Multipath is reflected television transmissions. Reflected off of buildings , mountains , hills , trees , airplanes , even trains if you live close to train tracks. Multipath causes ghosts in Analog tv pictures , you have analog tv transmitters at your location , A digital tv tuner can correct multipath up to point and then too much multipath will cause a digital tuner to not process the signal and you see the picture break up in to block or black out. Omnidirectional antennas do not reject multipath and omnidirectional antennas are not 100% omni. Turn the antenna to try and get the most channels. . DO NOT use a preamp at your location , the television transmissions are Very Strong and a preamp can overload and block out channels. Also because it is a omniantenna it is a good idea to move the antenna up and down or this way or that way to find a spot with the least amount of multipath. With some expermenting you might get all the channels you like. Read and understand this ,
http://forum.tvfool.com/showthread.php?t=695 ,
http://forum.tvfool.com/showthread.php?t=651 ,
http://forum.tvfool.com/showthread.php?t=231