[Antennas] tuning a TH6DXX

[DWAVE35 at aol.com]

I think Paul hit it right on the head.

The effect of ground (or the conduit or whatever might be under the roof) 
usually has much more effect on the lower bands than on the higher bands. This 
capacity to ground lowers the resonant frequency to a greater extent the lower 
the band under test since you're closer to ground in terms of parts of a 
wavelength for a given height.

All of my homebrew yagis were tuned hanging vertically (pointing straight up) 
on the side of tower where the DE is easy to reach and adjust. The change in 
resonant frequency is minimal when moving it to horizontal at the top of the 
tower.

Brian