB does the actual reception, with the dish acting like a giant mirror to concentrate the signal into the LNB.
Offset dishes.A larger dish is able to capture a larger amount of 'signal' and focus it into the LNB. In southern UK and northern France, a 60cm dish (or minidish) is sufficient to receive the Astra 1 (19.2°E) and Astra 2/EuroBird (28.2°E) transmissions. Further away, you will need a larger dish to capture weaker signals.
Most dishes are of the 'offset alignment' type. The LNB is situated low down in the profile of the dish, and you can see an example of how this works in the diagram.



Those annoying on-screen channel logos.
Example DOGs; JPEG 13K
Example DOGs



Electronic Programme Guide - the listing that appears when you press the TV Guide button.



Forward Error Correction - part of the 'type' of MPEG data-stream that is being used, along with the symbol rate.



This is the name given to a plan of the geographical coverage of a transponder. Some transponders are aimed to cover most of Europe, while others are aimed to cover a more specific area. The transponders carrying the BBC, for example, have a tight footprint around the UK. This means that people in the UK will receive a good signal, those living close to the UK (such as northern France) will receive an adequate signal, while those living further south will require larger and larger dishes (along with quality LNBs and sensitive receivers) to be able to watch the BBC.


FreeSat (original)

The free to view system that - with a card - allows you to watch Channel 4, Channel 5, and some other stuff via digital satellite (at 28.2°E). Now known as "FreeSatfromSky".
ITV used to be part of the FreeSat service, but they are now fully FTA.



The current name for the with-a-card "FreeSat" as described above.



A joint BBC/ITV initiative lauched in 2008 to bring free television channels to all British viewers by way of a simple receiver (which provides EPG and interactive facilities) and a satellite dish. A boon for those in poor/no DTT areas, and also provides more channels and scope than the DTT services.


free to air (fta)

Channels that can be picked up with any digital receiver capable of tuning into the given channel. The BBC are completely free to air, because they aren't cheapskates like some channels we could mention...


free to view (ftv)

A channel that you don't need to subscribe to, but for which you need some sort of card (this blocks you from watching it outside of the UK unless you lie about your address or take your Digibox with you on holiday). FiveUS is an example of freeview.



A digital terrestrial (DTT) service available in many parts of the UK, basically a BBC-led consortium that picked up the pieces of the failed digital television venture (note - we aren't all obsessed with football) and did something useful with it.



A 'secondary image' that sometimes occurs on an off-air (terrestrial) analogue television picture due to the signal being bounced off of large buildings, storm systems, etc. It is hard to explain, but once you have seen it, you'll know what I mean!



A momentary hiccup in the picture or sound. Not as severe as corruption, and may not even be that noticeable.


herringbone interference

Interference in the off-air (terrestrial) television picture due to interference from an adjacent station. It looks like a bunch of wavy-lines in your picture.
This, usually, is actually some equipment of yours (such as a VCR outputting its RF signal on top of Channel 5) or a neighbour (those old-fashioned cordless phones can muck up TV signals through a wall - but on the plus side, you can listen in to the call!).
In some extreme cases, unusual weather will cause transmitters that are not in your locality to affect your signal. Down on the south-east coast, sometimes French and Belgian television affects the English TV (and vice versa, I would expect). I have been told that it is similar in Scotland, but this time it is Danish, Swedish, and Norwegian television...



Integrated Circuit - a little black thing inside the Digibox that does something. I can't be more specific as there are about a hundred ICs inside the average Digibox!



Low Noise Block - the 'horn' thing fitted to the arm of your dish. This collects the signal from the satellite, according to the specified polarisation, converts it to a lower frequency so it can be sent down a wire, all for your Digibox to receive!



A method of compression where savings are made by discarding information. The picture you see on-screen is not the exact picture that the camera recorded; however in most cases the loss is too small to be noticed. However the more that a channel compresses its picture, the more 'lossy' the compression must be, and hence the more you'll notice chunky bits and flat patchy bits in the picture.

