I believe Bill is closer to being correct.
Comparison of a quad may be described as stacked, quarter-wave, end-fed
2-element Yagis. Perfomance (from what I've read, and also from my past 9.5
years experience using a quad) also approximates this configuration.
The only reason that a quad MAY be quieter, is that there is are no sharp
points to generate corona discharge.
Jim W4LC
---- Original Message -----
> From: <ve4xt@mb.sympatico.ca>
> To: "Bill Fuqua" <wlfuqu00@uky.edu>; <towertalk@contesting.com>
> Sent: Tuesday, November 29, 2005 01:46
> Subject: Re: [TowerTalk] ALTERNATIVE TRIBANDER
>
>
> > Hi Bill,
> >
> > I think you may be misunderstanding a quad antenna:
> >
> > A quad element is not a bent dipole or a shortened element in any way.
It
> > is a full-wave loop, an antenna that by itself exhibits gain over
dipoles
> in
> > directions perpendicular to the loop. The calculation for its length (or
> > circumference, since it's a loop) is 1005/f(mhz), vs. a dipole, which is
> > 468/f(MHz). So clearly, there is more than twice the amount of element.
So
> > an element centred on 14.2 MHz would have 70 feet, nine inches of wire
> > (forming a box approximately 17.5 feet on each side), as opposed to a
> > dipole, which is 33 feet long.
> >
> > If you put a reflector behind that (or a director in front), what you're
> doing is
> > putting another full-wave loop (plus 5 per cent length for a reflector,
> minus
> > 5 per cent for a director) to parasitically alter the pattern of the
> driven
> > element just as a yagi element steers the signal from a dipole antenna.
> >
> > Also, if you build the quad using a spider hub (so the spreaders extend
> > out from a central point at angles instead of from the end of the boom
> > perpendicular to the boom) you can place each element on a multiband
> > quad at an ideal spacing to maximize gain. (If you Google Gem Quad, you
> > can probably find some good pix to illustrate the spider hub idea.)
> >
> > It is generally accepted that a 2-element quad will perform comparably
to
> > a 3-element yagi.
> >
> > There are antennas on the market that look like quads (the Butternut
> > HF5B is one), but those aren't actually quads. The wires on those
> > antennas are actually used to resonate otherwise short elements on
> > various frequencies. So in essence, they are loaded dipole antennas.
> >
> > Full-size quads are actually formidable antennas, not just because of
> their
> > construction difficulties, but also because they work. A quad element is
> > generally quieter than a dipole because both feedpoint terminals, at DC,
> > are at the same potential.
> >
> > Is it possible you've seen an antenna like the HF5B and mistook it for a
> > quad?
> >
> > 73, kelly
> > ve4xt
> >
> > > From: Bill Fuqua <wlfuqu00@uky.edu>
> > > Date: 2005/11/28 Mon PM 02:03:07 CST
> > > To: towertalk@contesting.com
> > > Subject: [TowerTalk] ALTERNATIVE TRIBANDER
> > >
> > > 1. A quad is a compromise in a since because it is the same a 2
> > stacked
> > > shortened yagis with a separation of only 1/4 wavelength.
> > > It can be viewed as two 1/4 wavelength yagi driven or parasitic
> > > elements with capacitive loading from the 1/8 length ends turned up or
> > > turned down, which also serve as the feed lines to the upper half of
the
> > quad.
> > > 2. By what magic does a quad separate RF atmospheric noise from RF
> > signal?
> > > The idea that a quad is quite seems a bit strange to me.
> > >
> > > 73
> > > Bill wa4lav
> > >
> > > _______________________________________________
> > >
> > > See: http://www.mscomputer.com for "Self Supporting Towers",
> > "Wireless Weather Stations", and lot's more. Call Toll Free,
> > 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
> > >
> > > _______________________________________________
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> > > TowerTalk@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/towertalk
> > >
> > _______________________________________________
> >
> > See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
any
> questions and ask for Sherman, W2FLA.
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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