How The BBC (Still) Sends Audio To Transmitter Sites

Managing a radio station is, on the face of it, a simple complex challenge. Make a studio, hook it up to a transmitter, and you are good to go. But what takes place when your station is not a solitary Rebel Radio-model hilltop set up, but a nationwide chain of transmitter web-sites fed from a wide variety of metropolis-dependent studios? This is the problem facing the BBC with their countrywide Uk FM transmitter chain, and considering the fact that the 1980s it has been fed by a collection of NICAM digital facts streams. We described back again in 2016 how the ageing equipment had been changed with a modern FPGA-dependent implementation without the need of any listeners noticing, and now many thanks to [Matt Millman], we have a opportunity to see a teardown of the original 1980s units. The tech is reasonably quick to realize from a 2020s standpoint, but it however incorporates a several surprises.

In each studio or transmitter web page would have been a 19″ rack made up of a single of these units — a card frame with a selection of encoder or decoder playing cards. These are all tailor made-produced by the BBC’s engineering department to a incredibly high regular, and use period elements this sort of as the acquainted Z80 microprocessor and some Philips digital audio chips, which followers of high-finish client audio may perhaps understand. As you’d count on for a mission important gadget, lots of of the features are duplicated for redundancy, with their outputs in comparison to give warning of failures.

The surprise comes in the NICAM encoder and decoder — it’s a customized LSI chip created exclusively for the BBC. This implies the price range available to the countrywide broadcaster, and supplied that these units have in some conditions been performing for about 35 decades, we’re guessing that the license payers obtained their money’s really worth.

You can read about the initial swap-over in 2016, and a minor extra about NICAM, way too.