SDNomad wrote:
What are the physical characteristics of this antenna that would keep
it from having a gain of 5.1 dbi? Is the height the determining factor
for the amount of gain from an antenna?

Yes, for a base-loaded whip like this one.

Could the coil be wound in
such a way to get the increased gain from a 3' whip?

No, blood out of the proverbial turnip comes to mind.

Since this is a marine antenna, I suspect they are talking about gain
over salt water, i.e. close to a perfect ground. The antenna is a 1/2WL
vertical. EZNEC says the gain of a 1/2WL vertical over average ground is
about 0.5 dBi and over perfect ground is about 7.5 dBi. In free space,
it is, of course, about 2.14 dBi.

The gain of an ordinary 1/4WL monopole over perfect ground is about 5-6 dBi.
So this antenna has essentially no advantage over a 1/4WL monopole or even
a coaxial antenna. They obviously didn't model the "coaxial antenna" over
perfect ground or they didn't fold back the braid to furnish the other
half of the coaxial antenna.
--
73, Cecil http://www.qsl.net/w5dxp



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