Alex,
I am very familiar with 'sperical trigonometry' as well as many other
branches of Mathematics ... my degrees, BS & MA, are both in Math.
[Some say I have an ABD - 'all but dissertation' - didn't see any need
to spend $2500 for someone to call me 'doctor'].
I reiterate .. only a parabola/paraboloid will have a true focus .. [an
ellipse has two foci, but the unfortunate circumstance with an ellipse
is that rays must pass through one focus to meet at the other].
As I pointed out in my previous post, putting the TH7 at the 'focus' of
a curved-surface reflector requires placing the driven element in the
'focal position', and this would disable the reflector element of the
TH7 [unless it was within the surface of the 'new' reflector.
All this seems quite pointless to me, as the structure would NOT be
easily rotatable .. and, if you desire high gain in a single direction,
a STERBA curtain would serve much better, without the requirement of
multi-supports!
Don
N8DE
Alex wrote:
>
> I was describing the curvature of the antenna. A curtain antenna is never a
> closed loop, or in this case a cylinder. But it can have a
> specific curvature so there will be a focus!
>
> I wrote "cylindrical" - please observe the quotes- as opposed to "spherical"
> or "parabolic" surfaces. Please remember your spherical trigonometry :)
>
> In my case the curtain has a horizontal cylindrical angle of about 10 to 20
> degrees due to the limitations imposed by the trees which are used as
> infrastructure for it.
>
> Preliminary computations show a 70dB B/F ratio - for the composite system -
> with a quite a wide horizontal dispersment. Forward gain is only improved by
> 2.7dB. I kind's hopped to get some more. I think the curtain is to long
> horizontally for the 20m band. I'll try to make it exactly one lambda for a
> specific freq.
>
> Thank you for your reply.
> Alex
>
> > -----Original Message-----
> > From: antennaware-admin@contesting.com
> > [mailto:antennaware-admin@contesting.com]On Behalf Of Don Havlicek
> > Sent: Wednesday, June 12, 2002 9:07 AM
> > To: Alex
> > Cc: antennaware@contesting.com
> > Subject: Re: [Antennaware] Modeling a composite antenna
> >
> >
> > A cylinder has NO focus, a parabola/paraboloid does.
> > If you construct what you have suggested, only the RF entering the
> > 'reflector' along the line of the boom of the TH7 will be reflected back
> > to the AXIS of the cylinder .. and that is where you must place the
> > DRIVEN ELEMENT of the TH7.
> > A better arrangement might be to add additional reflectors to the TH7,
> > but that would be a mechanical nightmare, as they would be trapped and
> > placed at a distance equal to the DE/Ref distance of the TH7.
> > Don
> > N8DE
> >
> > Alex wrote:
> > >
> > > I am planning to erect a 60m long by 30m tall "cylindrical"
> > curtain and in
> > > it's foci a TH7.
> > > What software can model this combination and where can I get it .
> > >
> > > TIA, Alex
> > >
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> >
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