Mast Earth/Isolation Board

I remember this mast safety board from when I started at Rugby Radio Station as a Youth-in-Training (Apprentice) in 1964. This board was then still in use to inform all riggers and engineers of which masts were safe to work on.

The board was attached to the wall near the South exit of the transmitter hall. It has a rotating indicator for each mast which shows “Earthed”, “Earthed – Men Working” or “Isolated” and the board can be locked with a small padlock so that only the authorising engineer can change the indications.

Why was the board needed?

The Rugby Radio Station GBR 16kHz transmitter opened for service in 1926. It had worldwide coverage, sending morse code news messages and telegrams to ships and the commonwealth. Very high power and an aerial supported by twelve 820ft (250m) high masts were needed to transmit right around the globe.  To improve the efficiency and radiated power, the masts were designed to be insulated from earth as well as from the aerial. Ceramic (cheese shaped) insulators and eight Swedish granite blocks were installed at the base of each mast to enable this.

However, the masts needed maintaining and this took longer than the available transmitter downtime. The painting alone, was a “Forth Bridge Job”. Therefore, each mast had a large earthing switch at the bottom to allow the mast to be earthed and made safe for working on, whilst the transmitter was still on-air. This, of course, reduced the radiated power slightly.

 

When did the board go out of use?

In 1966, as part of the Navy’s communications upgrade during the Cold War, the GBR transmitter was replaced. The output power of the new transmitter was increased. It was then decided that it was worth a slight loss of efficiency to improve safety and all twelve 820ft masts would be permanently earthed. The board was no longer required but was kept at the radio station until donated to Rugby Art Gallery and Museum in 2007.   The final four 820ft masts were demolished on 2nd August 2007. One of the granite blocks has been preserved as a memorial in the Watts Lane cemetery in Hillmorton.  The “block and cross" sculpture was dedicated by Canon John Randall and unveiled by Councillor Bill Sewell on 2nd December 2008.

Malcolm Hancock

Worked at the GPO-BT Rugby Radio Station from 1964-2002 retiring as Station Manager