said by leibold:
It is best to do it like Jack_in_VA said but sometimes there is no power near the first split in the antenna cables. That is especially likely if you are using a splitter/combiner on the roof to combine the signal from the two antennas (to bring only one coax into the house).
Well, the cable would go from the antenna to a space under my basement stairs where my network cables and coax cables meet. So the split would be there, and I can put the power injector JUST before the splitter. (well, between the antenna and the splitter, whichever means before or after).
The second antenna would also go directly to that location, as both antennas would be a good 40 feet away from each others and that space under the stairs is between them.