Increasing Signal Strength for Broadcast TV

To Anyone who can Help,
Is there a way to increase the signal strength of broadcast TV?
I'm wiring my house for TV using an antenna mounted in the attic, fed to a 6 way splitter (1 Port Power Passive 5-2300 Mhz ) using coax cable (RG-6U). One of the runs is almost 80 feet long from the splitter. I tried to use a Pre-Amp (PA-18 UHF/VHF) to increase the signal but it did not work. I connected the Pre-Amp to the antenna lead, then to the splitter. I connected the power inserter (10 to 2050 Mhz) to the farthest TV and ran to coax back to the 1 port power passive on the 6 way splitter insuring that all of the connections were correct by the diagram that came with the Pre-Amp with no luck. Then I tried the power inserter between the Pre-Amp and the 6 way splitter with the same results. I get a better pictures without the Pre-Amp installed. How can I boost my signal strength?
Respectfully
PJ Peterson