It all started with Heinrich Hertz a physicist born in Germany in 1857 who first conclusively proved the existence of the electromagnetic waves predicted by James Clerk Maxwell’s equations of electromagnetism.

With the onset of radio use it was thought to be prudent to be able to monitor radio waves and that saw the beginning of GCHQ before WW l

During WW I spark transmitters were replaced by those using valves.

Bletchley Park was set up as a very secret unit near the start of WW ll .Transistors also came into use at about this time. Eddystone radio became Marconi and radios moved to include not just LF and HF but frequencies in the Gigahertz range for use with RADAR.

The famous 19 set was included in all tanks during WW ll.

As well as transistors the new Integrated circuits came into use

Paul had many projects to display and books to recommend.