My opinion based theory on how to build a Chronovisor. Get and analog tv and modify the signals to maybe 7.83 hz then see what happens on the screen.
Someone on another blog said this:
""Chronovisor" was the name given to a machine that was said to be capable of viewing past and future events. The chronovisor was portrayed as a large cabinet with a normal cathode ray tube for viewing the received events and a series of buttons, levers, and other controls for selecting the time and the location to be viewed. It could also focus and track specific people. According to its inventor, it worked by receiving, decoding and reproducing the electromagnetic radiation left behind from past events, though it could also pick up sound waves."