Tom, I'd guess about three feet out from the tower might do it as well as at
least three feet from your other antenna. Pvc is probably the easiest way to
accomplish that. Remember that any slack in the line will get it closer to the
pvc keeps it out so allow yourself a little wiggle room.
Tom
Tom Brennan KD5VIJ, CCC-A/SLP
web page http://titan.sfasu.edu/~g_brennantg/sonicpage.html