I saw this posted on one of the many Facebook groups I’m on. Right up my inner-geek street, so thought I’d keep it and share it.

Text from article:

Standing stark above London's skyline is an impressive landmark, the Post Office Tower. The Tower is the tallest building in Britain. Situated near Tottenham Court Road, the Tower is no 'head-in-the-clouds venture for it plays an important part in London's communications system.

Telephone conversations, besides being carried by wire are nowadays transmitted by micro-wave radio beams, each beam being capable of carrying over a thousand individual telephone calls at once. These beams are rather like searchlight beams, and are transmitted from aerials which are situated high enough to give the beams an obstacle-free path. Hence the reason for the Post Office Tower-to carry aerials high enough to transmit and receive beams far above the roof-top level of the highest of London's buildings. (See diagram below.)

From the Tower telephone calls are transmitted as far afield as Manchester.
Norwich, Bristol and Southampton-but not direct, however, as the beams are limited to a range of some 30 miles and must be relayed to their destination in a series of hops by relay stations which receive and re-transmit the beams.
Television programmes are also relayed from studio to transmitter via the Tower's aerials.

The Tower is 620 feet high, and weighs 13,000 tons. It is constructed of concrete reinforced with high tensile and mild steel and has no less than 50,000 square feet of glass on its outside covering. It will withstand high winds with the minimum of deflection-so as not to upset the alignment of the radio beams.

Gusts of 90 mph are estimated to induce a deflection of only 15 inches at the very top of the Tower!
The Tower viewing galleries are open to visitors, providing a vast panoramic viewpoint overlooking the whole of London.