[Top] [All Lists]

Making a parabola (was Swallow roost)

Subject: Making a parabola (was Swallow roost)
From: "MARTIN" mcgarnett
Date: Wed Sep 19, 2012 4:10 am ((PDT))

Hi Jose and David,

I'd be really interested to hear about your project making an 80cm diameter=
 parabola. I'd like a large enough parabola to successfully record cormoran=
ts nesting on a tall cliff not far from me here in north Wales. The cormora=
nts have quite low frequency calls starting at about 400Hz. Any ideas as to=
 how large a dish I'd need?

Is it easy to make one using fibreglass? I'm not very practical - any advic=
e much appreciated!

Best wishes,


--- In  "freitojos" <> wr=
> David,
> Your technical points are never boring. To me it is very important to ful=
ly understant what I am doing. Maybe you could said something (tchnical or =
not) about my project to construct in fiberglass one 80cm diameter parabola=
> Regards,
> Jos=E9
> --- In  "Avocet" <brini@> wrote:
> >
> > > my parabola is 60cm in diameter and the focus is exactely in the
> > > transition line between the inside and the outside of the parabola
> >
> > Jos=E9,
> >
> > Just to make a boring technical point, the diameter of most parabolic
> > reflectors is the point where the slope is at 45 degrees. With short
> > wave focussing, reflections from this point meet the point of focus at
> > right angles to the source because this is also the distance of the
> > focus from the centre of the dish. To complete the geometry, the
> > diameter of the parabola at this point is four times the focal length.
> >
> > Continung the dish beyond this point gives a double reflection, and
> > with radar and sound wavelengths, doesn't improve the reception in
> > practice. It's also neat when the depth equals the focal length, and
> > the radius is twice that, and the diameter four times.
> >
> > David
> >
> > David Brinicombe
> > North Devon, UK
> > Cogito cogito ergo cogito sum - Ambrose Bierce
> >

<Prev in Thread] Current Thread [Next in Thread>

The University of NSW School of Computer and Engineering takes no responsibility for the contents of this archive. It is purely a compilation of material sent by many people to the naturerecordists mailing list. It has not been checked for accuracy nor its content verified in any way. If you wish to get material removed from the archive or have other queries about the archive e-mail Andrew Taylor at this address: andrewt@cse.unsw.EDU.AU