Lossiness example; JPEG 90% quality 36K   Lossiness example; JPEG 50% quality 13K
This is always a hard comparison because what you actually see here depends upon your screen resolution/colour depth and, more importantly, upon the quality of the JPEG conversion software inside your web browser (or whatever). We'll try...
On the left (or upper) is a picture of the weather in Italy in the beginning of March 2004. It has been JPEG compressed at 90% quality, giving us a filesize of 36K.
The picture on the right (or lower) is the same, however it has been compressed at 50% quality. Hopefully the differences are really obvious with the two pictures side-by-side. This time, the file size is only 13K, so it is practically a third of the size of the higher quality picture, though it is noticeably 'worse'.
In digital broadcasting, there is much more to it than this, however this example perfectly demonstrates the principle of 'lossy'.



A method of copy-protecting videos, DVDs, and satellite programmes. It works, often, by adding strong peak-white and peak-black parts to the top of the video signal (up where you cannot see it). Below you can clearly see the black/white areas. This does not confuse a television (it'll show alsorts) but it certainly confused my digitiser - that's why the picture stops abruptly part of the way down.
Copy protection; JPEG 22K
Macrovision works by 'confusing' the automatic gain inside your video recorder. You see, this thing looks at the incoming signal and works out the best levels for the video to set itself to. In this way, video signals from different pieces of equipment will be recorded the same even if one device is outputting a slightly weak signal. The black/white stuff 'overloads' the automatic gain. It doesn't damage it, but it confuses it enough that the first half of the frame is likely to be recorded with the wrong amplification settings, hence an unwatchable picture - bonus Brownie Points if you can identify the movie!
It is particularly ironic that the older video recorders - such as my Betamax - are completely immune to the effects of Macrovision, while newer equipment suffers!



The dish supplied by Sky for their digital service. Unlike a regular dish, the minidish is wider than it is tall. It is more aesthetically pleasing than a whacking great white dish, however it has a reduced signal collecting capacity (due to it's smaller size). This is fine for the most of the UK, further south in Europe you'll need a larger dish. Up in Scotland, you'll have been given a slightly larger Minidish.
If you watch English TV but aren't aware of what the minidish looks like, recall those animated adverts Sky ran near-continuously. You know, the bouncing minidish and 'Bob the installer' that talked to the dishes...



Motion Picture Experts Group - this is the name given to a specific type of compressed moving image with sound, and is the de-facto standard used both for DVDs and also digital broadcasting.



This is short for "picture element" and basically means one individual dot on the screen. Some old-fashioned people may call it a "pel".



In order to squeeze more signals into less space, the signals coming from the satellite have alternate polarisation. This removes the problems of signals 'bleeding' into each other as an LNB working to vertical polarisation cannot receive horizontally polarised signals, and vice versa.
Another example of polarisation in use is the hi-fi audio track in a video recorder. This track is digital sound written to the tape along with the picture. It actually shares part of the tape used for the picture, but because it is polarised differently, you cannot see the sound information on the screen, and you cannot hear the picture information in the sound. They remain separate.



The device that alters the polarisation of your LNB. In the old days, some of these were actual mechanical things (wow!).
This explains, by the way, why your Digibox says it sends two different voltages to the LNB. One voltage selects horizontal polarisation, the other selects vertical.



Portable Mobile Radio - the new millennium's answer to the CB. These little things are shaped a lot like a kid's walkie talkie, and can transmit reliably for about 500 metres - though I've had it working to over a kilometre (it depends on the terrain). There are eight channels available and the units don't need a licence, so they are useful for friends to chat to each other if they live close. Alternatively, for two people attending a show, the radios allow them to keep in contact if they want to wander off and look at their own thing.
One of the requirements of the PMR radio is that it is not used for commercial purposes, it is a small fairly-short-range radio system available to the general public. So I was quite amused when a shelf stocker in Tesco (Camberley) approached me on the suspicion that I was listening in to their communications. As it happened, I like using channel 2. No reason, I just like 2. And it happened to be one of the several channels that they were using; possibly without a licence, as you can't tell me Tesco isn't a commercial organisation! :-)



Power Supply Unit. The device that accepts (usually) mains power and creates the lower voltages used by the device itself. In some cases, such as CDs and mobile phones, the power supply unit is a simple little 'black box' that plugs into a socket, the lead plugging into the equipment.
In the case of computers and the Digibox, the PSU is a highly complicated thing that creates a very stable and very regulated set of supplies - a typical computer PSU offers -12V, -5V, +5V, and +12V often along with some more eccentric things. In these cases, the PSU lives inside the box.



