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"This card is complementary to the normal Eurocard range,
but also intended for general OEM use by the industry. It is an RGB-input PAL
colour encoder with intercarrier sound, and was designed by Acorn for
manufacture by Astec International. It is of particular interest to the Viewdata/Prestel
industry for displaying high-quality colour graphics on a standard domestic
television.
It accepts Red, Green, Blue and synchronisation signals and
converts them to a composite PAL colour video signal; this is modulated onto a
UHF carrier to produce an output on channel 36 suitable for feeding the aerial
socket of a television. The board will also drive a monochrome TV to give a
black and white picture, with the intermediate colours appearing as different
levels of grey. The circuit includes a sound input, and the sound sub-carrier
oscillator may be tuned to either 51/2MHz or 6.0MHz. Separate presets are
provided for accurate setting of the spot frequencies for the colour and sound
sub-carriers, should this be needed. The card operates from a single 5 volt
supply, and is designed to fit a standard Eurocard rack.
The RGB PAL Encoder/UHF Modulator forms an ideal interface
between the Acorn Teletext/Prestel VDU and a colour TV. Connection to the Acorn
Teletext/ Prestel VDU is by an 8-way ribbon cable, which carries power as well
as the signal lines. Note that Acorn provide a separate UHF PAL colour board for
the Atom, and the two boards are not interchangable.