Top Tips

Problems can often be equipment-related. Check out our top tips before going further.


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Short for Amplitude Modulation. AM is the system used for medium wave (MW) and long wave (LW) broadcasts.  In practice, though, a radio possessing an "AM" band usually means it has medium wave, but not long wave.

Aspect Ratio 
The relationship between the width and height of the TV screen, thus defining its shape. A modern widescreen set has an aspect ratio of 16:9. Older traditional TV sets have an aspect ratio of 4:3 which means a compromise when displaying programmes, nearly all of which are now made in 16:9. 

A device that reduces the power of a signal to prevent receiver overload.  Normally fitted in the feed from the aerial to the receiver.

Audio Description (AD)
A spoken commentary on TV describing what is happening on screen, particularly for the visually impaired. The commentary fits in between dialogue and describes action sequences, facial expressions, costume, scenery and so on. Audio description is sometimes referred to as 'narrative' soundtrack or commentary.  AD is available in varying degrees on all digital TV platforms but not on analogue TV.



The amount of the radio spectrum used for transmitting a signal. Potentially the wider the bandwidth, the more information that can be carried by that signal.  Digital broadcasting makes more efficient use of bandwidth.    

Bit rate 
Speed at which data is transferred, measured in bits per second (bps). 

This popularly means high speed internet access provided either via a cable network or telephone line. It has the capacity to enable high-speed streaming (live viewing) or downloading of video and audio.



Co-channel interference (CCI)
Co-channel interference occurs when signals from two different radio or TV transmitters using the same frequency are received on top of one another. Mostly caused by unusual weather conditions, and therefore temporary. 

In digital broadcasting, ways of making more efficient use of bandwidth. Techniques include removing information before transmission which can be reconstructed in the receiver, and discarding completely that which would be unnoticed by the human ear or eye. Digital compression techniques are constantly being added to and improved.



Digital Audio Broadcasting: the transmission system used for digital radio. 

Double-screened cable
Standard TV coaxial cable has an outer screen of woven copper braid surrounding an insulated inner core.  Double-screened cable has a layer of copper foil wound over the braid.  This extra screening reduces interference pick-up as well as giving better electrical performance.  "Satellite" cable is always double-screened.  Such cable must not be bent sharply as this could crack the foil and compromise performance.

Digital Radio Mondiale: a digital radio system being used on shortwave, though also capable of use on long wave, medium wave and even VHF. Though DRM has clear technical advantages over conventional AM broadcasting, receivers tend to be expensive, and relatively few broadcasters use it at present.

Digital Satellite: TV received via a satellite dish.  Otherwise known as 'freesat' or 'SKY'

Digital Terrestrial Television: received through an aerial. Freeview is the UK's free-to-view DTT operator; Top Up TV operate a DTT subscription service.

Digital Video Broadcasting: the worldwide standard for digital TV. Any set-top box or digital TV carrying the DVB kitemark will be able to receive digital broadcasts.

Digital Visual Interface: a digital connection for high-quality video, suitable for high-definition TV. See also HDMI.



Services that are 'scrambled' so you need a viewing card to watch them. 

A digital radio term for a single frequency block that contains a number of radio channels. See also Multiplex.

Electronic Programme Guide: an on-screen listing of what's on TV and radio, usually for up to 7 days ahead. You can use the EPG to go straight to a programme you want to watch or to select something to record.


Short for Frequency Modulation. FM is the system used for broadcasting on VHF radio frequencies. 



Hard disk 
An electronic storage device used in personal video recorders (PVRs) as well as computers generally. You can store many hours of TV programmes on a PVR's hard disk.


High definition: HD TV has up to four times many pixels (dots on the screen) as standard-definition TV in the UK. The pixels make up the lines on a screen - standard screens have 625 lines, HD screens have 720 or 1080 lines. This gives a clearer, sharper picture with much more detail. HD TV also has better quality sound, often with multi-channel surround sound capability.

High-Definition Multimedia Interface: a digital connection using a single cable for high-quality video and audio.  You will need an HDMI cable to connect an HD set-top box to an HD-ready TV set.  


Integrated digital television: a TV set capable of receiving digital TV broadcasts without a separate set-top box. All TVs now sold in the UK are IDTVs, capable of receiving some form of digital television directly. Both Freeview and Freesat versions are available, though most TVs now sold in the UK are Freeview IDTVs.



Liquid crystal display: a technology that displays a picture on a flat-panel screen.

Light emitting diode TV: a technology that displays a picture on a flat-panel screen.

Letterbox format
A way of displaying pictures with an aspect ratio of 16:9 on a screen which has a 4:3 aspect ratio. It ensures the whole image is visible but means there are black bars at the top and bottom of the screen.

