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[antennaware] Antennas over steel and concrete

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Subject: [antennaware] Antennas over steel and concrete
From: Igor Sokolov" < (Igor Sokolov)
Date: Tue, 29 Dec 1998 23:35:52 +0500
I have to put all my antennas on the roof of a block of flats.  This is a
building made of steel and concrete. The roof is about 30 meters  over the
ground 15 meters wide and 50 meters long.

1) When modeling antenna over the roof should the height of the roof be
taken into account?

2) Should the conductivity and other properties of the roof be accounted

3)What sort of influence in general there is from the roof onto antennas for
different freq. from 3.5 to 28 Mhz?

All these questions emerged when I took 40 meters Delta Loop fed for
vertical polarization that worked perfectly over the ground and put it on
the roof (the bottom is about 3 meters over the roof and say 35 meters above
the ground). The impedance of the antenna changed from 60 ohm to 160 ohm
with a lot of reactive component.

I would be glad to get any comments on the problem.

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