[Towertalk] antenna question

[KB2HUK@aol.com]

Hello Guys !  I am putting up a 60foot tower and I plan on using a log 
periodic near the top of the tower .  I was thinking of also putting up a log 
periodic for vhf ,uhf and utility stations.  The question is this I know that 
two horizontally polarized antennas interact, but how does a vertically 
polarized antenna over a horizontally polarized antenna interact if at all?  
how high should I place the vertical beam over the lower horizontal beam?   
thanks for all replies