[Antennas] 1/4 wave sloper...whats really radiating?

[jkolin at optonline.net]

I'm using  two 1/4 wave slopers tied to one feed point at the top section of my 90' crankup twr. One is 75M and other is 40M. They are separated by 24" pvc pipe at the bottom end of the 40M wire. I run the twr up to abt 75' and both work very well at that height. 

Tower has 5 el 20M yagi on 42' boom at bottom of 12' Mast. A 3 el 10M yagi is at top of mast.

I think the yagis, their booms, possibly their individual elements and the 12' mast may be contributing to the actual total radiation.

I wonder how I can prove or disprove what components mounted above the slopers are actually radiating .

Neon bulbs or low wattage small flourescent  3/4" dia bulbs placed at possible high voltage points?

Any ideas ?

Thanks...    Jay, NE2Q