On 10/21/2011 02:23 AM, Tony Renshaw wrote:
> bunch of COAX. I am wondering if anyone has an opinion on the merits
> of building up this antenna or whether I should just bin it and use
> the Z shaped Bob Archer VHF antenna that I also have, and put it on
Go for the dipole antenna, it outperforms the Bob Archer stuff. The
latter is a compromise to save space in case your airplane is too small
to fit a decent half-wave antenna (dipole).
A dipole is the most "natural" radiator. It has 100% efficiency and
produces a toroid radiation pattern, which is exactly what you need in
an airplane. If an antenna-manufacturer claims gain over a dipole, it
means that it has gain in a certain direction but also losses in other
directions (they often forget to tell you that). Consider the antenna as
a light bulb. Sure you can produce gain in certain directions, but
regardless how you do it (lenses, reflectors) it also implies you create
dark spots (shadows) in other directions. Which is fine for a static
setup but not for an airplane. As a dipole radiates 100% of the energy,
it is not possible to create any antenna that beats this AND retains an
omnidirectional pattern at the same time.
Also, another advantage is that the dipole antenna can be placed further
away from the cockpit and tailplane assembly, which minimizes interference.
Frans
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