Digital signals.

What does digital mean?

What is pixelation on your TV?

What is the digital cliff effect?

How do i correct these faults?

This page attempts to answer all of these questions. 

What does digital mean?

Essentially digital tranmits in 0's and 1's like a computer uses 0's & 1's for data. Digital is a new way of transmitting and receiving TV signals in this way, that is far more cost effective and allows far more channels to be packed into the same amount of space. For example, where as before, you had one channel say BBC1

In 'times gone by' aerial signals were known as analogue. Aerials  in the UK)  used used to pick up the signal from an aerial transmitter, and, if all was well, you had great TV reception. If there was a problem it was usually 'ghosty' or 'grainy' on the TV. This usually meant a reflected signal, or, a weak signal, or both.

Analogue aerial signals used to need to be above something called threshold. Threshold means over 47dB in signal. If your signal dipped below this threshold, then the signals would be grainy. Above threshold (all other parameters being well) the reception would not be grainy.

For digital signals, the parameters are different as below.

What is pixelation on your TV?

Pixelation is that irritating block effect that you see on screen. Sometimes there is a delay in speech, sometimes the speech carries on even when the picture breaks up. This can be frustrating when you are watching television, however why does this pixelation occur.

Essentially whilst in the analogue days of transmission, TV pictures became grainy, for digital they pixelate. Essentially this happens through there not being enough signal, a reflected signal or an interfered with signal. There are often ways to help if this is an issue for you.

What is the digital cliff effect?

Digial aerial signals do not have the same luxury as analogue signals, in that once the signals go below a certain parameter, the picture degrades very quickly indeed. If you can literally imagine walking up to the threshold of digital signals,stepping over that threshold, then that is you passing the 'digital cliff effect'. There are other parameters that are quite important also, such as C/N ( carrier noise) ratio and BER ratio. Too much signal also will have the same effect.

C/N is the amount of noise (poor signal) that is allowed to enter as a ratio compared to the carrier (good signal). marignal reception or unreliable reception occurs at a ratio of 22dBuVor less. 23-25dBuV is marginal reception and over 26dB is good.

BER means bit error ratio. This is a lovely thing that digital devices do to correct the amount of errors in a signal. The ratio should be 2< 10,000 2 errors in 10,000 good bits of data.If it is worse than this, then the signal may start to pixelate.

Digital terrestrial signals need to be over 40dBuV in signal strength with a carrier-to=noise ratio of over 26dBuV with a B.E.R. (bit error ratio) of 2<10,000 bits of data tend to function well.

Signal leves should ideally be between 45dBuV and 60dBuV.

How do I correct these faults?

First things first. Before you call out an aerial specialist, check the simple things.

Is your aerial lead plugged in properly. Is the lead in good condition? Are the colex plugs correctly installed? If that is all ok, if you have an aerial socket in another room, try out the reception in that room, to make sure it is not a TV set fault.

Being too close to a powerful transmitter can also be a problem. Maybe try an adjustable attenuator to cut the signals down. In good reception areas, this often works.

Check to make sure that if you were gardening and trimming bushes, that you have not cut through the cable. This is surprisingly common in the spring and summer months.

Thereafter, it is proably a good idea to source a good aerial company to investigate further for you.


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