[CQ-Contest] radio interference

[Rick Dougherty NQ4I]

Hi all..I am sure that some one out there can assist on this one.....my 15 
mult antenna is on the same tower as the 20m 3 hi stack..i.e. its in the 
field of radiation...the operator on the 15m mult station hears the 20m 
station perfectly clear, no matter what frequency either station is tuned 
to...its some sort of if overload? I can greatly reduce the level of the 20m 
run station at the 15m mult by using a bandpass filter..I am also wondering 
if I put a 20m stub at the antenna feedpoint for the 15m station would that 
accomplish the same thing?? thanks and Happy Holidays de Rick nq4i