Generally, elevating the antenna somewhat will
improve performance. One reason for that is
reduced ground losses. But don’t put it up
too high: rooftop height should be fine.
One consideration is how well the metal panels
on the roof are bonded together. Painted metal
panels may work better if installed with roofing
screws rather than nails, as they tend to make
better contact to the underlying metal. In one
case we added a number of sheet metal screws
to an older roof to bond the panels - stainless
steel preferred, and they need to be sealed.
I don’t know about the bonding of flat metal
roofs on commercial buildings, but they
certainly can make good ground planes in
some cases.
One other note: you should be using an Un-un
at the feedpoint, rather than a balun. The
original design using a 4 : 1 voltage balun
was shown to actually force RF onto the coax
shield, which is what a balun is supposed
to prevent.
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Topic: Couple of vertical questions..... (Read 428 times)