kart29: If you needs are local, local repeaters, short range, a j pole could be horizontal though vertical is better, better range. Diagonal. neither fish nor fowl, an improvement over horizontal. As amaters, we use what we got and make it work. Cross polarizing our ANTENNA, we are just attenuating out signal. Your radiation pattern will be upset but not really bad. Assuming your attena is perfectly 90 degree upright, your signal radiates at so many degrees upward. If its tilted , the antenna pattern is lower on onme side andf much higher on the other side. If you have no repeaters on one side, that side could be titled away and you really won't miss a thing. If say the jpole was a twin lead design jpole,, like a dipole for hf, it can be setup with curves in them, you can get by. The only concern with attic mounted antennas is the space available to you for mounting. The xxxxxxx 2 meter J-Pole antenna is 69 inches tall overall. You will need a peak in your attic that is tall enough for the antenna to fit. If the top of the antenna touches the walls or roof, the performance may be affected slightly. If you attic isn’t tall enough, you could angle the antenna mounting to make it fit. Angling will affect the radiation pattern slightly, so you may need to consider which directions to favor the antenna for the best reception.
Attic mounted antennas are a great solution for amateur radio operators looking for an effective VHF/UHF antenna system installed in a limited or restrictive situation.
