1. Now. would I place the wire (effective capacitor) 1/4 wv length (of 15 meters) from the feeed point or fm the tip of vertical?
You want to put it at the point where voltage is maximum on 15m. But, of course, the
position of the added wire affects the voltage distribution!
Actually, for optimum results you'd place it so that that section below the wire + the wire length
is 1/4 wavelength, and the section above the wire + the wire length is 1/2 wavelength. Even that
is an estimate, because the length of the wire isn't the same as the effect it has on the resonant
So we may need to be pragmatic. First, measure the antenna as built and see what the SWR
curve looks like across the 15m band. Then, if it needs some assistance, put the 15m capacitance
up somewhat less than 1/4 wavelength - maybe 11' or so from the bottom. You can adjust the
capacitance by adding extra wires (forming them in a V and attaching to the vertical in two
places seems like a good approach), bending the 15m wires closer together or further apart (which
requires more than one wire, of course), changing the size of the wires, or sliding them up or down
the antenna somewhat. It all depends on how much adjustment you need to get a low SWR on 15m.
But the likely location is slightly less than 1/4 wave above the feedpoint.
2. Perhaps I misunderstood, but someone was doubting I could get enough capacitance fm the top hats for 40 with my 24 foot physical length.
No, I was doubting whether the type of capacitance hat (the V-shaped wires) used in the B&W
vertical would give you enough capacitance since your antenna is shorter.