This is a very typical problem for most antennas. OTA (over-the-air) broadcasts come from a lot of different towers, in different locations, and with different frequencies. Because of this, some channels can come in great, and others not so well. Antennas are designed to work best when pointed directly at the station. If the antenna is pointed north, all those channels might come in great, but stations from the south may appear very weak on your TV. To troubleshoot take into consideration the location of the stations, which frequency they are using, and how strong the TV station is broadcasting the signal.