Indoor antennas are a compromise on digital TV. For any of them to work, even the best of them, you need a strong signal and you need to be in an optimum location in the house, the right elevation off the floor, and pointed in the right direction. It's a daunting task that often doesn't work at all, even though it may have worked with analog.
It can be a maddening exercise to get all of your desired channels on every set, especially if you have to point the antenna in different directions to get different channels. Then there's the problem that you must rescan your converter or digital TV every time you make any antenna adjustment for the purpose of capturing new channels. If you don't rescan, you've accomplished nothing by making the change.
Sadly, some homes just won't get satisfactory results without an outside antenna. In many locations, a full size antenna in the attic is a viable option (I have one and it's great). Even sadder, many of the so called "digital" or "HDTV" antennas on the market work about as well as the box they came in. It's very easy to fall victim to an aggressive salesman who swears his "HDTV rabbit ears" is the best antenna around. As a local TV station engineer put it recently, it's all baloney.
The references below may be of help. Enter your postal code and other local info for a report on the channels you should be able to receive and what antenna is recommended. Be prepared for the likelihood that you need a full size outdoor model, outside.
(Only the first ref below works for Canada. Both for the U.S.)