Here is an illustration of the shorting stubs which M. J. Salvati calls an Isolation Network (see attachments):
The shorting stubs must be attached an odd number of 1/4 waves away from the UHF feedpoint. If they were attached to the feedpoint, they would short out the UHF signals. In the RCA ANT 751, they are attached to the top of the Tetrapole, which is 3/4 wavelength before the feedpoint through the Tetrapole.
In the RCA ANT7511, they are attached 1/4 wavelength away from the UHF feedpoint, B to C:
There are only two wire stubs on the 7511, which really isn't sufficient to cover the whole UHF band. The wires with one end not connected are a little longer because they aren't as wide as the flat strips. The 751 uses two sets of flat wide stubs to cover the UHF band; much more effective.