Ciro Santilli @cirosantilli  40

This was the first generation of commercially successful radios.

It uses a crystal detector as its diode, which is a crucial element of the radio, thus its name.

They were superseded by transistor radios, which were much more reliable, portable and could amplify the signal received.

The first diodes. These were apparently incredibly unreliable, especially for portable radios, as you had to randomly search for the best contact point you could find in a random polycrystalline material!!

And also quality was highly dependant on where the material was sourced from as that affected the impurities present in the material. Later this was understood to be an issue of doping.

It was so unreliable that vacuum tube diodes overtook them in many applications, even though crystal detectors are actually semiconductor diodes, which eventually won over!

For a long time, before artificial semiconductors kicked in, people just didn't know the underlying physical working principle of these detectors. What I cannot create, I do not understand basically.

This one took a while! Major developments were from the 70s! Perhaps it took the Internet revolution to make its importance clear.

Cool that there is actually a page for a change: www.ox.ac.uk/students/academic/exams/timetables e.g. working in 2024: web.archive.org/web/20240305013807/https://www.ox.ac.uk/students/academic/exams/timetables

And translating from their arcane vocabulary:

Some people have been creating YouTube channels that just post and go over a large number of Stack Exchange questions, some of them with a quick random intro video. Perfectly legal due to CC BY-SA but really weird stuff!