It was originally built in the 1980s as a fill-in relay for UHF analogue television.

It was sited at the clubhouse of the soccer ground at Ynys Park and consisted of a mere 3 m aluminium mast carrying a vertically stacked yagi array.

Alltwen transmitter re-radiated a signal received off-air from Cwmafan about 2 km farther to the northeast, itself a relay of Wenvoe.

It was possibly the lowest ERP officially provided TV relay in the UK, radiating just 0.5 W on each of its four UHF channels.

When it came, the digital switchover process rendered Caerhendy redundant.