Keywords
digital
television, transmission, reception, spectral mask, PAL-I,
DTT
|
Abstract
The
introduction of Digital Terrestrial Television (DTT)
in the UK will require the use of UHF channels adjacent
to those occupied by existing PAL-I services. There
are potential engineering problems resulting from
this, one of the most serious of which is posed by
the high level of PAL-I sidebands radiated within
the lower adjacent channel.
Work
carried out at BBC Research and Development has shown
that such interference can be avoided by ensuring
the PAL transmission conforms to a modified System
B/G spectral mask. (In effect, the new mask reduces
the width of the vestige from 1.25 MHz to 0.75 MHz.)
However, PAL-I receivers are designed to make full
use of the 1.25 MHz vestige, and modification of
the mask must lead to some distortion of the demodulated
signal. The extent of the distortion is evaluated
in this Paper.
The
conclusion is that the errors present at the output
of a high quality 'professional' receiver are small.
They are negligible for a domestic set.
This
Paper was originally written in 1997, and circulated
amongst groups interested in the subject. |
