The Digital Cliff Edge

Unlike analogue TV signals, which can be viewed down to weak signal strengths or in corrupted conditions, DTTB TV signal’s pictures and sound will either be perfect, or in the process of breaking up or non-existent. The penalty for the potential of obtaining perfect pictures and sound all the time is that DTTB reception exhibits a very rapid change from being excellent to disappearing. This phenomenon in general is referred to as digital cliff edge or threshold.

Figure 2: Picture and Sound Quality Versus Signal Strength

The recommended minimum level margin is 9dB (typically = 15dB with preferred >20dB) for the first level of caution to cater for short and long-term variations.

The cliff edge characteristic of digital reception invites the definition of a margin the signal has to achieve before this failure level or cliff edge is reached. By the insertion of an attenuator in the input of the receiver or the system’s amplifier, the level margin may be found.

Importantly all the channels expected to be received must be received reliably. Hence the level margin must be checked on all channels. Further quality checking must be assessed also on all channels.

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