Digital Television Aerial

April 17, 2016
Bailey Pursuit Plus | Bailey

TV AerialDigital Terrestrial Television (DTT) is one of a few ways of receiving Digital Television (DTV) at home. However, in order to receive DTT transmissions and fully realise the benefits available from this new medium the choice of antenna and its positioning needs to be carefully considered.

The antenna (or aerial for us Brits) is the first and arguably the most important link in the chain to receiving a high quality signal for our TV or digital TV recorder. If you live in an area of poor reception or do not have the correct type of antenna, then no matter what you do later in the chain, performance is likely to be compromised.

While this article provides an introduction to the antenna issues that directly affect the quality of reception, your local antenna installer should be able to advise which antenna is best suited for your particular location.

Signal Strength

While Digital Terrestrial Television (DTT) can offer improved picture quality over conventional analogue TV by eliminating traditional picture reception problems such as ghosting, a reasonable signal strength is still required.

All or Nothing

A weak analogue TV signal is easily recognised because it will suffer from increased noise or ‘visual snow’. Digital TV however will continue to provide clean reception until a minimum threshold is reached. Beyond this the digital data can no longer be accurately decoded and the output from the TV tuner will cease. A drop of 3dB on a Digital TV or set-top box is enough to make the difference between crystal clear reception and no reception at all.

Aerial transmitting a signalHowever, before this point is reached, parts of the digital signal will become lost or corrupted. While the sophisticated error correction algorithms used in DTT decoders can mask these effects to a certain degree, this is second best compared to having the full quality original signal, which is only achieved with a good quality antenna installation.

Frequency Ranges

Digital terrestrial television signals in the UK are transmitted on UHF (Ultra High Frequency) bands IV and V on channels 21 – 68 (471 – 847 MHz). Each channel occupies a bandwidth of 8 MHz, the amount of space required for one traditional analogue TV channel. Historically these channels have been grouped together in different frequency bands:

Group

Channels

Frequency

yagi-aerialBand Coverage Code
Group A

21 – 37

471 – 599 MHz

Lower 1/3 of band Red
Group B

35 – 53

583 – 727 MHz

Middle 1/3 of band Yellow
Group C/D

48 – 68

687 – 847 MHz

Top 1/3 of band Green
Group E

35 – 68

583 – 847 MHz

Top 2/3 of band Brown
Group k

21 – 48

471 – 687 MHz

Lower 2/3 of band Grey
Group W

21 – 68

471 – 847 MHz

All of the band Black

Matching the Aerial

To extract the maximum signal strength from any received transmissions, the associated antenna needs to be correctly matched to the local transmitter’s frequency band / group and polarisation. In the UK the coloured plastic cap at the end of the antenna indicates which group the antenna is designed for.

Yagi Antennas

Most TV antennas are of a specific type of antenna called Yagis. A Yagi antenna comprises a number of parallel elements or arms along a rod, a dipole (which collects the actual signal) and a reflector at its rear.

Source: www.richardfarrar.com
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