Low Noise Block downconvertor: the device mounted on the arm attached to a satellite dish that receives the signal, converts it and sends it to your set-top box.


Multipath Distortion
A 'gritty, scratchy or mushy' sound on FM caused by signals being reflected from objects or hillsides.  These signals arrive at the aerial along paths of slightly different lengths and therefore at slightly different times. This gives rise to distortion in the decoder, especially in stereo.  Using a more directional aerial aimed accurately at the transmitter can reduce this.

Multiplex (MUX)
A single frequency channel that contains a number of different digital TV or radio services. In the UK, six multiplexes carry all the digital terrestrial TV services and radio networks available on Freeview, plus one for HDTV. For DAB digital radio, there are two national radio multiplexes (also called ensembles) and a number of local ones.



Omnidirectional FM aerial (halo)
An aerial designed to pick up signals equally well from all directions.  It is less powerful than a directional type and can give rise to weak (hissy) reception in areas without strong FM coverage.  In some circumstances it can also lead to undue multipath distortion.  Directional aerials are preferred unless all-round coverage is a specific requirement.

This is the name given to reception problems caused by too much signal entering the receiver. Normally cured with an attenuator. 


Picture element: a single dot on a TV screen (or computer screen or digital photograph). Hundreds of thousands of pixels make up the picture, and the more pixels the sharper the picture. 

The 'blocky' effect seen on digital TV when reception is disrupted and the error-correction system is unable to compensate correctly. Pixellation is the commonest defect seen by TV viewers but can have many different causes.

A technology that displays a TV picture on a flat-panel screen by using gases behind the glass.

In broadcasting, a system for delivering TV and radio services. For example, TV is delivered mainly on terrestrial, satellite, cable and broadband platforms.

Personal video recorder. Also known as a DVR (digital video recorder), it records TV programmes onto a hard drive. It allows you to pause and 'rewind' a programme while you are watching it, or you can often record one programme while watching another.



Radio Data System: used on FM to keep car radios tuned to the strongest signal, as well as providing programme and station information, and traffic alerts. 

In digital TV, the process of turning a receiver or set-top box off, leaving for a short while, then turning on again.  Re-setting the software in this way cures many problems.

Red Button 
Used on the remote control of a digital TV receiver to reach extra services. 

A low-power transmitter that receives signals from a main transmitter and retransmits them to a localised area.

Rescan (add channels)
Rescanning your digital receiver checks for new channels and adds them to the memory, without removing those already there.

Retuning clears the memory in your digital receiver or set-top box, then finds and installs all the available channels. Retuning the receiver in this way cures many problems.  It may also be needed to allow viewing of a new service.

RF lead
An RF lead is used to feed a TV signal from an aerial to a TV, set-top box, or other device.

RF loop
The process by which a signal from an aerial is taken through one piece of equipment and passed on to another using an RF lead.



A SCART lead has a large, rectangular, 21-pin plug at each end. It is the simplest way to connect equipment such as TVs, PVRs, DVD players and set-top boxes.

Set-top box
Otherwise known as a digibox or decoder, an 'outboard' digital TV receiver to enable viewing on a separate TV.  Modern TV sets are now sold with built-in Freeview or Freesat reception, but for Sky or cable reception you will still need a set-top box supplied by Sky or your cable provider.   

Short wave (SW)
A band of frequencies used to broadcast between countries and continents, since SW signals travel long distances under the right conditions.  

The breadth of frequencies available for transmissions. In the UK, the total radio frequency spectrum is licensed by Ofcom and parts of it are set aside for broadcasting.

Sporadic E (Es)
A short-lived atmospheric condition allowing signals to be received strongly over hundreds of km.  Es is prevalent in the summer and is most noticeable on FM where local stations can be 'wiped out' by foreign interference, usually for minutes at a time, during daylight hours.

TV or radio programmes received 'live' down a broadband internet connection (as opposed to being downloaded and played back later). 

TV subtitles are principally for the hearing impaired although they are sometimes available in languages other than English.  TV subtitles can be switched on and off.


Tropospheric propagation
Sometimes called 'tropo' for short, this describes the situation when high pressure weather conditions allow signals to travel much greater distances than normal. Interference then occurs between signals from different transmitters using the same frequencies.  It most commonly affects TV and FM broadcasts and can result in picture loss or break-up on Freeview, and whistles and interference between stations on FM.


Widescreen TV pictures have an aspect ratio of 16:9, which is closer to that of a cinema screen than the traditional 4:3 TV shape. The programmes on most of the major TV channels are now in widescreen format; this is now the standard throughout much of Europe.  

The trade name for a popular wireless technology used in home networks, mobile phones, video games and more. Wi-Fi is supported by nearly every modern personal computer operating system and most advanced game consoles, printers, and other peripherals.



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