The development in telecommunications the last forty years is really a spectacular story. Apart from mobile- and data communications where most of the focus have been the last ten years, the trunk transmission systems is really what makes it all work. Sweden was very early in building a nation-wide network and the country had more or less 100% coverage around 1930 or so. For several years, the number of subscribers per capita was among the highest in the world.

I very well remember when travelling by rail as late as in the mid 1970s, although strongly on the decline, thes old type of aerial wires were still fairly common out in the countryside. Given that one speech channel requires two wires in such a setting, at some lines the number of wires could be huge and sometimes there were even more than one line of poles in parallel. Conducting calls to the countryside at that time meant crosstalk - a phenomenon that is for most people gone in the shades of history.

Apart from being vulnerable to storms, ice, falling trees and rust, the maintenance effort of maintaining these lines must have been enormous. The first strike to the aerial wires came as the railways started to be electrified and telephone wires had to be dug down. Modern multiplexers and carrier frequency systems became a reality by introduction of semiconductors and in the early 1960’s, the main trunks were replaced with multiplexed systems and ground cables. When the telephone networks were upgraded into the digital era, an effort that started around 1970 here, which almost eliminated the old type of lines. Today, only at some very rare remote locations, remains of the old era can be found. As far as I know, none of these lines are in use.

Fibre optics – yes. Amazing that thousands and thousands of speech- and data channels can be tunnelled through a fibre thinner than a human hair but these old lines with their ceramic insulators are amazing, I think.
.