First check all of the existing connections and leads. Make sure that all are correct and tight. Re-orient the aerial (antenna) if that can be done easily and safely. The lead should not have any bare metal showing, no kinks or hard bends.
Look for nails or staples that may have penetrated into the conductors. No corrosion or rust anywhere. Remove any unsused splitters, splices or other connections that may be present.
Try another TV - if the signal is good then the problem is the old Panasonic
If the signal is not good then try running another cable/lead from the aerial (or another source even) to see if that makes a difference.
Then the last option is to try another aerial (antenna).
The overall concept is to work from...