TRANSMISS/QN
.
SECTION
MAJOR PROJECTS
The Transmission Section deals with baseband audio and video
transmission systems, carrier transmission over cable, and digital
transmission. Voice communication and tone switching systems over cable
and wire are also covered. Particular attention is paid to network
transmission standards, and the Section is involved is international
discussions on such matters.
Ceefax
Co-operation with Transmitter Group has involved visits to several
transmitters of different types to
investigate their behaviour with
regard to the radiated Ceefax
signals. Sandy Heath, Hannington,
and Fremont Point have been visited
and various corrective techniques
using pre-equalisation and
regeneration have been proposed.
Suitable equipment to effect
improvements is being designed, and
a demonstration has been given which
indicated the need for such
improvements.
Digital Sound Transmission
Ceefax Regenepatop
Although further development of the 6 channel NICAM equipment has been
temporarily suspended the prototype equipment has been in use to provide
the sound channels in a 140Mbit/s bit stream which also includes two
digital television signals. This multiplexed system is a Research
Department project, and it has recently been successfully used on an
experimental fibre-optic link of about 18km which has been installed by
S.T.L. between Post Office exchanges at Hitchin and Stevenage. Recent
international proposals have suggested that it would be an advantage if
digital sound programme channels could make use of multiples of the
64kbit/s
used
by
the
Post
Office
for
telephone
channels.
These
proposals have stimulated further studies which may lead to a system
which would have improvements in quality and in error performance
compared with the original NICAM system.
Revision of Television Network Limits
Discussions have continued with Transmitter Group, Transmitter Capital
ProJects Department, and Communications Department, to see whether there
would be any advantage in reallocating the maintenance limits amongst
the various parts of our television distribution network. It has been
suggested that the limits which are employed at present do not enable
the most efficient use to be made of scarce maintenance effort and a
reallocation has been suggested which, it is hoped, will improve this
situation. These limits have been tried out on a transmitter chain in
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