Oscillograms cast in stonePieter-Tjerk de Boer, PA3FWM firstname.lastname@example.org
(This is an adapted version of part of an article I wrote for the Dutch amateur radio magazine Electron, June 2019.)
In eastern Stockholm one finds this 155 m high concrete tower, called Kaknästornet. This tower was built in the 1960s as a communications tower for radio and television signals. Several floors in the top of the tower were a restaurant and viewing platform; unfortunately, those have been closed to the general public since the autumn of 2018.
For radio amateurs however, the tower still is of touristic interest. This is because the concrete of the tower has been decorated with oscillograms of analog television test signals. See the pictures: the line synchronisation pulses are clearly recognizable, with various square wave and sawtooth test patterns in between.