I expect there is considerable difference between
concrete and structural steel roofs and conventional
wooden / shingle home roofs. Unfortunately,
George did not specify which type he had.
Tom N4KG
On Thu, 06 Dec 2001 VR2BrettGraham <vr2bg@harts.org.hk> writes:
>
> 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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