The device that 'receives' signals. If we are talking about a television receiver, we are often talking about the television itself. If we are talking about the Sky satellite receiver, then we are talking about the Digibox.



The MPEG data received by your Digibox contains a highly compressed description of what the picture should look like. As previously mentioned, for things such as a news programme it will contain a regular key frame (the entire frame as you see it) and then a number of frames in which only the 'changes' are sent, moving lips and the like.
'Reconstitution' is the process of putting all these bits back together to form a moving video image.



This means 'Radio Frequency'. The Digibox, most video recorders, and some DVD players offer an RF loop. You connect the aerial to the RF IN and the television to RF OUT. It is possible to daisy-chain a number of devices in this manner, such as:
Aerial -> Digibox -> DVD -> games console -> video -> television

Each device 'modulates' its video signal between the RF IN and the RF OUT. To the next device in the chain, it can be received as if it was a signal being received by the aerial, the video recorder and television don't make any special distinction between UHF 41 (BBC One) and UHF 21 (the Digibox)...



The TV screen contains three electron guns. Don't worry what this means, just know that one is for the red in the picture, one for the green, and one for the blue.
By mixing these primary colours, you can have any colour you could desire (usually a choice of 16 million colours; the human eye apparently can only tell four or five million different colours).
The colour system used in television is 'additive primary' which means the primaries are red, green, and blue (not red, blue, and yellow) and mixing all of the colours together makes white (not black). This is because the dots on the screen themselves glow, so it is pretty much the opposite of the colours used in paintings.
The worst signal quality comes from an off-air signal. This is because it is the video signal shoved into a UHF signal (a process called modulation). The TV needs to 'demodulate' this signal to arrive at an approximation of the signal that left the broadcaster. While it is a poor method, it is the only one viable for long-distance broadcasting across land.
Slightly better is composite video. This is a wire that carries the colour and brightness signals all mixed together. People who have used a domestic video camera are likely to be familiar with composite video.
Slightly better, the s-video cable. This weird little four-pin lead carries a mixed colour signal and a separate brightness signal. Because the brightness and colour are not together, you can afford more 'quality' to each. High quality video cameras (SVHS and Hi8, for example) often have s-video, as do many DVD players.
Finally, the best method. The RGB. Here, the brightness signals for each electron gun are sent to the TV on a separate wire. Usually, what is sent along the SCART lead as RGB is what is directly given to the picture tube. Computer monitors have been RGB for nearly two decades as anything else would result in a fuzzy picture...
Colours; GIF 3K
Incidentally, the 16 million colours is arrived at by using a 'byte' to hold the amount of each colour to show. Every programmer will tell you a byte is eight bits. In normal terms - a byte can 'hold' any number between zero and two hundred and fifty five.
Now, if we have 256 levels of intensity for our red, and likewise for green and blue, this is 256 times 256 times 256, which equals 16777216 - which we all call sixteen million colours (even though it is closer to seventeen million!).



A gadget you attach to your LNB. This thing provides you with some sort of signal to show how strong the received signals are. Some beep at you, some have a bunch of indicators that light up, the best type have a 'moving needle' display (like the VU meters on old tape decks).
I reckon the moving needle type is best as I believe it gives you the best clarity. If a moving needle has a sweep of two inches, you'll actually see differences that may not show up on something with, say, ten lights that glow according to signal strength.
Actually, the very best signal meter you can obtain is the 'error rate' readout of your satellite receiver, though for obvious reasons it sometimes isn't practicable to look at that while you are trying to line up your dish.



