On Wed, 07 Jul 2004 17:44:58 -0400, Albert wrote:
How much gain (dbd) should I expect and about what take off angle will
I have?

Hi Al,

Contrary to Wes' results, I do not find much more than 13dBi, and
certainly not from your proposed huge implementation running out
towards 50 wavelengths. In fact, I find antennas that are a tenth of
that (5M) have about as much gain as will be found.

My matrix of testing shows that doubling to 10 wavelengths and
doubling again to 20 wavelengths brings no further gain (except for
some opportunistic outliers).

As a variation upon a theme, I decided to play with uptilt on the 5
wavelength models, lifting the far ends by roughly 25 degrees. The
feed point is at 3M, and the far ends are lifted 5M. With this
configuration, there is some loss in gain, but the lobe looking at the
horizon is easily four times broader. That is, there is an even gain
of roughly 11dBi from 14 degrees above the horizon to 34 degrees above
the horizon. This occurs for the tips being separated by 30 to 90
degrees (the gain falls to 9dBi with wider separation).

When you separate further, out at 150 degrees between the tips, the
broad characteristic collapse, but recaptures gain, and puts it out
lower. At such a configuration you might observe 11dBi @ 4 degrees.
That lobe is only 3 or 4 degrees tall however.

Considering that common implementations of rhombics rarely go beyond a
couple of wavelengths to several, it seems that 20 or 40 or 50 has no
future. The law of diminish returns must occur somewhere as you are
constantly losing power as it trucks down the length. At that far
end, nothing added to little before it hardly piles up gain.

73's
Richard Clark, KB7QHC