George, G-something I presume, wrote:
>I am going to mount a short 8' high tower on the roof (concrete) of a 14
>floor block of flats. On this will eventually mount some sort of small
>compact beam and rotator. In the interim I wish to mount a vertical. I don't
>believe that verticals don't need radials so I am thinking of making a RF
>ground/radial on the roof.
A 2.4m roof tower will be too short for your final antenna, unless you are
thinking of 50 or 70 Mc. Even at more than twice that height, I find too much
interaction with the roof at 14 Mc with a tribander.
But using that 2.4m roof tower to support the base of a vertical, that's
different.
You will find that is high enough up that the typical 1/4-wave HF radiator will
start to show signs of reasonable decoupling from the roof with several
tuned & elevated radials.
A typical 1/4-wave HF radiator mounted on that tower, but working against
radials of any sort just on the roof itself, will leave much to be desired due
to the 2.4m distance between the radials & the feedpoint. Don't bother.
Although I prefer to go elevated, it sounds like you'd be better binning the
tower idea completely if you can't go higher, use a bucket of concrete for the
base of the vertical, then lay as much of whatever wire you can as a
non-reasonant radial system right on the roof & stick with that.
That's what I've learned in the past 15 years trying to put antennas on the
roofs of concrete buildings here.
73, VR2BrettGraham
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