Tivo's are Known to have tuners that do not deal well with less then perfect broadcast Tv signals.
-->All broadcast Tv signals are less then perfect.<--
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The HBU44 is a good choice.
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Attic reception is not the best place to get reception.
Radiant Barrier metal backed insulation.
Stucko - Wire -.
Concrete tile roofs.
Metal roofs.
And etc. .
Disrupt and block reception.
Recommend move antenna to above roof in such an manner that the roof and house are not impeding and blocking reception to the , South , South West , South East , East , North.
Aim the antenna at about , South.
Here is how to aim antennas ,
http://www.kyes.com/antenna/pointing/pointing.html.
Use a Old School magnetic compass to aim antenna.
With antenna above the roof , recommend Test reception without , preamp , preamp power injector , preamp power supply.