Related: Baird's Mechanical Television
https://paleotronic.com/2018/09/15/gadget-graveyard-bairds-m...
Also this site, which shows how the recorded Phonovision broadcasts were eventually recovered:
http://www.tvdawn.com/earliest-tv/phonovision-experiments-19...
alt Hacker News
Also this site, which shows how the recorded Phonovision broadcasts were eventually recovered:
http://www.tvdawn.com/earliest-tv/phonovision-experiments-19...