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organisations which use the 525 line standard. The tapes require a
leader
which
includes
the
standard
EIA colour
bar
signal.
Three
generators have been designed and are currently being constructed to
meet this need.
Diversity Switching System
A diversity switching system has been designed which will choose the
better of two television signals according to a number of important
parameters. The system includes a fast acting corrector of
luminance/chrominance gain inequality to treat the effects of fast
selective fading. The first units were installed at Alderney as part of
the system to provide a colour service to the Channel Islands and the
second pair on Fair Isle to provide a colour service to the Shetland
Isles.
PROJECTS IN PROGRESS
Ceefax Measurements
In co-operation with Transmitter Group an extensive series of tests has
been carried out to determine the Ceefax performance of the television
transmission system. This work has included long term measurements of
the quality of the Ceefax signals radiated from the transmitters at
Sandy Heath and Hannington. To enable the investigations to be carried
out in an expeditious and effective manner it was necessary to develop
and construct a number of experimental instruments.
Combined Linear and Non-Linear Waveform Generator
The television test signal generators currently in use for routine
testing of the television system were developed during the early years
of the colour service and are now obsolescent. A new generator which
combines all the necessary transmission test facilities is under
development. New and improved facilities, including automatic
sequencing of the test signals and remote operation, are also to be
provided. The new generator will become the BBC Standard for
transmission testing and it is estimated that more than 100 generators
will be produced for the service.
Integrated Measurement System
To complement the new combined television waveform generator described
above and to replace obsolete equipment currently in use a new measuring
set is required. A theoretical study is in hand. The forecast demand
for the new instrument is in excess of 100 units.
Video Tape Recording Line-Up Generator
A generator is being designed to replace equipment now worn out. The
new generator combines the facilities of two test generators of obsolete
design and provides a number of useful additional facilities. It is
estimated that the demand for the new generator will be approximately 50
units.
MF/LF Carrier Frequency Measurement Equipment
The reorganisation of radio broadcasting
wavebands has created a need for measurement
in the long
equipment to
and medium
check the
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