A rectangular concrete base, with raised platform, possibly for a hand-operated triatic (insulated antenna wire support) winch, with 150mm-wide iron loop at one end for taking the triatic rope strain (significant rope wear is evident to the underside of the loop, by touch).  Six threaded bolts of ¾ inch (imperial size). The loop is surrounded by lighter fine concrete, strongly suggestive of having been inserted into the base as a later addition.

Source: Rowlands, J., Marconi's Carnarvon Station 1912-1939: a journey into early commercial wireless in north Wales' Second Edition, 2023.