Backpacker, why do you keep coming up with your inappropriate dipole?
Well, my dipole antenna took 10 minutes to make from stuff I had lying around in the garage and works perfectly fine. Yes, there may be better designs but I doubt whether you can create them as easily as a simple dipole.
I don't know in which direction it is directional but since it's hanging vertically I think it's only the traffic that's directly overhead that might be a problem. And where I live, there's virtually no traffic overhead. (Too close to the field, but not in one of the extended centerlines.)
Also I have seen numerous ATC antennae that are dipoles, and for instance the antenna in the Europa is the exact same thing, just glued to the inside of the fuselage. Yes, dipoles may be directional and not send/receive straight up and down, but that's where the other party is normally not located.