[TowerTalk] Antenna interaction?

[John E.Cleeve]

I have an average sized, UK manufactured yagi, a Jaybeam TB3, which 
covers 14,21,28mhz, at the top of a 20mtr lattice tower. I am 
considering adding the Cushcraft D3W, 3 WARC band rotary dipole to the 
tower and attaching it to the rotary shaft, about 1.5ft below the 
existing yagi. Can anyone, perhaps with antenna design software 
facilities, advise on the possibility/probability of an adverse 
interaction between the two antennas. I look forward to a response in 
due course....sincerely, John G3JVC.