All I can say is don't pin too much hope on a better antenna helping much. I'm assuming that it's the closer station that's giving you the problem, otherwise you'd have put it down to distance. It may just be that there are buildings or high-ish terrain blocking the signal from the closer station. You could try taking your scanner as high as possible, like the attic, for example, and see if that helps. If it does, you might consider getting an antenna which you can mount in the attic or on the roof. Signal reception is notoriously unpredictable so you should gain as much information as you can with what you've got before splashing out on an expensive antenna.
How's that for a long-winded way of saying "beats me"?