Cheaper option
Up here in the land of stone houses and horizontal rain internal antennae don't work and external ones last 10 minutes.
Instead make a totally waterproof dipole out of plumbing parts for about £10.
You will need:
3 bits of 15mm copper pipe, two about 22cm long and another bit any suitable length for the upright
One 15mm Speedfit plastic Tee, or probably any similar push-on plumbing fitting.
Two solder on or push-on 15mm end caps. (Stop ends)
Two bits of copper wire stripped from some mains cable about 100mm long.
Some sleeving or tape
Some silicon sealant
Some co-axial TV wire, long enough to reach your TV.
A couple of 15mm pipe clips, Hospital clips are the best they stop the pipe rotating in strong winds and are made of brass.
Form a coil on the ends of your copper wire and solder to the inside of the short pipes.
Feed the wire through the Tee and sleeve them.
Fix end caps to the other ends.
Feed the co-ax up through the other pipe and join to the copper wires.
Push this pipe into the plastic Tee and seal the bottom end with a good squirt of silicon.
Fix your Tee shaped dipole to the chimney breast or wherever.
Result 100% signal strength!
100% waterproof as all connections are inside a bit of plumbing!