The big fat thing that plugs into the back of most modern TVs and VCRs. Your Digibox has two of these, one marked TV and one marked VCR.
People with a setup that is at all unusual (like a British VCR which tends to only have one SCART unlike the European models that tend to have two) will probably hate SCART. It is possible to have audio and stereo sound input and output on the one plug, but I've yet to see a plug with six phono sockets on it. In fact, I have, thus far, wired my own SCART leads. There is no need to have separate SCARTs on the Digibox for TV and VCR as every VCR I've used is capable of looping through the signals with only the one SCART (though two of them makes life so much easier).
The SCART is also supposed to carry R, G, and B signals. These give the best results on a modern TV. Perhaps this is the difference between the TV and the VCR SCART sockets on the Digibox?
Most video recorders do not support RGB as the encoding method is more closely related to the chromiance (colour) and luminance (brightness) method.



This is the ability of your receiver to sort out the useful signal from any crap that may be present. This is related to sensitivity, but it isn't the same thing.



This is the ability of your receiver to pick up a weaker signal, useful if you live in a fringe area.



Little 'flecks' of white or black that appear on-screen. A well-known and fairly common problem with analogue satellite reception; completely impossible with digital.
[having said that, the digital reception can be affected by the same thing that causes the sparklies in the picture, and if there are too many, the picture will break up]
A few sparklies; JPEG 29K   Severe sparklies; JPEG 13K
On the left (or upper), a few sparklies;
on the right (or lower), so many sparklies the picture is getting messed up.



Set Top Box - the generic description for a box that you plug into a television set. The Digibox is a STB. The "Bush box" (for internet access) is an STB. Heck, even a games console is an STB.
It is, possibly, ironic that most people don't actually put these things on top of their televisions!


Symbol rate

The 'speed' of the transmission of the MPEG data. In the Digibox, this is either 22 megabaud, or 27.5 megabaud. A typical modern modem claims to achieve about 56 kilobaud (this isn't strictly correct, but the difference between bauds and bits per second is boring for non-geeks), and the 'fast' ADSL is operating at roughly 2 megabaud. So you can see there's quite an amount of data being sent from the satellite.


switch tone (22kHz)

The 'universal' LNB can receive something in the order of 950GHz to 2000GHz. In order to increase the selectivity and quality of the reception, it does this by splitting its reception into two bands, high and low. The 22kHz tone is sent by your receiver to select the 'high' frequencies (which is most of the channels on Sky Digital; those on the older Astras are spread around more).



A transmitter on the satellite. Consider it like a reverse of your dish - a dish on the satellite sending a signal to you. There are 120 transponders on the old Astra satellites, 85 on the newer ones (the Sky ones).
There isn't one satellite with 120 transponders on it. At 19.2°E (the old ones), you will find Astra 1B, 1C, 1D, 1E, 1F, 1G, 1H, and 2C. At 28.2°E you will find Eurobird 1 and Astra 2A, 2B, and 2D. These satellite are approximately fifty kilometres apart (and closely monitored so they stay put) and given their distance (about thirty six thousand kilometres (some twenty-odd thousand miles)), they appear to your dish to be in the exact same place.
The transponders broadcast with a power of around fifty watts. Here, explanations are difficult. Typically, you'll hear people say "imagine trying to see a standard 60W light bulb that is twenty thousand miles away". Sadly this is a hopelessly flawed argument. A standard 4W CB transceiver might get you ten miles. Give an amateur radio operator ('ham') an eighth of that (a mere half a watt) and she'll send morse code to Japan... Electrical signals differ in their characteristics depending on the frequency used.
Besides, to be really pedantic, what do we mean by a 60W light? One of those energy saving lamps can provide a brightness on par with a 100W tungsten bulb, for only 15W of power!
What we can all agree on is that it is a piddly little amount of power for a transmission, so you shouldn't skimp on the LNB.



A thing that separates the frequency you want from all of the frequencies that are available. When you twiddle the dial of an FM radio to find a station you like, you are altering the tuner to pick up that specific station. Inside the Digibox, it's the exact same thing, only a tad more complicated (from the Digibox's point of view; for you it is easier as you just tell it what station you want).



Video Cassette Recorder.


ZIF (tuner)

A specific type of tuner distinguished with a metal box around a part of it. These things are used in later Pace receivers, and early ones apparently had reliability issues. They are also apparently less sensitive, so the receiver does not perform as well in areas where the signal is weaker.


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Copyright © 2004 (revised 2009) Richard Murray