When you pull the handle down a pin in the shaft engages the gear that raises and lowers the antenna, when you push the handle up it engages the base of the antenna allowing for it's rotation.
I have included a few photos which hopefully will help you understand its operation.
I bought new gears, base plate, wire, spring, bearings, and shaft last year from the manufacturer, Braund Mfg, now a Div. of Barker Mfg. Co Barker_Home
Parts needed: Fan for roof vent or whole vent fan assembly, vented catalytic heater.
My blog for the 1975 Tradewind restoration
, Has not been updated in a while but I am still working on it.