On Saturday evening, S4C’s Freeview viewers suddenly lost access to the channel in a fault that lasted nearly 15 hours. But how did a fire alarm in West London knock out Welsh TV?
Since the beginning of the year, S4C originates from the BBC’s playout facility in central Cardiff. Feeds are then distributed to satellite, cable and terrestrial TV providers so that the channel can be seen by viewers.
For terrestrial TV (Freeview), playout in Cardiff sends a feed to Red Bee Media in West London. This is so the channel can be added to Channel 4’s Freeview capacity.
From here, the bundle of Channel 4 services is sent to be multiplexed together with ITV and Channel 5’s services. Each region has its own variations. In the case of Wales, S4C is added to the bundle instead of E4.
Broadcast infrastructure specialists Arqiva is then responsible for distributing each regionalised multiplex to the the relevant transmitters. The signal from the transmitter is then received by viewers at home.
Red Bee’s part of the chain failed on Saturday night, resulting in viewers in Wales seeing E4 being substituted on S4C’s slot.
This fault persisted until Sunday morning.
The E4 substitution is made in Wales so that S4C can be given a high coverage slot, broadcast on both main and relay transmitters. E4 is then inserted on a different multiplex, but with lower overall coverage.
During the fault period, some viewers in Wales could temporarily see E4 on both Freeview channel 4 and channel 13 in Wales. Since then though, both E4 and E4+1 have had reported issues on Freeview in Wales.
Throughout this period, S4C continued to be available on satellite, cable and online, where different distribution chains, independent of Channel 4, deliver the signal.