Combination VHF/UHF antennas Winegard antennas in particular have a box
that combines the two half's of the antenna into one downlead.
It is possible that this item has gotten corroded, or eaten by some monster
that preys on the insides of these things....
I had to replace the one on mine once, and keep an extra for the next time...
A failure of this item will most commonly knock out either the VHF, or UHF
part of the antenna.... You should check this item first....
Here is an example:
http://www.solidsignal.com/pview.asp...8269&ss=457147
.