A crane camera system employs a hook camera transmitter to send wireless signals vertically upward to a trolley receiver, which are then relayed by a trolley transmitter to the operator cabin. This allows line-of-sight wireless transmission of signals from the hook to the cabin to take place reliably...http://www.google.ca/patents/US7656459?utm_source=gb-gplus-sharePatent US7656459 - Crane hook and trolley camera system
