The Radio Shack UHF/VHF combiner part number is, 15-2586
http://www.radioshack.com/product/in...ductId=2103923
Have you tested reception and fine tuned aim of each antenna, without any preamplifier installed? Simply connect the antenna to a short (50' or less) length of RG-6 coax and connect the coax to a single TV tuner... No other parts or accessories in line during the test. Once the antennas are producing reliable reception, then add the preamp to the 'equation'. Be sure to set the internal switches to 'VHF/UHF SEPARATE' and 'FM TRAP ON'.
http://www.voxxintlcorp.com/docs/com...PRAMP1R_OM.pdf
The covers for the switches are rather small rubber plugs on the bottom panel of the mast mounted amplifier housing.
If your TV has a signal meter function, it should be useful in confirming both the single un-amplified antenna testing as well as the combined/amplified arrangement. And just to be sure, verify that the TV has been configured for 'AIR' or 'ANTENNA' mode, not the default 'CABLE' mode. The tuner will not recognize OTA DTV signals when set to cable mode.