I would like to put up a 30m hw dipole on my small lot and have the following question.Because of space limitations one radiator would have to be about 5-8 ft. above a metal roof on a one story ranch house,the other radiator would be over clear ground.Would the metal roof have any negative effect and if not does it make a difference wheather the coax feedline shield side is over the roof or clear ground side?Max. antenna height about 23 ft.Any input appreciated,thanks. Jim
Jim, as the other commenters have said, yes, there will be an interaction: mutual coupling between the the antenna and any close by metal object. Often, the more massive and close in the metal object, then the more interaction. You may see the interaction manifest as 'difficulty to obtain a good match on a particular band or portion of the band'. Additionally, the radiation pattern may be skewed but this is hard to predict and hard to visualize exactly what it means. Our antennas work best when located well out into the clear (>1/2 wavelength ~).
If your max H above ground is 23' feet, then you would want to concentrate on operation for the 5 bands of 10M thru 20M. The antenna may even load 'nicely' on 30M and 40M but the majority of the radiation is skyward (esp 40M), so don't expect P29 to come back to you on 40M, though you never know!
GL, 73, Rich, K3VAT