Tom,
As I remember it, Lindsey in his famous Quad article, made all the
measurements and scaling of his Quads at 440 MHz. While at a VHF conference
I attended in California in either 1968 or 1969, Mike Staal, K6MYC, brought
a series of these Lindsey quads to test on our antenna range. They were all
QUITE A BIT LOWER IN GAIN THAN EXPECTED! End of story.
73,
Joe, W1JR
At 08:27 PM 2/6/01 -0500, Tom Rauch wrote:
>Hi Dave,
>
>I just read this from W4LC who hit the nail on the head:
>
>Quarter wave 2-element (driven & reflector)
>dipoles, stacked a
>quarter-wave
>apart and fed in-phase?
>
> > > Most of the benefits of quads are far over-rated. They do not,
> > > contrary to folklore, have "2 dB gain over a yagi".
> > >
> > >
> > [Dave D'Epagnier] As I recall, because Quads are almost always made
> > with conductors with much smaller diameter than Yagis, the full
> > theoretical gain advantage is usually not realized. FWIW, I've never
> > owned a quad but if they are quieter antennas that would be a big plus
> > to me. Maybe some day...
>
>Remember they are only quieter in some cases where corona is an
>issue. That would almost always be only during inclement weather,
>and even then in specific situations.
>
>It is not a good general rule.
>
>As for the gain, picture what a quad element is.
>
>It is two 1/4 wl long dipoles that are "end loaded" by the non-
>radiating bent ends. These two short dipoles do not give up much
>gain, because they are end-loaded and most of the ampere-feet are
>in the radiating area. They only give up a tiny bit of gain.
>
>Now you have two of these dipoles, but they are stacked 1/4 wl
>apart.
>
>If you look at the stacking gain in free space of two antennas
>spaced 1/4 wl apart (like on page 8-35 of the 18th Antenna
>Handbook), gain is about 1 dB. You'll find, if you model the
>antenna, that indeed a square quad element in freespace has only
>about 1 dB gain over a dipole!
>
>(If it was a perfect loop instead of a square, gain would be higher
>but still somewhat less than 2 dB.)
>
>Now if you add more elements in front of that one, the more
>directional you make the antenna the less gain advantage the
>"stack" you'll get using the quad configuration. If you place the
>antenna over earth, you'll see at some heights gain advantage is
>zero and at some heights about a dB or so.
>
>The problem with a quad isn't loss in the wire, it's the fact the
>darned thing has no real gain in an ideal case (freespace single
>element)...and anything you do to sharpen the pattern only makes
>it worse.
>
>We wouldn't stack two yagis 1/4 wl apart and bend the elements
>over so the tips touch and expect to see gain, so what the heck do
>we think a wire would have gain just because it is bent the same
>way?
>
>Where does the 2 dB come from?
>
>It comes from a mistake.
>
>A couple of fellows measured some quads on 440 MHz and
>assumed the measurements were accurate. That data made it into
>books. Unfortunately they overlooked some errors, and the results
>were flawed. But to this day people still quote the flawed
>conclusions, 2 dB gain over a yagi the same boom length.
>
>Now you see why I pick at measurements and insist they include
>and describe potential errors (and there are ALWAYS potential
>errors). Once something is in print, it remains almost forever even if
>wrong.
>
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>73, Tom W8JI
>w8ji@contesting.com
>
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