Limiters and Compressors
A high level of design activity has been maintained on programme
compressors, protection limiters and associated devices during the year.
This has been caused by a number of factors. Although the benefits of
overshoot-free operation are well known, little of such proved
techniques is offered in studio desk equipment by commercial
manufacturers. A large number of studio desks is being ordered from
several manufacturers on a replacement programme. These all require to
have built-in, select able, compression characteristics of BBC design in
a mechanical form compatible with each commercial desk.
To cater for the three present systems and to allow for future
suppliers, a "knock-down" printed card system has been developed on
minimum-sized cards which can be mounted and wired for switchiug and
metering. This general-purpose design, which includes all the currently
required facilities for studio programme compression, is being made by
Equipment Department as pre-tested circuit boards. These will be loaned
to the desk manufacturer who will mount, wire and function test the
complete desk system before offering it for BBC acceptance.
The introduction of the Geneva Plan of reorganised LF/MF transmissions
in November 1978 is being used as the starting point for a large
programme of re-equipment and re-arrangement of programme distribution.
One requirement from this is for a standard overshoot-free limiter
combined with a remotely-switched compression characteristic. This is
to obtain the best possible transmitter coverage, having regard to the
type of programme material being broadcast and whether it is daytime or
evening. As with all the other units being developed for the new
Programme Input Equipment, this special compressor/limiter is on a BMM
Noise Measurement
The results of decisions by the CCIR
affect the equipment needed by the
BBC to measure circuit and equipment
noise. It is necessary to use the
same methods as the British Post
Office and IBA nationally, and other
organisations internationally.
A suitable measurement card has been
developed which complies with the
latest CCIR recommendations, but the
implementation awaits decisions on
the procedure to be adopted in
changing from the traditional BBC
mothoda and agreement on change-over
dates with other organisations.
- 7 -
Noise Measurement Card for
the A. C. Test Set sho7JJn in its
Produ(Jtwn Test Jig