Re Pmotz's comments - I can only add that you can optomize an outdoor directional antenna by adding a rotor so you can point it directly at the station you are trying to bring in. I think that is why you wanted an omni, so you could get stations from different locations on the compass.
But here is an alternative if you mainly listen to a few long distance stations from the same point on the compass, but also would like to get a lot of local channels close by. In addition to a long distance fixed antenna, set up a small omni (even in the attic). Then run the two cables down to a switch at your system and select the antenna you want to use depending of the station you want to hear. That may be the reason why some tuners have options for selecting from different antennas. Anyway, it works for me.
But here is an alternative if you mainly listen to a few long distance stations from the same point on the compass, but also would like to get a lot of local channels close by. In addition to a long distance fixed antenna, set up a small omni (even in the attic). Then run the two cables down to a switch at your system and select the antenna you want to use depending of the station you want to hear. That may be the reason why some tuners have options for selecting from different antennas. Anyway, it works for me.