Re: What is the teleprinter
It used a current on and off for binary signaling and the words had five bits with start and possibly stop bits. The general speed was around 60 words per minute max.
The electronic UART was inspired by the signalling method. Because of the limited alphabet from five bits, there was a shift function that doubled the symbols. Letters were in upper case and in some models used by the government weather authorities the shifted functions were weather symbols for pressure and wind for example.
When these units were replaced by newer ones around 1950 and later, the old ones were sold to radio amateurs. The radio link used FSK on the HF band.
In the older cinema you can see these in operation in the scenes of journalists at their office.