A set top box won't improve the reception that much.

we had the same problem from time to time and I replaced the aerial and has worked fine since.

In your situation I think it's probably the 3 or 4 way splitter box  that takes the signal from the aerial and distributes the signal to other tvs as well as yours.  There may be a loose connection on your line to your TV or your outlet may be faulty.

Hope this helps