Bare copper antenna wire stapled directly on wood rafters causes loss of rf signal energy.
Ground wire in attic.
How to run wire through an attic step 1.
Insert the end of the 12 2 wire into the fans junction box.
Grounding of mounting hardware is not required indoors.
Measure the distance between the two sites you want to run wire between and make sure you will have enough wire.
Use wire nuts to connect.
As provided in 250 130 c the equipment grounding conductor shall be permitted to be run separately from the circuit conductors.
Check to ensure that the vent tube is firmly grounded before connecting the wire.
You have to inspect it along its full length until you reach a working ground wire.
This is usually a moveable piece of drywall or plywood that covers a rectangular hole in.
I found that a firm grounding of antenna mast gave a better reception as well.
The copper wire at the base of the antenna mast attaches to the copper vent tube that runs to the roof through the attic in a 55 year old house.
Strip away about 6 inches of outer insulation and 1 2 inch of individual insulation from the end of each wire.
Lets you do precisely what you are describing running a separate ground wire to an existing point on the equipment grounding system originating from the same panel.
With time bare copper oxidizes the wood where the wire is tightly stapled to absorbs some of this oxidization and forms a loose yet lossy bond with the wire.
Find your attic access.