TV signal high but quality dips
With antennas there are a lot of check boxes to tick. First it has to be installed and adjusted properly. Most TV antennas are directional and need to be pointed toward the TV station. If they are not pointed in the correct direction the signal will degrade. 

Next the connection from the antenna to the house is important. The two common methods are ladder line or coaxial cable (75ohm). Ladder line was all the rage back in the day. Ladder line is a flat cable, about a 1/2 in across, with the two conductors on the outside. Ladder line is very prone to interference. If your house has ladder line then an upgrade to coaxial is needed. If the house already has coaxial cable, then how old is it? Old cable can degrade the signal. 

Once inside the house, how long is the run to the TV? The longer the run the more signal you will lose. Are there any splitters? Splitters degrade the signal, particularly if nothing is connected to the second output (this is called unterminated). Replace any splitters with unions, or even better run a new uninterrupted cable. 

Interference can be an issue. Does the antenna cable run next to anything in the house like a sump pump or a furnace. It's possible that when something kicks on it is interfering with the signal. Does any event coincide with the lower signal? Re route the cable away from any such device. 

If everything else fails an amplifier could do the trick. When choosing an amplifier make sure it is rated for the frequencies that you are interested in you area. An amplifier right next to the antenna is best but difficult to install because it necessitates running power wires up to the roof. An amplifier in the house right where the wire comes in is the next best option. 

This list of stuff is just scratching the surface but enough to get you started.