Ok, the sector thing is interesting, but we've drifted FAR away from the question I was trying to answer.
Can anyone direct me to information, or modeling software (preferrably free) that can predict the pattern of an omni antenna, at various distances from a large cylindrical water tower? I'm looking to end up with an .ant file that I can use in radio mobile, but whatever the output form might be, I'm sure I can translate it one way or another.
