I know this is redundant, but as Don points out, just try a splitter first. Way so many people run out and add a "cheap" amp only to find their reception is worse. Only add an amp if one or more sets looses a channel after splitting the signal.
As Don points out, avoid at all costs buying a cheap distribution amp from walmart.
Notice the spec of the amp at 4
db noise figure. Here the larger the
db the worse the reception. It runs $24 plus your local tax and shipping.
Plus, if you need an amp, more than likely your signals will be much better the closer you get the amp to the antenna, if possible right at the antenna on the mast.
An "inexpensive" but not cheap amp. For $40 shipped to your door, you can pick up
Winegard HDP 269 SquareShooter Pre-Amplifier for SquareShooter SS-1000 (HDP-269) | HDP-269 [Winegard]. This amp you can if possible for you mount up on the antenna mast so the amplifier over comes the loss in your entire system if placed at the antenna mast. If not it's still a better amp.